21st and 22nd September. Another Cotswold Conservation Board lime mortars for beginners course, again held at the Ebworth Centre in the Cotswolds. By the efforts of another 6 wonderful students a little old one up one down stone cottage moved a little step along the road to recovery. We still have a way to go with much pointing and stone repair remaining to be done, whilst inside we are very close to having all the plastering close to completion.
Notes to the course:
Lime mortar mixes…………1 part lime putty to 2.5 parts sand ( however the sand was actually a mix of half sharp Cotswold sand and half Cotswold stone dust)
for some of the stone repair inside I made a mix of loam and quicklime to make an earth mortar similar in strength and character to the mortar used in the house construction.
The interior plastering that is being repaired is rather thin; it being a pretty low status building, however it is worth saving whats possible.
One beauty of lime is its versatility; the same mix being used for the pointing was being used for the plastering.
The pointing was pretty technical and, to be honest was more to do with stone repair and tile stitching than pointing but we did get a little straight forward pointing done.
The main points to remember in pointing as in all lime work is the timing; after the mortar has been troweled into place there is a period of waiting whilst it firms up enough to be tidied up, this will usually involve pressing in the pointing to compact it, which increases its strength and closes up any shrinkage cracks that often form, after this compaction it is normal practice to brush the surface to reveal the aggregate – avoiding any brush marks.
Of course, we had to mention hydraulic lime, and we used a bit of Breckweg NHL2 mixed with the same blended sand/stonedust at the same proportions as above.
I know some folks are turning away from hydraulic limes (and some have never been users) but its out there and can’t be ignored, I have been using this Breckweg NHL2 for a few weeks and I am fairly impressed – its initial set is not too rapid and its final set doesn’t appear to be too hard – although some might have other ideas – we all disagree a lot of the time!
(I added a bit of confusion after having been mixing lime putty and sand together by suddenly springing on the group some ready mixed mortar, after some explanation I think I managed to convince them it was just the same as what we had been mixing ourselves.)