Hi @GraveR,
Thank you for your question about repairing water-damaged gyprock in your bathroom.
We should start by assessing the severity of the issue. The slight bulging in the wall indicates the paper face of the gyprock sheet has been water damaged, but if the actual gypsum behind the paper is intact, we may not need to remove the sheet, rather, we can just remove the paper, plaster over it and then prime and paint to seal.
I would start by making a horizontal cut just above the line of the water damage with a utility knife. You will be cutting through paint and then a layer of paper. Remember to wear gloves and long protective clothing as there is always a risk of lacerations when working with knives. You will be cutting through paint and then a layer of paper.
I would then peel the paper off the plasterboard down from the line. This will expose the gypsum core of the plasterboard. If it is solid, then we can plaster over it. If it is crumbly and severely water damaged, we will have to cut it out and replace the sheet.
If the gypsum is relatively intact, grab some Gyprock Less Mess Multi-Purpose Joint Compound and apply a base coat using a Kango 150mm Stainless Joint Knife. Remember to give the plaster a good mix before applying so it is smooth for application. Allow it to dry, then scrape it with the joint knife to remove any lumps and bumps. Once scraped, apply a second coat to smooth out any imperfections and fill any small holes in the base coat.
After this second coat, sand it smooth with a sanding sponge, then prime and paint to match the surrounding wall.
If you find that the gypsum beneath the paper is severely water damaged, cut out the plasterboard, attach a new piece, then apply mesh tape along the join, plaster with the same Multi-Purpose Joint Compound, then sand, prime and paint.
There is an external angle running along the corner of the wall. If you are careful, you should be able to keep this intact so you can slip the repair patch in behind it, staple it in place and then proceed as described above.
Let me know how you go, and if you need further guidance, please don't hesitate to reach out.
Jacob
