Dirty lines on a lath and plaster ceiling

[yamahaliam]

Hi All,

My new house has lath and plaster ceilings in the bedrooms with emulsioned woodchip over the top.

There are dirty lines on the ceiling where all the muck & dust in the attic has seeped through the plaster.

I'm going to strip & paint the ceilings, but do I need to reskim to stop it coming through again, or is there another way of treating it? Would it soak through the new plaster anyway?

Nailing some plasterboard over isn't really an option as the ceilings curve down at the edges, and that's where the worst marks are...!

 

[JohnD]

how far apart are these lines?

they might be Pattern Staining.

 

[yamahaliam]

They match the gaps in the lath - probably an inch or so apart?

 

[JohnD]

and is the loft insulated, has it been insulated for a long time? what I am getting at is that dirt does not usually penetrate a ceiling and paper, except where there is a hole or crack.

however, warm air currents in a room deposit dust and dirt in certain places - especially at the top of walls, and on ceilings that are cooler than the air, usually uninsulated ones..

the most common pattern staining on celings is where you can see the lines of the joists, I have never noticed it on laths, but if that is what it is, insulating the loft with no gaps or spaces will cure it.

 

[yamahaliam]

Ah - so it could be dust from inside the room sticking to the ceiling from that side rather than penetrating?

Yes, it's insulated, but it's very old and dirty (the roof is clay tiles and the mortar has dropped out). And probably not that thick.

So do we need to replace the insulation, or just add more to fix any gaps?

 

[JohnD]

the modern recommendation is for 250mm of insulation in a loft (about 10 inches)

your roof timbers are probably 4 or 6 inches, so as well as filling between them, you need a layer over the top. If you want to be able to walk about up there, you'll need to put ither rigid plastic foam as the top layer, with flooring on it, or timber cross-battens at right angles to the existing timbers, with fibreglass between them. There should be no gaps or holes.

you will find the old loft is very dirty, but if the roof is not felted, it will quickly get dirt again.

pulling down a lath and plaster ceiling is a worthwhile job, but it creates so much dust and dirt that I would only do it in an empty house, with no carpets or furniture, prior to redecorating.

 

[yamahaliam]

Thanks John - I'm pretty sure the insulation is thinner than that, and in places it's just placed over old heating pipes that are up there. The heating is being changed at the moment, so I'll strip the pipes out and get the insulation topped up. The roof isn't felted, so cleaning it up is probably an uphill struggle!

 

[JohnD]

have a look at the rigid foam option - in mine, I used cross-battening, but the rigid systems are in the sheds now and might work out easirt.

Do not insulate all round cables for electric showers or immersion heaters as they will overheat, no round downlighters. Lighting cables are very lightly loaded so are OK (this is an abbreviated rule of thumb, you can get more on the Electrics UK page)

 

[roughcaster]

The best way of treating stains on an old ceiling is to paint it with cheap "oil based undercoat",,, and you're right about stains coming through new plaster,,,, they do unless treated.
You can buy sealers and stain blockers, but they are expensive, whereas undercoat does the same job, at nowhere near the cost. The fumes are a bit smelly, but with the windows/doors open for a couple of hours, it's not a problem.

 

[thatbloke]

why was it wood chip papered in the first place? my ceilings are riven lath and lime plaster that have been papered over with woodchip , ive removed the woodchip to reveal old distemper , this isnt easy to paint over unless i use more distemper although i will most likely clean off the distemper and apply some clay based paint , this i think is more suited to a lath and plaster ceiling than emulsion however because its a ceiling another coat of distemper wouldn't do any harm as no one will be up there rubbing their nice new dress on it. How old is your house? Ive seen brown staining on old ceilings due to water leaking down through the roof , is it possible that the lath could be getting damp?.

 

[yamahaliam]

Why was it woodchipped? The same reason they panelled over the lovely doors and ripped the picture rails and stair spindles out - 1970's "modernisation"

The dark lines are in the same places in each of the rooms - where the ceiling slopes and there's probably little room for insulation. It's not a damp or water leak thing.

I had a look at the upstairs loo ceiling tonight (which has been gloss painted along with the walls !!) and the lines wipe off, so full marks to John - it's where dust has been attracted and stuck.

 

[Nige F]

The old heating pipes are best left alone - unless they are copper