Rake it out if you like, to allow filler to get down to the bottom of the crack & adhere to each side & the base.
Filler "daubed on" with a finger tends to just rest on the surface, doesn't adhere to the sides & falls out in short order.
Ultimately what caused it to crack will crack it again unless addressed.
Indeed as some fillers shrink when setting/drying, leaving it proud to sand a little is a sensible move.
You dug it out first though didn't you?
Precisement
...and avoid being called back or tarnishing their reputation by being thought of as an "armchair expert" who doesn't know what they're doing.
What is the easiest way to seal with a hairline crack in the overskim of a plasterbaord covered wall.
Do I need to rake it out or can I apply something that will penetrate and fill it (Creeping Crack Cure?)
filler & a finger. Do not rake it out, that always makes it worse, wastes time & achieves nothing.
NT
Probably a joint with no scrim. If so, it will come back whatever you do.
The last professional seeing to an issue like this widened the crack and filled with flexible caulk to take up any movement.
Once many years ago a bloke I knew fixed it with... Balsawood cement and a finger.
Brian
I paint over with PVA a couple of times to bond the crack, then, if it's beyond what paint will fill, a smear of fine filler.
I've found mixing 'polyfilla' (the powder stuff) with a mix of water and some PVA, I guess the mix, works well- provided it isn't too wet when applied. It is hard to sand down, so don't leave too proud.
Don't leave it proud at all would be more sensible :) Plasterboard is prone to move a bit, reappearance later is fairly likely. You won't prevent that.
NT
It takes a while if you stick some lining paper on and feather it to blend in with the rest of the wall.
You basically paste the middle bit of the paper stick it over the filled crack, then when dry tear it off inwards to get the feathering. Then sand if needed.
Run some watered down pva into the crack first, using a small artists bush (10 for £1 at pound shops). Capillary action will draw the pva/water into the crack.
I've got an old ceiling with cracks between the plasterboard. Was originally lath and plaster, and could be the joist deflection is greater than a modern plaster skim allows. Filled them last time with a decent decorator's caulk, which is flexible. But also shrinks as it dries, so took several goes to get it level. That has been successful.
+1
Fine surface polyfilla, in the old days. The modern lightweight fillers are almost as fine.
This is the problem, hence needing a flexible filler. That also grips well to the board.
Assuming it flexes, true, but then I?d expect more cracks.
A bit of silicone sealer is good for small cracks if you need it to flex.
Flexible filler won't solve it, the percentage of movement in a hairline crack is too large. Filling it at painting time is trivial.
NT
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