|Plastering with gypsum is obviously different from rendering with sand and cement|
When doing ‘conventional’ works to buildings it is a clear distinction of trades between internal and external works. This is because there is a difference in some of the materials used and also because there is a large enough market to have specialist firms doing one operation or the other.
In the lime world, it tends to be that people do both rendering and plastering. This is driven by the fact that the materials used can be much more similar. Most people will use a NHL Hydraulic lime for both internal and external works.
If you look for a Lime Render course you will generally find one day courses that cover both plastering and rendering as well as everything else lime!
Given that plastering and rendering courses are normally at least two years long it seems a bit much to expect people to be able to render and plaster with lime after a couple of hours. Maybe this is why lime can have an application issue attached to it. After all lime is a much less predicable material than cement and gypsum.
Having seen the boys from Welsh Lime Works doing a very professional job on my house you realise that that there is no substitute for experience and knowledge. There have been a number of key points in the work where you just know that someone who has just done internal lime plastering would have made some fundamental mistakes.
Welsh Lime Works are keen that their workmanship and knowledge that has been built up over the years is not shared carelessly, so if you want any info I would recommend getting in touch direct with them. http://www.WelshLimeWorks.com. However I think that it is fair to say that the key points around door and window reveals, wall corners and floor junctions are where their work stands out and will pass the test of time where others may well fail. Not to mention the issues around potential lamination of the render. All of these key factors require a professionals eye and years of experience in order to get right. So it has been fascinating seeing the process, the method of application, the changes in mixes, the subtlety in timings etc.
So if you have been on a lime plastering course be very aware that applying lime externally is very different from doing the same internally. The effects of the weather, temperatures, orientation and the various pressures on the fabric due to the use of the building all need to be taken into account if the job is to be a long lasting and high quality one.