Advice Required - stained tile grouting

angelavdavis

Hi all,

I wondered if anyone can give me the benefit of their expertise.

I installed a shower cubicle into a large cupboard off my bedroom and turned it into an en-suite shower room. I used marine ply to box in the main pipes which take the supply up to the loft, and cover the connections from these pipes into my power shower unit. I also used ply on one wall to reduce the shower size slightly to fit the large tray I had purchased.

Then I covered the marine ply with white mosaic tiles and grouted (I used a flexible tile cement initially and grouted afterwards with standard white tile grout). I was really chuffed with the result and it has been a great usable space since then.

The problem I have is that four years on, it appears that some areas of the ply seem to be weeping sap through the grout. Therefore, if you bleach the grout clean, within a couple of hours, the brown sap has permeated again and it looks awful.

It is only in a couple of confined areas which have quite a lot of water contact, but it looks to me like I need to somehow remove the existing tiles (not a problem, as I have plenty of spares), seal the ply underneath with PVA or something similar, and retile/grout. In both areas, it looks like it is where a cut edge is present - ie the tiles and grout are sitting on a cut edge of ply, so I am guessing the adhesive/sap is seeping out from these edges.

Is PVA the right tool for the job in this case? Any other suggestions that could save me the trouble of stripping off the existing tilework such as a different type of grout to try? Thanks