dot and dab questions

CharlieB1981 · 8 May 2013

i'm going to give a bit of dot and dab a go in my house and have a couple of questions.

pva - been told that as its a brick wall thats previously been plastered and stripped bare it needs pva first or it wont stick, yet other posts here say you dont, is there a definitive guide as to when to pva and when you dont have to.

if you do, should the pva be dry or tacky when you dot and dab.

found another post that says not to d&D on external walls with no cavity- why is this? i need to fasten some insulated board to these walls but my wall is a 9 inch double brick wall.

thanks in advance.

stevethespreader · 8 May 2013

dry wall adhesive is made to use on low to high suction backgrounds no pva is needed some people use it on high suction backgrounds so they have more time but its not needed also dot and dabbing a single skin wall could lead to cold spots forming on the adhesive which in turn will grin through the plaster or if you get damp then the adhesive will be compromised

1john · 9 May 2013

You are better to batten and then board a solid wall leaving an air gap.

CharlieB1981 · 9 May 2013

cheers gents,

not worried about damp spots as such- the board has 2 layers of foil that should stop damp coming through to the board.

there is a thin cavity but only about 20mm but with bricks now and then at 90 degrees to tie the two walls together. the outside wall is rendered in waterproof render and the plan is to dot and dab a solid line around all edges of the board.

as these are small rooms and i want to lose as little space as possible i may take the risk on dot and dab.

dpt · 9 May 2013

If you are going to D&D you don't need to PVA the wall, just wet it down. Not the best method on an external brick wall but hay-ho.

stevethespreader · 9 May 2013

CharlieB1981 said:
not worried about damp spots as such- the board has 2 layers of foil that should stop damp coming through to the board.

foil backed boards need to be fixed with mechanical fixings as well as board adhesive as the adhesive wont stick to well

CharlieB1981 · 9 May 2013

Cheers for the replies, I'm planning to use mechanical fixing also as recommended by the supplier, they aren't foil backed as such, they have a couple of layers of foil in the middle, the side that sticks to the wall is paper as on a normal board

Must confess I'd already done half a wall before I saw the posts about not doing d&d on exterior walls-part of my reason to risk it, but since my earlier post I'm debating if to rip it off and battern the wall

dpt · 9 May 2013

I would batten it out if it's an option.

Jameswren · 18 May 2013

The glue is going to be about 18mm thick when you do it so consider that.

Wet the brick work so the moisture doesn't get sucked out too quickly - a saturated wall is a bad idea though.nmake sure all dust is hoovered and wiped off when you're going that.

Not sure what mechanical fixings you're considering - masonry compatible fixings will rip through the plasterboard with no bite.

Reeves2k2 · 12 Jun 2013

The reason pva is suggested by some is because of the dust can be hard to remove it all and prevent the adhesive from sticking
The general rule in my neck of the woods and the way I was tought was to use a very very weak mix of pva on old walls to be dabbed so the pva doesn't skin and prevent adhesive getting a good hold it acts more likes wetting down procedure and any loose dust is sorted in the process
Every spread has there own way of working and having been doing it this way the past 15 years never had a problem
Agree with the above about external walls but in some cases battons aren't an option
Another thing make sure the is a gap between floor and board to prevent moisture being sucking into the board giving problems later on
Always use a square in corners and spirit level to true up the walls

smp50 · 19 Jun 2013

Reeves2k2 said:
The reason pva is suggested by some is because of the dust can be hard to remove it all and prevent the adhesive from sticking
The general rule in my neck of the woods and the way I was tought was to use a very very weak mix of pva on old walls to be dabbed so the pva doesn't skin and prevent adhesive getting a good hold it acts more likes wetting down procedure and any loose dust is sorted in the process
Every spread has there own way of working and having been doing it this way the past 15 years never had a problem

How weak a mixture are we talking about here, can you put a rough number on it?

I have some bricks in my 1930s house that I'm going to be replastering one way or another. I've scrubbed as much dust off as I can but obviously there's an unlimited amount that will come off the more I brush them. So I want to PVA them just to tighten it up, basically, while I get on with the rest. What kind of ratio should I use if I'm going to be applying d&d plasterboard?

(hopefully this doesn't constitute a thread hijack!)[/b]

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dot and dab questions

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