waterproofing a shower

handyman.

why use marine ply?? Are you salty or something.

It is as obvious as the nose on your face that you dont use any type of ply in a shower area. You use aquapanel/tilebacker etc and tank it, followed by tiling using quality adhesives and grout (ie powdered cement based BAL, not premixed bnq rubbish)

As for plasterboard of any type, come on, are you mental......you can tank plasterboard, but spent an extra £10 and get aquapanel and do the job correctly.

As BP says, he has learned that PVA does not go with tiling, please just accept you are wrong, and be happy you will finally do a tiling job correctly

Lewis_Gerolemou

Handyman I don't wish to appear contentious but I have used well primed waterproof ply in two showers and it worked fine. I probably would have used aquapanel if it had been available to me. As for PVA, it is great for fixing tiles to plywood in dry situations. I agree only nutcases would use plasterboard in showers.

moneysavingplumber

If water makes it through the grout, it really makes no difference what is behind them, it will rot and continue to leak and will need to be pulled out and started again. The PVA is simply to aid adhesion and, as in on bare walls prior to plastering, not for any waterproofing properties. Treated timber is used in many instances in bathrooms where it is exposed to moisture, in flooring, furniture and countertops, as well as bath panels. The main reason that I have used ply I already explained, for strength. It should never come into contact with moisture if the tiling and sealing has been carried out correctly, and as I said, it's a myth that any of the aforementioned alternatives mentioned will benefit you if the grout cracks or the sealant does, I've seen the results many, many times, whatever is behind will rot once water gets through. My tiler (with about 30 years experience) has always preferred ply becuse it is more sturdy, that's all. Timber and ply have invariably been used as a base for resin trays for years where they need to come up off of the floor, under manufacturer's recommendations, which will also be prone should water breach the tiles or seals.

The key to waterproofing is in tiles, correct adhesives, correct grout, correct sealants correctly applied, and in minimising movement by making sure the structure is solid, all as previously mentioned.

But what do I know, I've only fitted hundreds of showers over the years and not had a problem with any of them :rolleyes: ? (Most of these for ongoing customers so I would have known had there been).

Alan_M_2

Tiling is not a water proof barrier, it has never been designed to be a waterproof barrier, it is simply there for aesthetic and hygiene reasons (fact, British Standards - feel free to check - or discuss with the Nation Tile Association).

This is why tanking systems exist and have done so for the all the years I've installed tiles (15 years). Also with the advance in material desgined, specfically tile backer boards there is no longer any reason to use plywood in showers, in fact the building regulations were changed in 1996 to reflect this, so if you've constructed a shower area in ply since that time, you've not complied with building regualtions.

It is a common misconception that a grout described as waterproof, provides a waterproof barrier, it doesn't, it means the structure of the grout when set is unaffected by moisture ingress, but it does not say anywhere that is provides a waterproof barrier, the same of adhesives, and tile backer boards for that matter. Again this is why tanking systems exist.

PVA is not a good primer for the reasons explained in the link posted by Bob, I was the auther of that article.

Tile primers are based on PVA - true to an extent but they also contian acrylic modified polymers that stop the problems occuring that I clearly explained in the linked post.

PVA does not aid adhesion to anything, it actually reduces it, if your srface requires a primer use one recommended by the adhesives manufacturer.

Plasterboard if tanked correctly, is perfectly acceptable as a substrate for tiling, although there are better products available.

Plywood or any wood for that matter is your last choice for tiling for one reason - movement. Tiles do not like anything that expands and contracts, any wood does this due to atmospheric moisture and temperature changes. Any stable substrate is far better, which actually means a tanked plasterboard is a better option than plywood.

Another poster has suggested a 2 pack Epoxy grout, these are very high spec grouts that are a two pack resin (much like Araldite) they contain no cement, however they also have no flexibility whatsover so are only really suitable for use with solid substrates (brick or block walls).

The only reason to use Epoxy grouts is where a high level of bacteria or chemical resistance is required (restaurant kitchens or industrial applications). Often high use changing facilities will be grouted in Epoxy materials such as sports club changing areas or swimming pools surrounds.

handyman.

msp, you said pva is to aid adhesion. Did you not read the link provided? Please expand further, as you are wrong in what you say.

And a general point, Alan says you have done your tiling wrong to building regs as of '96 if you used ply. Would any of the 'old school' tilers like to make any comments on this?

moneysavingplumber

handyman. wrote:

msp, you said pva is to aid adhesion. Did you not read the link provided? Please expand further, as you are wrong in what you say.

No I didn't, I didn't have the time sorry. PVA is an adhesive, it is marketed and used as an adhesive, although in this case it may appear it is not as suitable for this purpose as some of us have always thought, I'll concede, but to say it doesn't aid adhesion to anything is nonsense. It clearly does have uses as an adhesive.

handyman. wrote:

And a general point, Alan says you have done your tiling wrong to building regs as of '96 if you used ply. Would any of the 'old school' tilers like to make any comments on this?

Yes I can hear the building police approaching now. If you read my post you'll realise that I don't do tiling, and I personally do not construct shower cubicles (although I did give the impression by using first person, when in fact 'I' have never physically constructed one myself, apologies), I fit the trays and the valves. Since 1996 I have probably not acted as a main contractor either, I now insist the householder deals direct with trades on my jobs, so it has not been my decision or responsibility what materials are used (yes you got it 'wasn't me guv honest'), it is usually decided between the tiler and the householder. I have been involved in hundreds from start to finish and there really haven't been any problems with any. There may be minimal movement due to expansion of timber but it doesn't appear to have had any detrimental effect on any I've been involved in, unlike many I've seen where plasterboard has been used and the movement caused by simply leaning on the walls have caused grout to crack. I agree tiles and grout are not totally waterproof, this is obvious where a tray fitted that is too small for the gap and a ledge has been constructed of either timber or plasterboard and water laying on it has penetrated very quickly, which is of course a very bad idea. With vertical walls I have simply never known this to be a problem when the wall is solid, the water is not in contact with the surface long enough to penetrate.

If movement due to expansion of timber is the issue, then any stud wall will move to a degree no matter what, because the stud itself is usually constructed of timber.

However, in this case I do defer to the superior technical knowledge here and concede it was a mistake to offer advice that may send someone down the wrong path and contavene building regs, and I concede that Alan M's advice is the one you should follow. My apologies.

handyman.

I should have added "to aid adhesion when tiling", thats the context i wrote it in anyway.

robwend

well , cowboy builder has built one side of my shower recess with plywood, and the other with plasterboard, the other side is the original house wall.>its a recess>so from the info you have all given me tanking it will correct that problem as will a good waterproof grout,i could rip down and use a waterproof plaster board and start again, but that
would be costly, tanking seems to have been around for a fair old while so i think that will do nicely

robwend

ooh before i forget, the shower tray is supported on plywood, raised 4 inches for plumbing. do i treat the ply it is resting on?and how?

moneysavingplumber

The tray should usually be bedded down. Manufacturer's recommendations used to suggest sealing the ply base with P...... P...... .P.... (can't bring myself to say it now) PVA to aid adhesion , although in my own experience bedding trays onto ply with sand and cement mix is a nightmare as very often it either comes away from either the tray underside or the base. Most people now use silicone for this purpose, but the tray has to be level, which was one of the advantages of sand and cement if the base wasn't level or the underside of the tray wasn't flat. The only surfaces you need to worry about treating are those that will be exposed to moisture, i.e the plinth that will need to go at the front of the base and the edges it will affix to, which should be suitably primed.