Active job

Powder Room Wall

We are replacing our in-wall toilet cistern and need to have the wall fixed when this is done. Plumber advises the board behind the toilet pan needs to be done before the pan is refixed. The opening for the cistern then needs to be gibbed. The only issue is that the wall is currently thin wooden board (not gib board) so we are looking for solutions. Can we just replace the wood around the toilet parts and then plaster it without replacing the whole wall?