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Post by dave36 on Mar 8, 2020 17:28:11 GMT
“Plain old perlite/Portland” mix is a poor choice IMO for two reasons. Firstly it will not provide the thermal mass required of a WFO. This means you will not be able to hold high temperatures in the dome easily because as soon as you let the fire die a little the temperature will drop quickly. You will also be unable to do any retained heat cooking because there will be insufficient thermal mass to hold the amount of heat required. Secondly, the perlite/Portland mix is not very strong and will be subject to bumps and abrasions from tools and feeding wood into the oven. In addition Portland cement does not stand up to direct flame impingement so longevity is a big question. A far better solution is to use a dense refractory castable or fire brick. As these are both expensive, if cost is an issue, a homemade castable can be mixed yourself using the homebrew (3 parts sand, one part each of Portland cement, hydrated lime and powdered clay by volume). The lime takes over from the Portland as it fails as the temperature rises and the clay provides some refractory characteristics. This brew is not quite as good as a proprietary dense castable refractory which uses calcium aluminate cement, but it’s streets ahead of Portland/perlite. Better to save your perlite to insulate over a dense material. If weight is an issue a dense castable with walls 50 mm thick is sufficient to provide required strength and the required thermal mass but way lighter than a 4” thick brick dome. Hi all. Can I please resurrect this thread to ask if anyone has made home brew from clay instead of clay powered? I have some terracotta red clay left over the build and would prefer to avoid buying powdered unless I have to. I can cut it into very small pieces if particle size is important. Any experience or thoughts gratefully received. Dave Ps- if more background helps, I am building a new inner arch to push the door against. I doubt I can just use sand / clay mix as I suspect it would sag / take ages to dry ie I want something that I can cast (and would prefer not to spend a load of money on castable refractory plus postage). Sorry, An add on question if anyone has any views - I was planning on adding some steel mesh (think chicken wire but in squares) inside the new inner arch to help keep it together (if a couple of parts of it cracks, hopefully won’t collapse with wire in it). Am aware steel and home brew have very different thermal expansion properties...is this a good idea or a bad idea? Dave |
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Post by downunderdave on Mar 15, 2020 12:15:48 GMT
“Plain old perlite/Portland” mix is a poor choice IMO for two reasons. Firstly it will not provide the thermal mass required of a WFO. This means you will not be able to hold high temperatures in the dome easily because as soon as you let the fire die a little the temperature will drop quickly. You will also be unable to do any retained heat cooking because there will be insufficient thermal mass to hold the amount of heat required. Secondly, the perlite/Portland mix is not very strong and will be subject to bumps and abrasions from tools and feeding wood into the oven. In addition Portland cement does not stand up to direct flame impingement so longevity is a big question. A far better solution is to use a dense refractory castable or fire brick. As these are both expensive, if cost is an issue, a homemade castable can be mixed yourself using the homebrew (3 parts sand, one part each of Portland cement, hydrated lime and powdered clay by volume). The lime takes over from the Portland as it fails as the temperature rises and the clay provides some refractory characteristics. This brew is not quite as good as a proprietary dense castable refractory which uses calcium aluminate cement, but it’s streets ahead of Portland/perlite. Better to save your perlite to insulate over a dense material. If weight is an issue a dense castable with walls 50 mm thick is sufficient to provide required strength and the required thermal mass but way lighter than a 4” thick brick dome. Hi all. Can I please resurrect this thread to ask if anyone has made home brew from clay instead of clay powered? I have some terracotta red clay left over the build and would prefer to avoid buying powdered unless I have to. I can cut it into very small pieces if particle size is important. Any experience or thoughts gratefully received. Dave Ps- if more background helps, I am building a new inner arch to push the door against. I doubt I can just use sand / clay mix as I suspect it would sag / take ages to dry ie I want something that I can cast (and would prefer not to spend a load of money on castable refractory plus postage). For the clay to play it’s part in the homebrew mix it needs to be evenly distributed. This requires very smal particle size. Clay in a plastic or hard state requires some processing to make it workable for a castable mix.It must be broken into lumps no bigger than a fist and to be allowed to dry completely. It can then be crushed and sieved. This takes considerable time and effort without specialised equipment, but can be done. Personally I’d prefer to buy a bag of powdered clay. |
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