I have spent the last couple of days on a lime plastering course in Bedford. I am learning this skill so I can deliver more retrofit services to the customers of www.ecoalex.com. One of the key ways to improve the energy performance of older houses is to add internal insulation to walls. There are lots of people offering this service with celotex and other oil based insulation materials. These are very efficient and applicable in many more modern homes, however they do require careful installation of vapour barriers in the walls and have a risk of condensation. I want to be able to offer my customers something a little different, Natural Insulation. This will enable be breathable and allow moisture to pass through it naturally rather than gathering hidden inside the construction of the wall. After talking with a vegan customer I have been looking at wood fibre insulation in batts and boards. To get all this finished properly it needs plastering, modern plaster sets solid and isn’t breathable so I have been learning to work with lime.
There is a resurgence of interest in lime plaster at the moment, partly because of heritage projects like St Pancras station and partly because of a renewed interested in it’s flexibility and breath ability. This meant there was a choice of a few courses, however a lot of them were quite rural and a good distance from London so I chose DIY plastering in Bedford and I am very pleased I did. The course was one to one so I got plenty of help from Paul and could have it tailored to my requirements.
When I got there Paul had prepared two walls, one typical brick one and a second much flatter one to simulate the type of wall I am building using wood fibre insulation. After checking my fitness we agreed to try and plaster both walls so I could tackle any different lime issues. I started with the masonry wall applying two guides across the wall that would cover all the bumps and undulations and produce a flat surface. I then filled in with plaster and used a straight edge to get the plaster flat and even.
Then we left this to dry and I moved on to the flatter surface set up to simulate wood fibre board. Here I applied a much thinner coat of plaster, embedded some mesh in it and then a second thin coat. This was then flattened using the straight edge. Only 10-15mm of plaster are needed as the base wall is so much flatter than an older brick wall. Once these two walls had dried a little I went over them with a float, flattening the surface and adding some roughness for the skim coat. That was day one completed.
Day two was all about getting things smooth, very satisfying it was too. After drying overnight both walls had developed some cracks, especially the masonry one where we had a much thicker covering of plaster. Many of these could be sealed again with the floats but the larger ones needed a bit more compression from the trowel and some extra plaster adding. Next we added the top coat of plaster, this had more lime and less sand to make it smoother, but went on the same way using a trowel. Once the wall was covered with an even layer of topcoat we left it to dry. During this time Paul gave me a quick tutorial in filling holes in walls, very useful for my bathroom wall. Then I went over the wall with a float to even out the plaster further.
After this and some more drying I went over it with a trowel to get it even flatter and remove the air bubbles. It was all very pleasing to produce such a flat surface. At this point you can keep going making it flatter and smoother gradually using the trowel and the float. Looking forward to using the skills on an insulation project next month in Hertfordshire, get in touch if you would like me to help you with your house. I am based in Central London but can travel. There are lots more photos on my Google+ page.