"Egg Shell" type cracking in new plaster skim

by **Makin1976** » Sat Mar 12, 2011 5:44 pm

Hi All,

Bit of advice please re plaster skim cracking. Skimmed my walls with multi finish only to find after a few days alot of cracking. This was down to the old plaster being blown (Hollow sounding when tapped) so hacked it all off back down to the bare brick to start again.

Used Thistle hard wall plaster undercoat which was fine and solid. Allowed the hard wall to dry out so used two coats of PVA (1st diluted and 2nd almost neat) and applied the new Thistle multi finish skim whilst the 2nd coat of PVA was still tacky. Before the plaster has even dried out though I am getting and "egg Shell" effect type cracking across the wall. This is baffling me! As far as I know I've done everything I should and prepped the wall as I should. Any advice would be greatly appreciated!!

Cheers

Paul.

by **stoneyboy** » Sun Mar 13, 2011 5:06 pm

Makin1976,
The problem is because you have a high suction background and this is sucking the moisture out of the finish coat. You should have applied the finish coat as soon as the hardwall had set - before it had dried out.
I suspect the finish coat will not have adhered to the hardwall so you will have to remove the finish coat, flood the wall with diluted PVA and try again.
end

by **Makin1976** » Mon Mar 14, 2011 9:35 am

Thanks for the reply stoneyboy.
The finish seems to have adhered to the hard wall as there are no hollow sounding areas plus I've lightly picked at the cracked areas (hairline cracks) and none seem to be lose. Would a 2nd skim crack in the same way do you think? Or is the best remedy as you've already suggested?

Cheers,
Paul.

by **stoneyboy** » Tue Mar 15, 2011 10:47 pm

Makin1976,
If the surface is sound flood the wall with thinned pva (2 coats) and skim again.
end

by **Makin1976** » Thu Mar 17, 2011 7:27 pm

Cheers stoneyboy,

All sorted and got a really good finsh.

Paul.

by **chris_on_tour2002** » Fri Mar 18, 2011 8:45 pm

Makin - it's quite possible that the skim dried too quickly this can cause the kind of cracking that you describe.

there are two ways to avoid this - flood the wall with diluted PVA as stated by stoneyboy, this will prevent the background from sucking the moisture out of the mix too quickly. and regulate the room temperature, plaster skimming is best done in a cool (not cold) room - too warm and the plaster will set too rapidly.