Plaster Cracking

[Ian]

I know there are lots of plastering questions on here....... it's obviously a skill that needs to be mastered through experience!, still I like to give these things a go if only to convince myself that paying someone else to do it is money well spent!

It's only a small'ish area I need to plaster, about 3x1m but I've tried three sample areas and all have cracked.

1. PVA'd wall, 1 part pva, 5 part water, left to dry overnight. Applied 1pva

3water and then applied Thistle Bonding plaster after about 10 mins.... 5mm thick... result... CRACKED!

1. PVA'd wall, 1 part pva, 5 part water, left to dry overnight. Added plenty of water to wall applied Thirstle *Brown* plaster...5mm thick.... CRACKED!

2. No PVA, plenty of water on wall, applied Thirstle *Brown* plaster...5mm thick... CRACKED.

The plaster date is fine, still well within the expiry, I also bought from a store with a high turn over.

I have also googled this group and found stuff about mix consistancy but it sticks to the wall well and doesn't slide of the hawk and land on the floor. would the cracking be a result of the mix being too dry/wet ?

Should it just pour out of the bucket or need some encouragement ?

Please help! my last attempt now has four knuckle marks in it!!!

Cheers, Ian.

[Andrew Gabriel]

I would still be working on it after 10 minutes getting it flat and vertical so it wouldn't get a chance to crack in that time. It shouldn't have set in 10 minutes, or there's something wrong with it. If it shrunk in 10 minutes but isn't set, it's losing water rather fast.

What is the wall made of (not that I can think it makes any difference if you PVA'd it)? Was it a very hot day?

[JW]

If it sticks to the wall and is easy to spread, then its fine. A mate of mine had the same problem with his first attempt & it turned out he wasn't using anything like enough water. If the wall sucks the water out of the plaster, it will crack. You need to give the wall enough water to stop this happening. Buy a cheapo garden type spray & soak the wall until the water starts running down the surface. Repeat every few minutes.

hth

JW

[James]

As well as the other suggestions about soaking the wall, it could also be contamination of the mix, ie: does the bonding plaster get hot and go hard as well?, we use bonding mixed with cement powder to make a super strong adhesive to stick stone fireplaces onto walls, it dries in about 5 minutes.

The other reason I can think of could be a draughty area.

[Glen]

Really sounds like a moisture problem.

When you pva'd...did you slap it on generously? It also could be the symptom of duff plaster...try a new bag? The only other thing I can think of is that your mixing it too dry.

I would stick with the bonding...possibly getting a new bag and mix it quite wet. If you've pva'd the walls there shouldnt really be any need for wetting the walls first.

Glen

[Mark S.]

I read it that he applied the plaster ten minutes after the pva?? :-)

From my so far limited experience I've put any cracks down to the plaster drying too quick, I did half a wall (cheated and used those metal guides) then went about my business but kept coming back to spray it every so often and it was a lot better than the previous attempt as regards cracking.

The walls are very porous on the surface despite pva'ing etc.

Might just be that most beginners are frightened when faced with a very sloppy mixture and make it way too dry?

Mark S.

[Ian]

Thanks for all your suggestions...... I basically made everything as wet as I dare and finished the wall yesterday, got a good finish and 24 hours later no evidence of cracking!... fingures crossed.

I guess that if there's no sign after about a week I can assume it's job done.

Cheers, Ian.