# Forum Home Renovation Tiling  Tile preparation for painted hard set plastered brick wall

## celestem

Hi 
I am preparing to tile 1500mm up some walls in the laundrey and toilet.  The walls are painted hard set plaster on brick.  So I stripped the paint off with a wall scraper then belted all over the white set plaster with a welding slag hammer, as per attached picture.  Is the roughing up in the picture adequate, or should I be knocking more of the white set plaster off?? 
Cheers for any insight.

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## Dr Freud

I'll tell you the correct way first, as this is how I do all jobs: 
You need to get a (firm) metal paint scraper and run it at about a 30 degree angle and scrape all of the plaster off, to expose all of the concrete render underneath.  Getting a starting point then working along a line works well.  Then brush all debris off with a firm scrubbing brush, then sponge all dust off with a very wet sponge in bucket of water.  I wouldn't bother with waterproofing as long as your floor waste is close to your machine.  If you tile and grout well, the occasional machine splash is nothing.  If there is any doubt about floor falls or floor wastes, I would waterproof the whole job.  I don't care if the carpets of floorboards need replacing after a flood, my tiles will be there until demolition. 
Dodgy way: expose as much cement render as you can be bothered, as in the photo, then tile onto this.  Bear in mind if the white set plaster ever gets wet, it will turn to powder, and your tile system will be hanging on by whatever render you exposed.  I say tile system, because once the tile are all glued and grouted, roughly work out this weight (lift up a bag of adhesive and two boxes of tiles).  This is roughly the weight that will want to listen to gravity. 
Some people may have experienced a whole wall of tiles moving off the wall, but staying together.  This is the risk of poor substrates.  A small risk, but easier to do it once right IMHO. 
Scraping plaster sux, but second rate tiling sux more. 
Think of how toned your arms will be.  :Biggrin:

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## celestem

Hmmm- so it looks like I should aim to take off all of the white set plaster.  I wanted to leave some plaster behind, maybe 10%,  so it acts sort of like level guides as the wall is nice and flat as is. 
If there is no white set plaster is it that critical to water proof in a laundrey and toilet?
Or maybe just water proof the bottom 200-300mm - Is this sufficient? 
I'll check the fall of the floor too, but with 600x300 tiles I suspect that it will be nil.

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## Dr Freud

Take it all off.  :Biggrin:  
The render underneath will be just as flat.  But to ensure a nice flat tiled wall, use a straight edge as you go, across, up, and diagonally.  If you get it very close with a straight edge, it will look perfectly flat to the naked eye.  Don't use a spirit level (not the bubble in it anyway), walls rarely go straight up in my experience. 
With all render substrate, plus good adhesive and grouting, your system should be sound without waterproofing.  That said, pipes, cisterns, taps, machines etc have been known to spring a leak at the most inconvenient times.  If you are away for enough time, this water will absorb into the tiling system, and into the wall, then up, along and through the wall (paint on the other side?)  The tiling system will likely hold on until it dries, but the plaster/paint on the other side won't like it. 
So, a good fall and waste will keep any leak's flowing out and not soaking in.  If there is a chance of a puddle forming, I'd waterproof as a last resort (If I couldn't get the fall and waste done). 
A lot of tilers/tradies would call this overkill.  After seeing the effects of water damage a lot of times, I isolate water with the same respect I do for electricity.  If you don't give it somewhere to go, it will go where you least want or expect it to.  :2thumbsup:

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