Air Bubbles on a Plaster Skim

[hoyboy]

I've recently moved to a property and the walls are in pretty bad condition - after I removed some dodgy wall paper I found the original paint and skim underneath peeling cracking and badly marked... Not having enough money at the moment to hire a plasterer I decided to have a go at skimming it myself...

Anyway, I pva'd the wall and put the plaster on (Thistle multifinish). It all seemed pretty smooth and I was pleased- there were a couple of dents and drags but nothing a tiny bit of polyfilla wouldn't sort. I'm not saying it looks professional but it's an old house and the quality fitted in with the rest of the walls.

I've done 2 walls now.. one I painted about a week after putting it up and the other is not painted yet but only went up on Sun.

My problem - I've just noticed bubbles have started forming on the painted wall (and when I tap the plaster on the unpainted wall, some areas sound hollow, like they've not adhered to the undersurface correctly - could these be bubbles about to form?).

Anyone know what my problem is - I was wondering if it could be that I'd not cleaned the wall properly underneath. Can wallpaper adhesive do this?

Or is it because I painted the wall too soon after putting the plaster up?

Any other ideas?

 

[crewy]

Sounds like you didnt bond the wall with pva glue first. This isnt required all the time but it is good advice when new to plastering to apply a 5 to 1 mix ( 5 pva to 1 water) to the walls prior to plastering especially if you are to skim over old plaster. New plaster will not stick to old plaster unless the old is bonded first. unfortunately it sounds like your attempt at plastering is doomed and will probably need removing and starting from scratch.

 

[hoyboy]

I bonded it twice with PVA - once at 1:5 and the other at 1:2. Was that too strong? The second bond coat was a bit tacky when I applied the plaster - does that make a difference? I thought I read somewhere that was a good thing...?

 

[crewy]

Did you check the amount of suction in the wall first? If there is a lot of suction you should have bonded the wall with neat pva glue and left it to dry completely then just prior to plastering applied a 5 to 1 mix of pva and water and waited for it ti get tacky then start to skim with multifinnish. As for the bubbles, did you seal the new plaster with a 5 to 2 mix of white paint and water prior to painting it properly, right???
I have plastered over many differnt surfaces including walls which have been wall paperd and following the above steps have not had any trouble. unfortunatly the hollow sound you hear when tapping some parts is where it hasnt stuck properly which is more than likely due to the preperation rather than wall paper paste. You have two options, the first is to try and chip off just the areas that haven't stuck, pva it twice as above and try to patch them up with more plaster if your competent you should get a good result or you could use polly filler and sand it down when dry, The second option and the one i would choose is to chip of the bad areas roughly fill them with plaster after you have done the pva bit let it all dry nicely, then re pva the whole wall and plaster the lot again. Time consuming i know but you will get the best results that way.

 

[hoyboy]

No - I didn't check the suction. I don't know how too!! However, nothing seemed to be going off too fast so don't think it was this.

My first paint coat was straight from the bucket Could this have caused the bubbles? Or could painting it too soon after putting the plaster on (about 5-7 days) and not letting it dry enough first? Both?

You mention the hollow sound is more likely due to bad preparation... This is what I'd guessed but could anything else be wrong with the prep - could it be anything but the bonding coat as I'm pretty sure this bit I got right..?

 

[crewy]

Painting from the bucket is where your problem is, New plaster should always be sealed prior to painting you colour of choice. generally modern plaster is ready to paint when completely dry, around 5-7 days as you said but when more than 1 coat has been applied it could be longer. You said you did a bondingcoat? was that nescisary as in your original post you said you uncoverd the original plaster. I would have followed the pva steps, skimed it to a ok finnish, when it was fairly stiff skimmed it again with a second coat of multi finnish for a perfect finnish every time. Try it, the second coat goes on so easy and is much easier to bring to a top finnish. Bubbles can be caused by appling a second coat over the first to soon and trapping air in the process. These usualy polish out with a firm trowel just before it has set. To test suction you just apply a small amount of plaster to the surface, you should get around 20 min depending on conditions before it has set completly. Another reason that the plaster might not stick in places could be down to to much suction and the plaster drying out before its had time to grip in the setting process

 

[hoyboy]

Just to say - thanks very much. Neat PVA did the trick!