Lath and Plaster Materials

[GoodDIYjob]

Need to repair the ceiling in my airing cupboard which now houses the boiler.

It is on the 1st floor, below the lower extremities of roof directly above with no access from above except lifting tiles!

The ceiling is lath and plaster. There is a long section of laths exposed along one corner (about 20cmx120cm). This is where pipework for a gravity fed system used to run up into the loft and presumably had box work over the top (all done and removed before my time here).

There is also a separate section damaged where someone has butchered through 3 or 4 lathes beside a rafter and left a hole spanning across the cut laths for a reason I can not determine. This has caused the surrounding plaster to become quite unstable and is beginning to hang with several large cracks.

There also looks like there will be a tricky bit to deal with in the corner of the ceiling where the internal side wall of the cupboard meets the ceiling laths.

Not sure if that has ever had plaster because it is where the exposed area of laths is for pipework is (pipework now removed) but it looks like it would take quite a bit of plaster to fill in and hard to reach.

The main reason for wanting to address is not cosmetic but function. With these winds of late there is a small wind tunnel in the airing cupboard which positively ventilates the whole of upstairs through the gaps around the cupboard doors. Luckily it has not been that cold here with recent winds yet but if the wind was icy cold it would be terrible!

I have read two good posts on DIYnot and also looked at a lot of posts on the web generally to try to gain some background e.g..

//www.diynot.com/forums/viewtopic.php?t=251771

//www.diynot.com/forums/viewtopic.php?t=181561


I'm having trouble deciding on the best approach to fix from all the approaches available.

If I was to repair without plasterboard I'm comfortable with the prep - need to carefully remove damaged plaster, screw and support any hanging sections, but what products would be used for the layers?

On the web there seems to be specialist lime products, lime render for scratch coat and then a lime plaster for top coats but I'm not even 100% sure the existing was lime render / plaster. And it sounds like then I would have to use lime washes rather than emulsion which the whole inside house is already covered in.

The house is mid 1920s which may have already seen off lime based products - how would I recognise what it is already finished in? I have examined some broken plaster - can't see any hair...

If I went with conventional plaster products what products would I need for the the (three) layers?

Seems there is discussion of bonding coat for first layer on laths but others seem to say a render and other products seem to be mentioned as well....

The absolute smoothness and finish quality is not totally critical as it is the airing cupboard. But I would like to do the best job I can and I would rather do it properly once than needing to repeat.

Help most appreciated.

 

[skhudy]

When you say airing cupboard what size area do you mean? if it were me I'd locate the joists / some solid fixing and carefully cut and screw on some plasterboard and finish that off. If you can't find anything screw some batons around the top of the cupboard and secure the plasterboard there.
Ceiling can be very messing because of gravity. Repairing walls are one thing, but ceilings I wouldn't bother myself!
A picture may give a better idea of your problem.
I'm a DIYer, not professional so may be corrected.

 

[GoodDIYjob]

skhudy

Not huge. Presumably big enough for a hot water cylinder in the past. Has a top section with sloping ceiling and bottom section each with separate doors.

Had to measure it. In total approx 250cm high x 70cm wide x 80cm deep.

The ceiling is angled so a bit larger than the width and depth indicates and rolls into the wall plaster with a rounded curve profile which I wanted to avoid getting too close to as not sure how to deal with replicating that.

Yes plasterboard was another option I had considered but is it any easier and quicker than dealing with a multi layer finish on the laths?

By the time you cut out a large straight area, (which would probably be larger than if re-plastering onto laths), fix the board on, scrim tape all joints bond / scrim etc..

I also wondered whether the joints to existing plaster would hold up even with scrim tape?

 

[skhudy]

ok, not huge, but you said there are crack in the remaining plaster and it is hanging in some places, so i'd guess the whole thing would need to come off else your patching over plaster which possibly isn't sound?

From what i've read people tend to fix plasterboard rather than pull down ceilings as it can be messy, and it's what I've done in a few rooms. With your boiler there you want to avoid plaster / dust / dirt.

For a small space like a cupboard I'd try and cut and fix plasterboard as exact as possible and go round it with a good quality flexible filler, i'm sure it will be quicker than plastering / patching up the laths.


I'll leave it for a more experienced person to advise, but again a picture paints a thousand words

 

[roughcaster]

It's never advisable to overboard an old lath and plaster ceiling that has areas where the plaster is just hanging. That is hiding a problem. I know taking down an old ceiling can be messy, but that's the best thing to do.

 

[skhudy]

It's never advisable to overboard an old lath and plaster ceiling that has areas where the plaster is just hanging. That is hiding a problem. I know taking down an old ceiling can be messy, but that's the best thing to do.

Is this a general rule of thumb to take the lath and plaster down if you have the opportunity even if it is sound, or only when the plaster is loose / cracking?

 

[roughcaster]

Never take down/remove any lath and plaster if it's sound, no point at all. It's far stronger than the plasterboard you'll get today.
If the lath and plaster has failed, then that's different. If it's loose/hanging, then it is advisable to remove it for obvious reasons.
I have also worked on lath and plaster ceilings and walls that were cracked in many places, but they were very strong and secure, no reason at all to remove it. Each job has to be looked at individually really.

 

[GoodDIYjob]

OK some images, complete with authentic cobwebs. (Hope this link in works)

It's fairly small scale but lets in a lot of draught from the roof!!

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Roughcaster - I've read your previous posts with very good info but I need more hand holding please if you can.

Main questions if I went with repairing properly without splicing in or overlaying plasterboard.

Lime render / plaster or conventional gypsum to repair broken and missing areas.

If gypsum what products do I actually use? Bonding coat for scratch coat and float and multi finish for top? Or is it a render with some sand for scratch?

What do I do with the deep corners where ceiling meets wall where the pipe runs were on the RHS?

Do I need scrim tape or something similar to adhere new plaster to the existing where I cut back existing sound plaster to and for corners?

Does any widely available merchants sell laths for repairs as the hole shown 4 laths cut through at the rafter. I will probably need to remove a section the full width of the ceiling to replace laths.

Thanks V Much

 

[roughcaster]

To be quite honest, by the time you remove the damaged and loose area of plaster round the "butchered area", then remove the remainder of the old "pipe boxing", (which will loosen more plaster), there wont be much original plaster left on that sloping area of ceiling/wall. I think your best bet would be to remove "all" the plaster "down the slope/ceiling" to the "wooden shelf", then cut and remove the plaster "up the ceiling/slope", up as far as you need to go. Clean/brush off the old lath, then put 12.5mm foil backed plasterboard over the area, tape in the joints, then skim. Do the slope in 2 bits. Put a strip plasterboard above the shelf area first, then put in the larger area of board. Once the plasterboard is in place, tape the corners/joints. Form the "roll" in the plaster above the shelf with bonding coat plaster, you might need to bring it out in 2 coats. I think for you, this will be the easiest way to do the job.

 

[GoodDIYjob]

Yes I see what you mean. I did look at those battens and think they will probably pull the plaster off too!

That sounds like a good plan.

When fixing the board is it ok screwed into rafters onto cleaned up laths or does in need some sort of adhesive or coat under?

The rolled profile where ceiling meets wall makes me nervous. From your description the first small section would be flat with the wall at the back and overlap behind the larger sloping section for the ceiling. Then fill in the middle with bonding. Correct me if I've misunderstood.


But how do you get a nice rolled profile? Do I need a special trowel?

Thanks for all the advice.

Update 10/1: Looking more closely the bottom side of the roll (close to the shelf) this will roll into a plastered external facing brick cavity wall. So I won't be able to put in the smaller section of board you refer to as it will be in plastered brick work I presume, looks like there is a stud at the roll though.

Thinking I still do what you suggest with the sloping ceiling and then start to chip off the roll but will just have to rebuild that up and smooth into the plasterboard with Bonding coat?

Will be trying to tackle this early next week.

 

[roughcaster]

You'd be alright screwing the new plasterboard to the joists. Just remove the plaster, clean/brush off the lath, and screw it on. I'd leave the laths on too if they're in good nick. I wouldn't bother using an adhesive, but that's up to you. Tape the joints along the junction between the small flat area above the shelf and the slope. Mix up a small amount of Bonding, and using a small trowel, try and form "round" between the flat and the slope. It'll take a bit of practice, but that's how to learn. Give it a go anyway.
Just had a thought, maybe you can leave on the roll in the plaster. Very carefully cut the old plaster right across the wall,, use a spirit level, draw a level line across,, the cut into the plaster across the way. As long as the plasterboard is thinner than the original bottom plaster, no problem. Don't forget to tape the joints down either side of the slope, and the joint along the top.

 

[GoodDIYjob]

Thanks very much for taking the time to give advice and look at the specific situation.

Will give it a go with fingers crossed and revert for more advice if I get in trouble. I don't think I can make it worse than it is and it is only the airing cupboard!

 

[roughcaster]

Thanks for that my friend. Let us know how you get on, and it'll be good practice. If i lived nearer, i would have shown you and helped you out, because of the interest you've shown in doing your job, yourself.

 

[GoodDIYjob]

OK, ok. So it took me a little longer than I expected. Also had to repair some floor boards and some holes in the cavity wall first.

This cupboard was in a right state no wonder it was so breezy.

I have got the foil backed plaster board up - despite removing cupboard doors and then shelves to try and get in one piece it just wouldn't.

It is noticeably warmer and much better sealed with just the boards up before even jointing and skimming.

I am now looking at the sizable cavity around the top of the brick wall and plasterboard ceiling on the right hand side. Left hand side is pretty good and I think scrim tape would be ok? On the right hand side - is this a case for mesh wire, expanded lath or just fill with expanding foam first? The last option seems the easiest but not sure how bonding coat / plaster would adhere.

Photos below..

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[roughcaster]

That looks a good job you're doing there. Can you not dab a piece of plasterboard into that void? Stick it in with a grab adhesive,, Sticks Like **** or similar?