Strong light board for lime plastering sought

[Andys]

Ah, I see what you mean now. I don't know if anyone's ever tried a grid of some sort of stainless fixings to re-secure the lath but without actually covering it all with boarding. I suppose it might be a bit clumsy if they were left visible or risk collapse by trying to counterbore them and fill over...

 

[MikeG]

Ah, I see what you mean now. I don't know if anyone's ever tried a grid of some sort of stainless fixings to re-secure the lath but without actually covering it all with boarding. I suppose it might be a bit clumsy if they were left visible or risk collapse by trying to counterbore them and fill over...

I don't think it would be all that difficult to repair the ceiling structurally without covering it with a board. Decoratively, however, my plasterer isn't at all confident of getting a skim of plaster to stick to such a repaired ceiling. He tells stories of watching a whole ceiling of plaster just peel off and land on the floor. Hence my desire to find a decent substrate for a coat of plaster. This effect is exacerbated by the unknown paint covering the ceiling. If it really is emulsion on limewash, then no plaster will ever stick to it with certainty.

 

[livias]

My concern is that you have a lovely old house but if you are not very careful you will end up with a new house plus some old timbers. I have seen this happen far too often. It is very dificult but important to split yourself in two. Part of you is a builder and wants straight, sound workmanship, the other part is a conservator and wants to keep as much of the old material as possible. I have learned the hard way to make the builder take a step back for at least a day, to not wade in and make changes and allow the conservator some time to think...

With my conservators hat on I think you have a lovely old textured ceiling which adds to the character of the house. Your ceiling can be stabilised from below. Use stainless steel screws and stainless penny washers at 150mm intervals and screw them into the joists above. Countersink them and then when you have finished, use polyfilla to make good the holes. Do not replaster the ceiling, just give it several coats of limewash. Remember, you are a conservator, not a builder

I agree that the ceiling has been painted with emulsion. Luckily it does not tend to stick well to limewash and can be flaked off once your ceiling is stablised.

This is all time consuming and awkward work, but you didn't buy this house to get an easy life did you? For paint flaking I recommend getting the assistance of an art student on vacation as they are both good at attention to detail and poor

 

[MikeG]

That's all fair comment (although I am not a builder). Some parts of the ceiling are going to require re-plastering in any circumstance. For instance, there is a (now redundant) nasty plastic loft access hatch in the middle of what will be the bathroom ceiling, and there is a lowered section of ceiling between two tie beams which has collapsed (it's dangling 4" down off the structural timbers). That adds up to approximately a third of the total upstairs ceiling area.

 

[Me!]

Having now seen the photo of your sagging ceiling, I think you are going to struggle to fix any kind of flat board to it.
If I were to attempt to cover and strengthen it in the way you suggest, I think I'd try and fix up sheets of expanded metal lath using screws with large stainless washers on them, and into the joists above. Then a couple of coats of lime plaster onto the expanded metal to finish it off.

I should add that I've never tried doing this on a ceiling before, but I have on a wall and that worked very well.

 

[MatthewC]

I think I'd try and fix up sheets of expanded metal lath using screws with large stainless washers on them, and into the joists above.

You would need stainless steel expanded metal lath, not the galvanized stuff which can react with lime.

However, I prefer the penny washer solution:

Use stainless steel screws and stainless penny washers at 150mm intervals and screw them into the joists above. Countersink them and then when you have finished, use polyfilla to make good the holes. Do not replaster the ceiling, just give it several coats of limewash.

 

[Me!]

You would need stainless steel expanded metal lath, not the galvanized stuff which can react with lime.

Yes, I'd heard that as well, but this data sheet from St Astier Lime clearly states that galvanised is fine.

Has anybody actually experienced problems with galvanised steel in lime?

 

[livias]

Galvanised can rust ... and does do outdoors so should nevdr be used on exrerior walls. I suspect that internally stainless is used because it is less bulky and because labour costs way outweigh material costs and better be safe than sorry
Have never heard of galvanised metal lath

 

[MikeG]

......Have never heard of galvanised metal lath

Really? It's the most commonly used type, and the only one that a couple of local builder's merchants stock (the others have to be brought in especially). Here is your choice from the biggest manufacturer:http://www.expamet.co.uk/content/expanded-metal-mesh-and-lath/

 

[bennoa1]

Could you create a loft hatch in this room? You could then see what is going on and get access as a blind roof space isn't a good thing. Is there ventilation up there as there's so much fibreglass which I'm guessing is getting damp from condensation dripping off the breathable membrane under the tiles with no way of it drying out. Can you push sections up with your hand as if it is loose then it wouldn't take much for it to drop with gravity. Did you get a chance to inspect the lath prior to the roof going on and was the ceiling this bad then? Looking at the photo the laths look exposed with very little lime squeezing out between them so nothing holding the lime to the lath, hence your issue.

 

[MikeG]

Could you create a loft hatch in this room? You could then see what is going on and get access as a blind roof space isn't a good thing.

No, as I've explained, and as the photos show, there is no room to see anything at all.

Is there ventilation up there as there's so much fibreglass which I'm guessing is getting damp from condensation dripping off the breathable membrane under the tiles with no way of it drying out.

You ask if there is ventilation at the same time as mentioning breathable membrane, so you answered your own question. Because of the breathable membrane there is no condensation. Not only have I carefully run a dew-point calculation, but I still have access through the gable and have physically inspected: there is no condensation. This is before the mechanical ventilation system is fully installed in the house.

Can you push sections up with your hand as if it is loose then it wouldn't take much for it to drop with gravity.

They're mainly flexible rather than loose.

Did you get a chance to inspect the lath prior to the roof going on and was the ceiling this bad then? Looking at the photo the laths look exposed with very little lime squeezing out between them so nothing holding the lime to the lath, hence your issue.

Again, you answered your own question. I didn't just inspect, I cleaned every sq mm of it with a handbrush and vacuum cleaner. It was as a result of this work that I decided the best solution was to trap the weakened lath & plaster ceiling to the ties using a board screwed up from below. The ceiling isn't on the verge of collapse, by any means, but it needs help. Most of the curves you see in the photos are from the shape of the ties, rather than sagging laths. The ties are sound (except where they were cut for the loft hatch, but I repaired that area). As you rightly observe, there isn't a lot of squeeze-through of lime above the laths (I'm guessing that they just used too dry a mix). I want to retain the ceiling for posterity, and although screwing it up with washers would help, I'm not convinced that the ceiling acts enough "as one" for this to be a really sound long term solution.