Final layer on Rocket Mass heater

Hello there,

It’s my first post here and I’m glad to see that natural building is spreading everywhere

I had a question concerning last layer of plaster on Rocket mass heater: I would like to use pigments in clay plaster or lime plaster but I have no experience in this, is there anything to know or any specific documentation that could help me to finish our dragon...

Here is a picture of it, it’s in a straw bale house in Kosovo.

Thank you in advantage

Hi Alexandre;  Big Welcome to Permies!

Very nice looking rocket you have built! And in a straw bale house !  
We would love to see a few photo's of your house as well as your rocket!
Regarding your question;  There are finishes like you are wanting . However I am not knowledgeable enough about them, to recommend any.
There are others here who are and hopefully one of them will respond to your questions.

Alexandre Korney wrote:I had a question concerning last layer of plaster on Rocket mass heater: I would like to use pigments in clay plaster or lime plaster but I have no experience in this, is there anything to know or any specific documentation that could help me to finish our dragon...

A simple and straight forward documentation that has worked for me:  clay plaster recipe
As for adding colours, I have found that for the best vibrancy, you can't beat the cement pigments. Not a lot is needed and there are quite a few colours to choose from.
I have tried food dyes before and found the colours to be really unnatural and gaudy looking.
Sorry, no experience with lime yet.
I've tried some crushed charcoal in my last batch. It turned out to be quite chalky (without wheat paste) and the colour turned out greyish blue.

Look for natural pigments from pottery studios. They tend to have the most variety and the best prices, online purchasing tends to be expensive. As Gerry said, cement pigments can work as well. My finish clay plaster is a simple recipe I got from the talented Sigi Koko and I have used it as the finish for my entire house.

4 qts water
7.5 qts white kaolin clay
16 qts masonry sand sifted
1/2 cup pigment
1 qt wheat paste

makes about 5 gallons

You will notice this has no fiber in it. It is a finish plaster and needs to go on thin. Make sure whatever pigment you use stays under 15% of the binder (clay), or it will dust. I try to aim for 10% normally. The above recipe has 12.5% pigment to binder ratio.

More photos! Looks beautiful.

Personally  I am a fan of using cement plaster but not cement dye as it is expensive and not particularly effective .
Cement is so desperate to turn white that over time it seems to get its own way and defeats the dye, so I am a fan of paint!
I find exterior house paint will last for many years even in quite tough outdoor environments.
For really hard wearing places like floors, i will coat the paint with water based varnish and re coat every few years otherwise I find good quality exterior house paint will last for up to 10 years.

Waouh thank you so much for all your answers.

I think we will use earth plaster and pigments. As it is what we have the closest to our house (clay is digged out 1m from the house. But does the pigment loose a lot of color on earth plastering ?
Here are few pictures of the house. It is a block house that we are renovating to be an example of how you can turn a « conventional » house into when it comes to natural building.

beautiful work! That is a wonderful looking project and quite the inspiration.

Earth pigments won't be quite as bright if you are using a local clay that has a darker color. Kaolin is pretty bone white and so the pigments tend to be warmer then using local clay that tends to make the color cooler. Do a few experiments and see what you come up with. You can do a 7.5% up to 15% pigment ratio and apply them directly to the bench you built. I usually reduce the ratios so that I have about 2-3 cups worth of pigment so I have a big test area. You won't need to bother with wheat paste in the sample as you will just cover them anyhow.

on our bench I just used some nut oil that sealed the bench and clay. I did not use any pigment but you could put a layer of pigment clay on top and seal it with the oil?
I bought 5L but actually only used maybe 1 or 2L max