Before tiling, should I apply 6mm Cement Board to the Floorboards?

Hello, I have a total area of about 60m² to be tiled. There are old floorboards currently. I’m considering adding 6mm (1200 x 800) hardie backer cement board before tiling. What is best adhesive I can use for sticking the cement board to the old floorboards? Would tile adhesive be enough? Is there any recommended specialist glue type? Would the cement board need to be screwed in after laying it with the adhesive?

Asked by Karen on 5th Mar 2019
Expert Trade Answers
Best Answer
"Hello, I would definitely do this myself, so I encourage you to do the same. Below are my recommended steps to apply the cement board to your existing floorboards: First, you should check that all floor boards are fitted correctly and suitable to use. If there are any loose parts or corrections needed for the existing floorboards, now is the time to make them. Ensure the floorboards are clean afterwards to be usable surface. Then the mortar bed can be set by a thin set mortar (follow manufacturer’s advice of use where possible). After this, you can begin laying cement board. You should use cement board ideally between 6mm to 12mm, depending on your needs and judgement.
When laying the boards, ensure the first board has around a quarter of an inch gap from any walls nearby. Additionally, staggering the joints will make for a stronger base for the tiles, this can be done by keeping cement board edges no more than 8 inches to the joints. The board can then be fastened to the subfloor using quarter-inch cement board screws. These have special coatings and protection for this use – other nails would insufficient as they would corrode over time, leaving them ineffective and in need of repair/replacement. You can repeat this process for all the boards until the floor has been boarded. Continue to leave quarter-inch gaps between panels and staggering the joints – as mentioned above. For the last board of each row, they can be cut; holding a drywall T-square along the cutting line and indenting using a standard utility knife along the edge. Ideally have a few deeper scores through the fibreglass layer, which will allow you to lift the panel (along the indented edge) to snap the panel backward, to break the panel’s core. This makes it much easier to then cut through the remaining fibreglass layer, to finish the cut into two pieces.
These panels can then be installed for the remaining rows, continuing with quarter inch gaps for all panel edges. You can then use self-adhesive cement board joint tape to cover the joints between all panels. This will ensure it can bear contact with cement, unlike ordinary drywall joint tape. After the tape has been applied (be sure to double check it is adhering to the cement board correctly), add a very thin layer of mortar over the joint tape with a small drywall knife. Ensure that the mortar is applied smoothly and evenly, to be flush with surrounding surfaces. After the mortar has completely cured, then you can begin with the tile installation itself. "
Answered on 5th Mar 2019 - Member since Mar 2019 - report
"Hi karen,
I would not put hardie backer on the floor, instead i would use 12mm plywood screwed down every 6 inches to ensure a decent subfloor is underneath the tiles, then tile using flexible adhesive as you will always have a bit of movement in a wooden floor.
Answered on 10th Apr 2019 - Member since Nov 2016 - report
"Yes I would use a flexible adhesive aswell as screwing them down down. But make sure you fully fix floor boards 1st if there's any lose or not solid. Hardie backer is perfect for it as its hard waring lifetime guarantee (so they say)
Hope this helps.

Kind regards"
Answered on 22nd Dec 2020 - Member since Sep 2017 - report
"100% no tiles on wood. grout cracking maximum in 3 month."
Answered on 23rd Aug 2019 - Member since May 2019 - report
"everything tidy tillers has said is correct if you don't strengthen the floor first the tiles will loosen overtime you could do the same thing with plywood make sure you use flexible adhesive and grout its not as daunting as it sounds good luck"
Answered on 10th Apr 2019 - Member since Mar 2019 - report
"6mm 1200x600 Insulation boards fixed with screws & Washers is the best option. easier to work with cheaper to buy and the added bonus of keeping heat in the room. Simply cut using a new blade with no dust clinging to your lungs.
ATB Kierren"
Answered on 2nd Nov 2023 - Member since Aug 2023 - report
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