Home
Construction
Extensions
Foundations
Walls
Windows
Doors
Roofing
Insulation
Interiors
Flooring
Painting
Wallpaper
Tiling
Lighting
Heating
Boilers
Radiators
Cylinders
Thermostats
Pumps
Chimneys
Solar
Storage
Underfloor
Plumbing
Drains
Water
Gas
Leaks
Electrics
Wiring
Sockets
Consumer Units
Video
Audio
Computers
Bathrooms
Baths
Showers
Basins
Toilets
Kitchens
Ovens
Fridge
Dishwasher
Washing Machine
Fitted Units
Worktops
Furniture
Tables
Chairs & Sofas
Beds
Shelving
Garden
Tools
Drills
Saws
Grinders
Lathes
Routers
Spanners
Screwdrivers
Misc
Corrosion
Pests
Security
Woodwork
Sheds
Driveway

Plaster and PVA



I know it is a good idea to prepare old brickwork with PVA before
plastering.
brush it down properly and use water instead.
More wisdom from someone who's obviously never done any plastering
plenty of people do it. But maybe youre right, plastering never
occurred before the invention of pva. what a waste of time.
It doesn't need to dry before plastering
But the bricks where new then. ;-)
I think they used to soak the walls till they removed to suction and
took many months for the plaster to dry out but as lime takes ages to
set properly it didnt matter. Not acceptable today.
Well I've not used pva on any of the work I've done here and have had
no problems. And I'm far from the only one.
The lack of an effective sealer was the reason a lot of original plaster
and render was live from the start. If you had ever actually done any
plastering, or spoken to any halfway decent plasterer, you would know this.
Whether you like it or not, there have been improvements in the last
couple of centuries
You are IMM and I claim my five pounds.


I don't want to buy a great 5 ltr of it - can I use some watered down PVA
Woodworking adhesive - or similar Grips Like ???? stuff.
Water makes sand and dust motile. Wetting a wall before applying
plaster to it also helps the mixing process where the alkali or base
mixtures can get around small dust layers on a wall.

That is why you wet the scratch coat on a job you started the day
before or whenever. You can add pva and that too helps the mixture the
same way that Feb or surficants like fairy liquid will.
I don't see how surfactants and pva have anything in common. The precise
use of surfactants improves the properties of the mortar by reducing
gaps between particles and the amount of water required, which results
in a stronger mix. Plasticisers such as lignosulphonates work in much
the same way. Indiscriminate use of either introduces water sensitivity
into the end product.


Another way wetting helps is in slowing down the rate that water s
taken out of the mixture applied. This is why brick bonding can often
fail in the summer where the bricks have not been sufficiently wet
before being laid.

(Yes I do know that trouble can be introduced to the mix by adding
detergents such as fairy liquid.)

Putting a layer of PVA on a brick wall and letting it dry out is only
an expensive time consuming way of accomplishing what watering the wall
But instead of allowing

would have done in the first place, allow the dust to mix in the mortar
it provides a barrier that will soften on the water side and bond to
both the old surface and the "new one to be" and it encapsulates the
dirt and dust. Thus slowing

and slow the water loss through the brickwork.
Pva is nether expensive nor time consuming but I agree it may be
pointless if all the bricks have the same porosity and the mortar is in
good shape. If the porosity is unknown or variable then pva has the
effect of regularising it.
I thought I'd better explain that a little more thoroughly before the
fools start barking at my tyres as I run them over again.


If you wish to do that you will not damage the wall. Where it is used
primarily is on finished plasterwork where no amount of wetting will
give a plasterer a chance to work his magic.

This PVA layer stops any mixing taking place. There is a recent thread
here about concrete and cements, discussing catalysts that cause them
to set faster. Using water tainted with the previous mix to make the
next will cause finish to go off sooner than normal too.

It's a problem in the first applications but a trick used to speed up
the final working later in the day by the old school.

Another use for PVA is to make some fillers more pliant. It slows them
down and it can be used in finish to make a small amount of filler or
bonding in emergencies.
Fillers such as Polyfilla contain their own binder (which is possibly
pva powder anyway). I've never found any modification to be beneficial.


It may be used in a grout for self levelling cement for the same
reason.

Finally, I was told a long time ago that you can bond plaster to glass
if you splash a little 10 to 1 PVA on the glass. Why anyone would,
escaped me at the time as I was so impressed with the statement I never
gave that point much thought.

IANAP but I do know what I am talking about here. You must take my
words for what they are and also treat some of the other posters here
with similar circumspection.
Quite right. I observe the materials I use and draw conclusions from my
experiences with them. If others disagree I'm happy to be proved wrong.
What is not IMO a valid argument is "do it this way because it's always
been done this way".


Some of them are just chancers. Why they get upset when they have their
ears slapped is beyond me. How else are they going to learn not to be
silly?
Any PVA wood working glue will do but a 5ltr bottle of it is less than
a tenner at Wickes.
Erm! 1litre goes a long way.
And yes you are supposed to dilute it. :-)
Re-5Ltr going a long way. I just wouldn't expect to ever get around to using
it again as I don't envisage any future projects that would need it (he said
naively). Don't want more clutter
It goes mouldy over time too.
My 5 litre container developed a mouldy crust. My wife wasn't overly
impressed when she found me decanting it through a kitchen sieve.
Strange. I've had a couple of 5 litre containers for probably ~5 years,
and neither has gone mouldy or lumpy.
Had you opened either? It depends on the spores getting in I suppose.
Yes. One's nearly empty now. The other was bought when I forgot to
take it with me to plaster a friend's bathroom, and is about 3/4
full. They are stored in quite a cool cupboard, if that makes any
difference.
I guess it depends what preservatives are in it.
Sure. I got 500 ml of pva glue in the pound shop the other day. Or use
old emulsion paint you might have lying around, which is easier to use
and lets you see where you've been.