Bathroom tiling over plaster

Can I tile over painted plaster or do I need to scrap back to the brick?
My rental house is 1970 and double brick with plaster (WA).
It's a family house with 4 bedrooms and the bathroom walls attract dirt marks from fingers which are easier to paint over than wash off.
I thought it would be nice to tile floor to ceiling and never worry about painting again.
I retiled the shower because it was leaking water badly so now need to match the rest of the bathroom and the tenants are moving out so perfect timing.

One tiler says scrap back to brick so the bricks don't fall off and another says tile straight over the paint as it's so old it won't fall off.

Perhaps I am better just replacing the tiles that are already there and keep painting the room. It would be cheaper and quicker.

All thoughts appreciated.

 

Are bricks a suitable substrate for fixing tiles to? I would not have thought so.

Personally I would not try to tile over painted whiteset. I think it is too risky. I also would not try to tile over raw brick.

I have just completed a bathroom reno. I took the walls back to brick, rendered the walls with cement render and then fixed the tiles to that. For the shower and around the base of the wall I applied waterproofing (supervised by a licenced plumber) and then tiled over the waterproofing.

There is more info here:

https://www.ardexaustralia.com/pdf/spec tool/SRO915 - Tiling on Rendered Substrates.pdf

 

Thanks Perthguy

 

I think from memory (and was also suggested by a tiler) is hack up the plaster by putting lots of cuts into it to create a key for the glue to stick too. I think we used an axe from memory. Note: this may be bad advice

 

I started doing that, but with an angle grinder, not an axe. It really wasn't working that well and put a lot of dust everywhere. I ended up just using a hammer and chisel followed by a scraper, for small sections in the hall. In the bathroom, I used this machine and it was very messy. Dust through the whole house:

Ozito 1500W SDS+ Rotary Hammer Drill

 

Perthguy got me thinking and more research.
I discovered that houses made with internal brick walls, then have render over the brick then whiteset then paint.
So I only need to take the whiteset off if the render is good.
Then tile onto the render and that should hold the new tiles for many years to come.

Messy and dusty.

 

That's what I did in the hall. Hammer and chisel to loosen the painted whiteset and then a scraper to finish the job. It left behind cement render over brick which is a good substrate to fix tiles to. However, I found this slow and very labour intensive. The problem with using a power chisel is that the whiteset generally bonds to the cement render really well, so it ends up being easier to break the bond between the cement render and the brick, which is what you don't want.

 

For the best finish you should go back to brick then render again before tiling. That way you'll have a suitable surface that's also straight/level to tile.

 

@Adelaide - Who in their right minds would take off the hard set plaster unless the cement render is drummy? If you remove the cement render, how are you going to achieve a smooth surface for tiling?

@LifesGood - why recommend removal of the render (other than to cost a client money and additional time)? I wouldn't use a rotary hammer as per @Perthguy's suggestion unless you're removing all of the render (big job for no benefit).

Scabble the paint with a scabbling gun or grind with a very coarse grit sandpaper (on an angle grinder), then apply the waterproof membrane in accordance with the BCA where required. Glue fix tiles to the wall/membrane. White set is a solid substrate (composed of off-white cement, hydrated lime & sand) and is a very strong surface.



If the white set is in good condition (not crazed or drummy), I'd suggest patching where needed (polyfiller or similar) and painting with gloss paint not flat or semi-gloss which don't like fingers or cleaning without marking. You might also consider tiling up to 1200 mm or to door height if you have high ceilings (to get out of having to repaint constantly). I'd also replace the older style GPOs too.

 

Yes. The rotary hammer is definitely for removing everything down to the brick. In our case we wanted to tile 3m high walls with old, crazed, drummy whiteset covering cement render that did not bond to the bricks properly. It would not have held tiles. Because of this it was very quick and easy to remove. The big job was rendering the walls again. That took a lot of time.

White set is a solid substrate (composed of off-white cement, hydrated lime & sand) and is a very strong surface.
​

In Perth we make white set out of lime putty and white plaster powder (gypsum). I think the product is called hard wall? It can make a hard surface if applied correctly or else it is soft and crumbly. It can also be drummy which is not suitable for tiling over.

If the cement render under the whiteset is not drummy and a person is determined to tile I reckon the scabbling gun you suggested looks the business. I will have to keep that in mind for future jobs. It would not have helped with this one unfortunately.

 

Sounds more like Kalsomine not hard set render.

 

@Scott No Mates I did say "for the best finish". If you can remove whiteset or prep the 1970's walls to a suitable condition then go right ahead.

I got a local company to remove an entire bathroom's wall tiling and render for $500 then had my tiler render/screed. Extra cost but no other choice considering the age of my home and the condition of the crumbly render.

 

No waterproof membrane ?

 

Waterproofing after render, before tiles. Not necessarily required for walls that aren't in a shower.

 

Required behind/around splashback and bathtub too.

 

Our plumber, who signed off on our waterproofing, told us to also waterproof 200mm up the wall above the floor around the perimeter of the bathroom.

 

Yeh @Perthguy thatwould be the responsible thing to do. Some Project builders these days won't even waterproof a floor unless there's a hobless shower.

 

Definitely not. Its made from plaster, not chalk and lime, not glue. We can use powdered lime but it should be aged. Lime putty is just aged lime. Its also applied with a trowel, not painted on and needs to worked about three times to harden and smooth the surface. Here is a video of the process that was somewhat useful but misses a lot of detail it turns out



This is what I used:

https://www.bunnings.com.au/bradys-20kg-hardwall-plaster-mix_p0760178

https://www.bunnings.com.au/dingo-20kg-lime-putty_p0760455

Mix up. Trowel on. It's easy to apply. Its very difficult to get 100% right.

 

Thanks everyone. I am using the paint scraper and chisel. The whotest is falling off like magic.
Will get wire brush to finish it off.

 

Awesome! Glad we could help.