Build up level under hardiebacker with adhesive?

[slippyr4]

Hello,

I'm soon to be tiling my bathroom floor. It was tiled by a previous owner directly on to T&G floorboards, and miraculously no tiles ever cracked. The floor is quite stable and surprisingly level; I've replaced some damaged floorboards and removed the previous flexible adhesive, and screwed everything down tight.

The floor is perfectly level transverse to the floorboards with very minimal cupping (< 1mm across each board).

The room is small (about 1.7 x 1.3m of floor) and has the corner cut out where a chimney runs through the room. The last joist which butts up to the chimney is lower then the others and therefore the floor level drops next to the chimney, by about 5mm. When I lay a 6ft level along the length of the floorboards,they are perfectly level up to the last "good" joist, then there is a downward taper which causes a drop of about 5mm by the wall. this section is about 600mm wide and ~200mm deep, and it will be located underneath a semi-pedestal basin anyway.

I'm thinking that I may well be able to get away with building up this small section with additional adhesive under the hardiebacker board. I'm thinking of using 6mm trowel on the whole floor and then back buttering the hardiebacker in the affected section with a 10mm trowel at the edge, and a strip with an 8mm trowel next to that, and then using a long level to set the board evenly on the adhesive bed.

Does that sound realistic for such a small section?

thanks in advance

 

[Dan]

It sounds like an impossible task using all those trowels. You should just use the bigger sized trowel over the lot but start laying in the highest area, then back butter a bit in the lowest areas. That'll mean the adhesive spreads itself as you apply pressure. It'll make itself flat and take up the space in the bits needing more adhesive.

Got a picture of this setup?

 

[slippyr4]

Thanks for your reply. I did it a few weeks ago now. In the end I just spread it out with a plaster float to build up the low part, then did the hardiebacker the next day. Job is pretty much finished and I'm pleased with how it's turned out.