Lime plaster

[dmcquade]

Hi,

I am having a go at rendering a holiday home with lime. I am currently putting on the scratch coat (first time I've plastered) using St Astier NHL. All seems a bit like a black art and exact information is hard to come by. Everyone uses the same old well rounded statements, like don't use to much water! How much is too much, how much is too little? If you try to put on the wall too dry and it will not spread, too wet and it falls off. I now know when i take a trowel full from the mixer and put in the bucket the noise and the spread of the mortar as it drops tells me if it is right.
Use a well graded sharp sand - you try and find one that matches the specifications quoted on the internet for particle size, shape, void space and silt content! I plagued every sand supplier in ireland for sieve analysis and none matched exactly.
Should you use hydraulic or non-hydraulic limes - each side swears theirs is the best. I went for NHL as it is easily transported, stored and mixed.
Problems i have noticed are a few small cracks in the scratch coat. I have floated the side of the porch just to see the result, i got one small hairline crack (crazing), however, if you try to rub this out the next day with a float; because the aggregate is so coarse you mark the finish by dragging larger particles over the surface. Will limewash cover any hairline cracks that appear?
I have included some pics for reference. As you will see the house is mostly new with only one room of an old stone cottage remaining. Some will be horrified i used plastic windows - but then again i like them!


http://putfile.com/pic.php?pic=5/13608092264.jpg&s=f5

http://putfile.com/pic.php?pic=5/13608082691.jpg&s=f5

http://putfile.com/pic.php?pic=5/13608061383.jpg&s=f5

 

[Ian Bond]

The pics came out OK then.

Which strength of NHL are you using just out of interest? I used an NHL5 mortar for my roor ridge repairs.

The thing I like about non hydraulic lime is the extended working time, and the fact you can chuck the stuff that you didn't get 'round to using back in a sealed tub ready for the next job. It helps me (a very amateur plasterer) no end, as there's less waste and more time to 'improve' the finish.

Mike Wye does a good demo DVD / Video of building with lime, including rendering and lime washing. The rendering in the vid is with non hydraulic lime,

http://www.mikewye.co.uk/mikeprices.htm#video

The limewash should cover hairline cracks - but don't lay it on in too thick a coat as the wash itself will crack.

Ian

 

[dmcquade]

Hi Mike,

Thanks for the help with the pics. For the scratch i was advised to use NHL 5 and for the float NHL 3.5. I would gather up the droppings at the end of the day, knock them up and use them to daub out hollows on the stone part of the building to try and reduce waste.

Thanks.

David