Plaster over Kerdi Board

Members online

Total: 518 (members: 1, guests: 517)

Share this page

Scholesy

Scholesy

New Member
Hi All

I'm a DIYer in the middle of a bathroom project.

I've used Schluter Kerdi Board throughout as most walls are being tiled.

There are a couple of walls however that need plastering. Has anybody on here got any experience of plastering over Kerdi Board?

I've spoken to Schluter and they have said the plaster should adhere ok to the board but the biggest issue is that it flexes. They've suggested running a thin coarse of tile adhesive over the Kerdi and then plastering on top of that.

I've got a bag of BAL s*p*r*lex Plus tile adhesive - do you think that will be OK to use if I apply it with a 3mm square notched trowel? I'm thinking however the fact that it's flexible maybe defeating the purpose of applying it in the first place (ie to add rigidity)... then again it might be ok.

I'm also thinking of applying the adhesive layer myself and then getting a plasterer to apply the final skim coat (I know my limits). For me it would be easier if I simply combed on the adhesive with the 3mm and left the ridges in rather than smoothing. My thinking is (i) I can do that. (ii) the ridges would give a better bond for the plaster layer

That's my DIY brain - feel free to tear it apart as I don't have much of clue.

Amy advice / pointers appreciated.

Cheers
Andy
 
madmonk said:
Im thinking more suction mate just try it first if ok skim it
Click to expand...

aGree, try it. If you put tile adhesive on first, you’ll be getting a good 4-5mm build after it’s skimmed which might not look good next to your tiles. I’ve used a bit of 6mm tile backer board over my central heating chases with a scratch of tile adhesive on, but going over with a float and skim coat.
 

Attachments

  • 20201227_212400.jpg
    20201227_212400.jpg
    1.2 MB · Views: 263
ChrispyUK said:

Substrates & building | Schlüter-Systems

Whether you choose BEKOTEC, KERDI-BOARD or KERDI-SHOWER, with our innovative system solutions you can create the perfect substrate for your tiling needs. Pre-fabricated components including niches and corner parts make installation quicker and easier.
www.schluter.co.uk www.schluter.co.uk
Click to expand...
Its strange it says that on their website.

I've been emailing their technical department (Schluter UK) and they basically first said I shouldn't plaster on it and should take it down and use normal plasterboard. So I rang them and they then said if I really didn't want to take it down that I needed to first skim it with tile adhesive to give the boards more rigidity.
 
I'd originally planned half tiled (for the shower area plus half skimmed).

The walls on that side have 600mm centres - so I needed 19mm Kerdi Board for that.

I figured to keep it simple I'd just use Kerdi Board for the whole wall rather than splitting it. Plus (I think) for plasterboard on 600mm centres i'd need 15mm. So then I'd have had 19mm & 15mm board. I never thought skimming / painting would be a problem until I spoke to Schluter technical.

Hope that makes sense
 
Scholesy said:
Its strange it says that on their website.

I've been emailing their technical department (Schluter UK) and they basically first said I shouldn't plaster on it and should take it down and use normal plasterboard. So I rang them and they then said if I really didn't want to take it down that I needed to first skim it with tile adhesive to give the boards more rigidity.
Click to expand...
It’s designed for tile addy to stick to it. You can skim over tile adhesive if treated correctly but your adding to the thickness. If you started with skimmed walls before tiling, then your tiles would be sticking their thickness above the skim.
 
ChrispyUK said:
It’s designed for tile addy to stick to it. You can skim over tile adhesive if treated correctly but your adding to the thickness. If you started with skimmed walls before tiling, then your tiles would be sticking their thickness above the skim.
Click to expand...
I'm not too fussed about the extra thickness as it shouldn't cause any problems (at least not that my DIY brain can figure out)

If i used a 3mm trowel for the tile adhesive and smoothed it then that would only be an extra 1mm of thickness. Or if towelling and leaving the ridges makes sense (rather than smoothing) then thats still only 3mm extra.

Just not sure if I should use the BAL Super flex Plus I've already got or buy something less flexible. Probably overthinking it.

If I'm applying a layer of tile adhesive for skimming on top of is there anything I should do differently?
 
Scholesy said:
I'm not too fussed about the extra thickness as it shouldn't cause any problems (at least not that my DIY brain can figure out)

If i used a 3mm trowel for the tile adhesive and smoothed it then that would only be an extra 1mm of thickness. Or if towelling and leaving the ridges makes sense (rather than smoothing) then thats still only 3mm extra.

Just not sure if I should use the BAL Super flex Plus I've already got or buy something less flexible. Probably overthinking it.

If I'm applying a layer of tile adhesive for skimming on top of is there anything I should do differently?
Click to expand...
Maybe the plasterer can put a tight coat of bonding on, over the board and in bed mesh, then skim. It does say it will take plaster coats.
 
Gilbert75 said:
Maybe the plasterer can put a tight coat of bonding on, over the board and in bed mesh, then skim. It does say it will take plaster coats.
Click to expand...
It does.

It also says you can plaster over it in the marketing blurb on the website I bought it from. Not sure why Schluter technical are giving out a different message.

I've been out this morning and bought a bag of P9 tile adhi (white) - so less flex than the Bal. Most probably overkill but for the sake of £13 figured why not.

Also spoke to a plasterer and he's good with the approach. Also ok with me just troweling and leaving the ridge lines as he figures it will help the plaster grip (if needed) plus he'll also have some bonding agent if needed.

Cheers all for the advice. Might be a case of cracking a walnut with a sledge hammer but at least the finished job should be problem free.
 
Any reason you can't put some 9.5mm plasterboard over that?
Also could put metal lathe over and skim but id board it
 
You must log in or register to reply here.
Top