cracks in ceiling

[martop]

Hi,

We have a few cracks in the upstairs ceilings and as we decorating a room at a time I would like to find something that can be used to fill the cracks and if flexible so it wont crack in future, the bedroom we doing at present needed the old paint scraping off and I've skimmed it with plaster but there are cracks along the joints of the boards, there may be some movement in the joists above but fixing that is way beyond me, so does any one know of a good flexible filler that works ? These are hairline cracks by the way.

TIA,

Mart.

[Dave]

Swap positions with your wife. Put her underneath :-)

When she moans, then you will know it will be time to re-work the ceilings.

Sorry, I couldn't resist.

Dave

[martop]

Stuff that, its easier on me to remove the light bulb or get her a blind fold ! However, I wonder if her pie pastry is the sort of thing I'm looking for ;-)

-- Mart

[The Natural Philosopher]

No filler will work.

put scrim tape over the joins and re plaster.

Sorry to be the bearer of bad tidings.

[martop]

Thank, you confirmed my worst fears ! After considering different options I may as well go this route then its done for good.

Thank you :-)

-- Mart

[Chris J Dixon]

You may not actually have to re-plaster. I have had reasonable success with a ceiling with a crack which had kept opening up. Yes, certainly you need scrim tape, but covering that with filler and feathering the edge over a reasonable distance should not be too noticeable. Use a taping knife similar to this:

although the one I have has a plastic blade.

Chris

[Dave Plowman (News)]

That won't stop cracks.

[Dave Plowman (News)]

Rake out and use decorator's caulk. Because it shrinks when drying you'll need to apply several coats. But will eventually give an invisible repair which lasts.

[Tim Watts]

Dave Plowman (News) wibbled on Wednesday 31 March 2010 09:09

And stop worrying so much. There will always be cracks, but if you play your cards right, they'll be hairline rather than major.

[The Natural Philosopher]

did here.

Only cracks are where there aint no tape.

[stuart noble]

These are hairline cracks, right? A tub of ready-mixed "fine surface filler" might work. Quite different to standard filler IME.

[Dave Plowman (News)]

Loads here where there is.

[The Natural Philosopher]

It doesn't because what is happening is that the strength of the plasterboard - the cardboard - is compromised where the sheets butt join: The only way to give a uniform stress concentration is to reinforced the join with - normally - scrim tape. You could use anything really - bits of cloth PVA'ed to the bare boards - but there will always be hairline cracks between boards due to small movements, differential expansion, wood movement etc unless you somehow carry the stresed skin across.

The problem is merely that the tensile strength of plaster skim is way less than that of cardboard.

As far as flexible fillers go, they need a distance over which to flex: Hairline cracks ain't it. They will crack just the same.

[Dave Plowman (News)]

Likely only to work if flexible. Which most of these fillers ain't.

[stuart noble]

Most are, to a degree, because they normally contain a pva or acrylic binder but, the more flexible they are, the less sandable. They should be able to withstand hairline fractures I would have thought

[The Natural Philosopher]

then you should sue whoever built the house

[The Natural Philosopher]

wont work even if flexible.

A crack by definition varies from 0 to hairline. Its the 0 that is the key issue, because it means the filler has to cope with infinite expansion.. (hairline/0=infinity)

Flexible filler works brilliantly on right angle edges in a thick fillet. Its totally useless to fill butt joints.

To repeat for the THIRD time. UNLESS you provide a stress bridge across the stressed skin of the plasterboard, it will ALWAYS crack at the butt join. rather than expand or contract a little with the substrate.

[Dave Plowman (News)]

The house was built with lath and lime plaster. Where ceilings have been replaced with plasterboard - scrim and skimmed - some of the joints have cracked. Raking them out and using decorator's caulk sorts them. No other filler I've tried does.

[Dave Plowman (News)]

I've yet to find a sand able filler which doesn't crack, when used to fill a previous crack on things that move like ceilings under a suspended floor. But if you apply decorator's caulk properly, it doesn't need sanding.

[MM]

Using flexible filler from a gun was successful in my case. Also, Polycell do several products that are said to be pliable, e.g. "Crack-Free Ceilings" I used their ripple coat once and never saw a crack again.

MM