Plastering onto concrete bricks

[bob19472009]

Being a total newbie to plastering we (wife and I) have got into a bit of a bind. We are refurbishing a bathroom in our recently aquired 1950's bungalow. The tiling has not been touched in 30 years and was in a terrible state. Removing them tore off the wallpaper(!) underneath and removed the finishing plaster. When we removed the basin half the plaster on the wall fell off. The remaining plaster was blown and came off with very little assistance.
Underneath we found bright white concrete bricks (ordinary house brick size) that are very very porous. We treated them with lots of 5 to 1 PVA and applied bonding plaster at 10mm depth over 1 sq. metre.
The result is an area of plaster that is crazed with random cracks every 30 mm or so, adhesion seems O.K.. We plan to 100% tile the bathroom

Questions are:-

1) can we leave up what we have done?
2) can we tile straight on to this plaster without a finishing coat?
3) what did we do wrong and what should we do to put it right on the rest of the bathroom?

Help please!!

 

[opcom]

1) can we leave up what we have done?

I would not myself

2) can we tile straight on to this plaster without a finishing coat?

If the surface is flat and true then yes ( taking question 1 in to account)

3) what did we do wrong and what should we do to put it right on the rest of the bathroom?

The surface sounds as though it dried out to quickly, I would re-apply PVA in a slightly stronger mix leave it 24 hours then just before starting to plaster apply again and have a fairly strong coat of PVA put on, this should balance out the drying time.

 

[bob19472009]

Thanks for the advice, I should have realised we were in for a problem when In noticed that the old plaster was only attached to the mortar between the bricks. We will give another go next weekend.

Thanks again

 

[trowelmonkey1]

pretty much agree with opcom although i would have thought you can leave the exisitng plaster you applied AS LONG AS I HAS BONDED with the brick behind but for what it's worth you may be best taking it off as the last thing you want to do is to finish your lovely new bathroom to find you have to re-do it later on, easier to do it now.

to much suction definitely killed your plaster though, try using gyprime instead of PVA, more expensive but you may find it a safer option.