Hi really need your help! Refurb project. joists replaced, they aren’t small at 3inchx8 inch @ 350mm centers. joists coveredwith 18mm tongue and grove chipboard. We are looking to cover 18mm chip with ditra mat or backer board. My question will the 18mm chipboard be ok with tiles. The entire flat will have tiles including the wet room. What would you go for ditra or backer taking into consideration the 18mm ply. 18mm chipboard was picked, as it had the acoustic the membrane on the underside. Thanks for any help.