Patching large areas of plaster

[LLA]

Hi,

Re: 1880 mid terrace house

I removed wall paper in a spare room to find the plaster in a terrible state. It was peeling off with the paper. Furthermore I found a small area of damp. I chiselled away all the plaster back to the brick in the damp area. As this is a top room facing the front it looks like the is a small leak coming from outside (guttering area). I want to repair the plaster stop damp affecting the new plaster. I don’t need a perfect skim finish as I will use thick backing paper on the walls before decorating

My questions:

• What do I treat the damp area with? I can see rotten looking wood where the wall and ceiling meets.
• Is a One coat plaster a good product to use on bare brick and repair other minor holes?
• If I use a one coat, do I finish /skim it with the same product?
• Do I mix the PVA 3:1 and treat all areas? Or do I only apply the PVA straight onto areas to be plastered? How long does this need to dry before I plaster?

Many thanks from plastering novice

 

[JerryM]

Before doing anything you need to sort the damp otherwise wet rot will set in on any timber very quickly. there should be no damp up stairs in a house. it could be the guttering or the roof. if it's guttering then it may be something you can do yourself - it may even just need cleaning out. if it's the roof then bite the bullet and get a roofer in (ask neighbours and friends for word of mouth recommendation).

haven't used one coat. the trouble is whatever you use you have a thickish hole to fill. tech solution is browning then finish but for patches it’s a bit ott. finish plaster will do it but will crack if you fill in one go. So suggest you fill to 3mm below surface. let it dry out a while (couple of hrs) – you will get cracks. then apply final coat to bring level. apply PVA 1:1 immediately before the final coat. the bricks will have enough of a key without needing PVA.

for small areas would use something like decorators powder filler. it can be towelled on and there is not the same messing there is with plaster.

 

[LLA]

Thanks again Jeremy.

I ended up phoning a plasterer and he said pretty much the same. The damp was caused by an old leak in the roof, I think. I went in the loft and thoroughly checked around and could not find anything wet, however I found an area that looked like it was damp once(discoloraction in the wood) The roof was mended before I bought it.

So I have a dehumidefier in the room to dry the exposed damo area then will plaster over.

 

[joe-90]

Outside walls need cement render not lightweight plaster. Render is waterproof, plaster is the opposite.

 

[LLA]

Thanks Joe not sure what you mean as I was allways referring to internal walls

 

[roughcaster]

LLA,
If you have a room with brick external walls, that are, or were, damp on the internal side,give them a scratch coat of cement render,with a waterproofer additive,and THEN put on your one-coat,or any other plaster. Gypsum plasters are hygroscopic and will draw moisture/salts through from the bricks if there is ANY source of damp. The scratch coat + waterproofer will stop that happening. The source of the damp must always be found first and eliminated. This (i'm sure) is what Joe-90 was referring to...the internal side of an external wall.

Method:
Strip away old plaster as required.
Clean/ lightly wet down brick/blockwork, pva, and then scratchcoat, (4 parts of building/plastering sand to 1 part portland cement with w/proofer additive,) a good standard mix. Wetting the wall,pva,and the s/coat should all be done at the same time. Make sure you don't scratch too deep into the render,just enough for a good key for your plaster,but not deep enough to scratch through to the old brick/block wall.
Give it 2 or 3 days to harden,and then plaster your wall/walls etc as per normal.

Roughcaster.

 

[LLA]

Thanks Rough caster, Is the sand cement mix basically Mortar mix?

 

[roughcaster]

Good Morning LLA,
Yes, it is a mortar mix. But it has a waterproofing additive mixed in with the mortar.. I would recommend "Evoplast". Cost about a tenner for 5 ltrs. It's a plasticiser/waterproofer all in one. It's has an easy to understand mixing ratio, One(1) part evoplast to 30 parts water,whatever you use to measure it with. I use this product all the time. Don't exceed the ratio. To do your job this way is extra work,but it will certainly be for the best in the situation. For best results use a cement mixer,but if mixing by hand,give it plenty of work with the shovel.

Roughcaster.

 

[LLA]

Thanks again! Help much apreciated

 

[diyisfree]

apply PVA 1:1 immediately before the final coat. the bricks will have enough of a key without needing PVA.

I apply PVA mainly to cure suction NOT to aid adhesion. Maybe i am readibg this wrong.... then again it is christmas and i have been on the magners

edit

Ignore me. Read it proper now and i kind of agree...... Good stuff this magners