Lime rendering

[Macker]

I have checked all the FAQ's and DIY forums and can find no reference to the above subject. I live in an area, Vendee, where most of the older houses are made from limestone but I have been happily repairing various outbuildings and stonework with mortar or concrete. Some people who have been here some time said that I should be using lime (i.e a mixture of lime or 'chaux' and sand) as this allows to stones to 'breathe'. I was a bit sceptical to say the least but having since worked on some old buildings and found the main damp spots tend to gather behind lumps of concrete or mortar I thought it might be worth a try. I asked around and got a different opinion from every single person I spoke to, French and English. :Seven parts of sand to one chaux", said one. "Four parts of sand, one chaux, one concrete", said another and so on. I then tried the purist approach and used only lime and sand 7:1 with a retardant and it certainly makes for a very nicely workable mix. I repointed a whole large wall, let it dry for a few days and then rendered it. I then let that dry for a day and floated it with a wooden trowel. You can remove as much or as little as you want to reveal some of the stonework and the effect is very nice and 'rural' looking but if you run your hand over the wall it is very crumbly and unstable. My question for all you experts out there (at last) is;

A. Am I using the right mixture?

B. If so, can I use some kind of fixative before painting the wall or should I just paint it and let the paint stabilise it?

C. Any tips for getting a really nice finish on the render (the tools in our local builders merchant are mind boggling)

D. Any advice at all appreciated!

Cheers

Brian

[Ianhaycox]

I've used 5 parts sand to 1 part lime (chaux) for all my pointing. People have suggested adding white cement but personally I have found it goes off too quickly. The 5:1 mix can be left overnight then brushed with a stiff nylon brush to produce acceptable rresults with the minimum of effort.

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Virtually all mortal mixes come back to 3:1 Sand:Cement/Lime.

Adjusting the lime or cement depending on use and site conditions, but not much beyond 4:1. The sand for pointing and rendering mixes should be washed sharp sand 0/2 or 0/3mm (soft sand normally has too much loam and will crack).

I've had some real good old plasterers work for me in the past and several have said that the mixes used to be adjusted according to the sand delivered by sometimes adding a little more very fine sand. I think as far back as roman times powder was added to aid workability and set. Although nowdays I think the sand seems to be very well graded.

You could try a stabalizing solution to stop the powdering but I think I'd tend to hack it off and have another go.

2 coat work would be a first coat to eaqualize the suction on the wall, once set apply a second coat, straighten if necessary, and float with a wooded or plastic float (sounds easy). The small plastic type approx 200 x 200 mm with a triangular top work really well.

Start off with these and search the archives here on LF I'm sure you'll find lots of info.

http://www.lime.org.uk/

http://www.buildingconservation.com/articles/pozzo/pozzo.htm

http://www.scotlime.org/content/

[Kazanton]

As well as the above excellent information, I would like to add that if you do decide to paint the wall and not just leave it au natural, you must use a lime-based paint, or limewash to complete the process. Otherwise it will just be like putting the wall in a plastic bag (think damp.)

Try these links for information on lime-based paint that is available in a wide array of colours, besides just blinding white-wash white! A google search on 'lime wash' or 'lime paint' will also yield results. These are two companies I have personally purchased from. The Mike Wye site has really superior information that follows SPAB guidelines. (Society for the Preservation of Ancient Buildings) and has excellent guidesheets. Very comprehensive website. Plus they are a great bunch of people with answers to any lime question.

http://www.mikewye.co.uk/mikeprices.htm#limewash        http://www.stastier.co.uk/index.htm?nhl/data/limept.htm~rbottom

Kind regards and good luck!

[zeb]

Following on from Belinda's post, SPAB do excellent 1 day Lime rendering/mortaring courses all over the UK.

We went on one in Suffolk before moving to France a few years ago and, as well as a super lunch (!), it taught us most of what we needed to know about working with lime based products, all for £49!!

Go to http://www.spab.org.co.uk

 

regards.....helen (now a supreme being - LOL!!!!)