Refinishing old blockwork

[Richard C]

All of the plaster is removed from the blockwork (most of it fell off!), the new recessed shower mixer & plumbing is in, & I’m ready to start building up again to tile for the shower. Some of the mortar joints are not that great & there are a few cracked blocks but not all in the same line; I put this down to the bricky’s efforts when I had a new window opening put into the gable wall!

What’s the best way to proceed to fill the plumbing voids & bond the blockwork together to provide a sound base?

1. Render the whole lot - best mix to use?
2. Thistle bonding
3. Thistle Hardwall
4. Any other?

With regard to finish before tiling, will a Multifinish skim be OK or would it be better to fix Aquapanel & tile directly over that.

 

[diyisfree]

Richard,

Fill all the chases where the pipes have been installed with Bonding. If you followed the instructions correctly that came with your mixer then you should have about a 1" gap around the entire mixer unit.

It is important to leave access to the thermostatic mixer valve and also the diverter valves for future servicing. In other words, bond all the chases then leave the main body area open, your tiles will then cover this area so should you need to do any repair work in the future then its easy.

Is yours the type that comes with a chrome plate that sticks over the top of the tiles afterwards ?

if it is then cut your tiles to expose all the valves but make the finished opening slightly smaller than the cover plate so the self adhesive strips on the back of the plate can adhere to the tiles.

I always run a tiny bead of clear low modulus silicone around the plate once installed to ensure no water gets behind

No real need to skim with finishing plaster if you are tiling the walls afterwards. I always use bonding, Just leave a good key in the bonding then tile away.

ENSURE that the plumber (Or you) have installed check valves on the hot and cold supply to the mixer unit before you start tiling and enclosing the bath. Thermostatic mixers have a tendancy to allow cold water to pass through the unit and down the hot water supply cooling the hot water supply to other taps in the house.

 

[Richard C]

Thanks for the reply diyisfree. I intend to leave the mixer valve open below the chrome wall plate as you say. I’ve fitted full flow lever isolation valves to the mixer supply lines & it’s actually rigged as part of a whole house pumped system (no combi boiler!) so the pressure should be equalised across both the H/C supplies; I’ve not heard of the backflow problem you mentioned, how common is it? Presumably it indicates a fault on the thermo control valve? It’s a Hudson Reed unit & cost an arm & leg so I wouldn’t expect any problems!

 

[diyisfree]

Richard,

I would agree that it sounds like a fault with the unit but NO it isnt.

if you read the small print that comes with these mixers it actually says you must install a pressure reducing valve to the main cold water inlet to the house to equalise hot and cold water pressure

Combi boilers seem to suffer worse because even though the hot is "mains pressure" it isnt quite as powerfull as your cold tap so the cold is forced down the hot track and the pressure builds to a point that the boiler takes a while to sence a pressure drop so doesnt kick in straight away, so no hot water.

First time i fitted one of these, i ended up calling Baxi and saying there new 3 week old boiler was goosed. Then i noticed if the thermo valve was set to hot then the other taps were all ok. If it was left set to cold then all other taps were tepid.

Anyway, fitted double check valves and it was fine. Customer didnt want pressure reducing valve because he said washer, toilet, taps running and so on would be slower, who am i to argue

Glad to see you did it all correct.

 

[Richard C]

Thanks again for the info.