Bumps in polyurethane
 

Hi all,

I'm trying to put a polyurethane coat onto a bookcase I'm building. Since
it's a prototype, it's made out of cheap, soft pine. I've got it stained,
and I'm trying to put on the final coat of polyurethane. But I keep
getting small bumps about 1 mm in diameter in the polyurethane coat. If I
sand them down and put on another coat, they come back (although I'm not
sure if they're in the same spot).

This seems to occur no matter how thick or thin I put the polyurethane on.
When I apply it, I've tried both not dragging the brush across the rim of
the can and just knocking off the excess. I wipe down the surface after
sanding.

I think I've got about five or six coats of varying thickness trying to get
rid of these bumps. What the heck am I doing wrong?

Thanks in advance.
--
Michael White "To protect people from the effects of folly is to
fill the world with fools." -Herbert Spencer, 1891

I will give it a try Michael,
Are the bumps small craters, likely the remnants of bubbles breaking the
surface and then drying as they burst? If so I would add some solvent to extend
the drying time and switch to using a rag with the diluted poly if this does
not work. Light coats are almost always best. Sometimes the material can start
to polymerize in the can forming small crystals which you need to filter out or
buy a can from a different batch. Cheers, JG


Michael White wrote:

Hi all,

I'm trying to put a polyurethane coat onto a bookcase I'm building. Since
it's a prototype, it's made out of cheap, soft pine. I've got it stained,
and I'm trying to put on the final coat of polyurethane. But I keep
getting small bumps about 1 mm in diameter in the polyurethane coat. If I
sand them down and put on another coat, they come back (although I'm not
sure if they're in the same spot).

This seems to occur no matter how thick or thin I put the polyurethane on.
When I apply it, I've tried both not dragging the brush across the rim of
the can and just knocking off the excess. I wipe down the surface after
sanding.

I think I've got about five or six coats of varying thickness trying to get
rid of these bumps. What the heck am I doing wrong?

Thanks in advance.
--
Michael White "To protect people from the effects of folly is to
fill the world with fools." -Herbert Spencer, 1891

"Michael White" wrote in message
link.net...
Hi all,

I'm trying to put a polyurethane coat onto a bookcase I'm building. Since
it's a prototype, it's made out of cheap, soft pine. I've got it stained,
and I'm trying to put on the final coat of polyurethane. But I keep
getting small bumps about 1 mm in diameter in the polyurethane coat. If I
sand them down and put on another coat, they come back (although I'm not
sure if they're in the same spot).


Are you "painting" in on Mike, or spreading it on? Poly does not like to be
painted. Use a good natural bristle brush or a foam pad applicator and
spread the poly in one direction, as opposed to brushing it on as you would
paint. Lots of folks work the poly too much with the brush and inject air
bubbles into their finish and it sounds like this might be biting you.

I understand that you want to solve this problem, but on a different note,
since you have a build up of poly already, at least be aware that you do
have another recourse now. Sand down your finish with 1000 grit wet paper
and use a rubbing compound to bring it back to the shine you want. You have
enough poly there, after 4 or 5 coats to be able to do quite a bit of
sanding before risking a burn through.

--

-Mike-

Michael,

I can think of a couple of reasons for imperfections:

* Bubbles
* Dust particles (either airborn or reintroduced to the can)
* Cured chunks of poly contaminating the can.

How to mitigate the problems up front:


Bubbles: Thin the poly a bit (maybe 4:1 poly to thinner ratio) and watch
your application technique, as others have already suggested.

Airborn dust. Vac the area before finishing (but not right before, let the
kicked up stuff settle) wipe down your work with a tack rag. Thinning will
help with this as well. A thinner layer (created by the application of less
viscouspoly) will create a smaller "dimple" when the dust lands on your
work. Personally I thing full strength poly is only for "quick 'n thick"
protection, but appearance does not matter finishing.

Contamination: Always pour into a separate container and work from that.
Never pour back the extra. I find the yogurt cups work very nicely for
this... they come with lids too.

Chunks... It's time to buy a new can of poly.

How to recover from the imperfections that you have (there will always be
some unless you finish in an IBM silicon wafer production facility):

A cabinet scraper is your friend. This will knock off the high spots and not
remove any other finnish. If you don't have one, scrape the surface lightly
with a utility knife blace (just the blade, not in the knife) with the blade
scquare to the surface, and moving in the direction of the face of the
blade. You want to scrape, not cut. A light touch will knock off the dust
nibs .

Without the high spots, your between coats sanding will only lightly abraid
the surface. You should not be trying to level the finish. Use a block.

Cheers,

Steve


"Michael White" wrote in message
link.net...
Hi all,

I'm trying to put a polyurethane coat onto a bookcase I'm building. Since
it's a prototype, it's made out of cheap, soft pine. I've got it stained,
and I'm trying to put on the final coat of polyurethane. But I keep
getting small bumps about 1 mm in diameter in the polyurethane coat. If I
sand them down and put on another coat, they come back (although I'm not
sure if they're in the same spot).

This seems to occur no matter how thick or thin I put the polyurethane on.
When I apply it, I've tried both not dragging the brush across the rim of
the can and just knocking off the excess. I wipe down the surface after
sanding.

I think I've got about five or six coats of varying thickness trying to
get
rid of these bumps. What the heck am I doing wrong?

Thanks in advance.
--
Michael White "To protect people from the effects of folly is to
fill the world with fools." -Herbert Spencer, 1891

On Thu, 17 Mar 2005 04:39:20 GMT, Michael White
wrote:

Hi all,

I'm trying to put a polyurethane coat onto a bookcase I'm building. Since
it's a prototype, it's made out of cheap, soft pine. I've got it stained,
and I'm trying to put on the final coat of polyurethane. But I keep
getting small bumps about 1 mm in diameter in the polyurethane coat. If I
sand them down and put on another coat, they come back (although I'm not
sure if they're in the same spot).


I think JGS got it right. You might be going cheap all around. It's
likely lumps of polymerised urethane. Try sanding down with very fine
wet paper. Use a block, and don't press too hard, but lots of
sideways motion, not pressing. That is, take your time. Try on some
scrap material first after varnishing and drying adequately.

If so, go buy some new varnish and use the old to start the next
outdoor scrub-brush cleanup.

If only a few small bumps, filter the poly before using it. Otherwise, toss it
and get a new can. I'd remove what's there, and not try to sand it down.
Especially not with the 1000 grit mentioned, unless you have alot of time. You
could wet sand with 320 then 400 and recoat, but I suspect you'll still have
embedded pieces of cured poly that'll be visible.

Others suggested thinning, but that will rarely help. They also didn't ask if
you were using water or oil base poly, as the former should not be thinned for
hand application. As to bubbles versus bumps, if a real thin coat has them,
they're not bubbles. As to adding solvent to slow it down, it depends on the
solvent, as some will speed it up. And if it's water base and you add solvent,
it'll be a real mess.

GerryG

On Thu, 17 Mar 2005 04:39:20 GMT, Michael White
wrote:

Hi all,

I'm trying to put a polyurethane coat onto a bookcase I'm building. Since
it's a prototype, it's made out of cheap, soft pine. I've got it stained,
and I'm trying to put on the final coat of polyurethane. But I keep
getting small bumps about 1 mm in diameter in the polyurethane coat. If I
sand them down and put on another coat, they come back (although I'm not
sure if they're in the same spot).

This seems to occur no matter how thick or thin I put the polyurethane on.
When I apply it, I've tried both not dragging the brush across the rim of
the can and just knocking off the excess. I wipe down the surface after
sanding.

I think I've got about five or six coats of varying thickness trying to get
rid of these bumps. What the heck am I doing wrong?

Thanks in advance.

I assume they're tiny bubbles or dust specks. I've used polyurethane
quite a bit (I use a foam brush)and always have tiny imperfections in
the final coat. After it cures for several days I sand the final coat
with 600 paper by just barely touching the surface with the sandpaper.
This super light sanding does not change the sheen and removes the tiny
imperfections (at least to the touch). If I look very closely in the
right light I can still see some very tiny imperfections, but the
surface now feels smooth.

Charles

On Thu, 17 Mar 2005 04:39:20 GMT, Michael White

wrote:

Hi all,

I'm trying to put a polyurethane coat onto a bookcase I'm building. Since
it's a prototype, it's made out of cheap, soft pine. I've got it stained,
and I'm trying to put on the final coat of polyurethane. But I keep
getting small bumps about 1 mm in diameter in the polyurethane coat. If I
sand them down and put on another coat, they come back (although I'm not
sure if they're in the same spot).

Get a magnifying glass. I'm sure you'll find that they're bubbles
introduced by either the wrong brush or the wrong use of a good
brush. Why not try a REAL finish instead of poly next time?


----------------------------------------------------------
Please return Stewardess to her original upright position.
--------------------------------------
http://www.diversify.com Tagline-based T-shirts!

Real? What's unreal about poly? I'm not a fan of applying slow drying
solvent based poly, but to suggest that poly's aren't real is quite a
stretch of the imagination.

Dave

Larry Jaques wrote:

On Thu, 17 Mar 2005 04:39:20 GMT, Michael White


wrote:


Hi all,

I'm trying to put a polyurethane coat onto a bookcase I'm building. Since
it's a prototype, it's made out of cheap, soft pine. I've got it stained,
and I'm trying to put on the final coat of polyurethane. But I keep
getting small bumps about 1 mm in diameter in the polyurethane coat. If I
sand them down and put on another coat, they come back (although I'm not
sure if they're in the same spot).


Get a magnifying glass. I'm sure you'll find that they're bubbles
introduced by either the wrong brush or the wrong use of a good
brush. Why not try a REAL finish instead of poly next time?


----------------------------------------------------------
Please return Stewardess to her original upright position.
--------------------------------------
http://www.diversify.com Tagline-based T-shirts!

Thanks for everyone's input. To address a few questions:

- The polyurethane is oil-based.
- I've been careful not to paint the polyurethane on, and go over it once at
the end in strokes that span the length of the piece.
- They're definitely bumps, not craters. If I scrape them off, they're
polyurethane chunks.
- The bumps are quite numerous, and especially stand out in certain
lighting.
- I don't think I'm using the wrong brush, as it said it could be used for
oil-based polyurethane.

Some things that were said that may have a high probability of me screwing
up:

- Contaminated polyurethane. I don't remember these bumps on the early
coats when the can was new, but I didn't really pay attention either.
Also, I did inadvertently leave the lid off for several hours.
- It might be dust. I'll clean up a little better this time and see if it
makes a difference.
- I may be working the polyurethane too much as stated by Mike Marlow.

Larry Jaques, you recommended a "real finish" - what were you referring to?
I noticed that they have expoxy coatings, but the stuff I saw at Home Depot
was $25 for a quart that covers four square feet. Rather expensive.

Thanks again!
--
Michael White "To protect people from the effects of folly is to
fill the world with fools." -Herbert Spencer, 1891

Stephen M ) wrote on Thursday 17 March 2005
08:01 am:

Michael,

I can think of a couple of reasons for imperfections:

* Bubbles
* Dust particles (either airborn or reintroduced to the can)
* Cured chunks of poly contaminating the can.

How to mitigate the problems up front:


Bubbles: Thin the poly a bit (maybe 4:1 poly to thinner ratio) and watch
your application technique, as others have already suggested.

Airborn dust. Vac the area before finishing (but not right before, let the
kicked up stuff settle) wipe down your work with a tack rag. Thinning will
help with this as well. A thinner layer (created by the application of
less viscouspoly) will create a smaller "dimple" when the dust lands on
your
work. Personally I thing full strength poly is only for "quick 'n thick"
protection, but appearance does not matter finishing.

Contamination: Always pour into a separate container and work from that.
Never pour back the extra. I find the yogurt cups work very nicely for
this... they come with lids too.

Chunks... It's time to buy a new can of poly.

How to recover from the imperfections that you have (there will always be
some unless you finish in an IBM silicon wafer production facility):

A cabinet scraper is your friend. This will knock off the high spots and
not remove any other finnish. If you don't have one, scrape the surface
lightly with a utility knife blace (just the blade, not in the knife) with
the blade scquare to the surface, and moving in the direction of the face
of the blade. You want to scrape, not cut. A light touch will knock off
the dust nibs .

Without the high spots, your between coats sanding will only lightly
abraid the surface. You should not be trying to level the finish. Use a
block.

Cheers,

Steve


"Michael White" wrote in message
link.net...
Hi all,

I'm trying to put a polyurethane coat onto a bookcase I'm building.
Since
it's a prototype, it's made out of cheap, soft pine. I've got it
stained,
and I'm trying to put on the final coat of polyurethane. But I keep
getting small bumps about 1 mm in diameter in the polyurethane coat. If
I sand them down and put on another coat, they come back (although I'm
not sure if they're in the same spot).

This seems to occur no matter how thick or thin I put the polyurethane
on. When I apply it, I've tried both not dragging the brush across the
rim of
the can and just knocking off the excess. I wipe down the surface after
sanding.

I think I've got about five or six coats of varying thickness trying to
get
rid of these bumps. What the heck am I doing wrong?

Thanks in advance.

On Fri, 18 Mar 2005 01:29:07 GMT, the inscrutable Michael White
spake:

Thanks for everyone's input. To address a few questions:

Larry Jaques, you recommended a "real finish" - what were you referring to?

ABP. (_anything_ but poly)

Ackshully, poly isn't bad on its own, especially the oil-based stuff.
It's just that about, oh, 95% of people using it slop it on and it
looks as if the piece was wrapped in Saran.

Either toss that can out and buy some Waterlox (my current favorite,
and a gallon of it arrived at my door last Saturday) or get a new can
of that crap (or shellac or Watco) and be sure to filter it with a
paint-store sieve this time. Paint filters are inexpensive and worth
their weight in gold for a nice finish, especially with old cans of
pukey poly.

You didn't mention trying a magnifying glass. Did you make sure it
wasn't bubbles (popped or unpopped) you were seeing?


----------------------------------------------------------
Please return Stewardess to her original upright position.
--------------------------------------
http://www.diversify.com Tagline-based T-shirts!

On Fri, 18 Mar 2005 01:29:07 GMT, Michael White
wrote:
Thanks for everyone's input. To address a few questions:


(good answers snipped)

Some things that were said that may have a high probability of me screwing
up:

- Contaminated polyurethane. I don't remember these bumps on the early
coats when the can was new, but I didn't really pay attention either.
Also, I did inadvertently leave the lid off for several hours.
- It might be dust. I'll clean up a little better this time and see if it
makes a difference.
- I may be working the polyurethane too much as stated by Mike Marlow.

In one of George Grotz's books, he states that for ANY varnish product
you need:

-A scrupulously cleaned room.

-A NEW can of varnish

-A NEW brush.

Every time I've done all three, I've gotten good results with anything
in the varnish family.

When I haven't, I've done a fair imitation of Jurassic Park what with
all the insects trapped in resin and all.

As for the brush questuion, I solved the same problem by buying a $15
spray can from Harbor Frieght.
My other prob. has been temperature. In the winter I had a real tough
time getting a good finish. Not being able to heat my shop
suffeciently, what I have to do now is put the project, and the can, in
the house overnight if spyaying in the moring; problem solved.

Poly, urethane, acrylic are all suitable finishes for certain applications
when applied correctly. Lacquer is an interesting one that many endorse, but
the name itself is used for many different and sometimes unrelated compounds.
Except for shellac, many of them are plastic of one type or another. And even
shellac can be applied so that the result looks like a cheap plastic coating.
But, it does give us something rather harmless to argue about.

In the meantime, I'm a'goin to go and stain some cherry.
GerryG

On Thu, 17 Mar 2005 17:28:02 -0800, David wrote:

Real? What's unreal about poly? I'm not a fan of applying slow drying
solvent based poly, but to suggest that poly's aren't real is quite a
stretch of the imagination.

Dave

Larry Jaques wrote:

On Thu, 17 Mar 2005 04:39:20 GMT, Michael White


wrote:


Hi all,

I'm trying to put a polyurethane coat onto a bookcase I'm building. Since
it's a prototype, it's made out of cheap, soft pine. I've got it stained,
and I'm trying to put on the final coat of polyurethane. But I keep
getting small bumps about 1 mm in diameter in the polyurethane coat. If I
sand them down and put on another coat, they come back (although I'm not
sure if they're in the same spot).


Get a magnifying glass. I'm sure you'll find that they're bubbles
introduced by either the wrong brush or the wrong use of a good
brush. Why not try a REAL finish instead of poly next time?


----------------------------------------------------------
Please return Stewardess to her original upright position.
--------------------------------------
http://www.diversify.com Tagline-based T-shirts!

On Sat, 19 Mar 2005 02:44:03 GMT, the inscrutable GerryG
spake:

Poly, urethane, acrylic are all suitable finishes for certain applications
when applied correctly.

Ah! The key words are those last 3, which rules out most applications
in the real world. The way poly is applied in the real world is akin
to painting a Lambo with a latex and a pig bristle whitewash brush.


Lacquer is an interesting one that many endorse, but
the name itself is used for many different and sometimes unrelated compounds.
Except for shellac, many of them are plastic of one type or another. And even
shellac can be applied so that the result looks like a cheap plastic coating.
But, it does give us something rather harmless to argue about.

g


In the meantime, I'm a'goin to go and stain some cherry.

....and come back as a crotch crab in your next life.


--

People will occasionally stumble over the truth, but
most of the time they'll pick themselves up and carry on.
--anon

On Sat, 19 Mar 2005 06:47:28 -0800, Larry Jaques
wrote:

On Sat, 19 Mar 2005 02:44:03 GMT, the inscrutable GerryG
spake:

Poly, urethane, acrylic are all suitable finishes for certain applications
when applied correctly.

Ah! The key words are those last 3, which rules out most applications
in the real world. The way poly is applied in the real world is akin
to painting a Lambo with a latex and a pig bristle whitewash brush.

Well....I guess I've got no choice but to agree with you on this one.

snip
In the meantime, I'm a'goin to go and stain some cherry.

...and come back as a crotch crab in your next life.
Sorry, but I had to do it. Daughter already had a "commercial" coffee table in
their "cherry". Had to go to Jewitt to find out their finishing schedule, but
at least I managed to match it without using the glaze. I will say that
everybody liked the cherry better before it was stained, but the budget didn't
allow making a new coffee table also.
GerryG

On Sat, 19 Mar 2005 15:02:56 GMT, the inscrutable GerryG
spake:

On Sat, 19 Mar 2005 06:47:28 -0800, Larry Jaques
wrote:

On Sat, 19 Mar 2005 02:44:03 GMT, the inscrutable GerryG
spake:

Poly, urethane, acrylic are all suitable finishes for certain applications
when applied correctly.

Ah! The key words are those last 3, which rules out most applications
in the real world. The way poly is applied in the real world is akin
to painting a Lambo with a latex and a pig bristle whitewash brush.

Well....I guess I've got no choice but to agree with you on this one.

Thank you. It's not often that someone who actually uses the crap
will agree about its darker half (95%).


snip
In the meantime, I'm a'goin to go and stain some cherry.

...and come back as a crotch crab in your next life.
Sorry, but I had to do it.

Did not. You could have said "Get some jerk kid to ruin it for you."
Alternatively (if you wanted your daughter to speak to you again)
you could have stated it a bit more diplomatically "Let me finish
it and see what you think. If you don't like it, we can make it
look ****ty like your commercial piece of crap there with some
nice Minwhacked PolyShades." (Grain? What grain?)


Daughter already had a "commercial" coffee table in
their "cherry". Had to go to Jewitt to find out their finishing schedule, but

There ya go with the YB talk...


at least I managed to match it without using the glaze. I will say that

That's good.


everybody liked the cherry better before it was stained, but the budget didn't
allow making a new coffee table also.

Hindsight's 20/20, eh? sigh


--

People will occasionally stumble over the truth, but
most of the time they'll pick themselves up and carry on.
--anon

On Sat, 19 Mar 2005 18:20:49 -0800, Larry Jaques
wrote:

On Sat, 19 Mar 2005 15:02:56 GMT, the inscrutable GerryG
spake:

On Sat, 19 Mar 2005 06:47:28 -0800, Larry Jaques
wrote:

snip
In the meantime, I'm a'goin to go and stain some cherry.

...and come back as a crotch crab in your next life.
Sorry, but I had to do it.

Did not. You could have said "Get some jerk kid to ruin it for you."
Alternatively (if you wanted your daughter to speak to you again)
you could have stated it a bit more diplomatically "Let me finish
it and see what you think. If you don't like it, we can make it
look ****ty like your commercial piece of crap there with some
nice Minwhacked PolyShades." (Grain? What grain?)

snip
Minwacked PolyShades? Sorry, but I didn't go there. This was sprayed with a
mix of TransTint dyes, using several feathered coats to blend the cherry
pieces to the same shade. Sprayed with clear shellac to seal and scuff sanded,
then a light coat of amber shellac to darken it just a bit. Finish was three
thin coats of flat poly. With no pigments or glaze used, the grain is still
there.
GerryG

Bumps in polyurethane
 

replying to Charles Krug, NotSureAboutThat wrote:
Had all three and still had this same thing happen. I'm talking brand new
within min/hours of buying and a room that had been air filtered for days

--
for full context, visit https://www.homeownershub.com/woodwo...hane-2006-.htm

Bumps in polyurethane
 

replying to Larry Jaques, NotSureAboutThat wrote:
Why not post helpful information

--
for full context, visit https://www.homeownershub.com/woodwo...hane-2006-.htm

Bumps in polyurethane
 

On Wednesday, May 30, 2018 at 5:14:06 PM UTC-4, NotSureAboutThat wrote:
replying to Larry Jaques, NotSureAboutThat wrote:
Why not post helpful information


Why not respond to posts from this decade?