Simple lime plastering task

[michael]

I’ve never tried lime plastering before, I’ve always had it done by specialist tradesmen, however, I want to save some time and money by tackling a small task by myself and I would be grateful for some advice.
I’ve recently cut a channel in an old lime plastered wall for a light switch and associated cable and I want to backfill it. The channel is about 30mm deep by 30mm wide and runs from the switch up to the ceiling
I was planning on backfilling it with two coats of lime plaster, the first coat a mix of lime hydrate or lime putty with well graded sand in a proportion of 1 to 3 and then finally a finish coat.
Seeing this is quite a small but elongated hole, do I need any hair in the first coat? How deep should the first coat be and how long should I leave it before applying the finish coat? My last question is, what is the mix for the finish coat?

Many thanks

 

[fjpdesigns]

I wouldn't bother about hair at all unless your channel is down to laths. The top coat is usually a 2:1 mix of fine (silver) sand and lime. Jewsons sell it as kiln dried sand. Just make sure you wet the wall well before plastering, but wait till the water has soaked in before starting work. I usually leave the scratch coat to dry completely before top coating. This is dependant on the temperature in the room, but usually about two to three days. You can put the finishing coat on before the scratch coat is dry but you may get some cracking. If you do, just press over the cracks before the plaster has dried. I would be tempted to use three coats as the channel is so deep. The finishing coat should be about 4-5 mm. The first two, using well graded sand 3:1 could be about the thickness as eachother.

 

[michael]

Many thanks fjp

 

[michael]

One other question fjp. Is the finish coat of 2:1 mix of fine silver sand and lime good for filling fine cracks in lime plaster or are the usual ‘off the shelf’ ready mixed white fillers better for this?

 

[fjpdesigns]

Depends on the size of the crack. If it's a hairline crack then I would use a proprietory filler, or just lime wash over it.







.

 

[Wheathills]

For any Lime Plastering 'wannabees' we are hosting a Lime Plastering Course for SPAB at Wheathills in April. We have run them for several years now and they have proved to be very popular. This page gives a good idea of what to expect and the different aspects of the course:
http://www.wheathills.com/pages/lime_plastering_april.aspx

 

[Feltwell]

Wheathills - Looks very interesting, but is it suitable for beginners? Your web page makes no mention, but the SPAB site seems to indicate that it is more a "conversion" course for those used to gypsum plastering, and it isn't suitable for those without existing trowel skills.

I'm not a total beginner and could well be tempted to go, but I certainly couldn't describe myself as an accomplished plasterer.