Tiling onto Plywood - Prime/Seal?

[djjohnnyb]

Hi, hoping for a quick answer as I intend to start some tiling tomorrow. I've tried searching the net on this and it seems there are hundreds of opinions...

I have wooden floorboards subfloor in my bathroom. I have overlaid with WBP plywood, staggered joints, 200mm screwed centres. I have also boxed in the soil pipe behind the toilet, using timber battens and the same plywood.

Do I need to Prime / Seal the Plywood before I start laying the tiles? I am using Mapei Powdered Flexible Adhesive. It makes no mention of Priming/Sealing the Plywood substrate on the instructions, but I want to be 100% before I start.

I currently have PVA and Oil Based Primer, but I don;t think these are suitable. I can get an Acrylic Primer if needed.

Also, is it worth Priming / Sealing INSIDE the boxing in (plywood and/or timber battens) behind the toilet before I tile and therefore close off?

[Colour Republic]

what thickness ply is it?

[djjohnnyb]

9mm. I know I should have gone thicker, but the sub floor seems good and solid, and I was limited by the height of the previous flooring, and therefore the height for the toilet and plinth for the basin.

[djjohnnyb]

Ok so I ended up not sealing or priming the plywood before applying the adhesive. The instructions didn't mention it, and the guide on this site stated the same. Definitely didn't use PVA as per all the warnings against it.

I must say I hold my hat off to all the pros and DIYers who use the powdered adhesive. I found it horrible to use and messy. Probably as it was my first time floor tiling, but I don't plan on doing it again soon. I had all the tiles pre cut and planned out perfectly, but when it came to laying them it just didn't quite look the same. Oh well, it's done now and I'm still pleased with the results.