Replacing Water-Damaged Plasterboard in Bathroom - Insulation Question

kenny_david

Hi everyone,

I’m redoing my bathroom and after removing the tiles, I found that the plasterboard is water-damaged. It was insulated plasterboard with 25mm of styrofoam behind it. I’ve already removed all the wet plasterboard, but the styrofoam behind it is still there.

My question is: do I need to remove the styrofoam as well and get new insulated plasterboard, or can I just buy regular plasterboard and fix it to the wall using plastic wall anchors? Going to tile onto the plasterboard when replaced.

Any advice would be appreciated!

Thanks!

10-10-20

Hi there.

Yes, I'd remove that polystyrene for sure. Reasons being are that it was damp, has mold on it, and provides a poor surface to work off. Plus that existing plasterwork is in poor shape now. It's also likely that the insulated plasterboard was chosen in that room for a good reason, so in my opinion you'd be foolhardy to not also insulate in a similar way.

What I'd do is I'd take off all of the polystyrene back to the wall across that whole wall. Then I'd install insulated polyiso boards adhered with plasterboard foam to create a flat surface across the whole wall. Then in the area where the tiles are going I'd adhere using the same adhesive 12mm tile backer boards (same depth as the plasterboard) on top of the polyiso as a solid backing for the new tiles. These would also need to be screwed in to the block wall through the polyiso using metal washers, then tile directly onto the backer board. On the remainder of the wall I'd then install standard 12mm plasterboard and have it skimmed.

https://www.goodwins.ie/products/xtratherm-polyiso-rigid-foam-insulation-25mm-2-4m-x-1-2m.html?filter_set%5B%5D=1413,1426

https://www.goodwins.ie/products/botament-tile-backer-board-12mm-1-2-x-0-6mtr.html?filter_set%5B%5D=5160,6321

https://www.tilemerchant.ie/baseboard-washers-100pcs.html

All personal opinion - others would do this differently. 👍️