What to do with these timbers?

[Athers1971]

This photo shows part of the underneath of our stairs.

We’ve removed some ‘modern’ thin boards that were attached to the thin pieces of vertical beading. Underneath that was gypsum plaster laid on the laths.

On the other side of this, at the bottom of the stairs, is some plasterboard with lining paper attached.

We’re going to lime plaster over the laths after removing the beading and plasterboard on the other side, but what would you do with these two vertical timbers?

They are riddled with woodworm exit holes, must be historic as the room is dry. The other face of the timber is ok, and painted black.

We’d like to keep them from a conservation perspective. Could we just plaster over them?

 

[Kearn]

I’m not quite following which side you’re referencing - the rear of the posts in the image, under stairs or the black painted in the room?

Sounds like you’re going to reinstate lime plaster in the room side, which means you’ll struggle in the underside too unless you’re adding more lath? Plastering both sides of the same lath would need to be done at the same time so the nibs that push through to form the key become part of the rear coat if that makes sense. But the lath gaps aren’t too large and you’d need to minimise the thickness of plaster to not add too much weight both sides. I’m not quite sure how well it would work - it’s non traditional in that only one side of lath would carry plaster and the rear pushed through to form the key.

Therefore if you’re talking about plastering over the posts under the stairs, you’d need a seriously thickness of plaster on the lath to do so - way more that it will take, and especially in this situation.

Why do you want to plaster them? I’m assuming non visible under the stairs. If you wish to do anything, then a few more coats of limewash would be fine to top up the historic traces.

 

[Athers1971]

I’m not quite following which side you’re referencing - the rear of the posts in the image, under stairs or the black painted in the room?

Sounds like you’re going to reinstate lime plaster in the room side, which means you’ll struggle in the underside too unless you’re adding more lath? Plastering both sides of the same lath would need to be done at the same time so the nibs that push through to form the key become part of the rear coat if that makes sense. But the lath gaps aren’t too large and you’d need to minimise the thickness of plaster to not add too much weight both sides. I’m not quite sure how well it would work - it’s non traditional in that only one side of lath would carry plaster and the rear pushed through to form the key.

Therefore if you’re talking about plastering over the posts under the stairs, you’d need a seriously thickness of plaster on the lath to do so - way more that it will take, and especially in this situation.

Why do you want to plaster them? I’m assuming non visible under the stairs. If you wish to do anything, then a few more coats of limewash would be fine to top up the historic traces.

Sorry I wasn’t very clear.

Here’s the other side of the laths.



The plan was to remove the plasterboard etc and lime plaster this side (I.e. on the stairs) at a later date. But are you saying that if we are plastering onto laths then we need to do both sides concurrently?

The other side (original photo) whilst ‘under the stairs’ provides access through the door to the utility room and so is ‘part of the room’ and the lady of the house will want it looking ‘decent’.

Our plastering experience so far has been just the thick hemp insulating plaster so I’m guessing we need to stick to normal 3 coat stuff for lath work?

 

[Kearn]

Laths really wouldn’t be intended to take plaster on both sides - the basic premise is that the laths have enough of a gap between them to force a nib of plaster through in the scratch coat, this is then what holds the plaster to the lath. You see the challenge with doing the other side - the laths have no gaps anymore with plaster sticking through and bulging.

There’s a possibility, you could plaster both sides together and therefore the nibs are no more, and you’ve got two coats of plaster that join through the lath gaps as one.

3 coat is overkill for that setup - no need for the depth and the weight won’t be your friend.