tiling over crumbly render

[chellechelle]

I have rendered two small walls in my bathroom which I intend to adhere Kerdi membrane to followed by tiles, the room will be a steam shower cubicle with the kerdi providing the membrane. The render thus won't be providing any waterproofing function as it is under the kerdi.

The render is dry, sandy and the top surface could be rubbed down with my hand, it isn't blown. The render is easily drilled and can be gauged with screwdriver, it is quite soft. Is this a problem? Will it hold the tiles and stay on the wall?

Merry Christmas!

 

[roughcaster]

I "wouldn't" trust the soft sandy render you refer to. I know nothing about the Kerdi system you mentioned, but i've just watched a You-Tube video on it's method of application, and in my opinion, because the membrane itself is bedded into a trowel applied coating, i think the render/substrate it is applied to should be sound, and not soft and powdery/crumbly. There will be a fair weight overall by time the adhesive/tiles are fixed too. Could/would the membrane and it's backing coat pull away from the soft powdery background, due to the weight of the tiles?? who knows. It's also not easy to spread anything onto a soft, dry, powdery surface. This is all just my opinion on your question though, so let's see what the other guys think.

Merry Christmas to you too.

 

[joe-90]

How old is the render?

 

[chellechelle]

The render is about two months old. When I rub it with my hand it's quite dusty and numerous 'grains' are rubbed off. I haven't persevered to see if it is just the surface which rubs easily. It feels hard and sounds solid, though when drilled it creates a crater around the hole...a 7mm hole will be ~10mm in the render.

 

[joe-90]

It sounds to me like it dried before it had time to cure. I'd be tempted to remove it and use some kind of backer board.

 

[roughcaster]

It sounds to me like it dried before it had time to cure. I'd be tempted to remove it and use some kind of backer board.

Either dried too quick as Joe says or too sandy a mix. Good on ya for having a go, but it's too risky to spend a lot of money on your project, only to see it go wrong (maybe). I'd do the same as Joe, and use backer boards or re- render with a good mix, letting it dry out and cure as slow as possible.

 

[chellechelle]

Thanks for your advice, I think i'll go for the backer boards...though i'm tempted to have a go at rerendering! This is the first stage of a big project so i'm sure i'll be back with more questions soon

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• chellechelle
• 26 Dec 2012
• 1

Overview of wall

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• chellechelle
• 26 Dec 2012
• 1

Dust rubbed off wall

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• chellechelle
• 26 Dec 2012
• 1

Area where larger aggregate has been exposed

 

[Micilin]

Where in Herts are you?

 

[chellechelle]

kings langley.