When plastering a brick wall the plaster has cracks in it when drying
- it this because I should have use a paint on barrier? If so what is the trade name of a suitable barrier?
Will the cracking affect the ability of the plaster to remaining stuck to the wall? - the finish doesn't matter (and it needs more coats anyway) as I will be tiling over it.
What did you use to plaster the brick? Does the wall get warm ie is there a rad on that wall? Was the plaster within the date stamp?
What plaster did you use? What type of wall (particularly water absorbtion)?
Plaster shrinks as it sets. Too thick a layer can crack. It won't matter in bonding coat. Make sure the finish coat is a thin layer (which shrinks by getting thinner) rather than a thick layer which will also crack across.
Plaster was multi finish from BnQ
There is an insulated water cylinder on the other side of the wall in a cupboard
Plaster was well within the date stamp
Wall is an internal brick wall - some of the bricks have lost the smooth oustide finish which came off removing cement there previously
The plaster was put directly onto the brick.
Today there is cracking on thinner layers put on top of the base plaster coat as well. All carcks are quite pronounced 1-2mm wide.
Damn! you need a base coat on exposed brickwork first ie carling bonding coat or dot&dab the brickwork.
Not sure how easily rescuable this is going to be now...
If the finish coat (which you've used as a scratch coat) is well bonded to the brickwork and the surface is flat, you might be able to get away with just a proper finish coat reskim on top.
If the finish coat isn't well bonded to the brickwork (and finish coat isn't wonderful at bonding), you'll have to hack all the loose stuff off.
If the surface isn't flat, then that will need leveling off with something like bonding coat before skimming. Use a straight edge (i.e. a piece of unwarped planned timber) to check for flatness.
The word 'finish' means it's a top coat, IE it requires a backing of some kind, either plasterboard or backing plaster such as bonding, browning or render.
see above.
It's only meant o be put on at about 4 mm maximum, any thicker, regardless of the backing and it cracks up.
There is little you can do now to rectify this short of hacking it all off and starting again if you want to paint the wall, but as you stated earlier you intend tiling(?) - in which case, if the plaster is sound (tap it with your fingernails - if it's not stuck it will sound hollow behind) then you can tile over it, but you may require a few coats of diluted PVA to kill some of the suction.
HTH
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