Filling gaps between joists and plasterboard.

12 Apr 2011
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United Kingdom
This may be an obvious one, but I've not found anything on the best way to do this. We've re-boarded a sloping ceiling after doing some remedial work, and properly insulating. We have had to slot the boards up between the exposed cross joists, and because the ceiling bows in both directions, and the joists are all a few degrees off vertical, in varying directions, it has been impossible to cut the boards so they fit exactly around the joists.

My question is; how to fill the gaps between the joists and the plasterboard, prior to skimming. Some gaps are big - 2.5cm, others just a few mm. (see images below)

Also, once the gaps are filled, how do I prevent cracking at the joint between plaster skim and wood joist? (assume I need to PVA any wood that plaster is going to touch). Should I be using some kind of flexible caulking around the joists?

Any advice greatly appreciated.


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I would fill them out with some browning or even easifill, then tape around and over the gaps.

Me too,, only i'd use bonding. On the bigger gaps, tap a few small galvanised nails into the joists, to give the plaster something to grip onto. Just tap them half in, making sure they're clear of the finished surface.
i would consider tacking some eml to the side of the joist and bending the eml to fit the gap and then fill with bonding, tape and then skim
You could also just use scrim tape over the gaps
, put a few layers on top of each other and firm it up with some skim.... ;)
shaddow gap haha ;) if you just bond up to it surly you would still get a a gap round the outside when the timber moves and itll be a raw un-true edge where as if you use the shaddow bead the timbers can still move but itll be a nice straight edge around the timber and wnt look so much like a crack.
best thing if done in the past is get some plaster edge bead/stop bead bead it out say 2mm away from the joist max skim it job done
youll get a sharp edge pluss you know it wont crack coz its got room too move when finished and painter use a flexy painters caulk round it
to finish it off

nice job done thaats a pint please mines a fosters
Did you get that woodworm treated? :eek:

The house is Victorian/late Georgian with no signs of recent infestation - I think the woodworm holes are pretty old. However, we've treated all the wood we've covered up, and we're getting someone to do the whole loft, just to get an official guarantee for the mortgage company.

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