Hello,

I have some areas of loose plaster, where the top coat has come away
from the base coat. Is browning just another name for the base coat?

I think it has been mentioned here before about drilling holes and
pouring PVA down to glue the two layers back together but I've just
bashed off the loose plaster the good old fashioned way

I've had a read of the wiki "plastering beginner's guide". It mentions
using a dilute PVA mix somewhere between 5:1 and 3:1 water to PVA. The
base coat is very sandy and I am sure that the PVA is very important
to prevent the layers separating again. Are all PVAs the same? I am
confused because TS sells so many: interior PVA, exterior PVA, and
this:
http://www.toolstation.com/shop/Adhe.../sd3198/p59879

I presume that's the one I need but what are the differences between
the different types?

I had a pro plaster my ceiling and he poured from a 5L bottle of
Wickes' PVA but only added the slightest drop of water; far from being
5:1 it was more like 1:50! Why so strong?

I also found a post from this group where it is recommended to PVA
conduit before plastering on top of chases. I've never done that
before, should I start to do so? Does it give a rougher surface for
the plaster to adhere to?

Thanks.

In article ,
Stephen writes:
Hello,

I have some areas of loose plaster, where the top coat has come away
from the base coat. Is browning just another name for the base coat?

Browning is a particular type of scratch (base) coat.
When I did my plastering training, I was told it's rarely used
nowadays, and consequently, I've never used it. For the scratch
(base) coat, I use either bonding coat (which works on everything
except damp walls), or sand/lime/cement/waterproofer (for damp walls).

I think it has been mentioned here before about drilling holes and
pouring PVA down to glue the two layers back together but I've just
bashed off the loose plaster the good old fashioned way

I've had a read of the wiki "plastering beginner's guide". It mentions
using a dilute PVA mix somewhere between 5:1 and 3:1 water to PVA. The
base coat is very sandy and I am sure that the PVA is very important
to prevent the layers separating again. Are all PVAs the same? I am
confused because TS sells so many: interior PVA, exterior PVA, and
this:
http://www.toolstation.com/shop/Adhe.../sd3198/p59879

I presume that's the one I need but what are the differences between
the different types?

They are all the same except exterior PVA (which should more
properly be called EVA, but then builders wouldn't know what
it was).

They'll all work, but EVA is a waste (it's more expensive and
won't make any difference in this application).

The other thing to check is if the PVA is already diluted, and
it sometimes is in the 5l containers. Plasters often buy it this
way as it saves diluting it (it's not the easiest stuff to mix
with water, and when time is money, buying it already diluted
is probably cheaper).

I had a pro plaster my ceiling and he poured from a 5L bottle of
Wickes' PVA but only added the slightest drop of water; far from being
5:1 it was more like 1:50! Why so strong?

It may have been already diluted, or he may have been after
using it only for bonding (see below).

It is used for two purposes, often in 2 coats.

A dilute coat such as 5:1 acts to stablise the surface if it's
dusty and to reduce the tendancy of the base to suck all the
water out of the new plaster before it sets. You apply this
and let it soak in and wait until it dries (or at least, feels
dry).

Secondly, finish coat plaster does not have any bonding in it,
and only a limited ability to stick to things. Ideally, you put
it on when the coat underneath is not quite set, and then it
will bond well with that. If the coat underneath is well set,
then it won't bond well, and if it's something smooth such as
plastic, it will hardly bond at all. To get around this, you
put a more concentrated PVA coat on (3:1 is typical) and you
start plastering ideally whilst that is still tacky. This will
effectively glue the finish coat on, and by using this technique,
you can plaster just about anything that doesn't flex. It doesn't
matter if the PVA has dried by the time you get to the last bit
of plastering, as the water in the plaster will resoften the PVA.

I also found a post from this group where it is recommended to PVA
conduit before plastering on top of chases. I've never done that
before, should I start to do so? Does it give a rougher surface for
the plaster to adhere to?

It glues the plaster to the plastic.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On Tue, 29 Sep 2009 21:20:28 +0000 (UTC),
(Andrew Gabriel) wrote:

Browning is a particular type of scratch (base) coat.

Thanks. I had heard the name before and thought it was a synonym for
base coat; I had not realised it was a particular type of base coat.

[PVAs]
are all the same except exterior PVA (which should more
properly be called EVA, but then builders wouldn't know what
it was).

They'll all work, but EVA is a waste (it's more expensive and
won't make any difference in this application).

I once bought a litre of exterior PVA, perhaps I wasted some money
because I've only used it for interior gluing. I guess at the time I
bought it thinking it would cover all circumstances and I wouldn't
need to buy a second bottle if I ever needed to glue anything
outdoors. However for plastering, I would get through the bottle too
quickly and I agree it would be a waste.

The other thing to check is if the PVA is already diluted, and
it sometimes is in the 5l containers. Plasters often buy it this
way as it saves diluting it (it's not the easiest stuff to mix
with water,

I've had a look on Wickes' web site but it doesn't go into detail
about the different types of PVA they sell. They have "waterproof" PVA
which I guess means exterior PVA and "building adhesive" PVA which I
guess is interior PVA? All of them are described as being for sealing
and priming and being "ready mixed". I am not sure whether ready mixed
means ready diluted or whether it means it is a paste not a powder?

Anyway, my plasterer used the £9 rather than the £19 bottle, so I
think you must be right. It probably is diluted which is why it is
half the price of the others, which presumably are not diluted.

http://www.wickes.co.uk/PVA-Adhesive/invt/240701

A dilute coat such as 5:1 acts to stablise the surface if it's
dusty and to reduce the tendancy of the base to suck all the
water out of the new plaster before it sets.

This is what I need in my application. I will buy the 5L one from TS
as it's a bit cheaper than Wickes. Sadly TS and BondLoc's web sites
say very little about he product. I'll have to read the label when it
arrives.

Secondly, finish coat plaster does not have any bonding in it,
and only a limited ability to stick to things. Ideally, you put
it on when the coat underneath is not quite set, and then it
will bond well with that. If the coat underneath is well set,
then it won't bond well, and if it's something smooth such as
plastic, it will hardly bond at all. To get around this, you
put a more concentrated PVA coat on (3:1 is typical)

This is what he needed to glue the plaster to the ceiling. That
explains the difference, thanks.


[about conduit]
It glues the plaster to the plastic.

I have been experimenting with chases. I saw Wickes sold bags of
mortar advertised for filling chases and TLC sell quick setting
cement. Would PVA be needed for either of these?

I have used plaster in the past but it always cracked because the
chase was too thick, which meant a second coat was required on top. I
found that the cement cracked too. However, when using mortar there
were no cracks so it made a simple one-application process. I should
add that this is on a wall that will be papered over. I guess if you
have just a plastered wall you would need to skim over the mortar to
give the right finish.

Being a novice, mortar is easier to sand off if too much is put on
that the cement and the cement is stickier and not as nice to apply.
These worked for me as a complete beginner, but for people who can
plaster, plaster is probably the way to go.

Thanks again.

In article ,
Stephen writes:
On Tue, 29 Sep 2009 21:20:28 +0000 (UTC),
(Andrew Gabriel) wrote:

Browning is a particular type of scratch (base) coat.

Thanks. I had heard the name before and thought it was a synonym for
base coat; I had not realised it was a particular type of base coat.

[PVAs]
are all the same except exterior PVA (which should more
properly be called EVA, but then builders wouldn't know what
it was).

They'll all work, but EVA is a waste (it's more expensive and
won't make any difference in this application).

I once bought a litre of exterior PVA, perhaps I wasted some money
because I've only used it for interior gluing. I guess at the time I
bought it thinking it would cover all circumstances and I wouldn't
need to buy a second bottle if I ever needed to glue anything
outdoors. However for plastering, I would get through the bottle too
quickly and I agree it would be a waste.

EVA is more waterproof than PVA, but only in one circumstance,
when it's mixed with cement in mortar. When just used as a glue,
it has pretty much the same properties as PVA.

The other thing to check is if the PVA is already diluted, and
it sometimes is in the 5l containers. Plasters often buy it this
way as it saves diluting it (it's not the easiest stuff to mix
with water,

I've had a look on Wickes' web site but it doesn't go into detail
about the different types of PVA they sell. They have "waterproof" PVA
which I guess means exterior PVA and "building adhesive" PVA which I
guess is interior PVA? All of them are described as being for sealing
and priming and being "ready mixed". I am not sure whether ready mixed
means ready diluted or whether it means it is a paste not a powder?

I suspect that means already diluted.

Anyway, my plasterer used the £9 rather than the £19 bottle, so I
think you must be right. It probably is diluted which is why it is
half the price of the others, which presumably are not diluted.

http://www.wickes.co.uk/PVA-Adhesive/invt/240701

A dilute coat such as 5:1 acts to stablise the surface if it's
dusty and to reduce the tendancy of the base to suck all the
water out of the new plaster before it sets.

This is what I need in my application. I will buy the 5L one from TS
as it's a bit cheaper than Wickes. Sadly TS and BondLoc's web sites
say very little about he product. I'll have to read the label when it
arrives.

Secondly, finish coat plaster does not have any bonding in it,
and only a limited ability to stick to things. Ideally, you put
it on when the coat underneath is not quite set, and then it
will bond well with that. If the coat underneath is well set,
then it won't bond well, and if it's something smooth such as
plastic, it will hardly bond at all. To get around this, you
put a more concentrated PVA coat on (3:1 is typical)

This is what he needed to glue the plaster to the ceiling. That
explains the difference, thanks.


[about conduit]
It glues the plaster to the plastic.

I have been experimenting with chases. I saw Wickes sold bags of
mortar advertised for filling chases and TLC sell quick setting
cement. Would PVA be needed for either of these?

These are custom products, so you'll need to read the packet.
Bog standard mortar would, but a special product may include a
bonding agent in the mix.

I have used plaster in the past but it always cracked because the
chase was too thick, which meant a second coat was required on top. I
found that the cement cracked too. However, when using mortar there
were no cracks so it made a simple one-application process. I should
add that this is on a wall that will be papered over. I guess if you
have just a plastered wall you would need to skim over the mortar to
give the right finish.

Plaster shrinks a lot as it sets. Mortar much less so (and less
still the drier the mix used).

Ideally, use bonding coat plaster in the chase up to about 2mm
below the finished surface. You still need to kill the suction
with dilute PVA on the exposed plaster edges before using. It
will crack, and it doesn't matter (even makes for a better key for
the finish coat). When almost set, apply finish coat to level off
the surface. That won't crack, providing it's a thin layer.

However, buying and carrying two large bags of plaster just for
filling chases is rather silly unless you're doing loads of it.
What I actually do is keep hold of the end of a bag of outdated
finish coat plaster. Being out of date means it sets really quickly,
which is usually a pain, but in this case is an advantage. First,
I use it to make up some bonding coat by mixing it up with a _little_
PVA in it, and fill chase to 2mm below surface. Hopefully, it will
set in about 15 minutes (being old). It will crack, but again this
doesn't matter. Whilst it's setting, I can be mixing up some finish
coat (no PVA) to level off the chase. All done in 20 minutes.

Being a novice, mortar is easier to sand off if too much is put on
that the cement and the cement is stickier and not as nice to apply.

Eh? You don't use pure cement.

These worked for me as a complete beginner, but for people who can
plaster, plaster is probably the way to go.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On Wed, 30 Sep 2009 14:41:21 +0000 (UTC),
(Andrew Gabriel) wrote:

EVA is more waterproof than PVA, but only in one circumstance,
when it's mixed with cement in mortar. When just used as a glue,
it has pretty much the same properties as PVA.

So selling exterior PVA is just a way to part a fool and his money
then?

[Wickes PVA]
I suspect that means already diluted.

All of their PVAs say ready mixed, so I guess some must be more
diluted than others, otherwise why such a big price difference?

[about conduit]
It glues the plaster to the plastic.

Sorry if I am being dumb, do you use the PVA diluted or straight from
the bottle for this?

Eh? You don't use pure cement.

Cement is listed in the TLC catalogue, though perhaps that's for
repairing around back boxes rather than filling chases?

I had a bit of cement and a bit of sand and some holes to fill so
experimented with both.

I have used the Wickes ready-mixed mortar and it dries without
shrinking and sands to a smooth finish. It's nice for beginners like
me.

I tried homemade mortar but it was too grainy and needed a top-cot of
polyfilla; perhaps Wickes use a finer sand? Cement on its own is not
as nice to handle and impossible to sand if too much is put on.

For filling chases, since the conduit was just under the surface, I
did not need to fill very deep, so I just used a couple of mm of
interior filler. if I was more competent I would use plaster.