Lime plaster repair - advice/help

[lilygrace89]

Hello everyone!

We own a flat, which was converted in the 80's, in a Victorian property. It has been severely neglected by the landlords who owned it before and also by the freeholder of the building (delayed repairs to roof and cracks in rendering causing significant water damage and damp).

I have attached photos of our hallway wall, it's on an exterior wall. The big areas all fell off and crumbled away, as did the small patches of ceiling. There's also a photo where a previous owner has made a repair. We cannot afford to have the whole wall done (especially in lime plaster) and want to know the best/easiest way to repair this if anyone has advice?

So far advise has been to take all the plaster off the whole wall (something we don't want to do) or patching the holes up with plasterboard .

Thank you!

 

[Cubist]

Hi There and Welcome,

I'm sure that others will be along shortly with additional advice but for now these are my contributions. Noting that there has been, still may be, a damp penetration problem caused by damaged external render, the textured, and almost certainly water-proof, paint applied to those internal walls is a big contributor to the failure of the plaster. Water has been trapped between the paint and the external wall causing the plasters internal bonds to fail and may also have damaged the laths (the wooden strips). Top of the remediation list would be to get the external render repaired or replaced if at all possible . Right now it's the wrong time of the year to begin such an exercise, even if money were not an issue, and so that's best left until next year at the earliest.

Internally though there are some things you can do that will not cost an arm and a leg if you are at all handy. Here the first action would be to get rid of that textured paint with the aim of ultimately replacing it with a coating that will help it to breathe. Curiously, you may be surprised to learn, the failed plaster and the resulting holes in the wall, are in fact helping the house right now as they are providing a path via which, damp penetrating through the external wall, is being carried away by the internal air convection currents. However, this may be collecting elsewhere and you would be wise to keep an eye out for it in other places.

The next step would be to repair the existing plaster work by applying a new scratch coat to the laths that have been exposed in the walls. You need to be a little careful with this as the old lath may be a trifle delicate and they could break. The lath operates as an armature that supports the wet plaster when it's applied and becomes an intrinsic element of the walls structure as the plaster dries. Once the scratch coat has partially dried you can add the scratches, as seen in your last picture, to provide the 'key' for the skim coats that will follow when the scratch coat is very nearly thoroughly dry. One or more skim coats of finishing plaster can then be applied to achieve a final and smooth finish.

All the materials and equipment needed to do this are very cheap and readily available from any hardware store and there are many tutorials on YouTube you can consult to learn the various techniques you would need.

That said I need to reiterate that the key activity is to get the external render back in good order as this is likely the fundamental root cause of your issues.

Hope this helps and that other members will correct me if they feel Im being too optimistic/wrong or have alternative ideas or recommendations on how to proceed.

Cheers,
Cubist

 

[lilygrace89]

Hi There and Welcome,

I'm sure that others will be along shortly with additional advice but for now these are my contributions. Noting that there has been, still may be, a damp penetration problem caused by damaged external render, the textured, and almost certainly water-proof, paint applied to those internal walls is a big contributor to the failure of the plaster. Water has been trapped between the paint and the external wall causing the plasters internal bonds to fail and may also have damaged the laths (the wooden strips). Top of the remediation list would be to get the external render repaired or replaced if at all possible . Right now it's the wrong time of the year to begin such an exercise, even if money were not an issue, and so that's best left until next year at the earliest.

Internally though there are some things you can do that will not cost an arm and a leg if you are at all handy. Here the first action would be to get rid of that textured paint with the aim of ultimately replacing it with a coating that will help it to breathe. Curiously, you may be surprised to learn, the failed plaster and the resulting holes in the wall, are in fact helping the house right now as they are providing a path via which, damp penetrating through the external wall, is being carried away by the internal air convection currents. However, this may be collecting elsewhere and you would be wise to keep an eye out for it in other places.

The next step would be to repair the existing plaster work by applying a new scratch coat to the laths that have been exposed in the walls. You need to be a little careful with this as the old lath may be a trifle delicate and they could break. The lath operates as an armature that supports the wet plaster when it's applied and becomes an intrinsic element of the walls structure as the plaster dries. Once the scratch coat has partially dried you can add the scratches, as seen in your last picture, to provide the 'key' for the skim coats that will follow when the scratch coat is very nearly thoroughly dry. One or more skim coats of finishing plaster can then be applied to achieve a final and smooth finish.

All the materials and equipment needed to do this are very cheap and readily available from any hardware store and there are many tutorials on YouTube you can consult to learn the various techniques you would need.

That said I need to reiterate that the key activity is to get the external render back in good order as this is likely the fundamental root cause of your issues.

Hope this helps and that other members will correct me if they feel Im being too optimistic/wrong or have alternative ideas or recommendations on how to proceed.

Cheers,
Cubist

Thank you so much for your reply, that's really helpful! When I purchased the flat there was a tree growing out of the brickwork above this area of hallway outside, it's been removed and the roof repaired so I am hoping what caused this damage has been resolved. We do have problems with rendering but that's effecting a different room (a battle I am having with the freeholder to have it repaired!!)

We have been doing a lot of stuff ourselves so I will look into this and see if we can give it a go!

 

[a twig]

I’ve patch repaired similar sized holes in lime plaster on lath before, so certainly doable as a diy repair job rather than removing the whole lot. If you buy a few tubs of pre-mixed haired lime plaster from somewhere like Ty Mawr (other vendors available) it’s even easier.

Just give the base coat a good push in so it keys onto the laths. Plenty of videos exist on YouTube. Places like Ty Mawr will also sell you a pack of lath so you can replace any that are too far gone.

 

[Cubist]

Ooh, ooh, Twigs triggered an afterthought - nowt new there though, he's a provocative sort. A couple of days before you start getting plastered its wise to mist the lath a few times with a spray bottle. This helps to enhance the flexibility of the lath so that it at least tries to resist before breaking when you press the scratch coat in. It also helps to enhance the bond of the plaster to both the lath and the surrounding old plaster if you damp that down too beforehand.

Health warning - alcohol is not essential to doing the job but you will feel better about the finish that may result.

 

[Stevers]

I've done similar (and some more extensive) repairs with Thistle One Coat available from your local builders' merchant, with the precautionary caveat that there ought to be no source of damp or salts to affect the work.

Repair of Lath and Plaster Ceiling with Thistle One Coat

No affiliation with whoever makes Thistle One Coat - just a satisfied consumer for around 40 years. We live in a Victorian House (1879), and right from the moment that our plumber put his foot through the landing ceiling when a jet came over low and fast (1997), I've had to occasionally patch...

www.periodproperty.co.uk

In the past I've successfully replaced blown lime plaster with it, so it must have some tolerance of old building nastiness!

 

[lilygrace89]

Ooh, ooh, Twigs triggered an afterthought - nowt new there though, he's a provocative sort. A couple of days before you start getting plastered its wise to mist the lath a few times with a spray bottle. This helps to enhance the flexibility of the lath so that it at least tries to resist before breaking when you press the scratch coat in. It also helps to enhance the bond of the plaster to both the lath and the surrounding old plaster if you damp that down too beforehand.

Health warning - alcohol is not essential to doing the job but you will feel better about the finish that may result.

I will keep that in mind about the alcohol

 

[frustin]

I’ve patch repaired similar sized holes in lime plaster on lath before, so certainly doable as a diy repair job rather than removing the whole lot. If you buy a few tubs of pre-mixed haired lime plaster from somewhere like Ty Mawr (other vendors available) it’s even easier.

Just give the base coat a good push in so it keys onto the laths. Plenty of videos exist on YouTube. Places like Ty Mawr will also sell you a pack of lath so you can replace any that are too far gone.

How long will a bucket of that last? if i buy a bucket, use it to do a fill and replace a small area of concrete plaster. if i put the lid on a leave it in the garage, what's the shelf life?

 

[a twig]

Ty Mawr recommend theirs to be used within 4 weeks of delivery - it won’t carbonate much (if at all) in a sealed container but it may start to dry out and need water adding when knocking up.

You could try packing it into the tub and just pouring an inch or so of water on top to keep it for longer (as you do with lime putty) but I’ve never tried so no guarantees

Also if you have haired pre-mixed plaster, the alkali in the lime will dissolve the hair it if it’s kept wet, so after a few weeks your haired plaster will be hairless

 

[noj]

If you get the fibrechalk from Anglia the fibres are synthetic. It pretty much keeps forever...

Edit: website is being rebuilt at the moment but they're still on the end of the phone.

 

[Kearn]

Ooh, ooh, Twigs triggered an afterthought - nowt new there though, he's a provocative sort. A couple of days before you start getting plastered its wise to mist the lath a few times with a spray bottle. This helps to enhance the flexibility of the lath so that it at least tries to resist before breaking when you press the scratch coat in. It also helps to enhance the bond of the plaster to both the lath and the surrounding old plaster if you damp that down too beforehand.

Health warning - alcohol is not essential to doing the job but you will feel better about the finish that may result.

It may need more than a misting, normal advice tends to be a couple of weeks of soaking the lath. Mostly to stop it splitting when you nail / allow some flex if you’re using it through staves. It will also stop the lime drying too fast in the new lath by being sucked in.

I had a few 100 lathes to soak - rainwater butt came in useful!

 

[frustin]

Ty Mawr recommend theirs to be used within 4 weeks of delivery

So I looked at their product and put a 25kg bag of base and 25kg of top layer into my shopping basket - £17.16 - £66 delivery!

Any other recommendations on places to buy please?

 

[malcolm]

Anglia Lime will send a 25kg bag by courier. Postage still around £15.

 

[Lacan07]

So I looked at their product and put a 25kg bag of base and 25kg of top layer into my shopping basket - £17.16 - £66 delivery!

Any other recommendations on places to buy please?

This is why its very handy to live nearby a lime seller. The trouble is do with the weight, 2 bags of lime are bloody heavy, so it gets shipped on a pallet.