backer boards

[baht'at]

Hi All,
I have a floor to quote for 36m2 in all and intend using 6mm backer boards on all of it but 12m2 is old floor boards and the rest is New chipboard.
The old floor boards are bowed and intend to apply addy under the backer boards in this area but on the new chip board will it also require addy underneath it ??

 

[grumpygrouter]

You might want to lay SLC on the bowed bit before boarding. You should also put an adhesive bed under all the backerboard, not just the chipboard bit. Screw down at no less than 300mm centres.

Grumpy

 

[baht'at]

Thanks Grumpy,
I might not have explained very clearly its not the floor that has bowed but the floorboards them selves . the tounge and grove part has curled upwards slightly creating a slight concave profile with the edges.
As its not advisable to tile straight on to the TREATED chipboard floor as I have read the addy will not bond will it not be the same under backer boards ??

 

[grumpygrouter]

I knew what you were talking about with the bowing mate, I would still consider using a leveller first because as you screw down you boards onto the wet addy, it may get pulled into the curve of the board. You need the adhesive bed under all the boards to avoid leaving voids under the backerboard.

This is what is recommended by James Hardie's literature.

Grumpy

 

[baht'at]

Thanks again Grumpy.
Done a few floors but this is the first on wood hence the questions.
Just another question .
What size trowel do you use for under the backer boards please.

 

[grumpygrouter]

As small as you can get away with, probably 6mm should do but you still need to get good coverage.

Grumpy