Ply - Priming Back

[IHB]

I'm replacing the floor in my bathroom with 18mm ply and then over boarding with 6mm HBB. I seem to remember that it's advised to prime the back and edges of ply before it's screwed down.

Is it necessary? I'd don't really understand what this would be achieving.

 

[Qwerty]

To prevent any possible future water or damp ingress leading to possible swelling of the ply by it being treated all sides

 

[IHB]

But does priming it actually make it waterproof?

 

[Qwerty]

No

 

[IHB]

So. I'd read that priming is to stop moisture but if it doesn't waterproof it then how will it stop damp ingress?

 

[Qwerty]

Water resistance and waterproof are two different things

 

[DHTiling]

So. I'd read that priming is to stop moisture but if it doesn't waterproof it then how will it stop damp ingress?

It aids in slowing down moisture ingress. If you want to waterproof then that is different

 

[IHB]

I have primed the boards but couldn't help wondering if there was any point to it. Does adding a little more moisture resistance to exterior grade ply make any difference? Does the advice come from British Standards?

 

[SJPurdy]

In my experience the joiner or builder that has fixed the ply never seals the back or edges and so it doesn't get done. However if doing the fixing myself then I would give the back a coat as it only takes a few minutes and means that I would be working to the adhesive manufacturer's and BS recommendations.

 

[High Peak Tiling]

If you prime a piece of ply properly and drip some water on it, it should either separate the water into blobs or just sit there. It takes a lot longer to be absorbed

 

[Dan]

Keep the thread on topic lads.