Air bubbles in lime plaster (on top of tanking)

enorbs

New Member
Hello everyone. Hoping for some advice on these air bubbles.

Background:
We have a victorian cottage with no cavity. The previous owner applied bitumen paint on the inside of the wall (1m in height) as well as gypsum plaster on some walls and concrete on other walls. There were serious problems with condensation and penetrating damp due to plants growing on the outside walls as well as leaky roof.

Works done:
We have fixed the roof and removed all the plants on the outside.
We have stripped the inside back to the brick. We did not strip the bitumen paint.
We were advised to apply a tanking as the wall is below road level (with the road right up against the all of the house). We were also advised to inject the walls with a chemical course.
We decided to apply lime plaster on top of the tanking to allow the top half of the walls to breath (I realise there isn't much point applying lime on top of tanking... but we wanted a seamless finish on the walls).

The problem:
Unfortunately, there are loads and loads of air bubbles have appeared on the walls. See picture.

My questions:
1. What is the cause of all these bubbles? is it poor workmanship ?
2. What is the best solution to get rid of these bubbles? Can they be sanded down?
3. Was it a bad idea to apply lime on top of a tanking? :(

Plaster.jpg
 

enorbs

New Member
Top coat on too early
Thanks @bof . What do you think is best the way to fix this?
(1) Can it be salvaged by sanding down the bubbles?
Or (2) does it need another skim with fresh plaster and polish with a trowel to a smooth, even and flat finish? if so, would the existing surface need to be primed with PVA to aid adhesion?
 
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worthwords

Active Member
Thanks @bof . What do you think is best the way to fix this?
(1) Can it be salvaged by sanding down the bubbles?
Or (2) does it need another skim with fresh plaster and polish with a trowel to a smooth, even and flat finish? if so, would the existing surface need to be primed with PVA to aid adhesion?
I had similar situation [DIY renovating old house] -the walls had all sort of patches of lime, painted artex (with asbestos so couldn't easily remove) and i'd rebuilt a corner window lintel using diathonite as an insulating render on the thermal bridge - so quite challenging suction variability.

I used 2 coats of Baumit Premium Primer over the whole wall to try and even out the suction.
Worked brilliantly except for the bottom of the wall in which the base coat clearly was taking longer to dry over the painted artex so was pulling up bubbles.
my advice is to get a good finish despite the bubbles and every day afterwards take a flexi trowel and gently mist the the area and run the trowel over at a very low angle then leave it. Eventually as it dries the bubbles will stick flat and hopefully after painting you would never know.
If you sand them you will just expose a crater and it will look arse.

Having learnt my lesson on another similar wall i did the same - 2x primer but waited a lot longer for base of the wall to dry before top coat. No bubbles. The lime has bonded really well to the problem areas despite my concerns.

Some pics…
 

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enorbs

New Member
I had similar situation [DIY renovating old house] -the walls had all sort of patches of lime, painted artex (with asbestos so couldn't easily remove) and i'd rebuilt a corner window lintel using diathonite as an insulating render on the thermal bridge - so quite challenging suction variability.

I used 2 coats of Baumit Premium Primer over the whole wall to try and even out the suction.
Worked brilliantly except for the bottom of the wall in which the base coat clearly was taking longer to dry over the painted artex so was pulling up bubbles.
my advice is to get a good finish despite the bubbles and every day afterwards take a flexi trowel and gently mist the the area and run the trowel over at a very low angle then leave it. Eventually as it dries the bubbles will stick flat and hopefully after painting you would never know.
If you sand them you will just expose a crater and it will look arse.

Having learnt my lesson on another similar wall i did the same - 2x primer but waited a lot longer for base of the wall to dry before top coat. No bubbles. The lime has bonded really well to the problem areas despite my concerns.

Some pics…
thank you @worthwords. Very helpful! This was not a DIY job. But I might end up DIY fixing it!
 
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