PVA Drag!

[Choco]

Hi guys,

Ive been on the trowel now for 5 years and in recent months me and the firm i work for have come across something quite strange. Ive always been taught when skimming a PVA wall you apply the Pva not quite neat but almost and let it go 'tacky'. We were doing this one day like my boss and his brother have done for 20 years and when the first coat was apllied after a while we noticed that on the wall small what looked like cracks appeared in the wet plaster and when you tried to flatten it you couldnt help but drag over the wall!!. It seemed like it just wouldnt bond to the wall or pva. This went on for a couple of weeks so we tried skimming when the PVA had gone off completly and when it was still wet but it seemed to do the same thing! The weird thing is it didnt do it everytime and some walls that didnt do it were with the same PVA as the ones that did!! so we couldnt put it down to rogue PVA.Like i say my bosses have been in the game for 20 odd years and never come across it. Can anyone help? has anyone come across this before? Cheers guys

[Whitebeam]

I thought it was just me, stopped using one brand because I thought that was the problem. I'm the same as you guys, wait the pva get tacky then skim then waited for it to dry and still had the same problem.

Started using wickes pva and it's alot thicker that some of the other brands and did'nt seem to have any problem, even concidered using sbr instead.

If you find out let me know

Been plastering amonst other things for about 30 years and never had the problem so frequent

[chancer]

if its just for suction control try it a bit weaker,must admit i havnt noticed any thing like you say,i wouldnt use sbr for a gypsum materials lads itll peel off like skin when you skim it i now cause ive tried an it failed(on my own house many years ago!)i had to get a wire brush fitment for a drill an clean it off,caused me much grief.

[specialrider]

would try a weaker first coat to moderate suction and as a sealer.then glue as you said hit it when tacky.the cracking is probley because thirsty background taking all moisture so when your trying to flatten its just pullin it.not telling you how to suck eggs m8 but weaker first coat seal.second key.i do many times as you do and only a couple of times have had that problem so now i always seal and glue

[Choco]

Cheers for the feedback guys nice to know we are not the only ones!!
I know what your saying Specialrider about sealing with a wet first coat. The thing is its not because of the background having to much suction as its on old painted walls! not ones where the skim has come off old sand and cement. I know some plasterers are using this green stuff that you paint on the day before and leave overnight or is this sbr? as ive nerver actually heard of that. Cheers anyway

[chancer]

i think your problem is more lack of key than the pva mate !you can over seal an if the back grounds smooth be like scimmin glass,do you two coat the scim if so let the first tighten up a bit more before the last coat(i think your talking bondit,gypprime with the day after stuff not sbr this will give an exellent key and bond but is expensive and a bit of overkill for most jobs)
but if your one coating therin lies the probs

[specialrider]

chancers prob spot on with that. we did a old vicky terrace about 3 year ago long high hall stairs and landin,all paper had been removed and all that green paint had been put on from new in the days when thats what was used.walls were in good condition so just a re skim,anyway as pvad seemed to bring the old wall paper glue alive took ages to go tacky and basicly chacing it all round the wall a good hour and half before would accept second coat so probley pva 2coats had sealed it to death on top of old paper glue. bonding agent from wickes good gear as said pricey,but on most jobs havent really time to go day before and apply.