Hi Paul
I have been plastering my bathroom and although I am going to tile it
I wanted the practice of plastering. What I noticed was half the wall
was breeze blocks behind the old bath and the top half was old plaster
and paint after I removed the old tiles. The old plaster skim was a
light whitish grey colour and didn't look like multi finish at all.
I applied a bonding coat to the lower half of the wall after pva and levelled the wall. Then I applied a few coats of pva the week after to apply a skim coat. It turned out very nice over the bonding coat but
some areas over the old plaster I noticed it started cracking after a few minutes. In order for this not to happen again I applied a few
more coats of pva around the bathroom and areas that cracked. I waited
for the pva to go tacky and re skimmed and still some areas cracked.
Do you have any idea why?
I'm glad it happened because I am learning with these problems but
couldn't understand why. I even sprayed water to these areas to try to control the suction but some areas are just crazy.
Regards
Kibria
Answer
Hi Kibria
Finish plaster can be a grey/blue colour or pink - depending upon what area of the country it came from.
Sounds like a high suction problem so you did the right thing. Try applying even more pva - subsequent coats can be thicker - initially a watery PVA solution is good to ensure it soaks into the wall surface and is not just laying on the top (to peel off later). Subsequent coats can then be made progressively thicker by adding less water and more PVA that will act to seal the wall.
It is always better to control the suction before applying the plaster - rather than trying to slow it down by flicking/spraying water on at the troweling stage.
Also check the sun is not shining on it and drying it out - working in conservatories often gives this same problem. Use plenty of water if needed when troweling and try an additional troweling stage to really make sure you compress the plaster as it continues to set.
Paul