My First Disaster

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herds

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Had to happen sooner or later.

Well today I was skimming a big wall (for me around 4mx2.5m) and I found the plaster going off whilst I was doing the first layer :/


Even though I PVA'd the the wall it was about 60% fo the wall and after 3-4 minutes after applying the plaste rwould rip/tear, what i'd expect after 20-25 minutes.


So I cut my loses, flatened the wall best I could using a spray bottle to get the plaster moving.



I'm sure this must be due to suction, so the answer for next time? PVA the wall with a 3.1 the day before and then again before plastering
 
Could be suction and probably is.

You didn't use dirty water to mix or out of date gear did you????
 
It depends on the suction, how did the pva absorb into the wall? was it fully absorbed before plastering began? I prefer two coats of pva, one five to one ,one stronger..break between both..
 
Mate it depends on your surface,if its old plaster it will suck like nowt else.old plaster could do with 3 coats of 50/50 mix really.dont be disheartened.everyone gets it when they are learning,just learn from it and move on.better to have to wait 5 mins before skimming sometimes cos the pva hasn't gone off yet rather than not enough control and struggling.chin up.
 
Use Betakontakt if you can on ANY surface prior to skimming, let it dry over night and bobs your uncle. It wil cover 60 metres on average
 
Its an old plaster wall, the thing is this is the first wall out of around 15 walls that have done this and the wall behind this wall was fine.

Got it - more pva beforehand next time.

As for next time, how long do i need to leave the existing plaster that is now drying before skimming the wall again.
 
I reckon by the sounds of it 2 days max.if it was drying that quick when you applied it,it won't take long to dry out.
 
herds said:
Its an old plaster wall, the thing is this is the first wall out of around 15 walls that have done this and the wall behind this wall was fine.

Got it - more pva beforehand next time.

As for next time, how long do i need to leave the existing plaster that is now drying before skimming the wall again.
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if it is sound, you can do it straight away..
 
update - Went on fine this time.

I 50/50'd the wall an hour before and noticed that after 20 minutes that some of the areas were bone dry, so I 50/50 those areas again 3 times (!) until they were tacky. I waited another hour after this then pva'd the whole wall about 50/50 and then wall went tacky evenly and then skimmed as normal.

I picked up some SBR the other week for the damp proofing project I have soon, in retrospect I would have been better off just using this after I found that the wall was sucking in.

Freak wall :)
 
If it's an old wall, I'd assume it's a lime based plaster on there. Old lime work reacts with gypsum, it goes off really quickly and you'll really struggle to get a good finish.

Using SBR won't help! Follow the previous advice and use a bonding agent or failing that buy some stabiliser and mix that with your PVA. I've had some success with PVA in the past on lime, but it involved lashing loads of the stuff on and letting it dry overnight.
 
Thanks twitcher, i'll bear that all in mind. That was the biggest wall I have done at around 3.5m x 2.8m with one socket.

Finding that I'm now going into autopilot mode with plastering, not sure whether that is a good or bad sign :D
 
Hi Herds,

Like the others have said use 50/50 mix until you control the suction. Allow to dry before applying the subsequent coats. Also, apply the PVA evenly otherwise you'll have wet seams that take longer to dry.

Thereafter, I would use a 5:1 or 3:1 mix for the final coat. It should remain tacky for a good 10-20 mins. In general, the more concentrated the ratio, the quicker it dries.

Best regards,

Minh
 
Minh said:
Hi Herds,

Like the others have said use 50/50 mix until you control the suction. Allow to dry before applying the subsequent coats. Also, apply the PVA evenly otherwise you'll have wet seams that take longer to dry.

Thereafter, I would use a 5:1 or 3:1 mix for the final coat. It should remain tacky for a good 10-20 mins. In general, the more concentrated the ratio, the quicker it dries.

Best regards,

Minh
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You should start with a weaker solution and finish with the stronger one.
 
The wall that Herds is tackling is the biggest wall he has done to date. The reason I suggest he use a weaker mix is because the PVA will remain tacky for longer. For us guys we'd skim that size wall in 3 mins, but Herds might be taking 20 mins.
 
Minh said:
The wall that Herds is tackling is the biggest wall he has done to date. The reason I suggest he use a weaker mix is because the PVA will remain tacky for longer. For us guys we'd skim that size wall in 3 mins, but Herds might be taking 20 mins.
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what the tackiness stops it going off? ........weirdo
 
I see you're as pleasant as always Spunky.

If the PVA remains tacky for a good 10-20 mins then it means that the wall is sealed and ready for skimming. I have always worked with tacky PVA. Some on here don't, but each to their own.
 
Herds is struggling to control the suck of the wall minh, providing a bond with tacky pva ain't his issue:RpS_thumbup:
 
You could add a bit of water to the plaster you've already put on while continuing to put the plaster on, make sure its clean water. It just keeps it a bit more moist while putting your first coat on. Hope everything go's better on your next attempt! :)
 
The thing is with this attempt that it went off about 10 seconds after putting it on and on what is a big wall for me I would not be quick enough to get it right and make the wall decent.

I think previously I have been skimming too quickly after pvaing, usually about 5-10 minutes after. I will check in future for the tackyness.
 
As Superspread suggests, put 1-2 watered down coats on first, 5-1 should be okay. Follow this with 2-3 coats at 3-1. Touch the surface carefully to prevent the PVA from peeling off. When the surface is shiny and remains tacky for a good 10-20 mins you're good to go. If the surface does not feel like sellotape, it's not ready.
 
Minh said:
As Superspread suggests, put 1-2 watered down coats on first, 5-1 should be okay. Follow this with 2-3 coats at 3-1. Touch the surface carefully to prevent the PVA from peeling off. When the surface is shiny and remains tacky for a good 10-20 mins you're good to go. If the surface does not feel like sellotape, it's not ready.
Click to expand...

I will put that into practice next time. I'm just happy I didn't have a sucky wall the first couple attempts after the course, i'd have thrown in the trowel if that were the case.
 
Yeh stay away from 50-50 pva, to strong a mix for controlling suction.4-1 is watery enough to soak in in to the dry background.... or to save loads of coats of pva , use wba or similar. One coat the day before, then right onto it next day when its dry..:RpS_thumbup:
 
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