Cracking plaster

[JustMe]

Hi folks,

My house is exactly 100 years old. About 3 years ago most of the plasterwork was skimmed. The original plaster was left in place and a new, smooth coat was applied on top. I moved in 2 years ago.

The problem is that the old plaster foundation on which the skim was applied doesn't appear to be sound in some places. In some areas the base isn't stuck to the bricks so when I to apply pressure with my hand, I can feel it moving up to and away from the brick by a few mm. Where this is very bad I'm having to arrange for all plaster to be hacked back to brickwork and new plaster applied, because the plaster is cracking all over, but there's one area where there's just one crack, running from the top corner of a door frame diagonally up to the ceiling. I previously repaired it by scoring it out, filling it and repainting, but after a year the crack has returned.

I really don't want to hack this entire wall back for one crack - can anyone advise a solution that'll last?

TIA.

[The3rd Earl Of Derby]

This is the problem with skimming over 100 year old plaster, the plaster is crumbly and weak its inevitable cracks will appear due to slight foundation movment,banging of doors, ect.

The crack above the door is either of the two scenarios above again the plaster in that area is probably as you have stated the old plaster is coming away from wall, I doubt you will make good whichever method is used to repair it?

[Phil Anthropist]

"JustMe" wrote

If the plaster around this crack is loose, putting filler over loose plaster will not last long as opening and closing the door, and movement of the door frame and loose plaster, will eventually cause the plaster to crack again. You could try enlarging the crack to a wider channel, say 2 or 3 centimetres - the larger amount of filler might be stronger and longer lasting.

[Andrew Gabriel]

As you suggest, the plaster wasn't in a fit state for reskimming. You don't have to fix every last bit where keying is lost with the wall behind, but a large area of movement like this does need fixing, and it's very easy to do just before you reskim the whole wall. It could be dangerous to a small child or elderly person if it all fell out on top of them.

That's a different situation. 100 year old house will be built using lime mortar which allows the house to routinely move around. The original lime plaster similarly moves, and the horse hair in it prevents it forming large cracks. I assume the reskim was done with gypsom (pink or grey) plaster, which isn't flexible, so when there's movement in the wall behind, the gypsom plaster will crack. Often this doesn't happen enough to worry about, but if you have a crack where it does, then you could try raking it out and filling with a more flexible filler such as decorator's chalking. This shrinks as it sets, so you might need to go over it 2-3 times to get a flat level finish. The more movement you are getting in that crack, the wider strip you will need to rake out and replace with flexible filler to accomodate the movement. (I assume we're talking about hairline cracks here, rather than something you can push a pencil in, which would be a different problem.)

The other option would be to replaster with lime plaster, but that probably won't work with just a reskim -- you would need to replace the scratch coat too.

[Rednadnerb]

Paper the wall with lining paper, it will absorb hairline cracks.

[Stuart Noble]

I have a couple of rooms where only the lining paper is keeping the plaster on the wall but they look fine. Nature of the beast. Either that or have the whole lot hacked off if you (and your neighbours) can stand the dust

[Weatherlawyer]

It sounds like a real pain to replace if you think you need to. And there is no getting away with the fact that lath and plaster can be a major problem. Great if you have clay soil in the garden though.

I would choose the easy option of ignoring it until it fell off. Then strip the wall it fell from and redo that with lime and sand then a lime plaster.

After that I would consider myself capable of tackling the next one with modern plaster mixes. I suggest the old fashioned mixes to allow you time to work with them if you have never plastered anything before.

Of course if you don't fancy getting stuck in, put pasterboard up and skim that. Doing it that way is also a piece of cake. I find plastering quite relaxing. Messes with your cuticles though.

[Andrew Gabriel]

Plaster and cement can do quite nasty things to your skin. Use a barrier cream when working with them.

[Phil L]

The crack above the door frame is a cause for concern, especially since it has returned....if it were my house, I would remove the plaster above this door and check the lintel, even if the lintle is sound, there's a possibility that the brickwork has slipped, probably because of subsidence, what's the exterior brickwork like around that area?

[Dave Baker]

..cracking cheese too Gromit.

Sorry, couldn't resist.

[JustMe]

It isn't so loose as to be a danger, but the area with multiple cracks is to be hacked and replastered for cosmetic reasons. It's the single crack area (different wall, different part of the house) which I'm going to DIY.

That description seems pretty accurate and, yes, hairline.

One crack in an otherwise sound wall - I'd rather simply repair the crack - not heard of "decorator's chalking" before but will look in B&Q later.

Thanks Andrew :)

[JustMe]

subsidence,

It's an internal, dividing wall. The single crack area is downstairs (ground floor), the multiple crack area is upstairs (same side of same wall, above floor divide).

The upstairs area is worse because the wall isn't perfectly flat, but curved. In installing a false ceiling above the area of the upstairs wall, a piece of 2x2 batton was screwed VERY tight along the wall. The wood being reasonably straight and the wall being slightly curved, the wall was pulled a little by the tightly screwed wood, hence loads of cracks appeared in the loose plaster. Upstairs is a hack back to brickwork and replaster job, but downstairs is a single crack that was there when I moved in (before the false ceiling job), which I carefully scored and filled before and which has reappeared.

AFAIK the house isn't moving (survey info, other houses in the terrace, no other indicators on my house etc all point to the ground being sound). Exterior brickwork front and back (no sides cos mid-terrace) is sound.

[Phil L]

So the crack effectively goes from floor to roof? (discount the downstairs doorframe because it only starts above this)

I'd get this looked at ASAP, simply carrying out cosmetic work is a waste of money until the underlying cause of the crack has been remedied.

That tells you that it's getting worse - normal plaster cracks don't reappear, the crack *must* be in the brickwork behind.

All exterior brickwork sounds ok, this door downstairs which has the crack above it and underneath where the upstairs wall has slipped - has everyone in the block got this door in this position or has someone knocked it through in the (recent - ish) past? - my money is on the lintel - it's either rotted away or there isn't one in.

[JustMe]

You were quite right! No lintel of any description. Even the top of the door case sits inside the two sides (as opposed to resting on top which might have provided a small bit of additional support.

So fitting a new lintel (and door case) next week, before fixing up the rest.

Thanks for the advice.

[Phil L]

Glad to be of help :-)