Which plaster?

[meow2222]

Hi

which plaster do I need to level a wall before tiling? IOW I'm not after a fine finish, but the more strength and damp resistance the better. The wall's concrete.

thanks, NT

[John Rumm]

Bonding probably, since concrete is not particularly high suction. None of the gypsum plasters are exactly damp resistant though. (having said that, water should not be coming through concrete anyway)

[Andrew Gabriel]

Which direction is the damp going in?

All the gypsom plasters will fail on prolonged damp exposure, as gypsom itself is soluble (slowly).

[meow2222]

Its heavy transient condensation.

I've removed all plaster in the damp zones, and will keep that as concrete only. The plaster will go on the dry areas.

Thanks both of you... bonding it shall be

NT

[PeterK]

May be totally wrong but I thought plaster isn't a preferred base for tiles and it has (or is recommended ) to be primed? Is there a problem using an SBR mortar mix? From

(cement = cement based adhesive ) A) if it's cement V plaster, you have to prime it, the cement and plaster don't mix well and bond can become free in the future B) cement based adhesive are not waterproof, they're water resistant, so they allow water to pass through them and they don't break down, but the plaster or plasterboard behind will and can.

PeterK

[meow2222]

I suppose its an option, not going to handle as well as plaster though.

Thats what happened. It was all tile cement on plaster, and the area that got wet failed. But the dry areas were still perfectly sound.

Can SBR be added to plaster? Doesn't sound like its needed though, but hardly one of my areas of cluefulness.

NT

[meow2222]

just wouldnt handle well. Some of this has to go on very thinly.

On the damp areas all plaster has been removed, as that's what happened. I'm just looking to smooth out the dry areas with plaster, and that worked long term before.

Wacky question now... in dry areas can wall tiles be adhered on using plaster? I'm fairly positive the answer's yes. Is it a terrible idea?

- given that the current plan for those areas is to plaster and tile.

NT

[John Rumm]

I am sure you could get them to stick to bonding - it sticks to most things.

Yes. It would be a right bugger to plaster, and get it flat enough while still wet enough to stick a tile to.

Normally if its a wet service area, they suggest a waterproof adhesive, and to use a full bed of it - i.e. skim the wall with the glue to a couple of mm, and then add ribs the top - but not through to the wall. That way any water that gets through the grout, can't get as far as the plaster.

[meow2222]

The cunning plan was to patch plaster it flat, scratch it, and once dry to tile as usual, but using plaster. I'm sure the answer's yes, it works.

yes, I'll do that where it can get wet. The plaster thought was just for where it doesnt. I can't think of any good reason to spend many times as much on waterproof adhesive there.

NT

[John Rumm]

Yup, that would probably work. Be interesting to know how well, since there is a big difference in price.

The limitation may be the amount of slip you get compared to a good adhesive.

[mail]

Sorry, joined this rather late and am confused as to the purpose of the tiles and what is meant by heavy transient condensation not to mention the absence of an answer to the question as to thet direction of the damp. Howvever, on the assumption that the tiling is to stop damp going from the tile side to the concrete (as in a shower or bathroom) my tuppence happ'ths worth is that I would not go a country mile near any gypsum plaster and indeed (if it were feasible) would get shot of the existing gypsum that is allegedly sound. If this is not practicable on the grounds of qantum and you are, indeed, just patching up an existing wall with tiles that have failed I would a) ensure that the removal of apparently unsound plaster and tiles is extended at least one tile further than the "failure" b) remove all gypsum from the concrete where you are patching in and key the concrete c) apply a sand cement render to it with SBR (or if you can afford it Ardex render) d) tile and then regrout well into the old tiled area if not the lot

I may well have misunderstood so forgive me if I have the wrong end of the stick but the basics are water and gypsum are not natural bedfellows

Chris

[Andrew Gabriel]

Plaster rapidly changes consistency. As normally used, there would be too much slip -- it only just holds itself, and wouldn't hold a tile too. But it quickly sets, probably past the point where you can get suction to a tile-back. So whilst it might work, you probably only have a few minutes where it's capable of taking a tile, probably around 15 minutes after mixing.

Tile cement OTOH remains usable for at least half an hour, so you can get a reasonable number fitted and area covered with each mixing.

[Tim S]

[e-mail] coughed up some electrons that declared:

Is there anything that can be applied to sound gypsum to make it more water resistant?

[meow2222]

Can't I just mix it thick to avoid slip?

NT

[meow2222]

OK, bit more info. All the walls were gypsum plastered, and held out fine for decades. But eventually damp areas failed, the rest stayed strongly attached. So duplicating that situation in the dry areas I wouldnt expect to be a problem. The damp areas have had all traces of gypsum eliminated - I had hoped to eliminate all gypsum everywhere, but its just too big a job.

NT

[meow2222]

or is there a suitable additive? I expect not, but...

NT

[The Natural Philosopher]

Too right, since its in every bag of plaster or cement you buy..and in tile cement too ptrobably.

[Stuart Noble]

You're beginning to sound like a bit of a fruitcake.

[meow2222]

Structural elements of buildings have been constructed using just gypsum and tiles, but for asking if gypsum can stick tiles to a wall I'm a fruitcake? Uhuh, ok.

NT

[Stuart Noble]

If you could get away with plaster, tilers would be delighted I'm sure. Just spend £20 on a bag of tile adhesive and save yourself the worry