Blown Lath & Plaster - Repair or replace?

[Andrew Baker]

I stripped the wallpaper from a bedroom last night to find the plaster was rather more 'blown' than expected.

The house was build in about 1870. The affected walls are lath-and-plaster. Laths have a grey plaster coat of about 10mm - hair filled, so I presume it's the original lime plaster? Then there's a 3mm or so pink gypsum ('modern') plaster skim over the top.

In many large patches the gypsum is no longer bonded to the underlying plaster, so it's crumbling off. However, after digging a few holes, the grey plaster doesn't seem to be attached to the laths properly any more

- the keys are still generally attached and sit round the lath, but there's play between the plaster and the lath - they're not connected.

The whole wall in these large patches is 'springy' - there's a fair bit of give if you push it. You can hear the grey plaster cracking and crumbling as you do that. The grey plaster is pretty dry and crumbly in my fingers.

So... is that stuffed? (or, say, is some springyness to be expected) If so, can it be repaired at all, or would it be easier/better to redo with skimmed plasterboard? If so, I guess I could nail/screw plasterboard over the top of the existing lath/plaster into the uprights, but it would seem more sensible, though messier, to completely strip back to the uprights and start again?

[No issues with listed buildings or conservation area stuff here..]

Any suggestions or advice?

[The Natural Philosopher]

Unless you really want to keep it, junk the lot.

Its quicker in the long run.

You can repair lath and plaster, but its a long job.

[fred]

In article , Andrew Baker writes

It certainly sounds it and overboarding is the simplest solution.

In your place I would remove any really loose stuff, stabilise the crumbling bits with diluted pva then overboard it with taper edge board screwing at 12" centres up the edges and middle of the boards with long plasterboard screws. About 2/3 of the screws will bite into laths which will be enough to secure the board. If any screws spin at critical points like corners, pop another screw in a bit over. Tape and fill the joints (and other screw heads) with jointing filler making 2 passes, sanding between and you should have a finish good enough for a bedroom.

One point, you've said that the patches are springy, that does sound like the keys have gone and the patch is separating from the laths. If the whole lot was springy I would be worried that the support for the laths had gone in which case it might be time to rip it out, even if just to find out if any rot or other nasties are lurking behind.

[stuart noble]

Either paper it with a heavy duty lining paper (the paper is holding the plaster up in a couple of my rooms) or bite the bullet and strip the lot if you can put up with plaster dust in every nook and cranny in the house

[dom]

But don't strip the original lath and plaster - the mess, and particularly the fine dust, is unbelievable.

Plasterboard over.

Do it with plasterboard screws (long ones), screwed into the studs - having scanned for cable & pipe locations.

Drill a series of very narrow holes (say 3mm) to probe for the stud positions - once you pick up the stud interval, it's fairly easy.

You *can* do repair pieces in lath and plaster, if the laths are still ok - by chipping away the plaster and screwing a piece of suitable thickness plasterboard to the laths, adding more screws into the adjacent original plaster, then skimming over. However I'd only do this for smallish problems, like localised damage, rather than more widespread failures.

[Andy Dingley]

It always does that. So long as the "spring" isn't a problem, you can live with it.

It's not that hard to strip lath and plaster (I'd do it). The trick is to break it away round the edges, then lever the lath nails off the studs. Try to avoid disturbing the plaster as much as possible. Water sprays and ionisers help with the rest of the dust.

[NT]

If its an external wall, reboarding is a good time to insulate the walls.

NT

[Andrew Baker]

Sounding like a plan. If I just plasterboard over the existing plasterwork, what's the thing to do at the top/bottom of each sheet (i.e. where there's no horizontal studwork to attach too..?) Just screw through and hope I hit enough lath to secure it?

[Tim Watts]

For that bit you'd get away with a bit of dot'n'dab adhesive (or the modern PB fix loaw expansion PU foam). You're not trying to fix the PB at that point, so much as giving it support from behind so it cannot flex at the edge. As long as the stuff behind is reasonably solid it should be OK.

[Davao - Arthur55]

I had what sounds like an identical problem on a lath and plaster wall in my house. In my case the wall is at te top of a flight of stairs and over the years previous owners have leaned or impacted on this section and the cumulative effects of 90+ years of drunken fathers or stroppy teenagers had buggered up a few patches. One patch was about a square metre. I could carefully prised and chipped away at the loose stuff. You can minimise dust by spraying with water but you will get filthy. I then bought some base coat from a shed and laid up the patches myself. Mix the plaster wet and press it firmly into the laths. Plasterer came and skimmed it and its solid all over.

Arthur

[F Murtz]

If you board over it you will never find the bodies or hidden treasure.