Daniel Metcalfe
architecturedesignplanning
Copyright Daniel Metcalfe 2013

Advice on Lime Render

May 23, 2014

I have recently been assisting a friend who has had some trouble with a lime rendered house. The render has been falling off in chunks and what is left is powdery and friable. This is a common problem when the render is not allowed to dry properly. Unlike cement render which cures by chemical reaction, lime has a slower rate of cure and does so by carbonation. In wet, cold conditions this can take a surprisingly long time. In dry conditions the water can evaporate too quickly and create a failure in the coat. Some professionals advocate the addition of brick dust or cement to lime render or mortar to speed up the rate of cure. However this changes the properties of the render and is often a poor solution on historic buildings. The reason why older properties use lime is that houses without modern damp proofing need to ‘breathe’. Lime render, being permeable, allows this to happen. Sealing the outside of the building with cement render would mean the damp only has one place to go - inside!

Properly applied lime render can be beautiful and practical but it must be applied by good tradesmen and looked after with fresh coats of lime wash at regular intervals.

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