Ask the Question

James123 · Joined: 22 Jul 2008 Posts: 1 Location: London

When I put a top coat of multifinish plaster skim on to a base coat of hardwall, which I had PVA'd using 3 parts PVA 1 part water, the skim plaster started to form mud cracks as it dried. Although the skim coat was up to 4mm in places on the main wall, there were areas that were only 1mm deep which also formed mud cracks.

Can you tell me how to prevent these cracks from forming?

Thanks

Honda · Joined: 25 Feb 2008 Posts: 20 Location: Kent UK

Hello James
You're not the only one suffering this problem at the moment. I'm guessing you let the PVA get tacky before you applied the finish coat, yes? A plasterer friend of mine has been having the same problems and he's been plastering for years without any problems. I don't know if it's the PVA that's changed or the plaster but something has. He found that if he lets the PVA get virtually dry first it's far less of a problem.

oddjob · Joined: 28 Aug 2008 Posts: 1 Location: shropshire

Hi mate, the reason your plaster is cracking is because it is drying out to fast. paint the wall with unibond 3-1 realy thick coat and make sure you work it into all the cracks, then leave to dry for 24 hours. this now gives u a better stable back ground. after 24 hours paint with unibond again 3-1 or 2-1 and leave to go tacky or almost dry and it will work fine dont plaster onto the second coat when it is still wet or the plaster will slump

Honda · Joined: 25 Feb 2008 Posts: 20 Location: Kent UK

Hi Oddjob
That's exactly what we've always done without any problems at all, but lately, even if you let the PVA get really tacky, (so you're not left with any on your hand if you touch it), when you apply the skim coat it seems to turn the PVA liquid again and the plaster crazes. You can still leave it to dry out somewhat and then finish it but it is a pain.

uron1000 · Joined: 06 Sep 2008 Posts: 9 Location: Cambridge

Just apply it neat to the affected area and always scrim it