Polyfilla and others sell "No More Cracks" filler or similar for this problem.
Question: Would it be OK to use tile grout to fill the cracks? AFAIK grout is basically a thin cement mixture with some flexibility.
Or should I just leave the cracks -- they'll open up again if I fill 'em!
Bruce
Squirt in some 3:1 PVA, don't rake out the cracks first. Use a squeezy botle with a short length (2") of 15mm pipe lagging tied tightly around the bottle top. Cut off the foam lagging at 90 degrees with a sharp knife. Press the cut off end against the crack, squeeze until PVA has gone in, stop when drips appear at each side of lagging where it presses against the crack/ceiling. Repeat, following the crack along. Sponge off x/s with a damp sponge. Wear a hat or something. Protect floor and furnishings. Allow to dry, repeat optional, fill with polyfiller.
Bath sealant should do the trick I would have thought.
sPoNiX
Or just fill with some flexible decorator's filler...
Ahbut, sticking it together does a far better job, if the crack is "fine", say 1/2 mm, caulk won't take up the movement. The PVA treatment is also excellent for plaster & lathe ceilings, as it glues up any sandy stuff which would otherwise fall from above, bulging any paper and displacing filler... try it!
No, it won't. It will be very visible (shiny), and is not overpaintable.
While I'm a *big* fan of PVA, I've used flexible filler on all the fine cracks we had in our plaster, with very good results. Much quicker and easier IMHO.
I'd just waft a filling knife, float, or whatever over, with some ordinary filler, over plaster - however, the OP said "Hairline cracks have developed on the ceilings, where the plasterboard panels meet.". The benefit of squirting in PVA is that it sticks the lot together, not just the edges of the PB - it glues PB to joist, too, which re-inforces the joint considerably. I've used it doing odd jobs in lets, and on P&L ceilings - it really is much better than just filling the cracks, which otherwise just open up again in big oblong patterns in no time.
A problem with flexible filler is that it can "shine through" a couple of coats of emulsion. You can't really sand the stuff to feather it, either. However, I use quite a bit of it - the Ceramide stuff is good.
The non-silicone stuff should be overpaintable.
filling
couple
How about if I used some artex patch filler?
Bruce
As to the original question, IME grout is very inflexible.
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