Today I took an infared temperature reading on the exterior of my home; it was around 5:00pm on the western side where it soaks up the late afternoon sun….this is typically the hottest time on the inside of my home.
The reading was as follows:
~ area with Lime Plaster = 93 degrees
~ area with painted cinder block = 115 degrees
* cinder block is painted with a light grey/blue exterior paint (a ‘cool’ color)
The proof is in the pudding….white colors reflect solar energy. Lime Plaster is a simple method and extremely affordable. The production of lime is a method which consumes less energy and has a smaller carbon footprint than concrete/portland cement (stucco). With a little practice, anyone can apply a lime plaster. The plaster is very slow curing and ‘forgivable’ (unlike concrete plaster/stucco)…so no need to be in a huge rush while applying. And the icing on the cake is that lime plaster is a beautiful finish and leaves you with a bright, crisp, pure look!
If the surface temperature differs by 22 degrees in the middle of a Charleston August, then I can only imagine how much difference this might make with the internal heat gain my old house experiences in the late afternoon. Hmm…I think I’m going to have to keep going with this! Plastering the south and west walls would be a good passive solar cooling technique for hot weather places such as in the south where I live.
Here’s how to do it:
~ buy a bag of hydrated type S lime from your local masonry supply store (and yes, they will scratch their head and look at you like you are weird for wanting lime)
~ buy or dig up sand; mason’s sand works well….you will need 3 times the amount of lime you have
~ hydrate the lime in a bucket with water (be sure to cover) and let soak for 2 or 3 days
~ when ready to plaster, mix 3 sand: 1 lime. (this is a rule of thumb…..make samples!)
~ mist the surface with water where plastering will occur, then coat with 1/8″ thick layer of plaster.
~ smooth plaster as you go, smoothing out cracks; mist curing lime frequently. shade area from direct sun for several days and mist daily for 3-4 days
~ if a 2nd or 3rd coat is desired, sponge 1st layer as it’s curing and apply next coat when 1st layer is not completely dry, but also not flaking or moving
Be sure to pick up a nice finish trowel, it can make all the difference in the world!