basecoat for flushing villaboard

[royalty]

HI ..thanks for all the great info ...My querie is...Ive redone a bathroom using villaboard as shower walls and spa surround plus spa step and a concrete floor and intend to tile over the lot and walls to a hieght of 1200. I have flushed all the villaboard joints on the spa step and shower walls and main bathroom walls with a a gyprock basecoat mix (basecoat 140 i think) and the normal fibre mesh tape and then gave the joints a coat of bondcrete..i didnt give it much thought at the time and was all i had at the time and it has stuck well and the joints are good, strong and smooth ...Now i am wondering will i have trouble getting a tile adhesive to stick to the basecoat flushing compound or to the bondcrete over these joints ...anyone know if this will be ok for tiling over or should i rub it back and put a skim coat of a more appropriate compound over the gypsum basecoat before i tile... ...like i say its mainly at the joints and nail holes etc so a good section of the 300mm sq tiles will still be stuck direct to the villaboard... also pending what tile adhesive i use should the villaboard be primed with anything prior to tiling... ... Many thanks for any input....Kym

[Fossil]

The basecoat is fine. Prime the walls with primer from your tile shop, and use a good quality 1 part adheasive and you will be fine.

[arms]

hi you,ve hit overkill in a big way ,but then again its better to be safe than sorry.you have prepared the surface sufficiently now all you have to do is paint on a waterproofing compound over the joints and into the corners don't forget to use the tape supplied,bondcrete is not enough of a sealer for showers or any wet area

[mic-d]

Hi Kym, That's going to end up one lovely bathroom when its finised. Just a few comments and questions. From the photo, it looks like you glued the villaboard in the shower. For tiled applications the villaboard should be nailed or screwed only, due to the weight of the tiles. I just demolished a shower that had a few nails in it but mostly adhesive and although the wall wasn't going anywhere, that was mainly due to the taps and shower screen. I gave the wall a bit of a pull and it all came away. The adhesive was stuck to the studs but had failed on the villaboard.
In the wet areas, all those areas that have basecoat over them must be waterproofed before tiling, so there is no problem with tile adhesive not sticking to the basecoat. Where you don't have to waterproof, never use topcoat under tiles as the tile adhesive will not stick to it. Generally I do not set any joints under tiles with basecoat etc. If its a wet area I "set" the joint with a bead of sikflex and the waterproofing and elsewhere I "set" the joint with modified thinset (flexible cement tile adhesive) and just fill corners with a bead of Sikaflex Pro.
To waterproof the shower, you need to run a bead of sealer around the base of the villaboard to isolate it from any moisture from the floor that may wick up (and dig out any basecoat filling the gap and make a gap if its not everywhere). You need to apply waterproofing to seal all joints and corners to about 200mm from each side of the joint and all fastening points. Use reinforecement over all joints. Pay special attention to the ledge in the shower. That's the minimum you need to do and that's all my waterproofer has done for the last 20 years, but if you wish you can coat the entire wall with waterproofing. Waterproof the entire floor and up the wall 2-300mm. Do you still need to lay the shower mortar bed or is that the final sloped surface?
If you have bare villaboard, it pays to prime it with a primer like bondcrete or specific tile adhesive primer. You can use a modifed thinset tile adhesive (ie a flexible 1 part cement-based adhesive - not one with rubber particles in it tho') throughout. To make things a bit easier, you can use a good mastic adhesive (like Davco product) on the walls only and not the ledge either. I never used to use it in showers and some people will say not to still, but I made the change for several reasons. 1) I've demolished a few showers that used mastic and it was never the adhesive that failed. 2) I soaked some dried mastic in water for weeks and it never went to mush - once its gone off its stays that way( a bit like water soluble paint doesn't dissolve in the rain) 3) Most of the tilers use it 4)It is easier - no mixing, its white, and it does not slump. After you have tiled, seal the grout with something like Sureseal before you use the shower.
Cheers
Michael

[royalty]

Thanks Micheal for your detailed reply and to others for thier good advice ...its a bit of a saga but basically its an addition to an older part of the house comprising kitchen, bathroom and 2 living areas, all that is left of the older part is 3 bedrooms and then it steps down to the new slab with a lean to roof ...all up the new section is around 145sq....the bathroom floor including the shower is the slab that comprises the rest of the new addition with built in falls to a central drain and the shower falls to its drain... on top of this slab i used bricks for the hob and bricked 2 of the shower walls to the roof and the shower screen and villaboard made the other walls...the plan was to render the bricks and tile to that until i relised how bad at rendering i was and i wasnt happy with the level i left so i ended up with a brick wall with an unlevel render surface...i then put batterns to level the rendered walls up and screwed into wall plugs thru the render to the brick...these batterns in places were only 5-10mm and the villaboard was touching the render in others..i put brick plugs in and screwed the villaboard to the rendered wall and countersunk the screws the best i could and had to grind a few but still leaving enuff to hold the villaboard in... i used stud adhesive on the batterns to the villaboard and then filled the rest with cornice cement to get a bond on the rest... the shower floor is just the concrete slab but the falls are perfect so i was just gonna acid etch the floor and tile direct to that after waterproofing. ...the hard part is coz ive done it all myself i need a different tradies hat on each day and im not a tradesmans a**hole...ontop of that we are using the shower while im working on it ...i have enuff leverage to stop the villaboard wicking up water and will be able to seperate the floor from it...im glad u mentioned that as i didnt plan on it but it makes perfect sense. ...so basically if i use a waterproofing membrane up the walls enuff to cover the plaster basecoat i used on the joints i should have no problems getting the tiles to stick and this will waterproof the basecoat i used as well???? ....when all this is over i can then head to the kitchen for the next round... thanks for your help and advice....Kym

[mic-d]

. i used stud adhesive on the batterns to the villaboard and then filled the rest with cornice cement to get a bond on the rest...

Is the back wall stud wall or brick? If I understnd you right, the back wall is fixed as above, ie without screws? If so you need to fix it with screws/ nails - I wouldn't rely on stud adhesive/cornice cement.

...i have enuff leverage to stop the villaboard wicking up water and will be able to seperate the floor from it..

Don't understand what you mean by leverage ?

. ...so basically if i use a waterproofing membrane up the walls enuff to cover the plaster basecoat i used on the joints i should have no problems getting the tiles to stick and this will waterproof the basecoat i used as well???? ....when all this is over i can then head to the kitchen for the next round... thanks for your help and advice....Kym

Yes if you w/p as per the previous post to cover all the base coat you can't go wrong.
You need to let the shower dry out for a few days before you seal it (I would use sikaflex, not silicone) and w/p it.

Cheers
Michael

[royalty]

sorry i will explain better...theres 3 ways ive fixed the villaboard ...the batterns used for levelling are screwed to the brick wall and the villaboard is glued with stud adhesive to the batterns...where the villaboard is touching the brick wall i have screwed it to wall plugs direct into the brickwall and i also threw a few dobs of cornice cement on the back of the villaboard as well and these dobs are also contacting the brick wall .... the render was all over the joint so i batterned the hollows and the high points i left renderd and levelled up to it


leverage was a bad choice of words...i have about a 5 mm gap between the floor and the bottom of the villaboard

i aquired 20 litres of durabit shower proof membrane which is ample to go to the top of the villaboard and cover the shower twice.

its a bit of a pigs ass the way i fixed the villaboard but it seems very solid so i hope its gonna stay that way over the long term..