Substrate for lime render

[Howard Ogden]

I am shortly going to be lime rendering my partly renovated house and wondered whether there was any alternative to using a stainless steel metal lath. I am told that galvanised lath would be corroded by the lime. The lath will be fixed to timber battens over a Tyvek membrane. The house was originally weatherboarded over studs with brick infill but suffered the consequences of a cement render over everything including the sole plates on the inside. (There was not much left)I am tempted to weatherboard again but as the adjoining renovated property is rendered this is the preferred route. The reason for the search for an alternative to stainless is purely cost driven!
Any ideas??

 

[Mark]

people generally avoid using metal laths because it has very different expansion properties to the plaster. It is probably cheap though ?

Traditionally use wood laths, although reed/bamboo are being used successfully now. try searching this forum for plastering ceilings - thats where most people come up against laths so the solutions they use will be applicable.

 

[MdB]

http://www.mikewye.co.uk/reedmattech.htm
I've no idea how good it is.

 

[CHRIS]

I have seen both the products and they look good,

http://www.celenit.com/home_en.asp

http://www.skanda-uk.com/heraklithProducts.htm

both these are avalible from certain popular "Eco builders places" or from the distributors (you may pay less). you should be able to plaster straight on to these boards and have a breathing wall construction.

 

[Howard Ogden]

people generally avoid using metal laths because it has very different expansion properties to the plaster. It is probably cheap though ?

Traditionally use wood laths, although reed/bamboo are being used successfully now.

Thanks Mark. I hadn't heard of using wooden laths on the outside. I'd only, in my very limited experience, come across them on inside stud walls. Metal Laths are about £5-6 a sheet for 2500mm by 700mm. Stainless ones are £50- £60 for the same size; hence my original question re using a lime mortar on galvanised metal . ie will it really erode the metal and how long would the render last for?

 

[MrT]

When I stripped the lime render off the wall in one of my bedroom the galvanized metal
boxes for the light switches, sockets showed no sign of erroding. I can olny suppose the risk is in the drying period. I can't see a problem with galvanized metal. Perhaps the risk are
are greater with moisture problems and corrosion of the metal via water.

 

[skier-hughes]

Both my lime supplier - limegreen in Much Wenlock - and my electrician told me not to use galvanised but stainless due to corrosion.

 

[MdB]

I've just pulled two extremely corroded socket boxes off the wall but they were fitted into cement in a damp wall. My guess would be that moisture is more of an issue than the lime but I could be wrong.

 

[Nemesis]

Wattle and daub... that's the traditional way of rendering where timber studs are involved surely?

 

[MdB]

Half our neighbours have or had plaster and lath inside and out over a wooden frame (1850 ish sort of age). Older properties have cob walls but I don't know of any with wattle and daub. I guess it depends on the area you are in.

 

[Nemesis]

Yes - that's really an updated version of wattle (woven) means of attaching the mortar.

Metal lath came much later. I think that there migbt well be issues with glavanised, given that it could get damp in this situation.

 

[Howard Ogden]

Thanks for the replies. Everything has it's price! I'd really like to use a lime render, stainless lath will come to approx £2000, galvanised would be £200. Now what would the difference in cost be between lime render and cement based render? - is this the point where I duck out of firing range! Would anyone be able to give me suitable spec for wooden laths ie dimensions, spacing etc. how do you cope with returns into window openings etc etc? Thanks

 

[Gervase]

Sawn laths will be expensive for a whole house at 9mm spacings (and don't even think of the cost of riven oak or chestnut :shock: ). In your situation I'd use reed mat on 2x1 tanalised battens at 600mm centres, with battening around window and door reveals 'feathered' with a chisel or adze to take the plaster.

 

[Howard Ogden]

Thanks Gervase. That sounds like a much more realistic proposition. By 'feathered' I assume you mean keyed or similar. I do have some laths from the property that I guess could be used around window and door reveals if this would be preferable. Any recomendations for suppliers of reed mat?

Out of interest I contacted lime-green.co.uk who were very helpful and mentioned a product called Heraklith. Not a traditional raw material as such but a breathable, insulating woodwool board capable of taking a lime render and meeting all the ecological criteria. ???

 

[Gervase]

Heraklith is good stuff, and will certainly boost the insulation, but it does cost considerably more than reed mat. I get mine from Ty Mawr, but other suppliers like Mike Wye will almost certainly sell it.
And try the Period Property Shop at the top of this page!

 

[Howard Ogden]

This is all proving very informative - great forum and thanks for all the input.

Next question:- has anyone any tips for (external) lime rendering on Heraklith?

The property is in a not particularly exposed area of Essex flatland - so firstly should I use Hydrated or Hydraulic lime?

Apart from the weather proofing aspects and breathability this is a timber framed property and I guess I can expect some movement.

The finish will probably be a limewash.

How many layers should I expect to need on Heraklith and what consistency etc etc.

Thanks

 

[sue gazzard]

Hi Howard, Did you get anywhere with this? I am currently going through the same process of trying to find a solution that is affordable but kind to my old timber-framed/wattle & daub building. With 200sqm to do the stainless option just looks too expensive...and the insulating properties of Heraklith sound v appealing...hope to hear from you, thx, Sue

 

[DaveBrigg]

Gervase, your link to Ty Mawr had an 'i' missing, and goes straight to the Labour Movement for Europe! I wouldn't like to say how they are rendered...
If anyone is still interested in the reed option, they line the roadside around here and can be collected for free. You just need someone to turn them into mats.

 

[Schoolmarm]

Howard hasn't logged on since May 2007.

 

[Nemesis]

There's always the chance that he has enabled the e-mail bit which gives a message when a new post is made to the thread.