I will try to attach a couple of pix of my concrete front porch, showing "leprosy" caused by years -- decades -- of painting over old messes.

1. Best way of dealing with it, I am told, is hire someone with a grinder to strip down to the concrete. Doubt if I can handle the cost.

2. Was advised in store that the Jasco stripper I am using on the back (wooden) steps will work on concrete porch paint. ?? Neighbor said no, no, don't try. Before trying, thought I'd ask the NG.

3. Other alternative: Hire someone to put a layer of ?? over the mess to even out the surface for painting. I filled in loose paint years ago with I don't remember what. Didn't last.

QUESTION: Of all the (feasible) alternatives -- or other suggestions -- which is my best shot?

If you choose #3, what is the recommended product?

TIA

HB

http://s1350.photobucket.com/

I checked this and it didn't show my pix... woe! Hope you can diagnose anyway?

No, paint would just plug up an abrasive hand grinder wheel.

I think if it wuz me, I would go to your local Salvation Army to buy some old bed linens to use as drop cloths for easy clean-up and check out your local tool rental places to see what renting a sand blaster would cost.

The sand blaster will certainly take the paint off your concrete steps. You might talk to some sand blasting companies about using walnut shell dust in the sand blaster to take the paint off of the wood steps. Wood is softer and so you'd need a softer material to blast it without damaging the wood too much.

Otherwise, a heat gun will take multiple coats of paint off wood provided you have a reasonably calm day to do the work. Any breeze will scatter the hot air all over the place and cool off the surface you're trying to heat up; making using a heat gun outdoors a waste of time.

Another option for both the wooden and concrete steps is to use a chemical paint stripper. Paint the stripper on in a thick coat, and then cover with wax paper to prevent the methylene chloride in it from evaporating. Let the stripper work on the paint for an hour or two before peeling the wax paper back and scraping off the softened paint with a putty knife or metal paint scraper.

"Citrus" based paint strippers are a waste of time on oil based paints. Look for paint strippers that say on their packaging that they contain "methylene chloride", which is the active ingredient in traditional paint strippers and works reasonably well on oil based paints. 3M also markets a product called "Safest Stripper" that is surprisingly effective at removing both oil and latex paints considering how mild it is on skin. I have sensitive skin, but I can have Safest Stripper on my hands all day long without it hurting my skin at all. You can buy Safest Stripper in most paint stores, and it eliminates the need to wear uncomfortable rubber gloves, which are a necessity when using any stripper that contain methylene chloride.

I didn't see any pictures of painted steps on the web page you linked to.

On 6/3/2013 10:47 PM, Higgs Boson wrote:
I will try to attach a couple of pix of my concrete front porch, showing "leprosy" caused by years -- decades -- of painting over old messes.

1. Best way of dealing with it, I am told, is hire someone with a grinder to strip down to the concrete. Doubt if I can handle the cost.

2. Was advised in store that the Jasco stripper I am using on the back (wooden) steps will work on concrete porch paint. ?? Neighbor said no, no, don't try. Before trying, thought I'd ask the NG.

3. Other alternative: Hire someone to put a layer of ?? over the mess to even out the surface for painting. I filled in loose paint years ago with I don't remember what. Didn't last.

QUESTION: Of all the (feasible) alternatives -- or other suggestions -- which is my best shot?

If you choose #3, what is the recommended product?

TIA

HB

http://s1350.photobucket.com/

I checked this and it didn't show my pix... woe! Hope you can diagnose anyway?


Don't try stripper....Ive tried water-wash and other on concrete and it
temporarily lifted the paint blots and put them back down (you can't
scrape concrete as you can wood) ..not inspired about blasting stripper
all over the place. Not seeing what you have, I'll take a wild guess.
Pressure wash first...you can write your name in concrete if close
enough with the right tip ) Caulk cracks. If it was nasty enough,
and I wanted to paint it no-matter-what, I'd try some latex stucco
patching compound, let it set and then paint with whatever is in the
garage. If all that is left of the old paint is a few patches, mix up
some acryllic paint from the craft store to match the concrete, do some
faux concrete on the remaining patches, and you're good to go ) If
the faux finish comes off, you're back to bare concrete. Or you could
make a wood platform that sits on the concrete to cover it.

On Jun 3, 10:47*pm, Higgs Boson wrote:
I will try to attach a couple of pix of my concrete front porch, showing "leprosy" caused by years -- decades -- of painting over old messes.

1. Best way of dealing with it, I am told, is hire someone with a grinder to strip down to the concrete. *Doubt if I can handle the cost.

2. Was advised in store that the Jasco stripper I am using on the back (wooden) steps will work on concrete porch paint. ?? Neighbor said no, no, don't try. *Before trying, thought I'd ask the NG.

3. Other alternative: *Hire someone to put a layer of ?? over the mess to even out the surface for painting. *I filled in loose paint years ago with I don't remember what. *Didn't last.

QUESTION: *Of all the (feasible) alternatives -- or other suggestions -- which is my best shot?

If you choose #3, what is the recommended product?

TIA

HB

http://s1350.photobucket.com/

I checked this and it didn't show my pix... woe! *Hope you can diagnose anyway?

paint likely contains lead, chips and dust are a health hazard,
espically to little kids. pros must meet lead abatement
regulations..... costly hassle.

On Tue, 4 Jun 2013 04:46:43 -0700 (PDT), bob haller
wrote:

On Jun 3, 10:47*pm, Higgs Boson wrote:
I will try to attach a couple of pix of my concrete front porch, showing "leprosy" caused by years -- decades -- of painting over old messes.

1. Best way of dealing with it, I am told, is hire someone with a grinder to strip down to the concrete. *Doubt if I can handle the cost.

2. Was advised in store that the Jasco stripper I am using on the back (wooden) steps will work on concrete porch paint. ?? Neighbor said no, no, don't try. *Before trying, thought I'd ask the NG.

3. Other alternative: *Hire someone to put a layer of ?? over the mess to even out the surface for painting. *I filled in loose paint years ago with I don't remember what. *Didn't last.

QUESTION: *Of all the (feasible) alternatives -- or other suggestions -- which is my best shot?

If you choose #3, what is the recommended product?

TIA

HB

http://s1350.photobucket.com/

I checked this and it didn't show my pix... woe! *Hope you can diagnose anyway?

paint likely contains lead, chips and dust are a health hazard,
espically to little kids. pros must meet lead abatement
regulations..... costly hassle.
If the paint isn't white, it's possible there is no lead as the lead
in MOST house paint was a white pigment.. I'd use Methetenr chloride
stripper and scrape off as much as possible, then finish the job with
a pressure washer.

I wouldn't be telling people that because they'll think that if it isn't white, it won't contain lead.

It's true that lead carbonate was commonly used as a white pigment in house paints prior to 1974, but lead chromate was commonly used as a deep yellow pigment as well. And lead oxide was a red pigment commonly used in metal primers.

And, not only were both lead carbonate and lead chromate used in the coloured tint bases that were commonly available from paint manufacturers back then, but both lead carbonate and lead chromate were also used as pigments in the colourants in paint tinting machines. So, if a paint tint formula called for any white or deep yellow colourant in it, then lead carbonate or lead chromate would have been added to the paint when tinting it to it's final colour.

So, while it might not be obvious that a turquoise blue colour paint would contain a lot of lead, they way they would have made such a colour is by mixing blue, yellow and white colourants, and the yellow and white colourants could very well have been lead chromate and lead carbonate, respectively. And, in that case, there's a fair bit of lead in that turquoise paint.

But, I concede that paints that are white-ISH and yellow-ISH in colour are the ones most likely to have the most lead based pigments in them.

And, it's also true that lead pigments are of the most danger to young children because their rapidly growing bodies incorporate the lead they ingest into their bodies. In mature adults, our bodies are not growing any more, and we just poop that lead out.

Lead paint - Wikipedia, the free encyclopedia

Lead(II,IV) oxide - Wikipedia, the free encyclopedia

On Tuesday, June 4, 2013 3:04:17 PM UTC-7, nestork wrote:
;3073536 Wrote:



If the paint isn't white, it's possible there is no lead as the lead

in MOST house paint was a white pigment.



I wouldn't be telling people that because they'll think that if it isn't

white, it won't contain lead.



It's true that lead *carbonate* was commonly used as a white pigment in

house paints prior to 1974, but lead *chromate* was commonly used as a

deep yellow pigment as well. And lead *oxide* was a red pigment

commonly used in metal primers.



And, not only were both lead carbonate and lead chromate used in the

coloured tint bases that were commonly available from paint

manufacturers back then, but both lead carbonate and lead chromate were

also used as pigments in the colourants in paint tinting machines. So,

if a paint tint formula called for any white or deep yellow colourant in

it, then lead carbonate or lead chromate would have been added to the

paint when tinting it to it's final colour.



So, while it might not be obvious that a turquoise blue colour paint

would contain a lot of lead, they way they would have made such a colour

is by mixing blue, yellow and white colourants, and the yellow and white

colourants could very well have been lead chromate and lead carbonate,

respectively. And, in that case, there's a fair bit of lead in that

turquoise paint.



But, I concede that paints that are white-ISH and yellow-ISH in colour

are the ones most likely to have the most lead based pigments in them.



And, it's also true that lead pigments are of the most danger to young

children because their rapidly growing bodies incorporate the lead they

ingest into their bodies. In mature adults, our bodies are not growing

any more, and we just poop that lead out.



'Lead paint - Wikipedia, the free encyclopedia'

(http://en.wikipedia.org/wiki/Lead_paint)



'Lead(II,IV) oxide - Wikipedia, the free encyclopedia'

(http://en.wikipedia.org/wiki/Lead_tetroxide)

Thanks to all who offered advice

Let's get off the lead angle and back to methods of getting down to concrete. The last few years' layers are no-lead paint per California law. And there are no kids in the house.

I did say initially that I probably couldn't afford to rent a grinder to strip paint back to the concrete. And finding a handyman who has his own grinder sounds unlikely.

One of the other alternatives -- putting a coat of ? over the whole porch is still in contention. I asked for name of best product; would still like your recommendations.

I did a trial run of stripper (Jason) Possibly do-able? It was the last of a can, so I couldn't put it on too thick. Now got another large can (also need to do wood back porch) and will try again.

TIA for your help.

HB









--

nestork

On Fri, 7 Jun 2013 20:24:03 -0700 (PDT), Higgs Boson
wrote:

On Tuesday, June 4, 2013 3:04:17 PM UTC-7, nestork wrote:
;3073536 Wrote:



If the paint isn't white, it's possible there is no lead as the lead

in MOST house paint was a white pigment.



I wouldn't be telling people that because they'll think that if it isn't

white, it won't contain lead.



It's true that lead *carbonate* was commonly used as a white pigment in

house paints prior to 1974, but lead *chromate* was commonly used as a

deep yellow pigment as well. And lead *oxide* was a red pigment

commonly used in metal primers.



And, not only were both lead carbonate and lead chromate used in the

coloured tint bases that were commonly available from paint

manufacturers back then, but both lead carbonate and lead chromate were

also used as pigments in the colourants in paint tinting machines. So,

if a paint tint formula called for any white or deep yellow colourant in

it, then lead carbonate or lead chromate would have been added to the

paint when tinting it to it's final colour.



So, while it might not be obvious that a turquoise blue colour paint

would contain a lot of lead, they way they would have made such a colour

is by mixing blue, yellow and white colourants, and the yellow and white

colourants could very well have been lead chromate and lead carbonate,

respectively. And, in that case, there's a fair bit of lead in that

turquoise paint.



But, I concede that paints that are white-ISH and yellow-ISH in colour

are the ones most likely to have the most lead based pigments in them.



And, it's also true that lead pigments are of the most danger to young

children because their rapidly growing bodies incorporate the lead they

ingest into their bodies. In mature adults, our bodies are not growing

any more, and we just poop that lead out.



'Lead paint - Wikipedia, the free encyclopedia'

(http://en.wikipedia.org/wiki/Lead_paint)



'Lead(II,IV) oxide - Wikipedia, the free encyclopedia'

(http://en.wikipedia.org/wiki/Lead_tetroxide)

Thanks to all who offered advice

Let's get off the lead angle and back to methods of getting down to concrete. The last few years' layers are no-lead paint per California law. And there are no kids in the house.

I did say initially that I probably couldn't afford to rent a grinder to strip paint back to the concrete. And finding a handyman who has his own grinder sounds unlikely.

One of the other alternatives -- putting a coat of ? over the whole porch is still in contention. I asked for name of best product; would still like your recommendations.

I did a trial run of stripper (Jason) Possibly do-able? It was the last of a can, so I couldn't put it on too thick. Now got another large can (also need to do wood back porch) and will try again.

TIA for your help.

HB









--

nestork
I'd strip it, pressure wash it, patch any serious divots, and cover
it with FlexRock. Sold by Home Hardware here in Canada - sure to be
something equivalent south of the border.

The idea of covering the paint with some other kind of coating doesn't sit well with me. No matter what you put over that paint, it's only going to stay down as long as the paint does. Once that paint starts to let go, that's the beginning of the end of your repair.

I would remove the paint first, and stripping it off is as good an option as any (although sand blasting it off would be faster and cleaner, it would undoubtedly put more lead dust in the air.)

If it were me, I would apply a thick coat of paint stripper,
cover with wax paper to prevent the stripper from evaporating, and then scrape the softened paint off with a Nestor Scraper, named after it's inventor:

You make a Nestor Scraper by gripping a single edge razor blade:



in a pair of needle nose style locking pliers:



The resulting tool holds the razor blade at a near perfect angle for scraping. Deposit the paint you shave off in a soup can or something you'll be throwing away anyhow.

If your steps are wood, dull the edge of the razor on a belt sander first to prevent the razor from cutting into the wood.

The thin edge of the razor will cut into the softened paint fairly easily making removal faster.

Once the paint is off, then you can put whatever you want on the steps, including indoor/outdoor carpeting.

Higgs Boson wrote:
I will try to attach a couple of pix of my concrete front porch,
showing "leprosy" caused by years -- decades -- of painting over old
messes.

1. Best way of dealing with it, I am told, is hire someone with a
grinder to strip down to the concrete. Doubt if I can handle the
cost.

2. Was advised in store that the Jasco stripper I am using on the
back (wooden) steps will work on concrete porch paint. ?? Neighbor
said no, no, don't try. Before trying, thought I'd ask the NG.

3. Other alternative: Hire someone to put a layer of ?? over the
mess to even out the surface for painting. I filled in loose paint
years ago with I don't remember what. Didn't last.

QUESTION: Of all the (feasible) alternatives -- or other suggestions
-- which is my best shot?

If you choose #3, what is the recommended product?

TIA

HB

http://s1350.photobucket.com/

I checked this and it didn't show my pix... woe! Hope you can
diagnose anyway?

Just a thought . . . , maybe you could try using http://tinypic.com to
upload photos. I've used that and it works well for me. Photos would
definitely help.

About the lead paint issue -- yes, it is something to think about and to be
careful about. But, if it is your own home, and you do it yourself (meaning
you don't hire someone else to do the work for you), then you are not
required to follow the new stupid U.S. federal rules for lead paint removal.

On 6/8/2013 2:17 PM, nestork wrote:
The idea of covering the paint with some other kind of coating doesn't
sit well with me. No matter what you put over that paint, it's only
going to stay down as long as the paint does. Once that paint starts to
let go, that's the beginning of the end of your repair.

I would remove the paint first, and stripping it off is as good an
option as any (although sand blasting it off would be faster and
cleaner, it would undoubtedly put more lead dust in the air.)

If it were me, I would apply a thick coat of paint stripper,
cover with wax paper to prevent the stripper from evaporating, and then
scrape the softened paint off with a Nestor Scraper, named after it's
inventor:

You make a Nestor Scraper by gripping a single edge razor blade:

[image:
http://www.homedepot.ca/wcsstore/Hom...0_2_rgb_4.jpg]

in a pair of needle nose style locking pliers:

[image: http://www.jsproductsinc.com/media/3599.jpg]

The resulting tool holds the razor blade at a near perfect angle for
scraping. Deposit the paint you shave off in a soup can or something
you'll be throwing away anyhow.

If your steps are wood, dull the edge of the razor on a belt sander
first to prevent the razor from cutting into the wood.

The thin edge of the razor will cut into the softened paint fairly
easily making removal faster.

Once the paint is off, then you can put whatever you want on the steps,
including indoor/outdoor carpeting.





The front porch is concrete, and unless it is unusually smooth it would
be touch to remove anything with a scraper. If using stripper, citrus
stripper might work better because it doesn't evaporate, but it works
more slowly.

For wood, a razor blade would be a poor choice, especially trying to
grip it with pliers...there are nice little holders made especially for
razor blades.

The active ingredient in "citrus" based cleaners and paint strippers is a chemical called "d-limonene". There are different kinds of limonene chemicals found in orange peels, but the kind that's called "d-limonene" has a distinct "orangey" smell to it. So, it's what's added to air fresheners and cleaners to give them a "fresh citrus smell".

D-limonene is largely a useless substance, and it's only real claim to fame is that since the d-limonene would be released into the atmosphere and ground as orange peels rot, it's use in cleaners, air fresheners and paint strippers is environmentally neutral. And, it's biodegradable.

https://en.wikipedia.org/wiki/Limonene

http://www.floridachemical.com/whatisd-limonene.htm
Notice how the Florida Chemical web site talks about d-limonene as being the best thing since sliced bread whereas the Wikipedia web page doesn't.

Companies aren't making "citrus" based products cuz they work better.

It's because, the Florida Orange Growers have a powerful lobby in Washington, and they've succeeded in getting d-limonene classified as an environmentally friendly chemical, and so there are tax incentives available from Washington for manufacturers that use it in their products. So, the Florida Orange Growers lobby has been prompting manufacturers to include d-limonene in everything it could conceivably be put in; partly on the grounds that it's environmentally neutral, and therefore environmentally friendlier than using a chemical which otherwise wouldn't have been produced. And, partly on the grounds that Washington offers a tax incentive for manufacturers to use it, even if it's use in a product doesn't enhance that product in any way.

It's not because the Florida Orange Growers are big environmentalists, it's because the d-limonene that orange growers squeeze out of their orange peels represents an additional income stream for stuff that would otherwise just rot in their fields. So, their lobby group in Washington is trying to drum up demand for d-limonene.

My experience with "d-Limonene" is that it's a waste of time trying to use it to strip oil based paints. It does soften latex paints, tho.

Historically, the active ingredient used in paint strippers has been a chemical called "methylene chloride". Poly-Strippa contains methylene chloride as it's active ingredient, and so far as I know, it always has been and still is the most effective chemical for stripping oil based paints.

On Sat, 8 Jun 2013 20:17:20 +0200, nestork
wrote:


The idea of covering the paint with some other kind of coating doesn't
sit well with me. No matter what you put over that paint, it's only
going to stay down as long as the paint does. Once that paint starts to
let go, that's the beginning of the end of your repair.

I would remove the paint first, and stripping it off is as good an
option as any (although sand blasting it off would be faster and
cleaner, it would undoubtedly put more lead dust in the air.)

If it were me, I would apply a thick coat of paint stripper,
cover with wax paper to prevent the stripper from evaporating, and then
scrape the softened paint off with a Nestor Scraper, named after it's
inventor:

You make a Nestor Scraper by gripping a single edge razor blade:

[image:
http://www.homedepot.ca/wcsstore/Hom...0_2_rgb_4.jpg]

in a pair of needle nose style locking pliers:

[image: http://www.jsproductsinc.com/media/3599.jpg]

The resulting tool holds the razor blade at a near perfect angle for
scraping. Deposit the paint you shave off in a soup can or something
you'll be throwing away anyhow.

Using your "nestor" scraper on a concrete porch would waste a month of
Sundays. A hardwood scraper works MUCH better and quicker for the
first go-round. Just cut a hardwood board with a taper down to roughly
1/8 to 3/16 inch - about 3 or 4 inches wide - and use that to scrape
the goo off into a metal dustpan, cake-pan, shovel, or whatever to
dispose of it. Use a "gel" paint remover containing Methyllene
Chloride and DO NOT get it on your skin or in your eyes etc.

If there is much left after the first application and scraping, a
second application and scraping is often effective - and then you
wash it off, preferably with a pressure washer, working AWAY from the
house - and wearing goggles or a full face shield. After washing with
water a stiff bristle brush will remove any remains. Then etch with
muriatic acid, patch any hollows with modified patching cement (or a
strong sand-mix concrete mixed with BondFast or other PVA adhesive in
place of about quarter of the water) and coat the concrete with your
choice of concrete finish - FlexRock works well and stands up - there
are others - including the epoxy garage-floor kits you can buy from
the BORG or other building supply stores.

If your steps are wood, dull the edge of the razor on a belt sander
first to prevent the razor from cutting into the wood.

The thin edge of the razor will cut into the softened paint fairly
easily making removal faster.

Once the paint is off, then you can put whatever you want on the steps,
including indoor/outdoor carpeting.

On Sun, 9 Jun 2013 00:48:45 +0200, nestork
wrote:


Norminn;3075496 Wrote:

The front porch is concrete, and unless it is unusually smooth it would

be touch to remove anything with a scraper. If using stripper, citrus
stripper might work better because it doesn't evaporate, but it works
more slowly.

For wood, a razor blade would be a poor choice, especially trying to
grip it with pliers...there are nice little holders made especially for

razor blades.

The active ingredient in "citrus" based cleaners and paint strippers is
a chemical called "d-limonene". There are different kinds of limonene
chemicals found in orange peels, but the kind that's called "d-limonene"
has a distinct "orangey" smell to it. So, it's what's added to air
fresheners and cleaners to give them a "fresh citrus smell".

D-limonene is largely a useless substance, and it's only real claim to
fame is that since the d-limonene would be released into the atmosphere
and ground as orange peels rot, it's use in cleaners, air fresheners and
paint strippers is environmentally neutral. And, it's biodegradable.

https://en.wikipedia.org/wiki/Limonene

http://www.floridachemical.com/whatisd-limonene.htm
Notice how the Florida Chemical web site talks about d-limonene as being
the best thing since sliced bread whereas the Wikipedia web page
doesn't.

Companies aren't making "citrus" based products cuz they work better.

It's because, the Florida Orange Growers have a powerful lobby in
Washington, and they've succeeded in getting d-limonene classified as an
environmentally friendly chemical, and so there are tax incentives
available from Washington for manufacturers that use it in their
products. So, the Florida Orange Growers lobby has been prompting
manufacturers to include d-limonene in everything it could conceivably
be put in; partly on the grounds that it's environmentally neutral, and
therefore environmentally friendlier than using a chemical which
otherwise wouldn't have been produced. And, partly on the grounds that
Washington offers a tax incentive for manufacturers to use it, even if
it's use in a product doesn't enhance that product in any way.

It's not because the Florida Orange Growers are big environmentalists,
it's because the d-limonene that orange growers squeeze out of their
orange peels represents an additional income stream for stuff that would
otherwise just rot in their fields. So, their lobby group in Washington
is trying to drum up demand for d-limonene.

My experience with "d-Limonene" is that it's a waste of time trying to
use it to strip oil based paints. It does soften latex paints, tho.

Historically, the active ingredient used in paint strippers has been a
chemical called "methylene chloride". Poly-Strippa contains methylene
chloride as it's active ingredient, and so far as I know, it always has
been and still is the most effective chemical for stripping oil based
paints.
Another relatively effective (and nasty" stripper is Sodium Hydroxide
- the old "Gillettes Lye" or "red devil" mixed with corn starch and
water to make a thin paste. Effective on wood and concrete - nasty on
metals.

While I understand that new concrete won't stick to old concrete, and that the purpose of the Bondfast suggested in the previous post is to physically glue the new concrete to the old, a better choice would be a concrete bonding agent, like this one:



available from Home Depot and other stores.

A white wood glue like Bondfast, Weldbond or Elmer's Wood glue will re-emulsify (that is; dissolve in water, kinda) if it gets wet and stays wet for a long period of time. Furniture makers use wood glue for their furniture joints because it's strong AND because the joints can be taken apart to repair broken furniture by keeping the joints wet to dissolve (kinda) the glue in them.

Different concrete bonding agents work differently. Some use a resin (either PVA or acrylic) that gradually crosslinks with it's neighbors after the glue dries. That crosslinking turns the glue into one great big molecule which is too large to "dissolve" in water and is therefore no longer affected by moisture the way a white wood glue would be. Others have a chemical reaction that kicks in anywhere from a few hours to a few days after painting the bonding agent onto the concrete. The moisture from the fresh concrete re-activates the concrete bonding agent if it's dried up, and that re-activated bonding agent glues the new concrete to the old. However once that chemical reaction kicks in after the time window passes, the concrete bonding agent becomes unaffected by moisture, so that continuous contact with ground water won't affect it in any way.

Since rain storms only last a coupla days at most, you can generally get away with using white wood glue instead of a concrete bonding agent. However, if you're going to do any concrete repairs below grade or where the concrete can stay wet for long periods of time, then it would be better to use a concrete bonding agent instead of a white wood glue. Using a concrete bonding agent will ensure that any concrete repairs you do won't come apart if the concrete stays wet for a long time.

PS: You don't need to know the rest...
Re-emulsifying is different than dissolving. When sugar dissolves in water, the result is individual sugar molecules suspended in water, and so there is no solid phase present. When white wood glue re-emulsifies in water, you have polyvinyl acetate resins suspended in water. Each of those resins is a microscopically small particle of solid plastic, and therefore you do have a solid phase present. Incident light will reflect and refract at a solid/liquid interface because there's a difference in the refractive index of the two media. This is why white wood glue is white in colour while it's in the jug, dries to a clear colourless solid, and then turns the water milky white again as it re-emulsifies again in water. The solid resins suspended in water make the slurry look white for the same reason that clowds and snowbanks and the head on a beer is white; it's because incident light reflects and refracts at each phase boundary and your eye sees the resulting mixture of different frequencies of light as the colour "white". If white wood glue DISSOLVED in water, the water solution would be clear just like ordinary water because there wouldn't be any solid plastic present to reflect and refract light.

In fact, all the milky white liquids you buy that turn clear as they dry (like grout sealers, floor "waxes", white wood glue, etc.) behave that way because they contain solid particles that reflect and refract light. As the liquid evaporates, those solid particles fuse together, thereby eliminating the liquid/solid interfaces where that reflection and refraction occured, and that eliminate the white colour. The reason why latex paints darken as they dry is because they contain plastic resins as well, and as the paint dries, you no longer get the white colour being produced by reflection and refraction, and as that white discolouration disappears, the colour of the latex paint appears to darken.

On Sun, 9 Jun 2013 06:47:29 +0200, nestork
wrote:


While I understand that new concrete won't stick to old concrete, and
that the purpose of the Bondfast suggested in the previous post is to
physically glue the new concrete to the old, a better choice would be a
concrete bonding agent, like this one:

[image:
http://www.homedepot.ca/wcsstore/Hom...ve940ml_4.jpg]

available from Home Depot and other stores.

Which IS a PVA product.

A white wood glue like Bondfast, Weldbond or Elmer's Wood glue will
re-emulsify (that is; dissolve in water, kinda) if it gets wet and stays
wet for a long period of time. Furniture makers use wood glue for their
furniture joints because it's strong AND because the joints can be taken
apart to repair broken furniture by keeping the joints wet to dissolve
(kinda) the glue in them.

Different concrete bonding agents work differently. Some use a resin
(either PVA or acrylic) that gradually crosslinks with it's neighbors
after the glue dries. That crosslinking turns the glue into one great
big molecule which is too large to "dissolve" in water and is therefore
no longer affected by moisture the way a white wood glue would be.
Others have a chemical reaction that kicks in anywhere from a few hours
to a few days after painting the bonding agent onto the concrete. The
moisture from the fresh concrete re-activates the concrete bonding agent
if it's dried up, and that re-activated bonding agent glues the new
concrete to the old. However once that chemical reaction kicks in after
the time window passes, the concrete bonding agent becomes unaffected by
moisture, so that continuous contact with ground water won't affect it
in any way.


So what is your problem with PVA as a concrete bonding agent?
Since rain storms only last a coupla days at most, you can generally get
away with using white wood glue instead of a concrete bonding agent.
However, if you're going to do any concrete repairs below grade or where
the concrete can stay wet for long periods of time, then it would be
better to use a concrete bonding agent instead of a white wood glue.
Using a concrete bonding agent will ensure that any concrete repairs you
do won't come apart if the concrete stays wet for a long time.

PS: You don't need to know the rest...
Re-emulsifying is different than dissolving. When sugar dissolves
in water, the result is individual sugar molecules suspended in water,
and so there is no solid phase present. When white wood glue
re-emulsifies in water, you have polyvinyl acetate resins suspended in
water. Each of those resins is a microscopically small particle of
solid plastic, and therefore you do have a solid phase present.
Incident light will reflect and refract at a solid/liquid interface
because there's a difference in the refractive index of the two media.
This is why white wood glue is white in colour while it's in the jug,
dries to a clear colourless solid, and then turns the water milky white
again as it re-emulsifies again in water. The solid resins suspended in
water make the slurry look white for the same reason that clowds and
snowbanks and the head on a beer is white; it's because incident light
reflects and refracts at each phase boundary and your eye sees the
resulting mixture of different frequencies of light as the colour
"white". If white wood glue DISSOLVED in water, the water solution
would be clear just like ordinary water because there wouldn't be any
solid plastic present to reflect and refract light.

In fact, all the milky white liquids you buy that turn clear as they dry
(like grout sealers, floor "waxes", white wood glue, etc.) behave that
way because they contain solid particles that reflect and refract light.
As the liquid evaporates, those solid particles fuse together, thereby
eliminating the liquid/solid interfaces where that reflection and
refraction occured, and that eliminate the white colour. The reason why
latex paints darken as they dry is because they contain plastic resins
as well, and as the paint dries, you no longer get the white colour
being produced by reflection and refraction, and as that white
discolouration disappears, the colour of the latex paint appears to
darken.

On Sunday, June 9, 2013 2:33:25 PM UTC-7, wrote:
On Sun, 9 Jun 2013 06:47:29 +0200, nestork

wrote:





While I understand that new concrete won't stick to old concrete, and

that the purpose of the Bondfast suggested in the previous post is to

physically glue the new concrete to the old, a better choice would be a

concrete bonding agent, like this one:



[image:

http://www.homedepot.ca/wcsstore/Hom...ve940ml_4.jpg]



available from Home Depot and other stores.



Which IS a PVA product.



A white wood glue like Bondfast, Weldbond or Elmer's Wood glue will

re-emulsify (that is; dissolve in water, kinda) if it gets wet and stays

wet for a long period of time. Furniture makers use wood glue for their

furniture joints because it's strong AND because the joints can be taken

apart to repair broken furniture by keeping the joints wet to dissolve

(kinda) the glue in them.



Different concrete bonding agents work differently. Some use a resin

(either PVA or acrylic) that gradually crosslinks with it's neighbors

after the glue dries. That crosslinking turns the glue into one great

big molecule which is too large to "dissolve" in water and is therefore

no longer affected by moisture the way a white wood glue would be.

Others have a chemical reaction that kicks in anywhere from a few hours

to a few days after painting the bonding agent onto the concrete. The

moisture from the fresh concrete re-activates the concrete bonding agent

if it's dried up, and that re-activated bonding agent glues the new

concrete to the old. However once that chemical reaction kicks in after

the time window passes, the concrete bonding agent becomes unaffected by

moisture, so that continuous contact with ground water won't affect it

in any way.





So what is your problem with PVA as a concrete bonding agent?

Since rain storms only last a coupla days at most, you can generally get

away with using white wood glue instead of a concrete bonding agent.

However, if you're going to do any concrete repairs below grade or where

the concrete can stay wet for long periods of time, then it would be

better to use a concrete bonding agent instead of a white wood glue.

Using a concrete bonding agent will ensure that any concrete repairs you

do won't come apart if the concrete stays wet for a long time.



PS: You don't need to know the rest...

Re-emulsifying is different than dissolving. When sugar dissolves

in water, the result is individual sugar molecules suspended in water,

and so there is no solid phase present. When white wood glue

re-emulsifies in water, you have polyvinyl acetate resins suspended in

water. Each of those resins is a microscopically small particle of

solid plastic, and therefore you do have a solid phase present.

Incident light will reflect and refract at a solid/liquid interface

because there's a difference in the refractive index of the two media.

This is why white wood glue is white in colour while it's in the jug,

dries to a clear colourless solid, and then turns the water milky white

again as it re-emulsifies again in water. The solid resins suspended in

water make the slurry look white for the same reason that clowds and

snowbanks and the head on a beer is white; it's because incident light

reflects and refracts at each phase boundary and your eye sees the

resulting mixture of different frequencies of light as the colour

"white". If white wood glue DISSOLVED in water, the water solution

would be clear just like ordinary water because there wouldn't be any

solid plastic present to reflect and refract light.



In fact, all the milky white liquids you buy that turn clear as they dry

(like grout sealers, floor "waxes", white wood glue, etc.) behave that

way because they contain solid particles that reflect and refract light.

As the liquid evaporates, those solid particles fuse together, thereby

eliminating the liquid/solid interfaces where that reflection and

refraction occured, and that eliminate the white colour. The reason why

latex paints darken as they dry is because they contain plastic resins

as well, and as the paint dries, you no longer get the white colour

being produced by reflection and refraction, and as that white

discolouration disappears, the colour of the latex paint appears to

darken.

All this has been VERY interesting and educational -- for future projects. Large thanks to all who contributed.

On my porch paint project, I have to report that hand stripping is a no go.
To strip an area approx 3x3', I put in so much effort AND SO MUCH EXPEN$IVE $TRIPPER that, extrapolating to the full job, it would cost so much just in stripper, with no guarantee of a good job, that it becomes a loser's game..

Will just have to bite the bullet: locate a handyman capable of running a grinder and get that *&&%$$%^&* job finally done. In retrospect, this is a classic "penny wise, pound foolish" calculation, but in my defense, I do like to see if I can do [project]-- but enuff is enuff.

Again, thanks to all for valuable info.

HB

I don't have a problem with either PVA or PMMA as a concrete bonding agent.

There are hundreds of different kinds of polyvinyl acetate resins used to make paints, primers, adhesives and other products that I can't think of right now. Ditto for PMMA resins.

What I'm saying is that PVA resins that are used to make wood glue will re-emulsify if they stay wet for a long time. That's important so that you can repair wood furniture by taking the joints apart with moisture if you need to.

PVA resins that are used to make concrete bonding agents need to ultimately form a solid that's completely unaffected by moisture. That's important in a concrete bonding agent because concrete that's outdoors could potentially remain wet for a long time from rain, flood or snow melt. You don't want your concrete repairs coming apart because the glue used in the repair is dissolving (kinda).

So, even though both kinds of adhesives will come as a suspension of PVA plastic resins in water, the wood glue will dry to a solid that will re-emulsify if it gets wet and stays wet for long enough, while the concrete bonding agent will dry to a solid that won't re-emulsify under the same conditions. And, what I'm saying is that it's precisely for those reasons that some kinds of PVA resins are chosen to be used when the gameplan is to make white wood glue whereas others are used when making a concrete bonding agent.

I have nothing against either kind of resin being made of polyvinyl acetate plastic.

Higgs Boson wrote:

All this has been VERY interesting and educational -- for future
projects. Large thanks to all who contributed.

On my porch paint project, I have to report that hand stripping is a
no go.
To strip an area approx 3x3', I put in so much effort AND SO MUCH
EXPEN$IVE $TRIPPER that, extrapolating to the full job, it would cost
so much just in stripper, with no guarantee of a good job, that it
becomes a loser's game.

Will just have to bite the bullet: locate a handyman capable of
running a grinder and get that *&&%$$%^&* job finally done. In
retrospect, this is a classic "penny wise, pound foolish"
calculation, but in my defense, I do like to see if I can do
[project]-- but enuff is enuff.

Again, thanks to all for valuable info.

HB

In case it helps, here is a link that shows two types of concrete surface
grinders that Home Depot rents:
http://www.youtube.com/watch?v=drgB7J-ckbA .

They also rent a smaller hand-held concrete surface grinder.

How big is the area? And, it would really be great to see a photo although
I know you tried that once but it didn't upload correctly. I mentioned
earlier that I have had good luck uploading photos with http://TinyPic.com .

Good luck.

On Mon, 10 Jun 2013 01:01:54 +0200, nestork
wrote:


;3075965 Wrote:

So what is your problem with PVA as a concrete bonding agent?


I don't have a problem with either PVA or PMMA as a concrete bonding
agent.

There are hundreds of different kinds of polyvinyl acetate resins used
to make paints, primers, adhesives and other products that I can't think
of right now.

What I'm saying is that PVA resins that are used to make wood glue will
re-emulsify if they stay wet for a long time. That's important so that
you can repair wood furniture by taking the joints apart with moisture.

PVA resins that are used to make concrete bonding agents need to
ultimately form a solid that's completely unaffected by moisture.
That's important in a concrete bonding agent because most concrete is
outdoors, and the repair could stay wet for a long time from rain, flood
or snow melt. You don't want your concrete repairs coming apart because
the glue used to glue the new concrete to the old is dissolving
(kinda).
The high Ph of the concrete apparently has an effect on the
crosslinking of the PVA resin making it more water resistant than when
it is used solo as a wood glue.
It's common to use white wood glue in brick mortar when repointing
bricks because the only moisture the bricks high up on an exterior wall
are every going to see is the occasional rain. But, at the other end of
the spectrum, you'd never use a white wood glue to repair a concrete
swimming pool or concrete underground sewer pipe because that
environment will be wet for long periods, and the wood glue used to glue
the new concrete to the old is going to come apart, causing the repair
to fail.
But the PVA is IN the concrete, not used as a glue between the
concrete -the hydrating of the lime in the portland cement combined
with the PVA resin apparently has a different effect.
It's in those situations where the concrete repair could stay
wet for a long time that you'd be better off using a concrete bonding
agent than a wood glue. And, it's all because the concrete bonding
agent will ultimately form a solid that's unaffected by moisture,

Which APPARENTLY is what happens when PVA resin is combined with
portland cement. An old construction worker next door has used
bondfast in concrete as a bonding agent for decades with good results
on porches and garage floors - and also in foundation parging.
-
whereas the wood glue will always re-emulsify in water if it stays wet
enough for long enough. And, that's true no matter how long the
furniture has been dry.

Higgs Boson:

Hiring someone with a hand grinder to grind that paint off is going to be expensive and any grind wheel he uses is going to get all gummed up with paint quickly. Instead, just mail order a cheap hand grinder:



from Harbour Freight or wherever and fit it with a rotary wire brush, like this one:



or, if that seems kinda scary to you, consider buying a "cup" style rotary wire brush:

http://i.ebayimg.com/00/s/NTg5WDY0MA...d= 8800005007

and you'll tear that paint off your concrete real fast without harming the concrete.

Several important points:

1. Hand grinders spin at about 20 to 25 thousand rpm which is a LOT faster than bench grinders, and most rotary wire brushes in hardware stores and home centers are only meant for use on bench grinders. They will only be rated for about 6,000 rpm at the most. Go to any welding supply store and you'll find rotary wire brushes there rated for 25,000 RPM and more. Those are meant for use on hand grinders.

2. A wire brush spinning at 25,000 rpm WILL occasionally lose a wire, and those wires WILL go through your clothing and occasionally stick into your skin. You might have to stop work and pull the odd one out. But ALWAYS ALWAYS ALWAYS wear eye protection when using a rotary wire brush on a hand grinder. If you're using a regular wire brush and not the cup style, then ALWAYS wear leather work gloves with it as well just in case you inadvertantly touch the spinning brush or it throws a wire at your hand.

3. Normally, the safety guard on a hand grinder is meant to fit over and around a grinding disk, which is very much thinner than a bursh. It won't fit over a rotary wire brush because they're generally a lot wider then a grinding disk. So, you almost certainly will have to operate the hand grinder without the safety guard on it. That's a good reason for wearing leather gloves anyhow. I can't remember the last time I had the safety guard on my grinder because like most people, I use it without the safety guard. If you opt to buy a cup type rotary brush, it won't be dangerous at all because your hands won't be near the spinning wires.
But, since the safety guard will be off your hand grinder anyhow, try to get a rotary wire brush that screws onto the arbor of your hand grinder (like the two shown above) rather than just slips over the arbor and is held in place with the hardware that came with the hand grinder. Brushes that have a nut welded to them so that they screw on will be held further away from the hand grinder so that the brush is a bit further from your hands and well away from the grinder itself.
The standard arbor size used in North America on hand grinders is a 5/8 inch National Coarse threadm or 5/8 inch diameter by 11 threads per inch. Make sure any hand grinder you buy has that kind of arbor, and that any brush you buy will screw onto that kind of an arbor.

4. If you're concerned about inhaling lead dust, wear a dust mask and work only on windy days.

How do you know this?

The PVA resins used to make general purpose primers and inexpensive paints are generally LESS alkali resistant then acrylic resins used to make specialized primers and higher priced paints. That is, a general purpose PVA primer will crack and peel when painted onto fresh concrete before an acrylic paint or primer would.

But, if high alkalinity supposedly makes PVA more moisture resistant, supposedly by promoting denser crosslinking, then the resulting PVA film would be stronger because of that denser cross linking as well, and so it should hold together better than an acrylic primer or paint film. But, in fact the opposite is true. Acrylic primers and paints are MORE alkali resistant than PVA primers and paints.

So, what you're saying about alkalinity enhancing the moisture resistance of PVA just doesn't seem to ring true at first glance.

You should also know that the only reason fresh concrete is highly alkaline is because it's made with lime, or calcium hydroxide. Calcium hydroxide is Ca(OH)2, and it's those hydroxyl (OH) groups in the concrete that make it alkaline. Gradually, over the course of one or two years, most of the calcium hydroxide near the surface of the concrete reacts with carbon dioxide in the air and is converted to calcium carbonate, CaCO3, also called "limestone" or "chaulk". As that chemical reaction happens, those OH groups disappear and the alkalinity of the concrete subsides. That conversion of hydroxide to carbonate is part of something called the "Lime Cycle", and it happens in every cementatious material made using lime, including tile setting thin set mortars, brick mortar, stuccos and real lime based plasters. Lime, Ca(OH)2 is highly alkaline, but chaulk is only a weak alkali; so weak in fact that we swallow it in the form of TUMS tablets to neutralize excessive stomach acidity.

What is Lime? | Products | Graymont

So, whomever told you that the pH of concrete affects PVA's moisture resistance didn't know that only FRESH concrete is highly alkaline. Old concrete is not highly alkaline, and so the PVA resins that get painted onto the old concrete would NOT be affected by the alkalinity the way any PVA resins actually mixed in to the fresh concrete might.

Believe it or not, no one actually knows what actually happens when you mix water with a mixture of portland cement, lime and stones to transform it into the hard waterproof compound we call "concrete". We've known what we have to mix together to make concrete from Roman times, but we don't actually know why that particular mixture of materials, when mixed with water, cures to a compound that's harder than any of the constituent materials used to make it, or why the resulting compound doesn't dissolve in water. Obviously, chemical bonds form that are stronger than the hydrogen bonds that would cause it to dissolve in water, but what actually happens at a detailed technical level is unknown. It's one of the most mysterious substances that we're completely comfortable using because we've learned how to use it very well over the past 2000 years.

So, what happens inside concrete when you add PVA resins is also unknown, but if I had to guess, I'd certainly say that the PVA plastic remains a separate material within the concrete. That is, there would be no chemical reactions between the concrete and the plastic.

Since you use a concrete bonding agent by painting it onto the surface of the old concrete you want the new concrete to stick to, AND, that the concrete bonding agent can dry before you apply the fresh concrete and the moisture from the fresh concrete will reactivate the adhesive quality of the bonding agent, then I'd say that the concrete bonding agent sticks to the old concrete and diffuses into the fresh concrete. So, what you have inside the concrete at the repair would be a matrix that goes from pure concrete to pure PVA over a distance of less than 1/4 of an inch, and the PVA plastic on the pure plastic side is sticking to the old concrete. Based on the way concrete bonding agent is used, that's what makes the most sense to me.

If you can point me to any website that confirms that the high initial pH of concrete has any effect at all on the moisture resistance of the PVA resins used in white wood glue, I'll spend some quality time on that web site.

I have nothing but respect for your neighbor, but like so many other people of his generation, he learned his trade from others who knew exactly what to do, but never understood the science behind what they were doing and why they were doing it. I fully expect that he put Bondfast wood glue into lots of the concrete he used for repairs with the full knowledge and approval of his boss.

But, I also fully expect that neither of them knew that there were different KINDS of PVA resins, and that if he had used a different PVA resin which would have crosslinked after it dried to produce a completely waterproof glue, then those repairs would have been done even better than they were.

Finding old guys with 600 years experience that can't explain why they're using one chemical in one situation and another chemical in a different situation is NOT uncommon because they learned their trade from master craftsmen that didn't know those things themselves, and therefore couldn't explain it to their underlings. Nowadays, with many of the people doing repair work on their homes (whether amateurs or professionals) having university science backgrounds, those people are asking the technical questions that the previous generation never did, and so the old explanation "But, we always did it that way!" is more and more being questioned by people who understand the basics of the science and chemistry of it all and can tell a good answer from a lousy one.

And, of course, the internet is causing an explosion in general public knowledge just like the printing press, the radio and the television all did in their respective times. People are learning from communicating over the internet because regardless of their educational background, they can recognize a correct explanation when they hear one because it MAKES SENSE to them.

These are both things that have happened just over the past 20 to 40 years since your neighbor was learning his trade, so it's not surprising that there's a totally different mind set between people doing the same kind of work only one generation apart. Your neighbor probably never knew what was in the Bondfast he was adding to his concrete; only that it was sticky and made new concrete stick to old concrete. Nowadays, just one generation later, you and I are discussing why you'd use one kind of PVA resin for assembling wood furniture but a different kind for fixing an outdoor concrete step.

On Mon, 10 Jun 2013 10:19:44 +0200, nestork
wrote:


;3076053 Wrote:

The high Ph of the concrete apparently has an effect on the
crosslinking of the PVA resin making it more water resistant than when
it is used solo as a wood glue.

How do you know this?

The PVA resins used to make general purpose primers and inexpensive
paints are generally LESS alkali resistant then acrylic resins used to
make specialized primers and higher priced paints. That is, a general
purpose PVA primer will crack and peel when painted onto fresh concrete
before an acrylic paint or primer would.

But, if high alkalinity supposedly makes PVA more moisture resistant,
supposedly by promoting denser crosslinking, then the resulting PVA film
would be stronger because of that denser cross linking as well, and so
it should hold together better than an acrylic primer or paint film.
But, in fact the opposite is true. Acrylic primers and paints are MORE
alkali resistant than PVA primers and paints.

So, what you're saying about alkalinity enhancing the moisture
resistance of PVA just doesn't seem to ring true at first glance.

You should also know that the only reason fresh concrete is highly
alkaline is because it's made with lime, or calcium hydroxide. Calcium
hydroxide is Ca(OH)2, and it's those hydroxyl (OH) groups in the
concrete that make it alkaline. Gradually, over the course of one or
two years, most of the calcium hydroxide near the surface of the
concrete reacts with carbon dioxide in the air and is converted to
calcium carbonate, CaCO3, also called "limestone" or "chaulk". As that
chemical reaction happens, those OH groups disappear and the alkalinity
of the concrete subsides. That conversion of hydroxide to carbonate is
part of something called the "Lime Cycle", and it happens in every
cementatious material made using lime, including tile setting thin set
mortars, brick mortar, stuccos and real lime based plasters. Lime,
Ca(OH)2 is highly alkaline, but chaulk is only a weak alkali; so weak in
fact that we swallow it in the form of TUMS tablets to neutralize
excessive stomach acidity.

'What is Lime? | Products | Graymont'
(http://www.graymont.com/what_is_lime.shtml)

So, whomever told you that the pH of concrete affects PVA's moisture
resistance didn't know that only FRESH concrete is highly alkaline. Old
concrete is not highly alkaline, and so the PVA resins that get painted
onto the old concrete would NOT be affected by the alkalinity the way
any PVA resins actually mixed in to the fresh concrete might.

And exactly what do you not understand about using PVA as an
"additive" to patching cement? Is it not "fresh" concrete? I'm not
alking about a primer or a sealer - I'm talking about an additive to
fresh patching cement..

And even IF I was talking about using it as a primer, the alkalinity
of the fresh concrete used for the patch would DEFINITELY have an
effect on the pva applied to the old concrete, wouldn't it???

;3076053 Wrote:

But the PVA is IN the concrete, not used as a glue between the
concrete -the hydrating of the lime in the portland cement combined
with the PVA resin apparently has a different effect.


Believe it or not, no one actually knows what actually happens when you
mix water with a mixture of portland cement, lime and stones to
transform it into the hard waterproof compound we call "concrete".
We've known what we have to mix together to make concrete from Roman
times, but we don't actually know why that particular mixture of
materials, when mixed with water, cures to a compound that's harder than
any of the constituent materials used to make it, or why the resulting
compound doesn't dissolve in water. Obviously, chemical bonds form that
are stronger than the hydrogen bonds that would cause it to dissolve in
water, but what actually happens at a detailed technical level is
unknown. It's one of the most mysterious substances that we're
completely comfortable using because we've learned how to use it very
well over the past 2000 years.

And I guess we really don't know how or why the PVA crosslinks to
become a solid rather than an emulsion in the concrete while it
remains an emulsion when used as a wood glue. All I know is what I've
been told and the results the old guy next door has had using BondFast
white glue as a concrete patching additive.and what I've learned by
doing some internet searches on the subject, trying to figure out the
"why".

So, what happens inside concrete when you add PVA resins is also
unknown, but if I had to guess, I'd certainly say that the PVA plastic
remains a separate material within the concrete. That is, there would
be no chemical reactions between the concrete and the plastic.

Since you use a concrete bonding agent by painting it onto the surface
of the old concrete you want the new concrete to stick to, AND, that the
concrete bonding agent can dry before you apply the fresh concrete and
the moisture from the fresh concrete will reactivate the adhesive
quality of the bonding agent, then I'd say that the concrete bonding
agent sticks to the old concrete and diffuses into the fresh concrete.
So, what you have inside the concrete at the repair would be a matrix
that goes from pure concrete to pure PVA over a distance of less than
1/4 of an inch, and the PVA plastic on the pure plastic side is sticking
to the old concrete. Based on the way concrete bonding agent is used,
that's what makes the most sense to me.

;3076053 Wrote:

Which APPARENTLY is what happens when PVA resin is combined with
portland cement.


If you can point me to any website that confirms that the high initial
pH of concrete has any effect at all on the moisture resistance of the
PVA resins used in white wood glue, I'll spend some quality time on that
web site.

;3076053 Wrote:

An old construction worker next door has used bondfast in concrete as a
bonding agent for decades with good results on porches and garage floors
- and also in foundation parging.

I have nothing but respect for your neighbor, but like so many other
people of his generation, he learned his trade from others who knew
exactly what to do, but never understood the science behind what they
were doing and why they were doing it. I fully expect that he put
Bondfast wood glue into lots of the concrete he used for repairs with
the full knowledge and approval of his boss.

But, I also fully expect that neither of them knew that there were
different KINDS of PVA resins, and that if he had used a different PVA
resin which would have crosslinked after it dried to produce a
completely waterproof glue, then those repairs would have been done even
better than they were.

Finding old guys with 600 years experience that can't explain why
they're using one chemical in one situation and another chemical in a
different situation is NOT uncommon because they learned their trade
from master craftsmen that didn't know those things themselves, and
therefore couldn't explain it to their underlings. Nowadays, with many
of the people doing repair work on concrete (whether amateurs or
professionals) having university science backgrounds, those people are
asking the technical questions that the previous generation never did,
and so the old explanation "But, we always did it that way!" is more and
more being questioned by people who understand the science and chemistry
of it all and can tell a good answer from a lousy one.

And, of course, the internet is causing an explosion in public knowledge
just like the printing press, the radio and the television all did in
their respective times. People are learning from each other over the
internet because regardless of their educational background, they can
recognize a correct explanation when they hear one because it MAKE SENSE
to them.

These are both things that have happened just over the past 20 to 40
years since your neighbor was learning his trade, so it's not surprising
that there's a totally different mind set between people doing the same
kind of work only one generation apart. Your neighbor probably never
knew what was in the Bondfast he was adding to his concrete; only that
it was sticky and made new concrete stick to old concrete. Nowadays,
just one generation later, you and I are discussing why you'd use one
kind of PVA resin for assembling real wood furniture but a different
kind for fixing an outdoor concrete step. Learning and communicating
that knowledge is something we humans do extremely well; it was
absolutely pivotal in our evolution from apes.

I'm no expert on this stuff either.

But, I do know that PVA wood glue re-emulsifies if it gets wet and stays wet for a long time, and that concrete bonding agents are made so that they DON'T re-emulsify if they stay wet for a long time because it's often necessary to repair concrete in areas that are wet for long periods. You wouldn't have confidence in your repair if you couldn't count on the glue not to come apart on you.

And, I just don't accept that if PVA has poor alkalinity, that using it in fresh concrete is going to improve it's performance in any significant way, including making it more moisture resistant. If you can find a credible web site that says it does, I'll read it carefully, but otherwise, I just don't believe that.