What type of render for tiling onto in a shower situation?

[Richard C]

no dont pva the wall just damp it down,

Agree with that, your better off just using water but don’t overdo it if the bricks are low absorbtion or you’ll have problems getting the render to stay on there; build it out in stages as recommended previously.

Sorry steve but it then starts to go a bit wrong;

but if i was you i would give the wall a skim first

Definitely not advisable in this case due to the weight of tiles (32 kg/sqm + addy) ; Gypsum skim will only take 20 kg/sqm & it must be primed when using a cement based addy or it’ll react with the Gypsum. I think the OP may still have trouble with the render bonding where it’s only 5mm thick.

followed by a coat of pva before you tile it

PVA is brilliant for plastering but never use it over a tile base, particularly with heavy tiles in a wet area such as this. PVA remains water soluble & the water in the tile adhesive causes it to re-emulsify reducing initial adhesive “grab” & give tile bonding problems; used in a wet area it could result in your tiles falling off the wall.

 

[stevethespreader]

no dont pva the wall just damp it down,

Agree with that, your better off just using water but don’t overdo it if the bricks are low absorbtion or you’ll have problems getting the render to stay on there; build it out in stages as recommended previously.

Sorry steve but it then starts to go a bit wrong;

but if i was you i would give the wall a skim first

Definitely not advisable in this case due to the weight of tiles (32 kg/sqm + addy) ; Gypsum skim will only take 20 kg/sqm & it must be primed when using a cement based addy or it’ll react with the Gypsum. I think the OP may still have trouble with the render bonding where it’s only 5mm thick.

followed by a coat of pva before you tile it

PVA is brilliant for plastering but never use it over a tile base, particularly with heavy tiles in a wet area such as this. PVA remains water soluble & the water in the tile adhesive causes it to re-emulsify reducing initial adhesive “grab” & give tile bonding problems; used in a wet area it could result in your tiles falling off the wall.

looks like i should keep my mouth shut when it comes to tiling ive never bothered looking into tile wieghts and it seems im wrong again with the pva im just waiting for all my tiles to fall off in the bathroom now thanks for correcting me rich

 

[stevethespreader]

no dont pva the wall just damp it down,

Agree with that, your better off just using water but don’t overdo it if the bricks are low absorbtion or you’ll have problems getting the render to stay on there; build it out in stages as recommended previously.

Sorry steve but it then starts to go a bit wrong;

but if i was you i would give the wall a skim first

Definitely not advisable in this case due to the weight of tiles (32 kg/sqm + addy) ; Gypsum skim will only take 20 kg/sqm & it must be primed when using a cement based addy or it’ll react with the Gypsum. I think the OP may still have trouble with the render bonding where it’s only 5mm thick.

followed by a coat of pva before you tile it

PVA is brilliant for plastering but never use it over a tile base, particularly with heavy tiles in a wet area such as this. PVA remains water soluble & the water in the tile adhesive causes it to re-emulsify reducing initial adhesive “grab” & give tile bonding problems; used in a wet area it could result in your tiles falling off the wall.

looks like i should keep my mouth shut when it comes to tiling i've never bothered looking into tile weights and it seems im wrong again with the pva im just waiting for all my tiles to fall off in the bathroom now thanks for correcting me rich

im a bit confused now i admit to being a tile noob but i've just looked on the tile adhesive tub i was using (b&q) and it says to seal ALL porose surfaces with a diluted mixture of pva @ 5-1 and it does not give any further recommendations when it mentions wet or splash rooms ect i was just following the advice given on the tub so why are b&q saying use pva?

 

[Richard C]

looks like i should keep my mouth shut when it comes to tiling i've never bothered looking into tile weights

Like the 49 degree temperature limit, it can be a bit of a surprising when you first come across it. I already knew about the weight restrictions of Gypsum, but I found out the hard way & to my cost about the temperature restriction as I had a major plaster failure around a new stove install. I now always research & double check the spec. sheets before using or trying anything new; I’d always put problems right but I really don’t like throwing me money away.

and it seems im wrong again with the pva im just waiting for all my tiles to fall off in the bathroom now thanks for correcting me rich

Wet areas can be a particular problem if any moisture get’s back to the PVA, it re-emulsifies & that’s all that’s between your tile adhesive & base you’ve stuck the tiles onto. A search through the Tiling Forum will throw up several cases of tile failure which can be attributed to the use of standard PVA to prime the tile base. Unibond & others also make a waterproof PVA for external use which I suspect an SBR sealer so why they call it waterproof PVA I’m unsure; just seems confusing. SBR is the one tillers use but it should only be used when specified by the adhesive manufacturer. Here’s a couple of links one of which I’ve posted the Tiling Forum before;
http://www.ultimatehandyman.co.uk/tiling/diy_Tiling_Why_not_to_use_pva.htm
http://www.diyuniverse.com/tiling/70-pva
Too late to worry now & if the tiles are up there, you should be OK if not too heavy & it’s not a wet area.

im a bit confused now i admit to being a tile noob but i've just looked on the tile adhesive tub i was using (b&q) and it says to seal ALL porose surfaces with a diluted mixture of pva @ 5-1 and it does not give any further recommendations when it mentions wet or splash rooms ect i was just following the advice given on the tub so why are b&q saying use pva?

If you need to seal/prime a porous tile base use an SBR sealer but, again, only when specified by the adhesive manufacturer which is not often. Peek-a-Boo aren’t exactly famous for giving accurate trade advice, selling quality trade tiling products (although they now stock Mapei) or even tiles come to that. I’ve got a pretty good idea who actually made the one you used as the tub advise is the same as one product in particular which has such a poor reputation in the trade, it should breach the trade descriptions act being sold as tub tile adhesive; their cement powder addy seems OK though if your tiling a concrete base & stuck getting hold of your preferred brand. Price is usually a very good guide; I use nothing but BAL (but there are others equally as good) & it can be 3x the price of cheapo DIY stuff but that’s’ far cheaper than having a major tile failure for the sake of saving, maybe, £50 - £100 on materials costs.

 

[stevethespreader]

thanks for that rich it was only 2 walls that were tiled , the shower wall was tile on tile because the tiles were on ply and a bugger to get off,and the other wall was the wall running along the bath on skim, the only reason they were tiled is so i can have a shower all the rest was skimmed and painted if it all goes tits up ill just have to do it again. That was my first bit of tiling and it took me a week incuding the end of the bath(boxing in)
it would have taken a tiler one day i suppose ,i did think of a tiling course to compliment the plastering but i hated laying those tiles so much ive decided not to bother

 

[mattshaw]

OK, I've put on the scratch layer as recommended. Damped down the bricks which were quite low absorbtion, waited ten minutes and applied a dryish mix, with the evermix 3 in 1 additive. It appears to be drying slowly and not cracking. How long do I need to wait before applying the second layer, and what type of finish will I be best giving it so the tiles grip?

 

[Richard C]

Put the second coat up as soon as the first coat is firm enough to accept it without dragging or breaking up. Don’t over trowel it but keep working across the whole area to get it flat & plumb; when it’s sufficiently set, level it all off with a suitably sized length of wood. When it gets to the stage where it’s fairly dry & set, a light brush over with a soft hand brush will give a suitably keyed finish for tiling but you don’t want to be brushing it off, just exposing the top layer of sand slightly. As parts of the render will be 20mm thick, don’t attempt to tile it for at least 2 weeks.

 

[mattshaw]

Thanks Richard, It is drying as we speak as I did it last night. Would it matter if it was totally dried out when I put on the second layer? I assume the second layer also needs to be quite a dry mix?

 

[Richard C]

Thanks Richard, It is drying as we speak as I did it last night. Would it matter if it was totally dried out when I put on the second layer? I assume the second layer also needs to be quite a dry mix?

Put the second (float) coat on now or as soon as you can; if you let it dry out you will have serious problems with suction & the float coat may not stick well to the first (scratch) coat; the surface should also be scratched (hence scratch coat) to provide a good key for the float coat but the surface is probably too dry now & you may have missed the boat.

 

[mattshaw]

Balls!! What to do now then? - give it a try when I get in?

 

[mattshaw]

I'm ready to put on the final coat. The scratch coat is almost dry but I'm afraid I have had no choice. I will damp it down slightly before I put on the final layer.

With regard to the additive, I am using Evermix 3 in 1. As I have a whole tub of this stuff just for this job, - if I mix it stronger than advised on the pack will it give me more moisture resistance or will it weaken the mix? - anyone any idea?

 

[Richard C]

Overdosing is not a good idea & results in increased setting time; large overdoses can produce very long setting times & in some cases the render may not recover its strength within a reasonable time.

 

[mattshaw]

Understood, sorry for dumb questions but just needed to understand.
thanks