Hi,

I have just finished preparing my bathroom for tiling.

I have bought 17.5Kg/m2 tiles (32x45cm) and I have Mapei Keraflex maxi cement. Around the shower area I have Aquaboard fixed to studs and I also have some areas of plasterboard fixed to studs. Both of these should be OK from what I read.

The problem is one particular wall (not a wet wall) where I have a mixture of bare bonding plaster and skimmed plaster. This is because a lot of the previous skim came off with the (smallish) tiles and also a lot of the previous bonding.

I asked the plasterer to make the wall "flat for tiling" and he made the level up to the remaining skim coat with bonding.

I am now aware from reading this forum that my tiles + cement + grout push just over the 20Kg limit for Gypsum (putting aside any concerns over whether I should even tile on the bonding at all).

So to get to the point of this post, I'm now considering my options, some ideas I've had:

1. Rip it all off and dab platerboard to it (not appealing)

2. Just tile on it and take the risk. Surely 20Kg is a conservative figure. What's the worst that could happen?

3. 9mm Plasterboard covering, but not sure how to fix through the plaster to the wall.

4. 9mm Backerboard or plywood etc with something like frame fixings through the plaster to the wall.

Has anybody else got any other ideas or advice?

Many thanks,

Rob.

Hi rob

your best option is to dot and dab the walls as bonding is unsuitable substrate to tile to

Get him to skim that bit of wall, as you mentioned the weight of tiles and not in the shower area

If the plaster may be subject to breaking then best bet is to overboard, your plasterer should be able to do this,if not it's fairly straight forward.

same as 'beam from me, if your plasterer skims over the bare bonding, you'll be ok with weight issues

Just to throw a question in, if skim plaster is strong enough to hold dot and dab plasterboard which is only adhered in small areas plus the tiles and addy, why not just tile onto skim coat over the top?

Thats kind of aimed at everyone....??

Thats what I suggested Scott, no need to board over the skim coat just tile directly

Originally Posted by whitebeam

Thats what I suggested Scott, no need to board over the skim coat just tile directly

Yeah isaw that Mark sorry, it didnt come out clear.What i meant was kinda seperate from this.

We know the weight limits for skimmed plaster and that unskimmed plasterboard is higher. My point is if the skim wont take the weight of a tile which is 75+% coverage how come it will take the plasterbaod which is dot and dabbed at maybe 50% coverage, plus the tiles addy and grout?

Does that make sense?

Originally Posted by Scottley

Yeah isaw that Mark sorry, it didnt come out clear.What i meant was kinda seperate from this.

We know the weight limits for skimmed plaster and that unskimmed plasterboard is higher. My point is if the skim wont take the weight of a tile which is 75+% coverage how come it will take the plasterbaod which is dot and dabbed at maybe 50% coverage, plus the tiles addy and grout?

Does that make sense?

its the bonding that was being d n d over but as mark has rightly said , skim the bonding and tile as normal

I didnt know you d n d onto a skim , whats the point in that

Originally Posted by mikethetile

its the bonding that was being d n d over but as mark has rightly said , skim the bonding and tile as normal

I didnt know you d n d onto a skim , whats the point in that

none..

Of course there is a point!

The point being that people have asked about weights for skim plaster and their tiles have been too heavy, the advise then is to dot and dab over it as unskimmed plasterboard will take more weight, but its only adhered to the skim in the first place.

Originally Posted by Scottley

Of course there is a point!

The point being that people have asked about weights for skim plaster and their tiles have been too heavy, the advise then is to dot and dab over it as unskimmed plasterboard will take more weight, but its only adhered to the skim in the first place.

.. so there is no point in dot and dabbing onto it

But its been suggested...... I for one have just fixed over skimmed but that was screwed into studs with dot and dab to level off and by god it was flat as a pancake!

so it'd been mechanically fixed too

Originally Posted by doug boardley

so it'd been mechanically fixed too

Yes mine has but all im saying is i have seen it suggested to others but cant see why!

if you d&d onto skimmed plaster, without mechanical fixing, you're adding more weight to an already unstable substrate, the boards and tile weight will pull the skim off the basecoat

okay first remove all loose surfaces from existing wall even go back to brick as if its loose or failing(crumbling) you cant stick anything to it once you achieve a solid surface then dot and dab plasterboard to solid background the addition of mechanical fixing would be beneficial as it increases strength as said above

Originally Posted by whitebeam

Get him to skim that bit of wall, as you mentioned the weight of tiles and not in the shower area

I was thinking that the limit for skim plaster was 20Kg/m2, but after your suggestion I looked again at the tile bible and it seems that 28KG is possible with "skim & set Plaster" and 20KG is only for skim over plaster boards.

So, just for the avoidance of doubt, does "Skim & Set Plaster" mean bonding plaster backing with a skim coat on top?

Thanks,

Rob.

Originally Posted by tinca

I was thinking that the limit for skim plaster was 20Kg/m2, but after your suggestion I looked again at the tile bible and it seems that 28KG is possible with "skim & set Plaster" and 20KG is only for skim over plaster boards.

So, just for the avoidance of doubt, does "Skim & Set Plaster" mean bonding plaster backing with a skim coat on top?

Thanks,

Rob.

can't see any point of skiming plasterboard prior tiling, you will just waste time and money, plasterboard itself hold up to 32 kg per sq metter while skimmed plasterboard or plaster hold up to 20 kg, so why to skim plasterboard prior tiling? if you go over 20 kg per sq meter with tiles which you will do if you will lay porcelain tiles, then tiles might debond between bonding compound and skimed plaster, i done some test and if you pull porcelain tiles from skimed wall on bonding compound, so adhesion will brake between skimed plaster and bonding compound, so the best choice would be dot and dab plasterboard with drywall adhesive and + fix plasterboard mechanically