Hardiebacker on timber floorboards water proofing query

[ajpercival]

Hi I am new to this forum and it’s a godsend for information and tips however there is one thing I cannot seem to find clarity on. I am tiling my bathroom floor small area 1.5x1.5m which is t&g floorboards very solid and screwed down no deflection. I am overlaying with 6mm Hardiebacker glued with Keraquick s1 (possibly S2 with the latex plus as I hear this makes it suitable for timber) and screwed with 25mm turbo golds. Plan to use 600x600 porcelain tiles although not decided yet.
I’m concerned that by applying a wet adhesive direct to the floorboards will result in them absorbing some of the moisture from the adhesive and swelling/cupping etc.
So my query is:

Is this concern negated by the use of the latex plus instead of water to make it S2?

Should I prime the floorboards first to reduce/stop the porosity? If so what Mapei product?

Also I’m aware the Hardie backer doesn’t need priming/tanking prior to tiling even though it will let water through…all the way to the timber floorboards!. How can i create a waterproof barrier under the tile?

Starting this job this week so appreciate any advice/tips. And I want a belt and braces job not fussed about cost to get it right. Thanks

 

[Dave]

The adhesive is to take up any undulations in the substrate. Simply screw the hardi down with adhesive underneath and then for a belt and braces job. Apply Ditra over the top.

 

[ajpercival]

The adhesive is to take up any undulations in the substrate. Simply screw the hardi down with adhesive underneath and then for a belt and braces job. Apply Ditra over the top.

Thanks Dave but this didn’t address my issue with treating the timber floor/S2 addy and I wouldn’t need Ditra over Hardie especially for such a small area. Very unusual to use both.

Perhaps I’m worrying too much but just don’t want water in contact with my floorboards during install or later when bathroom is used.

 

[Dave]

Thanks Dave but this didn’t address my issue with treating the timber floor/S2 addy and I wouldn’t need Ditra over Hardie especially for such a small area. Very unusual to use both.

Perhaps I’m worrying too much but just don’t want water in contact with my floorboards during install or later when bathroom is used.

It was overkill as you wanted. Personally i think your worrying too much. The adhesive will chemical hydrate without affecting the boards.