SBR primer or slurry on breeze block prior to fitting hardiebacker


New Member
Hi all, new here and a complete DIYer so go easy on me!

Have found loads of useful stuff on this forum in the past so hoping someone can help me out!?

We're currently fitting a new bathroom, have spent today chipping away old loose plaster/render from exterior wall where a shower bath will go, to expose blocks ready to fix hardiebacker. There is a window on this wall that collects a lot of water from the shower so I want to try and get this as watertight as possible.

Plan on fixing Hardie to the blocks with tile adhesive and mechanical fixings, and then use Mapei shower waterproofing kit prior to tiling.

Planned to prime the exposed breezeblocks with SBR before using adhesive but I'm wondering if mixing up a slurry to brush on would give better adhesion/waterproofing? And if so what sand/cement/SBR ratios should I be using?

I've got the stuff and I don't imagine mixing a slurry will take much longer than priming alone so I'm not worried either way, just wanna do a proper job!

Any help would be great, thanks all!

Just sbr 1 to 1

Wouldn't slurry in that scenario unless rendering

Adhesive wants a stable base, that's all