Depth of Plaster Undercoat

[Barney78]

How thickly can you apply undercoat plaster?

I have removed a chimey breast in my bathroom (following the instructions of a structural engineer) but it has left a large recess where the wall goes from a double skin to a single skin of bricks.

I've applied a thick layer of mortar over the brickwork to get it vaugely flat but want to now plaster but need to know how deep i can get away with.

 

[legs-akimbo]

what exact depth are you talking, maybe better to dot and dab half inch boards with good thick dabs.

 

[Barney78]

at its deepest it a good 55mm!

 

[AdamW]

Might be easiest (not to mention quick) to fix wooden battens to it, then plasterboard, then plaster over the plasterboard.

You say 55mm at the deepest, what is the shallowest? If we take it to be all 55mm, then you could have 12.5mm plasterboard, 30-35mm of batten and about a centimetre of plaster. Should be easy to get the plaster flat; use a straight edge and run it up the plaster, using the existing plaster either side to rest the straight edge against.

 

[Barney78]

The problem is is that there is a huge variance in the depth of the cavity, because of the change over between the double and single skin of bricks, which doesnt even occur vertically due to the line of the old flue and is less than regular. Would filling the cavity with more sand and cement to a depth where a 10-13mm layer of plaster would be possible be ok?

 

[oilman]

What about bricking the cavity and then plastering? There will be problems with any thick wet mix as it will shrink .