Render - Lime Putty or NHL3.5 mix?

[Tom]

What should I use to render my house when I come to re-do it? It's built with Blue Lias, with Ancaster quoins. The walls are 2' thick, rubble infill.

At the moment it's covered in cement render and I'm in the process of removing it. Another winter with this stuff on will be worse than a winter without anything on! I plan to re-render it in lime next year, probably in the autumn. Am I right in assuming that I should re-do it using Lime Putty? That's what I used inside...I got it in tubs from Mike Wye's. Or would I be better using a mix made with NHL3.5? The only reason I ask is that the house is detached and quite exposed and gets a battering from the weather on all sides. Will Lime Putty be up to the job? I'm not bothered about a little penetrating rain (I don't want to live in a sealed box anyway!!) but I don't want whatever I put on to fail, particularly as it's going to cost quite a lot to do. I'd be grateful for any advice. Thanks.

Jaqy

 

[charlie-ia]

good question Jaqy!
we'll probably end up keeping our cement render. the regulars on here seemed to think that the non hydraulic lime was the stuff to use to mend the render with.

i did get the impression somewhere that the hydraulic limes stood up better in complete renders for exposed areas. is that right? we definately get plenty of weather up our little mountain so id be interested to know more too

 

[Moreteyne]

We re rendered our 6 storey windmill a few years back, we had the same dilemma. I would go for the 3.5 NHL if you are exposed. If you are near the sea or mountains I may even go higher. The lime putty is great but not for exposed areas.

( Will get shot by the loony limeys for that quote ) :lol:

 

[Gervase]

If it's exposed and you're just rendering rather than going for roughcast or harling, then NHL3.5 is probably going to be your safest bet.

 

[Tom]

Gervase, sorry to be a bit slow in this area but, can you explain the difference between render, roughcast and harling, please? And, is one better than the others in certain situations? Is it a regional thing? Or is it just down to preference? Thanks

 

[Nemesis]

I'd read up a bit more on the differences between hydraulic and non-hydraulic before you make up your mind.

In general, non-hydraulic lime is pretty robust stuff, especially if regularly limewashed. Not sure why people think it isn't.

Hydraulic has the advantage of a quicker set as it's chemical - but also harder and that isn't always an advantage, as with cement.

http://www.spab.org.uk/html/advice/technical-qas/technical-qa-1-dealing-with-inappropriate-cement-renders/?PHPSESSID=3aaf24d33a1fbc1d6e2ad3229d7246d3

 

[MdB]

Harling coat is a slightly watered down mortar which is chucked(*) onto the wall using a harling trowel.

It produces a thin layer of lime mortar which sticks well onto lose surfaces such as cob and is good as a base coat for the other layers to stick to. It ends up looking like pebbledash which has been painted over (ish).

I'm not sure what a roughcoat is. I'm sure somebody will explain.

(*) this is a technical lime term which takes years of practise to learn to do properly. At least the couple of goes I had on the lime course did a good job of covering my boots rather than the wall..

 

[Gervase]

Roughcast - known as harling in Scotland - is where coarse aggregate and lime are mixed as a slurry and dashed against a wall which has been dubbed out and given two or even three base coats. In Scotland and Ireland strongly hydraulic (NHL5) limes are used, whereas in England and Wales non-hydraulic or feebly (NHL2 hydraulic limes) are used. The finished effect is similar to pebbledash, but much softer in texture. It gives excellent protection against weathering and penetrating damp because of the hugely increased surface area the aggregate gives.
Render is simply lime and sharp sand. Again, traditionally non-hydraulic lime was used, but this was given an annual coat of limewash. Given that few people are today prepared to limewash the entire exterior of their house every 12 months, many builders working with lime will specify NHL2 for everyday render or NHL3.5 for exposed positions on the basis that they will be limewashed every three years or treated with a breathable clay or silica paint.

 

[Nemesis]

I know the National Trust has been experimenting in the Lake District with lime render, and using limewash with I think linseed oil or wax (certainly not just plain wash) and has found, I understand, that it has stood up very well and didn't need annual recoating.

It's pretty exposed and it might be worth calling and asking what they did and why.

If I can remember any more I'll post about it!

 

[charlie-ia]

has anyone heard of "scutch"? (any spelling you like, or a word that sounds like it?)
the external walls that arnt cement rendered are covered in so many flaking layers of different stuff, its hard to tell what they were pointing at.

 

[Nemesis]

http://www.tooled-up.com/Product.asp?PID=3600&MAN=Faithfull-Scutch-Combs-box10-1in-Pre-Packed

Maybe what they mean?

 

[Nemesis]

Tallow I think - this is interesting though about the Romans leaving it seven years (although whitewash and limewash are not the same).

http://www.lake-district.gov.uk/index/understanding/archaeology/limekilns.htm

 

[Gervase]

I've found that, for longevity, tallow seems the best additive. Where I've used tallowed limewash on render it's lasted the best part of three years, and on stone for at least two. Linseed oil has been OK, but exposed parts have needed a touch-up after 18 months or so.
The tallow does cut down a bit on the breathability (though not significantly) and has a tendency to encourage algal growth which can lead to your sheltered parts going a bit green (oer, where's Brunhilde?). Both it and the linseed oil react with the lime to 'saponify', effectively forming soap-like molecules which help bond the wash to the substrate.
If you have the time/nergy/cash, the more thin coats of limewash or whatever flavour you put on at the beginning, the better. The exposed west wall of our place, which used to suffer terribly from penetrating damp, had seven coats of linseed oil limewash and a topcoat of tallowed wash, and looks as good as new after two years exposure to the winds of wild west Wales blowing straight in from the Irish Sea. The first time I treated it I used just three coats of plain 'vanilla' limewash, and that proved to be very poor - weathering badly on the edges and allowing some penetrating damp in the middle of an upstairs wall. There was also a problem with lichen re-establishing itself and 'blowing' the limewash. So off it came and on went a biocide, followed by the multi-coat treatment.
To be honest, it was a wall which really ought to have had a roughcast finish, but I liked the detailing of the window arches and thought I'd persevere with just limewash and plenty of it. And, so far....

 

[Gervase]

When I lived in Suffolk 'kutch' was the word used for the creosote-like liquid that nets were dipped in to stop them rotting before polypropylene came along.
A scutch-comb or scutch-hammer is used for dressing surfaces to get rid of rough bits, cement and plaster.

 

[Gervase]

Traditionally, tallow limewash was made by adding grated tallow to the mix as the lime was slaked, so the the heat generated and the bubbling steam encouraged it to mix well with the lime.
You can make tallow limewash with putty, however - provided you can get hold of a boiler. Put the tallow (from your local butcher) through a coarse mincer and, as the putty is mixed with the boiling water, mix it in bit by bit using an electric paddle mixer. For a plastic dusbin full of wash I used about a pound and a half of tallow (well, a chunk the size of one and a half packs of butter!). It's much easier with an extra pair of hands to help.

 

[Nemesis]

It's all complex! It's a matter of suck it and see in many cases. I don't think our ancestors had all this angst - they used what was near.

I know that Wordsworth House in Cockermouth was limewashed with that rather nice pinky red and that seems to have lasted well - I don't think it's been redone since re-opening in 2004.

Sorry - posted this in another thread too - but good pics!

http://www.visitcumbria.com/cm/wordhse.htm

 

[Gervase]

Nice pictures, and nice to see the gentle weathering of a coloured limewash. Of course, that pinky red was one of the boons of the same industrial revolution that so dismayed the Romantics - the ochre and red tints were valuable by-products of iron-ore processing.

 

[Nemesis]

The whole house has been done with care and sensitivity - it's somewhere I know well (although sad that no longer can you have a NT cuppa there).

The kitchen is particularly interesting - restored as a working kitchen and used, although the wall oven is a cheat - for H and S purposes it's now ye olde electrified!

The fire is cooked on though, a simple Geo range with all the bits n pieces.

 

[Ian Bond]

What a lovely building. And to think what could have happened to it ...

The house was a private dwelling until the 1930's. In 1937 the Cockermouth Library tried to raise the money to buy it, but then the local bus company bought it, with the intention of demolishing it to build a bus station. This gained national press and radio attention, and enough money was donated for the town to buy it back. Cockermouth handed the house to the National Trust in 1938. On June 3rd 1939 it opened as a Wordsworth memorial, becoming a Grade 1 listed building.

 

[Nemesis]

Country Life did a major feature on it last month - it was good to see it getting the publicity it deserves. That green paint by the way is on paper and is distemper.

I like Cockermouth - Jennings Brewery is an added attraction.


http://www.visitcumbria.com/cm/brewery.htm