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looking for some advice on how to DIY fix this.
bulge is under a window where 2 sheets of plasterboard meet. Has been like this for at least 5 years with no changes, but I’m just sick of looking at it.
the bulge is quite obvious. No issues with plasterboard above the window.
Sorry about that @katiendeira. Please feel free to reach out if you ever need assistance getting the most from the site. You can certainly post as much text and as many images as you like in a single post.
Welcome to the Bunnings Workshop community, I'm sure one of our resident Bunnings D.I.Y. experts will be keen to assist as soon as possible.
Jason
Hi @katiendeira,
Apologies for that.
There are two main reasons I can think of that there would be a bulge in the wall.
The first is that the joint in the plasterboard was not recessed, so the compound is bulging out further than it would be in a normal plasterboard joint.
You can see the slight shadow at the front edge of this plasterboard sheet. It is a very slight recess that allows for jointing tape and layers of plaster. If the plasterboard was cut so that this join didn't have a recess on each side, the plaster and tape would not have a recessed area to sit and would consequently bulge out.
The other potential reason is that the timber stud behind the plasterboard is out of line with the other studs, so the plasterboard itself is bulging out, and the plaster applied over the top has magnified the issue.
Depending on the severity of the bulge, which is very hard to see from images alone, you could try making a relief cut on each side of the bulge, peeling off the plaster compound, tape and paper face of the plasterboard, then using a plaster rasp like this Intex PlasterX 140mm Block Plane Rasp, to create a recess in the plasterboard that you can then apply a base coat of Multi-Purpose Joint Compound, mesh jointing tape, then a topping coat. Allow it to dry, then sand smooth with a sanding sponge before priming and painting.
The other option is to cut the plasterboard back to the nearest stud on each side, assess whether there is a bulge in the stud, and plane it back if needed. You would then need to install a new sheet of plasterboard following the same process to create a recess on each edge of the plasterboard, apply the compound, tape, topping coat and then sand, prime and paint.
Unfortunately, there isn't a simple solution. You could try simply sanding back the bulge and applying some multipurpose compound over the crack, but I doubt you'd be able to entirely sand out the hump.
Allow me to tag @Nailbag to see what he thinks.
Jacob
Good Evening @katiendeira
I have done the same with photos and text 
Easily done and easily sorted.
@JacobZ and @Nailbag have given great advice. And Im pretty much adding in my two bobs worth
Depending on how much the buldge is, say its 2mm ish, you could smooth the area over with plaster and then sand smooth, so I am talking about the whole width between the window frame and that other edge. I had a similar buldge in a spare room (previous owners kids had been bouncing around id say and a rubbish repair job) and I tried sanding it flat but was starting to go through the paper of the plaster sheet, so I extended the bump in effect, instead of a short sharp bump that you have now, make it a long smooth bump that teh eye and hand dont see. say 30cm on the low side smoothed up to almost the bump height and then down 30cm on the other. As you sand it the tip of the buldge will smooth out.
Just another option to consider.
Dave
