Truing rendered block wall prior to tiling

I'm renovating a small bathroom and want to tile onto a block wall that has been finished with a sand/cement render. The 30 year old plasterwork that was on has been removed - it more or less fell off. The wall is out of plumb by about 1.5cm bottom to top, and surface hollows of about 8mm over 2m. I don't think I'll get a good result tiling onto it as-is

I was originally planning of getting a plasterer in, but was starting to think about DIY as the final surface does not need to be perfect - just good enough to take tiles.

What about using something like Ardex AM 100 "Rapid Hardening One Coat Tiling Render"

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which apparently will apply in 2mm-20mm in one coat. How hard is it for a novice to get a decent result with this type of thing? The short working time is a bit of a concern.

Another option would be to dot-and-dab 9.5mm plasterboard - but I will lose more space this way - but it would be a lot easier.

Niall

Reply to
Niall Smart
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Personally, I would put another scratch coat on. You could either put this on the coat already there if it's well attached and you can afford the loss of 1.5cm of room, or you could take it off first, but that could be hard work.

I've posted in some detail how to get a scratch coat vertical, flat, and true. See:

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substitute sand and cement for plaster. You could use plaster, although sand and cement would be slightly better for tiling onto.

Reply to
Andrew Gabriel

I agree with the other post

Use 3:1 sand and cement. Add a glue such as Feb SBR to ensure adhesion. it is best for an amateur to use the "screed" method whereby you put on vertical lines about 4 to 6" wide near each corner and get these absolutely right first (much easier) and once they have set you can just fill in between Plastering is not that difficult if you are reasonably competent DIY and read up on the techniques. Chris

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mail

Thanks for your replies - very useful, I think I will give it a go myself and save a few hundred euro. I was wondering how to setup screeds to make it easier - that plumb dot and plaster screed technique you describe sounds like it will make it fairly straightforward. The sand/cement render already on the wall is fairly solid, so I think I can apply the new coat over it. The nice thing about the Ardex AM100 was that it can be applied thinly, and sets quickly - apparently you can tile onto it the same day - wouldn't I have to leave a regular sand and portland cement render 2-4 weeks?

Niall

Niall

Reply to
Niall Smart

Yes you would, but I'm not familiar with the product you mention. Check if it requires any type of bonding layer on the existing render. Mortar has a two-stage set. The first happens within 24 hours at which point it won't move anymore, but will break easily (or at the micro level, you can brush the surface off with your hand). The second stage takes about 6 weeks to reach its final strength, and then you won't be able to brush the surface off with your hand. For tiling on, you don't need the full 6 weeks, but it needs to have dried. Most tile adhesives require the surface to be dry, which usually requires waiting some days depending on the thickness of the coat, weather, etc.

Reply to
Andrew Gabriel

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