Lime Render

Lime render is different types of lime mortar;

• Backing coat, ultra porous. Prevents wind driven rain penetration by not having interconnected pores and draining downwards internally like a wall heart with gravity.

• Mid coat, normal lime porosity. Draws water, when possible, from the backing coat towards the face.

• Top coat, dense porosity. Prevents 'casual' rain from penetrating by creating a smoother surface for rain to run over. Allows the passage of vapour as a minimum. 

• Lime wash. Sacrificial coating that protects the other layers from erosion. Dries faster too due to the increased lime content. It's also more hygienic to apply hot lime every few years.

The ratio of lime to aggregates should increase towards the face and the size of them should get smaller. ie. 3:1 backing, 2:1 mid, 1:1 top and 1:0 paint. Sharp sand 4mm down for the backing, plastering sand 2mm down for the mid, silver sand 1mm down for the top coat.

There are obviously a lot of variations of this but ultimately you need two things; highly porous back coat and surface protection from erosion. So a minimal requirement would be an earth mortar, lime washed. I have seen a lot of old housing stock that would have  been for poor people which is just dirt out of the ground mixed with quicklime and hair, thrown on and limewashed. Hoylake is plastered using the sand out of the ground which is a silver sand. This was applied very hot and then limewashed or roughcast. North Wales is similar in that a lot of cottages are coated in the same way. I've seen decomposed Granite and slate as well as the usual sand/clay/limestone aggregates. stigious buildings in cities are more likely to have complicated coatings.

•  I suspect that contrary to popular belief that Olde Worlde Folkes would be a bit disgusted with our approach to maintenance and hygiene with regards to masonry. We never wash it anymore...