Homebrew Mix

[gream0604]

I am almost at the stage where I can start laying the Storage Heater Hearth, and then start building the vault. I have a couple of questions about the famous 'Homebrew' mix. I think after doing a lot of reading on here that I am going to us the 5:1:1:1 ratio of sand, cement, lime and fireclay. I am using soft red bricks for the vault, so I dont want it too strong if I have understood correctly?

My main question though, is what sort of sand should I be using?

Cheers

Matt

[oblertone]

Any 'sharp' sand should be ok, it's not too critical I don't think. I used a washed grey from Wickes and it worked fine on my red brick dome, although I used a slightly different ratio i.e. 3-1-1-1 for the brew.

[jspaolonzi]

Homebrew mix question.....
Read that a mix with ash included is what is used in Portugal. Anyone tried ash in the mix and was it successful?
Thank you
Joan

[downunderdave]

5:1:1:1 sounds a bit lean to me. 3:1:1:1 is what seems to be the traditional mix. It sounds rich but the theory is that if the portland cement gets destroyed by the heat and it doesn't like anything north of 300 C, then only the lime is acting as the bonding agent because clay is really just a very fine aggregate. It is just decomposed rock after all. At higher temperatures the clay will sinter (become hard and permanent), but that only occurs north of 573 C, which you are unlikely to achieve in a WFO.
So, if the portland is destroyed it also counts as aggregate leaving you with 5:1 aggregate ,lime (for the 3:1:1:1 brew. Or, 7:1 for the 5:1:1:1 brew. There is probably a good case for using a calcium aluminate based mortar for the top third of the dome which does see those portland destroying temperatures.

Don't know about the addition of ash or what qualities it would impart. It is added to some cements to increase the flow of mixed concrete. Do a search on the net and report back.


try here first

en.wikipedia.org/wiki/Mortar_(masonry)

Wood ash glazes in pottery produce some very interesting results and I've done a bit of experimenting with them .The composition of ash varies considerably depending on what's been burned. If you use it, make sure you sift it well with a fine sieve because there is usually quite a lot of unburnt carbon in it and you probably don't want that creating voids in your mortar when it burns away leaving you with a weaker mortar.