Plastering with my own Lime Rich Mortars

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I have been lime plastering for a number of years and over those years I have usually bought in ready mixed course stuff and fine stuff, however I have recently developed my own finishing plaster as mentioned already and I think it is the best finishing plaster I have ever used and it should be as I developed it for that purpose.

Recently I began to think about the course stuff, that too could be better and I have just done a job where I made my own.

I have been thinking for some time that there is never enough lime in the mix. Most mixes nowadays are in the region of 1 part lime putty to 2 1/2 parts aggregate and in the Cotswolds that is usually a mixture of sharp sand and Cotswold stone dust. For me that is not enough lime.

The recipe I am using at the moment is 1 part lime putty to 2 parts sharp sand, this gives a really sticky mix to which can be added a lot of hair. It is a happy fact that when you add a lot of lime, the plaster will tend to crack as it dries out, but being so sticky it will hold more hair and that hair stops the cracking. This is a rule worth remembering, the stickier the mix the more hair it will take, of course the best way to get a sticky mix is to add more lime putty – not more stone dust.

Lime putty has never been easier to produce so why skimp on it?

Once you have a really sticky plaster the technique of plastering changes – you don’t really spread it on directly off the hawk but apply it to the wall in dollops and then spread it flat, it’s amazing how easy the process of plastering becomes when the mix is right (and how difficult the job is when the mix is wrong).

Another penny dropped the other week when I saw a scratch coat of render that hadn’t rendered the wall flat, it was almost as bumpy as before. there is no point in this, if you are after a flat wall the scratch coat is the time to get it flat – dub it out to even out the surface, apply the first coat, get that as flat as possible and any undue thickness, due to the undulating surface might well crack a little, even with plenty hair, but this cracking is in the first coat and as long as the plaster hasn’t become detached from the wall (which can happen) it is of little consequence. Once you get it flat, and you can use a straight edge such as a rule, or derby float for this, then you scratch it ready for the next coat.

Scratch coat applied

The next coat is now easy to apply, it is of even thickness, dries even and is easy to get flat. This second coat is brought up to within 4 mm of the final level and trowelled or floated flat, corners crisp or nicely rounded.

second coat ready for the finishing coat

The finishing coats can then be applied in a couple of passes and trowelled flat and smooth.  By getting the wall flat as soon as possible makes every other stage really easy and efficient.

All of this is so much easier with a mix with 33% lime putty by volume and loads of hair – you really do need to be able to see the hair in the mix – they need to be really obvious – horse hair is best, don’t bother buying the nicely wrapped in string stuff, find yourself a friendly horse owner or two and ask them for the hair off their horses. It’s cheap and it works great.

so there you have it my own recipe from now on is a minimum of 33% lpbv (lime putty by volume) for backing coats and a minimum of 60% for the top coat.

Lime rich, fibre rich mortars for excellent results

(The blue colour is caused by the slate granules used in recipe for the top coat – 66% lime putty : 33% slate granules – it will dry white of course)

finished!

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just needs the dado rail and fire surround fitting… and the skirting painting.

by John Byrne ~ Artisan Lime Plasterer

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JB Lime Finishing Plasters

The first field trials began this week. After a number of weeks of trials, adjusting recipes and readjusting recipes I sent 130 litres to the Cotswolds to be applied by someone else outside of my own house.

The feedback was most gratifying:

“Easy to use” I gave it one good coat and then kept going back and trowelling it up. It is very nice to use, closes in so well you get a lovely flat finish – it’s the best I’ve used.”

There is a facebook page  now as well –

https://www.facebook.com/jblimefinishingplasters

I supplied it at 58% lime putty by volume. (that’s 10 units of lime putty to 7 units of aggregate). I won’t be using all this 3:2, 1:2 etc I want to be clear about just exactly how much is lime putty without any ambiguity.

 

 

 

 

 

 

 

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lime plastering plasterboard. with the correct tool and material it works well.

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This intriguing little tool I purchased from  Arford enterprises – www. Arfordenterprises.co.uk. it is manufactured for the rubber industry apparently

I bought it because I have had occasion to apply lime plaster to plasterboard. you will wonder how it applies to plasterboard and why use lime anyway? I explain what I bought it for below but to to answer the inevitable why not simply use gypsum:

a. I don’t like the stuff

b. I want a consistency of surface finish on all the walls, not just in appearance but in the paint used.

c. the simplicity of using one type of material.

So following the received wisdom I bought the recommended Baumit DG27  and primed the board and applied the plaster.

Then I got thinking whether my own special recipe lime finishing plaster would stick to the plasterboard without the DG27, which is, afterall pretty expensive, and I found it sticks very well indeed, and I am preparing a test which I will video and share with you all to demonstrate how well it sticks but being of a cautious nature I thought about applying some sort of key and came up with the idea of a spiked roller and after an internet search I have one.

As you can see below the key is quite discrete and narrow but it is quick to apply in a regular criss cross pattern and it raises the paper just enough to give an adequate key.

 

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The roller is not cheap and although they are available wider I thought the smallest width was ok to start with and if it does provide a good enough key – baring in mind my plaster seems to stick very well without primer or key – then I need not buy anymore primer for plasterboard.

The DG27 does have its uses elsewhere and the roller will not replace it entirely but for prepping plasterboard it looks just the business.

So if you do want or need to save money and use plasterboard instead of laths for stud walling then this tool and my own JBLime finishing plasters are what you should be using.

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JBlime finishing plasters

JBLimeplastering will soon be producing high quality lime finishing plasters, They are designed to overcome the drawbacks of many other ready mixed finishing plasters,

They are designed to minimise cracking, to spread easily, to be applied up to 4mm thick and to set hard.

They will be suitable for most substrates including plasterboard.

They will initially be available in two grades with the finest being designed to give a finish similar to modern gypsum plasters.

Although easy to use they will still require the usual care and attention as any other lime plaster.

They will not feature hydraulic lime or artificial binders and will typically contain more than 50% calcium hydroxide by volume.

 

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NEWS

John Byrne – director of JBLimeplastering has moved to Appledore, North Devon. Although JBLimeplastering is still operating in Gloucestershire it is branching into the SW peninsula creating and repairing lath and plaster walls and ceilings and other lime plastering projects – Training and Advice, Limewash colour matching and consultation.

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The colour of a house

One of the privileges I enjoy is the opportunity to make my mark on the landscape, and when a client has the boldness to choose a rich colour for their house it is a chance to make a statement.

The project involved the removal of a white painted cement roughcast render on the gable and replacing it with a low profile lime roughcast render. Following on from a previous project of lime washing the panels in the timber framed elevation and removal of masonry paint from the rubble masonry and it’s replacement with lime wash, this second stage project continued the colour scheme and will be added to with the removal of further swathes of white masonry paint on two more elevations sometime in 2016

a white painted cement rendered gable

Choosing a limewash colour can take some time as there is such a variety of shades and tones that can be achieved even with the basic pigments of yellow ochre, raw and burnt umbers, red oxide and black.  The first thing is to establish the colour will dominate: red or yellow, then how the colour is to be influenced; will it be green yellow or a brown yellow, a purple red or an orange red.  then we have to decide on the depth of colour.  I am not a musician but it reminds me a bit of how a tune might be constructed, the dominant colour leading the melody, other colours coming in to add complexity with the umbers acting as the bass to bring richness to the tune.

All this colour design is done with the landscape and location in mind, in this case the soil and stone colour is in the red category so that gave us our starting point for or theme, but we wanted something more refined than a simple red oxide and we certainly didn’t want pink or peach.

I think we got it right what say you?

swan house

We entertained ourselves on this project by a little experiment: nothing too outlandish or risky it was just that I had a few feather pillows to get rid of so I added the feathers to the render. So this render is reinforced with feathers as well as hair. which I think is fitting as the house is called Swan House.

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swan house in its habitat

It is so pleasing when a customer is bold enough to go with a colour this rich rather than the more conservative ice cream colours of the houses in the foreground. the trick is for it not to be too loud and garish. It must look like it belongs there not like it’s on a day trip.

 

 

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Recipes and

Apparently the top search on this site is for  “correct mix ratio silver sand nhl2 lime” .

I can answer that, There is no correct ratio but a good one would be between one and one and half portions of sand to one portion of NHL2.

did you know that there is no really discernible difference between Playpit sand, Silver sand and Kiln dried sand.

Pompeii

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According to one of our guides in Naples red was the predominant colour used in the City as it was the colour of Pompeii. But this plaster shows the yellow gradually turning red. knowing that yellow ochre when heated sufficiently turns red and considering the heat that the plasters of Pompeii were subjected to, and with the evidence of this picture, I might suggest that Pompeii was Yellow rather than red.

 

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Smooth and crisp and even.

There is this house and the owners had done a considerable amount of the work themselves, and very good it is too. However they did need some help with the plastering.

They had already got a first coat of hemplime on the walls and there was a host of other surfaces for us to plaster as well : woodwool board, Cork, Calsitherm sheets, bricks, stone ain addition to their first coat of hand applied hemplime.

Half the house is newly built so we wanted the limeplastering to be as regular as the multi finished walls.

I am afraid that the DIY applied hemp was not very flat and so I used string lines and screws to get us some flat screeds to work from. The walls came up lovely and level with derby floats and feather edges in much use. We let it all dry and then returned for phase two – the finish.

I might already have mentioned this but for my taste there is not enough lime in the commercially available finishing plaster so I bought a ton of it and several tubs of sieved lime putty. To 45 litres of finestuff as supplied I added 15 litres of lime putty and for my needs and technique that was ideal. The plaster is nice and sticky, spreads well and the suction is much reduced – yes! to reduce suction and increase spreadability add more lime not more water.

This plaster was applied about 5mm thick as flat and even as possible onto an already flat surface, the plaster was then floated with felt floats this gave a realy good finish for the final skim. The recipe for this I will keep secret for now because it is still in development but I will tell you it gave us a finish very similar to the modern stuff with very limited cracking, smooth to the touch and close grained with an eggshell type sheen to it.

The same plasters were used on all the surfaces with the occasional modification: for instance on the woodwool board ceiling I added loads of short horse hair to the finestuff, an idea taken from the Chalklime I had been using elsewhere, loads of hair mixed with  fine lime rich plaster – a joy to use, spreads beautifully and cracks not a jot*, two coats on the boards, hair in both coats, trowelled smooth and flat.

*Oh yes there are! After the heating was turned on an the house began to warm up the timbers began to shrink a bit so not just the woodwool board ceiling but the cork boarded stud wall too began to develop hairline cracks. It is being monitored and it is expected that the cracks will be dealt with at the time of decorating.

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Chalk lime plaster from AngliaLime

It might seem a recipe for trouble if the aggregate in the plaster is not sand but crushed chalk, very sticky and smooth yes but tremendous shrinkage also. Yes that is true but Anglialime put so much hair or fibre in that there are no shrinkage cracks – it still shrinks but en masse about 10% of the thickness so beware – you might get it flat when you trowel it up, and you can’t float it either, in fact it is pretty difficult to get it flat but nonetheless, when you have and then walk away it starts to shrink and as it does the thicker areas shrink back more than the thin areas so I am afraid what might have been flat is that no longer.

When we first started using it we though what on earth is this rubbish, you can’t dig it out of the back unless you use a fork, you can hardly knock it up – in the end we used a hedge trimmer! We got funny looks from the builders. But to be fair to the suppliers when we started to use bags that hadn’t been sitting around a month it was different. And so we learned that it doesn’t keep well as the fluid drains away and it gets too stiff to work. When it first arrives from the supplier it’s good stuff.

We found that you could really lay it on, for common work you could get away with one coat about 15mm thick, for a better finish that could be skimmed over with some fine stuff.  We found that any coats less than 5mm thick were really not ideal and that the optimum thickness was probably 10mm and applied in two coats on laths or masonry and the results were very good.

One benefit we discovered was that you drop very little on the floor, what we did drop was often when we tried to take part of what was on the hawk instead of it all and the fibre being so great it all tended to come off the hawk at once.

It is not like regular lime plaster in many ways, it is claimed to be very similar to medieval plasters and I have seen very white, extremely hairy historic plasters so hairy indeed that it can be pealed off the wall in a sheet as we found, or to be exact, the electrician found for us.

I would say it was a plaster for cottages and other situations where regularity is not required because it is difficult to get it really flat with crisp corners but it has charm and it dries and sets extremely hard and tough, in many ways it is remarkable stuff however it is almost twice the price of my regular course stuff so cost is a bit of an issue but it has got me thinking.

for more info on the product:

Click to access FibreChalk%20Usage%20Guide.pdf

a nice cottage with chalk lime plaster

a nice cottage with chalk lime plaster

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lath problems

This is a quick aside. A customer had a ceiling he needed me to plaster, he had already fitted the laths, sawn oak, he had fitted them really well with very good spacing, the job was simple the ceiling only 15 square metres – easy.

I got the first coat on on a Friday and on the Monday got a call that quite a lot had fallen off.

As the picture shows it hadn’t all fallen off but even so there were a few patches and it wasn’t immediately clear why. What was plain to see was that some of the laths had bent forcing the plaster off.

In the end we settled upon the likely cause – the laths had been tightly screwed rather than nailed and they were too tightly fixed to allow any stretching as they absorbed moisture from the lime. and so they had to bend.

If they had been nailed they would have split and and although adequately fixed would have been able to move just that little bit and wouldn’t have needed to bend.

If you think about it, each individual lath needn’t be fixed very securely or need be very strong as one lath isn’t doing much work and neither is one nail or screw in this case.

the expanded bent laths that pushed off the plaster

the expanded bent laths that pushed off the plaster

Posted in ceilings, Lime Plaster, technical stuff | 4 Comments