Tanking a shower without foam boards

[MortarThePoint]

I have mixture of two substrates for my shower walls. One shower is 1 side MR plasterboard and 1 side blockwork, another shower is 2 sides MR plasterboard and 1 side blockwork and the last is 2 sides blockwork. I know the 'easy way' of doing is to use a foam board like Jackoboard/Abacus Elements/Marmox/... but we're not using any foam products inside the airtight envelope. Why we are doing that is a different debate and once we've started down the road backing out undoes all the sacrifices made up to now. It's very hard as building today without spray foam is hard to do. This also precludes foam tile backer boards like those mentioned.

 

I know you can get tanking kits to tank plasterboard and make it suitably watertight for a shower, but what about the blockwork?

[markc]

Tanking brush or roller applied will work great on blockwork 

[markc]

I’ve used the Everbuild Aquaseal stuff a few times and it’s been great

[MortarThePoint]

Just now, markc said:

Tanking brush or roller applied will work great on blockwork 

 

Thanks, Can you think of any product names, or is it the same stuff as the plasterboard tanking kits?

[MortarThePoint]

Just now, markc said:

I’ve used the Everbuild Aquaseal stuff a few times and it’s been great

 

Cool thanks

[markc]

Just now, MortarThePoint said:

 

Thanks, Can you think of any product names, or is it the same stuff as the plasterboard tanking kits?

Everbuild Aquaseal, I hit submit before finishing typing doh!

[MortarThePoint]

4 minutes ago, markc said:

Everbuild Aquaseal, I hit submit before finishing typing doh!

Should I use a tape like the one below at the blockwork / plasterboard junction, or will I need something more flexible?

 

https://www.amazon.co.uk/Everbuild-Aquaseal-Waterproof-Tanking-Tape/dp/B0086FC8S8

[markc]

I prefer the Mapei jointing tape from Screwfix, it’s wider with mesh edges and flexible.

 

https://www.screwfix.com/p/mapei-jointing-tape-white-grey-5m-x-120mm/69510

Edited May 30, 2022 by markc

[MortarThePoint]

2 minutes ago, markc said:

I prefer the Mapei jointing tape from Screwfix, it’s wider with mesh edges and flexible.

 

https://www.screwfix.com/p/mapei-jointing-tape-white-grey-5m-x-120mm/69510

 

Brilliant, I'm feeling a lot more optimistic now.

 

Thank you!

[MortarThePoint]

On 30/05/2022 at 17:04, markc said:

I prefer the Mapei jointing tape from Screwfix, it’s wider with mesh edges and flexible.

 

https://www.screwfix.com/p/mapei-jointing-tape-white-grey-5m-x-120mm/69510

 

How should I deal with the junction between plasterboard and screed? I know normally you raise plasterboard up but that leaves a gap for tanking. Can you recommend something to fill the gap with in the shower area as would be good if there is something waterproof. Or do you have the plasterboard come all the way down to screed?

[markc]

Morning squire, not sure if it’s the right way but i would/do keep the plasterboard about 1/2 inch above the screed and use the wide joining tape to bridge the gap and maintain waterproof “tank” between wall and floor. A compressible foam could be used to fill the gap.

[MortarThePoint]

On 30/05/2022 at 16:45, markc said:

I’ve used the Everbuild Aquaseal stuff a few times and it’s been great

Having discussed the bathrooms with the plasterer it seemed a good idea to sand and cement plaster the blockwork walls before tiling. Would that make for the following running order?:

1. Sand and Cement (S&C) plaster blockwork
2. Aquaseal tanking kit to S&C plaster and bare plasterboard in shower area
3. Tile

Can you prime the tanking surface to get a good key for plaster skim if I end up going a bit into the non-tiled area? I'm thinking of something like Bostik primer of BG Bond-It?

https://www.bostik.com/uk/en/catalog/product/construction/emea/uk/bostik-plasterer's-stabilising-primer/

[markc]

Morning squire, the tanking stuff leaves a good tacky surface, very like PVA bonding. Tile adhesive grabs hold well so no reason plaster won’t.

[Conor]

We boarded our block wall and tanked using the mapai kit from Screwfix. Tape and loads of tanking compound on the board joins. Siliconed the gap between the board and the screed, then taped over. Seems to be working.

[Onoff]

I'd infill / tidy up the blockwork joints so they're flush with the blocks. Be easier to tank on a smooth 'ish surface.

[MortarThePoint]

2 hours ago, Onoff said:

I'd infill / tidy up the blockwork joints so they're flush with the blocks. Be easier to tank on a smooth 'ish surface.

 

Good tip thanks. The plan is to S&C plaster all the blockwork so the tiles aren't too far behind the skim. That means tanking S&C plaster which should be nice and smooth.