For the heat battery,, does anyone have any ideas as to why I shouldn't use a very weak portland sand concrete as opposed to clay/sand? With winter around the corner, I just don't have the time or resources to track down and transport a supply of clay, where it would seem a several bags of portland mixed with the masonry sand would accomplish much the same thing. (by very weak, I mean weak enpigh that you could almost break it apaprt with your hands once set.) Thanks.
posted 5 years ago
obviously, I will have quite a bit of gravel in it as well.
(Paul you posted a link in response to a chemical battery by mistake?)
David; concrete is destroyed over 400 degree F, your mass will not get that hot except close to your transition area. You really need clay/ cob in that area. after you are just a few feet away the temps will fall below the danger level , and you can switch to concrete if you want. Have you considered buying bags of fire clay ? Locally i can get a 50 # bag for 14.00 $ I have heard of it being as low as 10.00 a bag if you buy in quantity. Some building supply's will not know what fire clay is ... just try another supplier. I went to three before they not only knew what fire clay was, there was a pallet of it in the back room !
Mortar Clay (Fire Clay) can usually be sourced at the same location as Portland cement. Here in Tenn., Lowe's carries it for around $8 per 50lb bag. Mix it with sand and gravel, or sand and quarry fines / crusher-run, for your thermal mass / thermal bench fill.