How dry does new plaster need to be to tile onto?

gcol · 27 Sep 2005

Hi,
I had my bathroom wall plastered (patched up about 3 Metres sq) on Friday and it's still not dry. It's gone hard but still mostly dark grey - only the very thin skims have gone light grey. Bonding was used.

Questions:
1. Do I need to wait while the plaster has gone completely light grey before I tile on it?
2. What will happen if I don't?
3. If I need to wait until it dries completely; how long could it take?
4. We're still having baths. We leave the window open for a while after, then close it. Am I better leaving the window open all the time (even in this damp weather) or shall I move the dehumidifier in there?

Thanks,
Gcol

HandyJon · 29 Sep 2005

1. Yep, best wait till wall is dry. *
2. If the wall is still wet, the adhseive won't dry out fully and the tiles will easily come off. *
3. Difficult to say, but a good few weeks especially if there is bonding underneath the skim. If just skimmed, then it only takes a few days to dry out.
4. The humidity is actually quite dry at the moment coming into autumn/winter - even with the rain! Leaving the window open will help, but it preferably needs a good air flow to remove the moisture from the room so the door will need to be open too. A de-humidifier is the best option as the days get colder!

Will still take some time to fully dry out though.

* - I've had no personal experience of tiling on wet walls.

gcol · 29 Sep 2005

Finally a reply, thanks HandyJon!
Well tomorrow it'll be a week since it was plastered and there's been a dehumidifier in the room since Tuesday so I'm hoping that it won't be too much longer. I could do with getting the tiles up so that the shower can be fitted - baths aren't that convenient.
It was just a bonding coat - no skim.

No sign of drying yet - dammit!

Thanks again,
Gcol

jbonding · 30 Sep 2005

has the bonding been keyed,ie with a float with nails in it?

p.pittstop · 30 Sep 2005

Plaster needs 4 weeks to dry out before you tile on it. Also you need to get it skimmed because it's the skimming plaster that you need to tile to and not he bonding. Skimming plaster is a lot stronger than bonding.

P.

gcol · 30 Sep 2005

The first coat of bonding was scratched but the second coat was left smooth. My plasterer and tiler pal (that did the work) said it would be fine to tile to.
He used a bonding and dry wall adhesive mix and it's set like rock.... it's just not drying out as fast I I expected.
The tub of wall tile adhesive i've got says to leave new plaster for 2 weeks before tiling on it. I think i'm just gonna wait until it looks dry and then tile onto it - 4 weeks seems a bit much to me.
Cheers,
Gcol

HandyJon · 1 Oct 2005

gcol said:
He used a bonding and dry wall adhesive mix and it's set like rock....

First I've heard of drywall adhesive being used in this kind of situation. I would have thought it would have been easier to skim properly in the first place rather than use this weird mixture of bonding & adhseive. Is it a method of tanking?

gcol · 1 Oct 2005

No it's not a method of tanking. Apparently, you don't need to skim the walls if you're just putting tiles on them - bonding is sufficient. It's just my mate adds drywall adhesive to the mix because and I quote "it sets like rock and sticks like s**t". I didn't notice how much he put in though, I'll ask him if he's in the ale house tonight.

Cheers,
Gcol

HandyJon · 1 Oct 2005

gcol said:
Apparently, you don't need to skim the walls if you're just putting tiles on them - bonding is sufficient.

I've always been taught to skim before tiling. Tile adhesive doesn't like bonding as it suck up the moisture from the adhesive too quickly. I suppose the drywall adhesive stops this suction process, but if that was the case then skimming would have worked as well. Would be interested to hear what your mate says about it. Not saying it's wrong, just an unusual method.

jbonding · 2 Oct 2005

i've floated walls in the past for tilers to tile onto, i've keyed the surface to take the adhesive and i presume the tiler PVAed the surface to kill any suction but i bet any tiler would prefer to tile on a skimmed wall rather than just floated. Like handy jon says there is still a lot of suction in a floated coat. Adding drywall to anything it will set hard and i've mixed different plasters together in the past only because im stretching it, each plaster has a purpose so mixing them on purpose apart from adding cement to gypsum for a quick set is pointless, the next coat will only stick to a keyed surface so no matter what you mix together if you don't key the surface it wont stick wether you use a mechanical key (scratch coat) or man made key (pva) it wont stick and a mechanical key is stronger than a man made key.

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How dry does new plaster need to be to tile onto?

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