Friday, 27 January 2012

Hemp Lime Plaster - use with Rubble Sandstone

Hemp lime plaster (above) with damp patches (September 2011)
Hemp lime plaster being applied (April 2011)

I am monitoring progress on our new hemp lime plaster walls in the "extension" this week. The old walls had been mistreated and sealed with almost neat cement render in places. They were re-plastered by Andy Lawson of Limecraft in the Spring of 2011 dubbing out with hemp & lime supplied by Womersley's and then plastering in several coats up to 50mm thick. The basecoat was finished with Special Fine Finish lime plaster supplied by Rose of Jericho.

In hindsight it would have been better to use an intermediate coat with a finer grade of hemp or haired lime, as the walls are very uneven, but it certainly has "character". The walls have taken a long time to dry out compared with haired plaster (over 9 months) and this has been variable even though the substrate was prepared in the same way. Some damp patches were evident about a metre above the floor level, unrelated to rising damp. The central heating has now drawn the damp through the wall internally with resulting patches of efflorescence on the surface of the painted plaster.

This week, following Nichola Ashurst's recommended treatment for efflorescence when damp walls are drying out, I have dry vaccumed the patches of efflorescence and have re-painted the walls with casein distemper supplied by Rose of Jericho. At the moment it looks fine and the visible damp has gone. It's going to be interesting to see if we get the damp returning when the heating goes off in the spring, especially if there is a temperature inversion and the building "sweats". Lime is so forgiving - I love it. The spare tub of lime finishing plaster can be used indefinitely for patch repairs when the children whack the walls!


  1. Experience makes people, professional in their field. After having this article, i realize that you have a deep knowledge about plastering technique as well as various plaster work.Plaster wall finishes

  2. Hi, I have recently rendered one of the wall in our house (An old chapel in Cornwall) with lime plaster. It looks very much like the picture above taken in Sept 2011. It did seem to dry well initially but since we moved in and started lighting the fire regularly it seems to have developed what seem to be random large dark patches, which I assume is damp penetrating the wall. My walls are about 2ft granite so I assume it may take a long time to draw all the moisture out. - Do you know if you can you apply casein distemper over the darker patches, or do they have to dry fully first? - they are not wet to touch. Any info you may be able to share would be appreciated!

    Many Thanks

    1. Hi Doug, I did paint the walls with casein distemper whilst they were still damp, and it dried out uniformly, without any problems, but it took over 12 months. You could check with the supplier of the distemper what they recommend, but as casein distemper has a short shelf life, I would risk it. Bear in mind that with the amount of rain we have had over the last few months, that we are seeing a great deal of penetrating damp. Lime is not a panacea to all damp issues, if there are other defects. If you have also pointed the outside of the building with a lime mortar and have removed all potential sources of damp (leaking gutters, etc.) then it can take up to 12 months for the building to fully dry out. During the spring & summer months try to ventilate the building really well, especially as you are having fires rather than using central heating. Interestingly, I find that the walls still absorb moisture and a temperature inversion (i.e. warmer outside than inside) has also on the odd occasion created temporary patches of "damp" but they have been short-lived.