bit of advice please.

[boldydave]

hello all.after 6 months of browsing this site and doing a 2 week tiling course i had a look at my first job today.it`s for my nephews landlord which is perfect for me as i can take my time without a `real` customer looking over my shoulder.it`s an 18smtr bathroom,mostly replastered(bonded and skimmed) which was done 2 weeks ago.my questions are,
1. he`s having the bath removed and fitting a shower tray.can i dot and dab some plasterboard into the hole on the wall where the bath was then tape the joints,and as this will now be a wet area do i need to use water resistant plasterboard or will waterproof adhesive and grout be enough.
2. do i need to prime the rest of the new plaster in the room ,and what product to use.
3. can we take up the floorboards and screw 28mm plywood directly onto the joists,and then we can tile straight onto that.also i know i need to prime/seal the underside and sides of the ply,but do i need to prime the face i`m laying onto aswell.
4. which flexi powdered adhesive would you recommend.
5. do i just tile down to the showertray and seal with silicone.
i know i`ve read the answers to most of these on the forum somewhere but i wanted to check it out for my peace of mind.i`m sure some more questions will come up but this will get me started.thanks to all in advance. dave.

[mikethetile]

Hi dave

use normal plasterboard and tank the shower area, incidently showers are classed as intermitant wet areas

prime with primer g , no need to prime tanked areas

only prime the face of the ply if reccomended

use mapei keraflex

double silicone the shower base, so you seal around the base and when tiled seal the gap under the tiles


what tiles are you using as you will neeed to watch the weight on skimmed walls

[whitebeam]

I would dot and dab plasterboard where the bath is removed, I would standard board but tank the shower area.

An acrylic primer for plaster

A single part flexible for the ply, read manufacturers instructions for priming.

[boldydave]

thanks for your help. ok, this is where i look a bit dumb.i`ve read on here about tanking kits.what is included in a tanking kit and do i need to tank the whole shower area or just the bottom which will be plasterboard.i thought the top half would be ok because it`s plaster.

[mikethetile]

I would tank the lot

theres the paint on system like bal wp1 or the mesh such as homelux

the mesh is better to use and you can tile straight over it, no waiting for drying

[faithhealer]

usually tank a metre and a half high min dave

[boldydave]

having a bit of trouble sourcing 28mm ply.is 22 or 25mm acceptable?also does it need to be exterior grade.

[Sir Ramic]

Any ply over 15mm is acceptable usually its 18mm and it needs to be WBP ( commonly called marine ply) dont use the cheaper shuttering ply.
Actually you have to be careful with ply these days, there are some inferior types out there at the moment.

[boldydave]

thanks for all the help so far.b and q or wickes do exterior ply.is this marine/wbp

[DJS]

Not sure if the B&Q/Wickes stuff is inferior imported stuff already mentioned. The inferior stuff is know for de-laminating when it comes into contact with moisture, I.e The tile adhesive!

I would advise finding a local timberyard and asking them to supply you. My local TY has 18mm & 25mm Malasian Hardwood WBP. Few pounds cheaper for a sheet of 8'x4' (2440x1220) than B&Q too!!

[Dave]

A lot of ply is also imported from china, this contains higher levels of resins etc and these can leach out when ply is wet from adhesive causing it to discolour grout and also delaminate the adhesive.

I only use cement boards now..

[Burnsy]

Any ply over 15mm is acceptable usually its 18mm and it needs to be WBP ( commonly called marine ply) dont use the cheaper shuttering ply.
Actually you have to be careful with ply these days, there are some inferior types out there at the moment.

I think he was referring to plying straight onto the joists. Would you be ok with 18mm ply straight on to the joists?

[mikethetile]

there is a big difference between marine ply and wbp

marine ply has different resin in the glue which will leach up into the grout and discolour it , do not use marine ply under tiles

wbp stands for water and boil proof and is the correct stuff to use

[mikethetile]

I think he was referring to plying straight onto the joists. Would you be ok with 18mm ply straight on to the joists?

I wouldnt use anything less than 22mm as a subfloor straight onto the joists, cement boards glued and mechaniclyfixed are a good idea

[deanotile]

same as Dave i do not tile directly on to ply.