Early 1900's plastering

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Hi, we're in the process of moving in and in my enthusiasm to 'get to know' the old house went straight for the 4-5 layers of wallpaper and paint. Now that it's all off I can better see what I'm dealing with.

Starting with the ceiling. I know it's wooden laths attached to the joists. They are covered in a half inch thick layer of greyish blue undercoat which I assume is lime/hair/sand, topped off with a thin layer of lime plaster of some kind.

The walls have the same setup, brick then the same gray undercoat and finally a thin layer of plaster.

Obviously the plaster has blow off in large patches, but at least 70% of it is still on the walls and ceiling quite solidly.

I'd like to know what the best approach would be to dealing with it. I intend to do the work myself and I have ordered the following from Conserv:

2 x Natural Goat Hair (500g), 1 x Non-Hydraulic Lime Plaster Base (25kg), 1 x Non-Hydraulic Lime Plaster Finish (25kg), 1 x Traditional Lime Wash (10 Litre),

Ideally I would like to patch the large areas that are missing the old plaster, prep the whole surface, limewash and either limewash colour or claypaint.

Should I do anything to the cracks in undercoat?

I do not wish to overboard up the ceiling or the walls. I want a fresh layer to paint over, for both walls and ceiling.

Thank you!

 

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Anyone?

 

[Socksitis]

I know more will come along and provide their expertise. Is it grey because the local sand is grey? Down this end of the country my old lime mortar was an off white or a beige colour, but our local sand is the same beige colour.
Glad you are doing the work yourself, very satisfying. Although I am having doubts about the process as I complete the plastering.
My bible has been Clay & Lie Renders Plaster & Paints by Katy Bryce & Adam Weismann.

The lime suppliers, in my case Mike Wye have also been a font of knowledge.

Good luck.

 

[MikeG]

Those grey patches aren't lime plaster. I don't know what they are, but I'm certain that's what they aren't. Can you get us a close up or 3? Also, can you break a bit off and drop it in vinegar, then tell us what happens.

The rest of the covering over that grey appears to be peeling. You will have to remove it before doing any plastering, otherwise your new plastering risks ending up on the floor.

 

[plasticpigeon]

Are you certain it can't be lime? The old lime plaster in my circa 1900 house was dark red from the red sand used with the minimum of lime the cheapskate builders could get away with for it to hang together. Could ash or some other aggregate have been used in areas with lots of ash to get rid of? As far as the skim is concerned in my house I am pretty convinced it was a mix of lime, sand and plaster of paris. I think this, as it is much harder than lime would be, and it just feels like plaster of paris. It might sound like heresy, but I would be tempeted to fill in with modern gypsum. I don't think lime is needed for breathability unless there is no dpc, and the fine aggragate in modern plasters makes it much easier to fill in holes with. 3 cheers for keeping the laths and original base coats. I gave up and overbaorded in my house as there were no cornices and it was much easier, and doing up the house is a chore at the best of time (especially if ones aspires to a decent finish).

 

[MikeG]

Well, I've never seen lime like that. As I say, some close ups, and the vinegar test, and we'll have a better idea.

I don't think it heresy at all to overboard. It preserves the original fabric of the building much better then stripping and re-skimming would. It gives a decent surface to plaster to, and there are no mouldings to worry about here. If that peeling top coat doesn't come off reasonably easily I'd suggest that might be the best way forward.

If you do overboard, here's a tip I've given before. Don't use pink gypsum plaster. Use something called Universal One Coat. It's white, and it produces a finish much more akin to lime plaster. Just don't keep wetting it and trowelling......stop when you've got the toolmarks out. It's much easier to use than lime plasters.

 

[livias]

The grey could be lime mortar. I used to live in Bristol and the basecoat of my Victorian house was lime with an aggregate which turned it grey. I was told that it was leftovers from the local coal mine

More locally to you Mike - I once conserved some exterior lime plaster on a medieval merchants house near Ipswich docks which had been pargeted with a grey mortar, probably in Tudor times. I guessed that the house had been owned by a merchant who was bringing in coal by ship to the docks and so had access to the unusual pigment. No proof of that, though

 

[MikeG]

The grey could be lime mortar. I used to live in Bristol and the basecoat of my Victorian house was lime with an aggregate which turned it grey. I was told that it was leftovers from the local coal mine......

Well, you live and learn. Thanks livias, and I withdraw my assessment. I still think the best course of action is the same.

 

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Thank you all very much for the input.

Here are some more detailed photographs of the room in question. The house is in south wales so I assume that ash/something related to the local coal mining was used as aggregate. I have found some large chunks of base and top coat that fell off from laths in one of the cupboards where the boiler lives and I can clearly see hairs within the gray mortar/basecoat. I will put a small chunk in vinegar and report back.

Here are some more detailed photos: https://postimg.cc/gallery/28ud3q7zs/

The corner with mould had a significant looking ingress of moisture due to failing on flashing or brickwork in chimney a couple of years before I purchased the house (according to neighbours). This was rectified externally, but obviously putting more wallpaper and paint over the problem didn't do much to address the moisture retained on the inner walls and ceiling. Since ripping all that off it's dried out nicely and the mould is superficial (ie. if I scratch the surface about half a mm we're back to clean white surface coat lime).

The blown plaster on ceiling I haven't really touched since taking the paper down, and have not gone carefully around walls to get any more loose edges off. Most of what is still on (except on edges of blown patches) is very solidly on, including the area which had the leak. Tapping and chipping at the white surface coat in that area does not make it fall off the base coat.

I've since cancelled order from Conserv and will be going on a two day lime plastering course at Ty Mawr in June. I'll let the room air our further during this time.

A specialist at Ty Mawr has suggested stripping the top coat and re-skimming. On the ceiling this may be plausible but a couple of the walls are largely intact and I would prefer to simply patch the smaller areas. What are the potential problems with this provided I use equivalent superfine fatty lime top coat?

 

[livias]

Damp down the surrounding thoroughly before you begin as it will be very dry after 100 years
Work the new into the junction of the old to get a good physical bond
Take lots of care to make sure that the junction of old and new is level - that both are the same depth
Have fun ☺

 

[plasticpigeon]

It is hard with lime as even with very fine sand in the skim, it is hard to blend the edges. It is possible to buy lime topcoat with marble dust as the aggregate. Maybe that would be easier to blend in. An absolute godsend is a sponge float. It may be possible to get the skim right with the trowel first time but if not, a spongle float spreads it around nicely and gets a flatter finish but which is a little rough, which can then be smoothed with a trowel. The sponge float seems to bring the lime to the surface, so I guess it not good to work it too hard with the sponge, just enough to get it even. Have a play, the great thing with lime is you have a long working time, and can pull it off, mix it up and try again if not happy!!!

 

[squarepeg]

Thanks for all the very useful input. I'd like to clean the plaster top coat which is currently there thoroughly before patching. What would the best process be?

Thanks
Fred

 

[Socksitis]

I was told that if I primed the old area with DG27, then top skim over all of it. I am going to get the sander on the old plaster to try and get some of the layers of old paint of - with a mask

 

[Pennyviz]

I live near Bristol and most of the mortar in this house in the parts dating from Victorian phase is almost black too.

I've seen Febond Blue grit being used to help stick a top coat of lime plaster to help patching, but don't think it is very breathable. I've used ecomortar in places to patch which has worked well.

Pennyx

 

[MatthewC]

I was told that if I primed the old area with DG27, then top skim over all of it. I am going to get the sander on the old plaster to try and get some of the layers of old paint of - with a mask

I used DG27 on my house - there were huge areas that needed complete replastering in lime, and a good amount of old plaster that could be retained. DG27 helps a new skim to adher to the old plaster, and seven years later you still can't see the join so I reckon it works - and as I recall it is breathable as well

 

[paulc]

I've seen Febond Blue grit being used to help stick a top coat of lime plaster to help patching, but don't think it is very breathable.

I have also used FeBond as a primer under lime plaster. To a certain extent, it will allow moisture through - Had a patch come off a wall I was doing, and the plaster behind showed signs of being damp (pink gypsum plaster).

At a push, you can get marble dust from L. Cornelisenn: https://www.cornelissen.com/marble-dust.html or from a supplier that specialises in fibreglass & resins (it is used as a filler powder). Chalk could also be used (Cronelissen call it Whiting).