Finishes for hempcrete - The Hempcrete Topic: Designing and Building with Hemp-lime - page 402

Plaster

Mix ra-
tio

Aggregate size Thickness of coat

Basecoat 5:2 0-2mm sand Up to 6mm (or less, as necessary to achieve an even

surface)

Topcoat 2:1 Silver sand or silica

sand

1-2mm

Render

Mix ratio Aggregate size Thickness of coat

Basecoat 5:2 0-4mm sand 10-12mm

Topcoat 5:2 (use 3:1 if you want to see

more of the sand colour in the top-
coat)

0-4mm sand (or
0-2mm for a smoother
finish)

8-10mm (for 0-4mm
sand) 4-6mm (for 0-2mm
sand)

The mixing method is as follows:

Wear appropriate PPE and follow safe working practices for mixing lime plasters (see
Chapter 9 ) .
Mix only a small amount of plaster to start with, until you get used to how quickly you
are using it up. As your technique improves and you use it up faster, you can double
the amount you mix at a time.

Measure out the lime and aggregate into buckets, e.g. 1 bucket of lime and 2.5 buckets
of coarse sand for the basecoat.
Tip both dry ingredients into the mixer and start it turning.
Leave it mixing for 5-10 minutes, as this gives the mix a more even consistency.
Add water little by little until the mix is rolling around the mixer nicely and resembles
a very thick cream. When you pull some out on your trowel it should stick to the trowel
blade when held vertically. The water takes a while to dissipate through the mix, so
adding it slowly prevents you ending up with a very wet mix.
Leave it mixing for at least 20 minutes, and leave it to rest in the mixer for 10-20
minutes before use. Double-check the consistency when you come to use it, as it may
have dried out a little and you might need to add a bit more water.
When it is ready, tip the mix into a bucket, making sure you have your goggles on, as it
can splash.