What is the best way to stabilise crumbly plaster before tiling?

[Tzimi]

Hello, I've started to remove the old tiles from my bathroom wall, prior to refurbishing my bathroom & re-tiling. But I've discovered that some of the plaster behind the tiles is a bit soft & crumbly. After Googling the subject, it seems that the plaster can be hardened by applying a few coats of 1/4 diluted waterproof PVA and allowing it to soak in. I've tried this in a couple of places, and it really does seem to stabilise the old plaster. The plan is to then fill any holes with new plaster and generally level the area, PVA again, & re-tile. I just wondered if anyone had any additional tips or advice on this subject?

I'd either chip all the rubbish plaster off and fill it or re plaster completely rather than try to stabilise.

You are spending money on a nice bathroom and if you skimp on the plaster base the whole thing could be compromised quality

I would also agree it's better to chip it off and re plaster the walls than all of a sudden find tiles start coming off the wall and damaging your new bathroom.

@2beautifulbabs @purringpaws Thanks, I was afraid you'd say that! I've only looked at the wall behind the far end of the bath area so far (opposite end to taps & shower), so I don't know what the condition of the plaster is in the middle & at the shower end. I'm hoping it will be better...

Could you use backer boards?
www.toppstiles.co.uk/knowledge-base/backer-boards
We used waterproof ones on old wonky walls in the bathroom. Also meant we didn’t have to wait 4+ weeks for plaster to dry out before tiling

@Iheardit Hi, it's a good idea, although I was hoping not to have to use any additional boards. I was hoping just to fix the walls & level them enough so I can re-tile once I have fixed the new bath in place. I'm still waiting for some bits to arrive, and meanwhile I'm experimenting with treating the existing plaster with PVA, and then temporarily sticking some tiles on to see if they will stick firmly! The rest of the bathroom has, believe it or not, Artex on the walls! Again, Googling this, opinions are mixed- some say it's fine to tile over this, and others say not. I'm experimenting with some temporary tiles on this as well. If it works, it should be fine, as the Artex seems very solid.

hack it all off.

I think a water-resistant backing board such as Hardiebacker would be best, but ask the person doing the tiling what they want done. If the walls are not modern with CWI you could use an insulating board which will reduce condensation on the cold tiles.

Most people are not very good at plastering but can render with sand and cement mortar (which has a longer working time and is resistant to damp)

A bolster and club hammer will take off bad plaster, but a spade is faster.

@PigletJohn Thanks for your reply. I'm going to be doing the tiling myself. I was really hoping not to use any kind of backer board, but to tile directly onto the plaster. Now that I've had a better look at the plaster, it seems that only some of it is soft, so I should be able to remove the bad patches & fill in the holes with new plaster. I guess I'll have to let it dry for a while before tiling.