Must exterior lime wash contain linseed oil/tallow?

[Nigel Watts]

Having chosen the limewash I like and agreed the shade with the CO (it's from Ty Mawr) my builder is trying to dissuade me from using this supplier because it doesnt come with added linseed oil or tallow (at least that's the reason he's giving me). The supplier says it can be added on site but my builder "doesn't want to take responsibility" for it not working and says that it should in any event be added when the lime is slaked, not later. He claims that without the addition "it wont be waterproof". When I pointed out that that limewash was supposed to be porous, not waterproof, he replied "it will be that too".

I think he is being fed a line by his preferred supplier. I'm reluctant to give in, but need some more technical understanding. Can anyone help?

 

[Nigel Watts]

Having asked the question, I have sought to answer it myself. I have just come across this in Building with lime (Holmes & Wingate, Intermediate Technology Publications, 1997) - an excellent read by the way:

in the section "4.3 Additives to the basic limewash" it states:

"Tallow

Perhaps the most common is tallow, which is used to increase the water-shedding properties and, in rough work, make it harder for the limewash to rub off the wall. On the other hand tallowed limewashes do not allow such good "breathing" and tallow has an unpleasant smell which may linger for many months. Tallowed limewashes are liable to support mould in damp conditions and so biocides such as formulin are added to counteract the problem.

Tallow is a clarified animal fat, especially from the hard fat from around the kidneys. A lump of tallow should be shredded and added to a maximum of about ten times its volume of quicklime immediately before slaking. In the heat of the slaking reaction the tallow melts and some of it combines with the lime to form a soap. This allows the remainder to form an emulsion of tallow within the limewash.

When a tallowed limewash dries it can be impossible to apply further coats as they run off the wall just as water runs off a duck's back. Tallow should thus be used, if at all, only in the final coat of limewash. The presence of the tallow will reduce, or even eliminate, the chance of a good set of the limewash by carbonation. Tallowed limewashes should be used only where, for some reason, it is particularly difficult to achieve carbonation."

Not just not needed, it would seem, but quite possibly deleterious.

 

[FamilyWiggs]

Nigel, I'm beginning to get just a little bit suspicious that your period builder's credentials may not be quite all that they first appear... :wink:

 

[LadyArowana]

If all logical and reasoned arguments fail just tell him you are vegetarian and won't countenance dead animal on your house, end of.

 

[Nigel Watts]

Nigel, I'm beginning to get just a little bit suspicious that your period builder's credentials may not be quite all that they first appear... :wink:

Quite possibly, but I've yet to come across a builder who studies carefully the theory behind what he does. To be fair to my current one, the lime supplier he quotes is Mike Wye, a man for whom I have a great deal of respect and who has given me good advice in the past.

 

[worms]

I tend to put a splash of linseed oil in my home-made limewash. It makes it less chalky when dry and smells nice! I have no real evidence for whether it helps with waterproofing, hinders breathability or encourages growth of moss and algae, but it doesn't seem to be disastrous.

 

[AMc]

Waterproof (almost) and breathable aren't mutually exclusive - goretex et al are microporous which allow moisture to move outwards but the holes are too small to allow rain to penetrate.
If you make the decision you will have to take responsibility for the results. IMHO if you don't take the decision you'll still end up dealing with the results so I would suit yourself after researching as much as you can!

 

[Gervase]

Where was I?
Ah yes...
With any additive to limewash, the crucial factor is 'how much'. An eggcup of raw linseed oil in a 20-litre bucket will aid adhesion but not hinder breathability. Similarly with small quantities of tallow (which will only work with a hot limewash; ideally made by slaking the lime with grated tallow, but which can be made with putty and boiling water) - what you get is a process called saponification, where alkaline lime reacts with fat/oil to form a soap, which promotes adhesion. Too much fat or oil will indeed result in a water-repellent finish which should only be used for the last coat (and which can encourage green algae in sheltered locations)
Neither additive is essential, however, and the vast majority of limewashed buildings were done with no additives at all. And some of the additives endorsed by our forbears are actually detrimental - salt was used at one point, which isn't a good idea.
What does need bearing in mind, however, is that our forbears generally had the time and manpower to slap on a coat of limewash every spring, or at least every couple of years. After four or five years, even the best-applied finish of finest limewash will begin to look a little tired. It is, after all, essentially a sacrificial coating. So be kind to your scaffolder, or invest in a tower and some decent ladders; they'll be needed!

 

[Nigel Watts]

Thanks Gervase. My limewash is currently going on and it looks great - so much more interesting than all the other houses in the street which are painted in vinyl emulsion. My house will have to be scaffolded every time the window frames need doing, because it is so tall, so I am planning on limewashing at the same time - probably every five years.

Limewashing of London stucco houses is so rare now - I don't know of another single example, other than a National Trust owned one in Hackney - that I really don't know what will happen over this period. The air in London is pretty dirty, but nothing like as bad in the days of the pea soupers, so we shall see. Perhaps I should take a photo every year to recorrd what happens.

 

[worms]

What does need bearing in mind, however, is that our forbears generally had the time and manpower to slap on a coat of limewash every spring, or at least every couple of years.

Well said! On my house (single storey, ex-farm-building) it is a couple of afternoons work to "slap on a coat" each spring. I might think twice if I had a three-storey Georgian London town house!

 

[Nigel Watts]

Inspected the work today. The colour is quite variable. This is not of itself a bad thing, but the decorators clearly havn't twigged that to imitate stone a change in shade between two different tubs is best blended in by picking out individual blocks of the imitation ashlar. The limewash also has much more body than I expected. Will repeated applications progressively obscure the architectural detail in an irreversible way?

I am paying a hefty premium to get my exterior restored and decorated in this way. I do sometimes wonder if I am doing the right thing. On balance I still think I am.

 

[worms]

Its looking good!

Repeated layers of limewash will build up in body, but it will surely always be softer than the ashlar and hence not irreversible?

Now that we can see the overall effect, can we revisit the discussion over the eaves soffit? Painting it green is probably much more correct but I think it looks good as it is and helps blend the colour scheme into that of the neighbours.

 

[Lime]

Its looking good!



Now that we can see the overall effect, can we revisit the discussion over the eaves soffit? Painting it green is probably much more correct but I think it looks good as it is and helps blend the colour scheme into that of the neighbours.

I agree. It looks excellent.
I'd like to see the eaves green myself.
The one disadvantage is that white reflects light into the rooms so much better.
however if light is no great problem I'd go green.

 

[JoceAndChris]

Nigel - that looks wonderful! The colour is so warm and interesting, and such a good imitation of stone. I love it.

 

[Feltwell]

Inspected the work today. The colour is quite variable. This is not of itself a bad thing, but the decorators clearly havn't twigged that to imitate stone a change in shade between two different tubs is best blended in by picking out individual blocks of the imitation ashlar. The limewash also has much more body than I expected. Will repeated applications progressively obscure the architectural detail in an irreversible way?

Nigel, it looks great, and I'd offer money that you are the only person who will notice the colour difference and that it will be less noticeable once the scaffold is down so you can't see it up close all the way up, and it's weathered in a bit.

I guess that repeated limewashings may obscure some detail but a lot less than if modern masonry paint was used, which doesn't gradually weather off in the same way that limewash does - even allowing for the fact that the limewash will need redoing more often.

 

[Nigel Watts]

The next question is what colour to paint the modern extension. This was not rendered in lime and was done in a modern style. Rather than trying to match it in with the limewash I am tempted to do it white, or slightly off white to give a deliberate contrast. I also have the issue that limewash won't stick to the existing surface unless I strip that too.

This is an old pic taken shortly after it was built:

 

[Gervase]

Be wary of applying to limewash too thickly - it should be watery; the consistency of single cream at most, and you should aim put on five coats on to bare render, with time to carbonate between coats. It will obscure some finer detailing over time, but ashlar scoring should still be early visible.
Colour inconsistencies are part of the charm of the finish, but clearly the same volume of tint should be present in each coat - so ensure that they're mixing enough to do at least each full elevation with one batch to avoid patchiness.
Whereabouts in N7 are you? I'm now a near neighbour in N5, and would love to have a shufti at the project 'in the flesh'!

 

[Nigel Watts]

I've sent you my address as a PM. Please feel free to drop round some time and I can give you a mini tour.

 

[worms]

I also have the issue that limewash won't stick to the existing surface unless I strip that too.

I know that is the established wisdom, but I limewashed over my concrete and masonry paint garage and it doesn't seem to have been a problem. :?

 

[andrew gayton]

For what its worth, I limewashed my flint and brick house with limewash made from hydralime - with a maximum addition of 1% raw linseed oil - some 6 years ago and it is still ok. Not bad considering 'hydrated' lime is considered by many to be the work of the devil and that flint offers no 'suction' like other substrates.