Lime plaster repair / replacement advice

[Kearn]

Hi all, I've been reading through this really helpful forum for a while and up to now that, plus some common sense has been enough in my renovations. However, today is the day that I could do with some specific advice as I haven't quite found what I need through searching!

A quick snapshot - our home is a 2 bay, 2 storey Tudor timber cottage. With a marginally later external brick single storey animal shelter which has since been incorporated into the house. At the rear we also have a two storey plus cellar early Georgian addition. And a later 1980s kitchen/conservatory addition.
It was lived in by a lady all her life until she was 82, then unfortunately other owners got in for 7 years before we bought it and 'renovated' with good intentions - familiar story! I am currently un-picking many of these errors in addition to making other changes to the layout and bringing back features and materials as they should be.

To date we have
- removed all external plastic paint, gypsum and concrete
- repointed and repaired palled bricks
- re-limed the upper panels in the frame
- repaired the lower frame posts which were all floating
- repaired and redecorated wroght iron windows and frames
- dug out a French drain
- opened up one of two Georgian inglenooks (wip)
- stripped out an upstairs bathroom

Still to come
- complete the Georgian fireplace (new hearth, repoint0 and open and finish the second one in the room above
- open up the Tudor inglenook (help here as there is not much left of the piers and no beam)
- dig up the concrete floor in the once external room and relay limecrete (assuming original bricks are beyond repair)
- finish refitting a bathroom upstairs
- remove gypsum skim over lime on other external walls and replaster / repair
- remove carpets in lower Tudor living and Georgian ground floor rooms and renovate the floorboards...

My current challenge is the upstairs bathroom, but will apply to other areas where I also need to remove the gypsum skim from original lime plaster and repair - I have no idea why this was done, mostly it hasn't even produced a flat uniform finish!? Oh well...

So, the external wall of the timber cottage is where I could do with some thoughts and recommendations - I have removed the gypsum skim and concrete infills in the wall, leaving original plaster where it hasn't blown. My intention is to fill in the larger gaps with a thicker haired plaster coat first and then finish with a skim, probably lightly going over the existing original skim as I'm not sure I will be able to create a good join between the two. The original lime skim is a very thin couple of mm finish directly onto the insulating earth and straw, with no base coat so I plan to replicate this to prevent extra depth sitting proud of the frame.

And finally (!) my Q - for now I think ready mixed plaster is the way forwards at this stage, I am based in Sonning, Berkshire - what would you recommend product wise for this (incl tools) and also any comments / opinions / suggestions on the approach most welcome. This is the first job of many where repairing / replacing lime plaster will be happening so my trial run so to speak! However, I'm not sure about the total volume required through the other jobs yet so can't really buy bulk at this stage and may mix myself later down the road anyway - but for the bathroom I am keen to catch up some time so taking the quicker option.

Apologies for the lengthy post, clearly a function of spending so many days at home on my own going stir crazy and talking to myself!!

Thanks in advance,
Kearn

 

[Abi Cott]

Nice piccies, I haven't got a clue on the answer, I've been reading a lot, but have yet to have any hands on experience with lime plaster, but you are now back at the top of the list

 

[a twig]

For now I think ready mixed plaster is the way forwards at this stage, I am based in Sonning, Berkshire - what would you recommend product wise for this (incl tools) and also any comments / opinions / suggestions on the approach most welcome. This is the first job of many where repairing / replacing lime plaster will be happening so my trial run so to speak! However, I'm not sure about the total volume required through the other jobs yet so can't really buy bulk at this stage and may mix myself later down the road anyway - but for the bathroom I am keen to catch up some time so taking the quicker option.

I'll leave your other queries to those who have experience of timber buildings, what I will say though based on my experience is this:

If you are going to be working on your own, don't have a powered mechanical mixer and have a large area to cover, 100% buy ready mixed. A pallet delivery will cost around £30-40 no matter how full the pallet so order a couple bags extra, if its fat lime it will keep. I used to mix my own, but it really becomes a slog, every couple of square metres or so having to down tools and go and mix more.

Having the readymix next to you, you can just crack off the lid/slice open a bag and crack on - making more progress and saving your energy for the actual plastering.

 

[livias]

Well done, it all looks good. Nice quality timbers too

Yes buy ready mix CHALK lime putty mortar or hydrated chalk lime mortar. If you get it delivered then it doesn't matter where it comes from. I buy from Anglia Lime or Warmcote though there are many others. Old House Store is fairly near to you but I don't know if they do chalk & lime. You don't want a sand & lime mortar. Warmcote has the advantage that you do not yet need to pay VAT and that Martin is mate of mine.

You need a chalk lime mortar for the thin interior skim, mixed with lots of synthetic hair. Stir it up well before use to 'get it moving'. You will be plastering a mat of hair onto the wall. I expect you have already seen areas of old plaster in your house which are mat like. Next spring you could use this mortar for the external too but I am using a thicker layer of chalk lime onto lath as that is what was there before and specifically Warmcote for its insulating aggregate

I would not skim over your old plaster because you would have to scratch it up to get a good bond damaging the original in the process and don't forget there might be some wall painting lurking under white limewash. Instead, paint the edges with rather liquid lime putty and then plaster up to it. Spend some time getting the level of the join correct and then once it is limewashed / chalk painted it will look just fine.

Tools
- A small stainless plasterers trowel. You can buy them readymade but its as easy to get a full size one Marshalltown and Tyvak are good and then cut it down to something like 80mm *120mm
- A small tool. Leaf and spade are most common. Cue the old joke "Every plasterer has a small tool"
- A gauger for getting lime out of buckets
- A 4" joint rule for getting a perfect join between old and new plaster
- A hawk
- A plasterers bath or tray is handy for fluffing up a bucket of lime mortar in. A cement mixer will save your back, but for small quantities it is too much faff to clean it up afterwards

 

[Andys]

Hello, good luck with all of that, it sounds like you're doing great work. Repairing a panel is quite therapeutic after the horrific mess involved in getting well-intentioned gypsum plaster off the wall.

I used a very thin haired coat of fine (sand) lime plaster to patch the topcoat on our daub panels, which looked much like yours. A few chunks of daub had to be patched in first, leaving a couple of mm for the thickness of the plaster skim to go on next, butting up level with the sound areas of plaster.

Having done it with fine sand based plaster, I'd be interested in the results with the chalk-based stuff because I think it'd give a better match to the surviving surface finish. The trouble was that the new skim still had a gritty look even after several coats of limewash. Fixed by sponging on a thin coat of lime putty, applied neat, kept damp for a day or so and then limewashed over, burnishing up with the limewash brush as the limewashed dried. The lime putty crazes if it's too thick so the sponging needed a bit of care and I was worried about it going powdery, hence the extra limewash coats.

Burnishing up the limewash is quite satisfying and gives it a kind of satin finish so, hopefully, you won't get dusty elbows whenever you brush against it - you need to catch it at the right stage in its drying process, just as it ' gels'

Mike Wye will deliver sand-based plaster with the hair already mixed in, so much less effort than mixing your own. Their website's pretty informative too. For knocking up batches to make the plaster more pliable just before applying it, I've made a table with an upstand at the back and a kind of T shaped potato masher implement. Using this to ram the mortar towards the upstand is better for me than trying to lift and shove it with a trowel.

 

[paulc]

I've only just started with lime plaster - Chimney breast last spring, and now skimming a ceiling. My toolkit consists of a cheap 14" s/s trowel, an 11" carbon steel one with the corners rounded off, and two sizes of the Pavan 825 trowels. Bucket scoop is a large plastic pet food scoop, which is robust enough to dig putty out of a tub.

I haven't needed to mix up more than a 15 litre tub at any one time, so use a heavy duty paint whisk in an electric drill - It does tend to collect a build up of fibres, so I may well invest in a paddle stirrer if/when I can find one at a price I like (maybe ebay).

My finish coats are mixed from lime putty and marble dust - This has to go on very thin (slap it on, scrape it off), and will crack & flake off if gone on too thick. But it polished up real nice and gives a hard surface. Mix some pigments in for a dash of colour, and there is no need to paint afterwards.

 

[Zebra]

You could try these guys
http://www.oldhousestore.co.uk/

 

[Kearn]

Nice piccies, I haven't got a clue on the answer, I've been reading a lot, but have yet to have any hands on experience with lime plaster, but you are now back at the top of the list

Thanks Abi - seemed to do the trick!

 

[Kearn]

If you are going to be working on your own, don't have a powered mechanical mixer and have a large area to cover, 100% buy ready mixed.

Totally agreed - now that Zebra has kindly pointed out how close the Oldhouse Stores is, I can easily grab what I need when I need it rather than weigh up delivery costs...

 

[Kearn]

Well done, it all looks good. Nice quality timbers too

Yes buy ready mix CHALK lime putty mortar or hydrated chalk lime mortar. If you get it delivered then it doesn't matter where it comes from. I buy from Anglia Lime or Warmcote though there are many others. Old House Store is fairly near to you but I don't know if they do chalk & lime. You don't want a sand & lime mortar. Warmcote has the advantage that you do not yet need to pay VAT and that Martin is mate of mine.

You need a chalk lime mortar for the thin interior skim, mixed with lots of synthetic hair. Stir it up well before use to 'get it moving'. You will be plastering a mat of hair onto the wall. I expect you have already seen areas of old plaster in your house which are mat like. Next spring you could use this mortar for the external too but I am using a thicker layer of chalk lime onto lath as that is what was there before and specifically Warmcote for its insulating aggregate

I would not skim over your old plaster because you would have to scratch it up to get a good bond damaging the original in the process and don't forget there might be some wall painting lurking under white limewash. Instead, paint the edges with rather liquid lime putty and then plaster up to it. Spend some time getting the level of the join correct and then once it is limewashed / chalk painted it will look just fine.

Tools
- A small stainless plasterers trowel. You can buy them readymade but its as easy to get a full size one Marshalltown and Tyvak are good and then cut it down to something like 80mm *120mm
- A small tool. Leaf and spade are most common. Cue the old joke "Every plasterer has a small tool"
- A gauger for getting lime out of buckets
- A 4" joint rule for getting a perfect join between old and new plaster
- A hawk
- A plasterers bath or tray is handy for fluffing up a bucket of lime mortar in. A cement mixer will save your back, but for small quantities it is too much faff to clean it up afterwards

Thanks for all of this, a massive help! Turns out the Oldhouse Stores is very close...

A Q - why do you say chalk only and not a 50:50 sand mix top coat for example - is it a question of potential finish and smoothness, or something else? Oldhouse Stores don't mix chalk, but do have a good selection of sand mixes coarse and fine. And goat hair to mix.

Agreed on the old plaster - I will just feather up against this, I have no desire to remove / cover what is there. How does the liquid lime putty work - simply a bond to get adhesion?

Thanks again...

 

[Kearn]

You could try these guys
http://www.oldhousestore.co.uk/

Thanks Zebra, I knew there was somewhere near, but they had been evading my up until now!! Popped down the other day and the guys were great, can see me returning here quite often!

 

[Kearn]

thanks all for the replies above, got distracted with another job as always!

I have added a few Qs, hopefully by quoting in specific replies, but we will see if I have got this right or not soon when they post...

livias - my main Qs were regarding your detailed response, regarding chalk vs sand. Hopefully this will post, if not I will message you - still getting to grips with the administrative side of this forum!

thanks again - progress pics to follow, just waiting for daub to dry currently...

 

[livias]

When I started lime plastering everyone was using sand lime mixes but it became more and more apparent that this was a relatively new innovation and that any lime plaster in my part of the country (East Anglia) which was more than 150 years old was a completely different beast. Instead of being a sand based render it was a mat of hair held together with lime and chalk. Why this went out of fashion in our area is a mystery but I could hazard a guess that it was in tandem with the development of reading skills and craft colleges.

Sand lime is great for plastering on to brick, block or stone. They are all rigid substrates and hair is optional. Timber frame and daub on the other hand is slightly flexible and you dont want a rigid final coat. The general rule is that the layers should be -less- rigid nearer the surface or at least not -more- rigid.

So these days in East Anglia on timber frames chalk lime hair mat is derigeur and in my travels to other parts of the country I have noticed that -old- plaster onto timber frame will be the same chalk hair lime mat. But in other parts of the country there is much more local building stone so most old houses are built of solid construction and the lime suppliers have not cottoned on to what for them would be a minority requirement for chalk hair lime mat mortar

 

[livias]

... and yes liquid lime putty is just a bonding layer. Think of it as old fahioned pva

 

[GPHouse]

I've been looking into similar things recently and been having a bit of a play. for me getting of old flay paint limewas etc was a bit of a pain anf getting a goood surface key.

Dont know what others think but it might be worth looking at Baumit DG27 prior to skimming over the old lime. Provides a breathable surface with a sandpaper like key.

G

 

[GPHouse]

I've been looking into similar things recently and been having a bit of a play. for me getting of old flay paint limewas etc was a bit of a pain anf getting a goood surface key.

Dont know what others think but it might be worth looking at Baumit DG27 prior to skimming over the old lime. Provides a breathable surface with a sandpaper like key.

G

 

[paulc]

Dont know what others think but it might be worth looking at Baumit DG27 prior to skimming over the old lime. Provides a breathable surface with a sandpaper like key.

I've been looking in to lower cost alternatives for DG27, all be it for skimming over plasterboard/gypsum (Thistle multifinish). On the test pieces I've done, Febond Blue Grit works quite well, although coverages isn't anywhere near as good as they claim on the tin. An acrylic tile adhesive primer with a handful of silver sand mixed in also provides an adequate surface - In both cases, it is early days as it has only been a few weeks since I coated the boards.

Baumit claim that DG27 is an acrylic based primer that improves the hydrophobic quality of the substrate yet doesn't inhibit vapour diffusion. But they don't give any data for the vapour diffusion rate. It would be interesting to do some comparisons under laboratory conditions.

 

[GPHouse]

Look forward to hearing how it goes.

 

[Zebra]

You could try these guys
http://www.oldhousestore.co.uk/

Thanks Zebra, I knew there was somewhere near, but they had been evading my up until now!! Popped down the other day and the guys were great, can see me returning here quite often!

Yes they are, aren't they. I popped in a few years ago a complete novice, came away with a bag of mortar mix, a pointing trowel, a churn brush, and somehow the confidence to tackle my first pointing job!

 

[Kearn]

Bit of a progress update - I'm certainly no master lime plasterer, but reasonably pleased with my first attempt and fortunately(!) much of my repair attempts will be obscured behind things once the bathroom is back in! Getting a flat finish was damn near impossible, but then the existing plaster that i butting up to isn't either, so hey ho.

Mixing goat hair into the lime was frankly a pain! (but good exercise) and in future I will go for ready mixed (wasn't available from my local store in fine finish).

I did find this a very useful lateral use of a 'tool' - a stainless cake spatula, round end and flexible - great for coaxing off the gypsum and old paint/paper without damaging. It then also doubled up as a good edge for finishing my skim coat in smaller areas.

https://www.amazon.co.uk/gp/product/B004W75YBW/ref=oh_aui_detailpage_o04_s02?ie=UTF8&psc=1 A bit of a bargain compared to stainless tools designed for the job!

I've got a bit side tracked since this was done, with bringing the early Georgian pine boards back to life, building some freestanding cabinets to go in the room, and preparing a section of timber frame panel for an inset mirror. oh, and trying to solve the Krypton Factor challenge of finding a bath that will actually work in the room for waste / trap / taps etc....!

PS. Sorry for the skewy images - not sure if/where the option is to rotate?!