Failed tiling/plasterboard

[patrick29]

Any one out there that can give me some good advice please. My house is about twelve years old and the internal walls on the first floor are made up of egg-box like plasterboard. The builders had tiled the en-suite directly onto the plasterboard and I had to change it last year because of a leak. I replaced the old board with new, tiled it with good quality products and fitted a new cubicle that sits on a 1100 x 800 solid ceramic/resin base. I've just found that that the unit is leaking where the cubicle and tray meets the wall, probably in the corners. Obviously the tiler has not used enough sealant.Consequently the plasterboard has failed right around the first row of tiles. I've stripped out the wet plasterboard and tiles to let the timber dry out - I don't want to knock the tiles off and start from scratch with aqua-panel, so I was wondering if it's possible to replace the old plasterboard with aqua-panel up to the dry plasterboard, seal the joints with tape and waterproof tile adhesive and re-tile over that. If so, my concern then is that as the aqua-panel is porous, if this happens again I can't afford for the timber frame to become comprised so I want to protect that. Finally, any tips on the best shower trim to use between the tiles and the tray - I would prefer a one piece strip rather than using two sections. Any pro advice greatly received. Thanks

[LJW61]

Doesnt matter if the base is porous as the tile adhesive & grout are fully waterprof when dry

[Spr0cket]

Careful on how you interpret the term waterproof. This simply means the grout or adhesive will not break down or fail when exposed to regular submersion or prolonged moisture. It does not mean it is a barrier to moisture penetration ...

Only really long term solution is to tank the wall, from a height that water application would be typical (say 1 to 1.5 mtr) down onto top of the shower base, thus any moisture that passes to tile back can only reach the tanked surface which is non water permeable. This moisture with gravity will run down to the taped shower tray, over the edge and into the trays usual drainage system.

You can reapply board, but it's likely that the water is entering from anywhere up the tiled wall surface, so applying a moisture barrier at the bottom will likely simply prolong the next failure further up the tiled surface. Also as you've found, once that moisture gets back there, the plasterboard being as "sucky" as it is will normally just keep pulling it through.

The only other true solution would be to remove the existing grout, and regrout using an epoxy based grout. Which whilst being messy and trickier to apply / clean up than regular grouting ... does provide a sealed grout layer, which, assuming tile surfaces are sealed or glazed to the epoxy grout join, will not allow further moisture to penetrate.

[patrick29]

Thanks Spr0cket, sound advice which tallies with the research I have done so far. Don't really want to hack off up to a metre and start again, but I know it's time and money down the pan if I take a chance, do a localised repair and it leaks further up the wall. I'm certain that the problem has arisen due a faulty seal around the trim as the plasterboard was only really wet in the corners and not from above the first row of tiles. So I really am in two minds as to what to do. Had a visit from a tiler today who suggested repairing the wall with marine ply and tiling over that. Not so sure of the effectiveness of such a remedy - never seen that one during my research. Any one got any views on that? Additionally, this leak has left black mould / mildew patches on the back surfaces of the dry plaster boarding and the wooden battens. Any one know an effective remedy to properly clean and kill that? Thanks.