Best filler for a hair line crack?

[htmark98]

We got our walls re-plastered last year about 3 weeks after we bought the house (1900), now the house was empty for 2 years before that, anyway last year about Feb05 we noticed a hariline crack going up the whole wall top to bottom and the same on the other side of the joing wall. (one side our licing room, the other study room) Now as we took pics before anywork was done it can be seen that this is where the electrian cut out the wires for the sockets and filled them back in. The guy who done the plastering came back up and said if it starts cracking the coving or any other part of the wall to call him back.

Ok skip on 11 months and it's not moved an inch but i want to fill it back in, it's not massive at all 3mm if that maybe 5mm max. Now my friend said i could by flexi filler to expand if it needs to to prevent it re-cracking.

Is there such a thing and if so is this the best stuff to use.

Many thanks

[Dave Liquorice]

Eh, Thought you said it was "hairline"? 3 to 5mm is a gaping chasm...

Not a good move on a plastered wall. The flexi stuff tends to shrink and you can't sand it to get a smooth finish. Flexi stuff is good between walls and timbers such as skirtings and door frames as it allows the timber to move without cracking.

For plaster cracks I'd use good 'ole polyfilla or similar, mixed fairly stiff. If the crack really is a hairline open it up with a some thing pointed, clear the dust, brush in some water and fill. When the filler is almost set skim over it with a wet trowel to remove most of that which is not in the crack. Leave to fully set, 24hrs or so then a quick rub with a bit of medium sandpaper on a block will remove the surface residue and feather in the actual filing nicely.

[htmark98]

Ok thanks for the reply, ok i gussed the gap but i was way out it's 1mm only 1 line on the my gage.

So is this the best for this as it's only 1mm?

[chris French]

In message , htmark98 writes

I would either just use standard filler as Dave suggests - , or , if the crack is fine enough - as in a hair line crack then I would use 'fine surface filler' - basically a very fine polyfiller in a tube or tub, I used this on some fine cracks in new plasterwork and it worked fine, very quick and easy to use wipe it over the crack with a filling knife., a light sand when dry and voila.

[htmark98]

Thanks everyone, will have a go tonight.

Would it be better sanding by hand or using my power sander?

[Dave Liquorice]

IMHO yes, still rake it out though.

[sPoNiX]

Use decorators filler,the type that comes in a cartridge.

Before applying, rake the crack out to form a 'V' shape. If it were me I'd also apply some PVA solution to the exposed plaster and let dry before filling.

Apply the filler using a cartridge gun and leave for 15 minutes. Then smooth carefully using a suitable wettened tool (I find an old credit card ideal.

sponix

[Dave Plowman (News)]

Trouble is it always shrinks. Not a problem at a ceiling wall junction, perhaps, but not much good on a flat surface.

[sm_jamieson]

I always use a cement-based powder filler now (no shrinking). I learnt the hard way. Filled loads of screw holes with pre-mixed, and they all shrunk into a hollow. What a pain ! Simon.

[chris French]

In message , htmark98 writes

Hand, if you do the job properly it will only need a light sand

[Chris Bacon]

Pollyfilla or similar, mix some up (on the runny side), apply it using a filling knife, scraping off excess, let it go off, apply more if necessary, give it a light rub down when dry using fine glass-paper on a wooden block.

[Chris Bacon]

IME/O raking out a crack is likely to make the filler much more likely to come loose after a while (unless you can undercut), and is anyway unnecessary.

[Chris Bacon]

It can also "shine" through paintwork, there's also the raking out issue, and if you try and smooth the acrylic type filler after a quarter of an hour, it'll drag the skin off and ruin the finish (also some cartridge fillers are sods to rub down).

[sPoNiX]

I haven't had any problems myself but then again I only use (expensive stuff) on hairline cracks.

The prob with filling hairline cracks with a 'rigid' filler is that they always seem to oven up again!

I suppose it's a case of suck it and see. Try one type of filler and if that proves unsatisfactory then try the other.

sponix

[Dave Plowman (News)]

What make? I've got Unibond, and that certainly shrinks.

They do indeed. Plasterboard on a wood framework is likely to crack at the joins.

[Harry Bloomfield]

htmark98 wrote on 02/01/2006 :

3 to 5mm is not an hairline crack. If the movement has stopped, you should be able to fill it with ordinary finish plaster or the likes of Pollifilla. If the movement has not stopped then you should be concerned as to the possible cause.

[Dave Plowman (News)]

Joists in an insulated roof void will move according to the season. Same as outside doors.

[htmark98]

Thanks everyone, it's only 1mm. So i'll go for a cement based one and see how that goes.

[Nick Atty]

I've yet to find anything that beats coving adhesive for filling fine cracks.

[MM]

I know raking out, or Vee-ing, is always recommended, but why, exactly? In my case the drying out cracks are less than a millimetre, mostly. Why can't I just force filler (e.g. Polyfilla) into the crack, e.g. with a cake decorating pump (not the bag sort, but the plunger). That way, the edges of the crack should permit a completely invisible repair even if a little sanding should be necessary.

MM