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33 inch cast homebrew Kent

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  • 33 inch cast homebrew Kent

    I've done my base and I was going to make a start on the floor today as my 32 firebricks turned up yesterday afternoon, unfortunately they turned up damaged, looks like the delivery company dropped the pallet smashing every brick, then they've re-wrapped the pallet to hide the damage.
    While I'm waiting to sort out the replacements, I have a couple of questions for
    david s, or indeed anyone who wants to jump in.
    I'm going to build a 33" cast dome and aiming for 60mm wall thickness, what thickness do you think I should make the gallery and flue, would 40mm be about right?
    Also, I'm using pumice and rockwool as my insulation, (it's free), I won't have any vermiculite but I want to do my flue like David's with the three tabs in an oversize hole packed with vermiculite to allow for expansion. Would pumice do the job? in my mind the answers no because there's no give.
    I will be adding photos as I go but I want to make a bit of a start first so the posts don't drag on for months.
    Attached Files
    Last edited by hughjamton; 07-11-2020, 01:04 AM.

  • #2
    Murphy's Law. FYI, Rockwool is not the best material, due to it compresses easily, reduce insulation value and very water absorbent. It cannot be used under the floor bricks because it is too soft. So your choice. I cannot tell you what ratio to use with the pumice but leaner is better as far as insulation value but too lean is not strong enough to support the oven. Here is a chart for perlite/vermiculite cement that gives you some info but not apples to apples so you may have to experiment. Click image for larger version  Name:	Vcrete K values.JPG Views:	0 Size:	159.3 KB ID:	425751
    Russell
    Google Photo Album [https://photos.google.com/share/AF1Q...JneXVXc3hVNHd3/]

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    • #3
      Originally posted by UtahBeehiver View Post
      Murphy's Law. FYI, Rockwool is not the best material, due to it compresses easily, reduce insulation value and very water absorbent. It cannot be used under the floor bricks because it is too soft. So your choice. I cannot tell you what ratio to use with the pumice but leaner is better as far as insulation value but too lean is not strong enough to support the oven. Here is a chart for perlite/vermiculite cement that gives you some info but not apples to apples so you may have to experiment. Click image for larger version Name:	Vcrete K values.JPG Views:	0 Size:	159.3 KB ID:	425751
      Thanks for replying Utah, I'm using thermalite blocks under the floor with about 35mm of 5/1 pumice directly under the bricks, and a skim of sand to level the bricks.
      I intend to coat the homebrew dome in 40mm of 10/1 pumice, 75mm of rockwool bats, firmer than loft insulation, then a further 50mm of pumice over weldmesh, then a final render.
      I know David s recommends a thinner gallery than the dome, I wondered if 40mm would be about right? I don't think pumice would be suitable for an packing around the flue for expansion, I was hoping David would confirm either way.

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      • #4
        FYI, Perlite has a K value of 0.031 were volcanic rock K values run from 0.5 to 2.5 so perlite is 16 more thermal efficient than pumice at the best end of the scale.
        Russell
        Google Photo Album [https://photos.google.com/share/AF1Q...JneXVXc3hVNHd3/]

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        • #5
          Originally posted by UtahBeehiver View Post
          FYI, Perlite has a K value of 0.031 were volcanic rock K values run from 0.5 to 2.5 so perlite is 16 more thermal efficient than pumice at the best end of the scale.
          Hi, I was kindly gifted 120 kgs of pumice by a member on here.
          I have, along with my partner, taken early retirement, we are living off of our savings until my pensions kick in in 3 years time, she thinks the oven is an unnecessary expense, I'm out to prove I can do a reasonable job for minimum cost.
          Out of necessity this will be a budget build, therefore it would be foolish not to adapt and use the pumice, around the dome I'm going to have 90mm of pumice with 75mm of rockwool sandwiched in between.
          The base will have 100mm thermalites and at least 35mm of pumice under the fire bricks, maybe more once I've crushed it all and I see how much it looks like then.
          So far I've built the base for a touch over 100, I'll gout and take a picture of the base and post it in a minute.

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          • #6
            Click image for larger version

Name:	base.jpg
Views:	268
Size:	75.2 KB
ID:	425772 The other side is a mirror image, except there's a step down so it's taller.
            I'm going to render it leaving the brick arches exposed.
            There's a central wall giving me a log store back and front.
            I've got to drill some drainage holes yet and I'm toying with the idea of making a "disc" of waterproof mortar for the thermalites to sit on raising them above the outer base slightly.

            Comment


            • #7
              Originally posted by hughjamton View Post

              Thanks for replying Utah, I'm using thermalite blocks under the floor with about 35mm of 5/1 pumice directly under the bricks, and a skim of sand to level the bricks.
              I intend to coat the homebrew dome in 40mm of 10/1 pumice, 75mm of rockwool bats, firmer than loft insulation, then a further 50mm of pumice over weldmesh, then a final render.
              I know David s recommends a thinner gallery than the dome, I wondered if 40mm would be about right? I don't think pumice would be suitable for an packing around the flue for expansion, I was hoping David would confirm either way.
              Pumice is a good insulator and although it has a higher thermal conductivity than vermiculite or perlite, once you start mixing cement with it the resulting material will have a similar insulation value. It absorbs water at about the same rate and takes about the same length of time to dry out again. Not sure how big your lumps are, but if mixing it with cement I’d be crushing it so the stuff will pass a 1/4” sieve, but don’t overdo it and take it all down to powder. You want plenty of grains containing air.
              Not sure why you want to put weldmesh in the middle of your insulation layers because steel is highly conductive and also extremely hard to form over a compound curve.

              If you keep the mix fairly lean, say 5:1 around the flue pipe it will be sufficiently strong to support the pipe at the same time as having a little flexibility to accomodate the flue pipe’s expansion.It will then have much the same characteristics of a vermicrete brew.

              Regarding the thickness of the flue gallery, thin means reduced strength, but also reduces the heat sink effect of it. I made mine as thin as I dared because of this, also to reduce overall weight and use of expensive material (I use proprietary castable refractory and reinforce it with stainless needles). I’ve gone down to less than an inch in some places, but also have buttress reinforcing. If you are doing homebrew I think you’ll be fine with 40 mm.

              That's a pity about those firebricks. My initial thought was that you could cut them in half and still use them to build a brick dome by placing the broken edges to the outside. But that will be no good for a floor where you need full unbroken bricks. With luck they'll replace them and tell you to keep the busted ones. That's happened to me a couple of times as it costs them more to freight them back.

              Click image for larger version  Name:	P6160027.jpg Views:	0 Size:	116.4 KB ID:	425775 Click image for larger version  Name:	P6160029.jpg Views:	0 Size:	184.0 KB ID:	425776
              Last edited by david s; 07-11-2020, 01:57 PM.
              Kindled with zeal and fired with passion.

              Comment


              • #8
                Thanks for replying David, I was going to use weldmesh over the rockwool because its stiffer than chicken wire so I thought it would help to stop excess compression.
                I'm not looking forward to crushing 120 kgs of pumice I must admit. I might put a little bit through my garden shredder and see what happens.
                How thick do you think I should do the cast for the gallery, at the moment it's going to work out at about 35mm?

                Comment


                • #9
                  As I said, I made mine as thin as I dared and discovered a weak point at the shoulders, so I added the buttressing which works really well. Another option which also makes the casting and moulding much easier is to do it like this. Instead of using brick sides you could precast some thinner sides set them in position and cast the top section over them.or do them all separately and mortar the three sections together.
                  Click image for larger version  Name:	P6060733.jpeg Views:	0 Size:	337.5 KB ID:	425781
                  Last edited by david s; 07-11-2020, 01:44 PM.
                  Kindled with zeal and fired with passion.

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                  • #10
                    Ha ha, you edited your post as I was typing, never could type fast.
                    I'm going to cast the gallery, I like a challenge, I'm going to set the flue back a bit as well.
                    I'm waiting for the brick supplier to get back to me, but your right, the delivery was almost as much as the bricks.

                    Comment


                    • #11
                      Originally posted by hughjamton View Post
                      Click image for larger version  Name:	base.jpg Views:	8 Size:	75.2 KB ID:	425772 The other side is a mirror image, except there's a step down so it's taller.
                      I'm going to render it leaving the brick arches exposed.
                      There's a central wall giving me a log store back and front.
                      I've got to drill some drainage holes yet and I'm toying with the idea of making a "disc" of waterproof mortar for the thermalites to sit on raising them above the outer base slightly.
                      That's a good idea, no that's an excellent idea. When you lay the thermalite blocks some slightly wider unmortared gaps between their sides would also help water elimination, but don't overdo it, you don't want to encourage sucking cold air up from the supporting slab either.
                      Last edited by david s; 07-11-2020, 01:55 PM.
                      Kindled with zeal and fired with passion.

                      Comment


                      • #12
                        Originally posted by david s View Post

                        That's a good idea, no that's an excellent idea. When you lay the thermalite blocks some slightly wider unmortared gaps between their sides would also help water elimination, but don't overdo it, you don't want to encourage sucking cold air up from the supporting slab either.
                        Waterproof mortar disc done with drainage channels, still got to drill some holes through the base. Click image for larger version

Name:	IMG_20200713_081153108_HDR (2).jpg
Views:	275
Size:	35.0 KB
ID:	425872

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                        • #13
                          [QUOTE=david s;n425774]



                          "That's a pity about those firebricks. My initial thought was that you could cut them in half and still use them to build a brick dome by placing the broken edges to the outside. But that will be no good for a floor where you need full unbroken bricks. With luck they'll replace them and tell you to keep the busted ones. That's happened to me a couple of times as it costs them more to freight them back".

                          Hi David, you were right, they don't want the broken bricks back, trouble is every brick is damaged, I might get the odd corner for a cut, maybe 4 or 5
                          Is there any point in crushing them and including them in the homebrew mix, I don't mind the work crushing them, I've just crushed 40 square metres of concrete slabs for hardcore with a 4lb hammer, but I don't want to waste my time if there's no benefit.
                          By the way, anyone in the U.K., the brick supplier, Vitcas, have been very helpful, the damage wasn't their fault, it was the delivery company.
                          I spoke to Vitcas yesterday and they've arranged delivery for today.
                          They were also the cheapest but like all the UK suppliers the delivery cost is a killer.
                          I think I've accidentally discovered a way to get a discount from them, I didn't get it, I was offered it too late, I don't want to shout it out in case they read the forum and stop it but if people want to PM me I'll let you know.

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                          • #14
                            I’m sure they’d be saleable to a brick oven builder because the bricks are normally cut in half. I’ve crushed up insulating firebricks to add as an aggregate to make an insulating mix, but I wouldn’t even contemplate doing it with dense firebrick.
                            Kindled with zeal and fired with passion.

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                            • #15
                              Originally posted by david s View Post
                              I’m sure they’d be saleable to a brick oven builder because the bricks are normally cut in half. I’ve crushed up insulating firebricks to add as an aggregate to make an insulating mix, but I wouldn’t even contemplate doing it with dense firebrick.
                              I don't think they'll be saleable, they are really damaged, you'd struggle to get one undamaged half brick with 4 good corners.
                              I might try one of the bits to see how difficult it is IF, and only IF, it would be of any benefit in improving the performance of the homebrew, if you don't think it will I'll give them to my mate who's going to rebuild his bbq.
                              Talking of crushing, the pumice is a nightmare, it'll take me years to do it by hand, one 30mm piece at a time. It goes through my garden shredder ok but after passing it through 3 sizes of sieves I get about half the amount back kind of 10/12mm, about a gallon bucket of 5mm, and a bit more than that of dust, I loose about a third of the bulk I start with, most of that turns to dust.
                              some of the 10/12mm I'll use on top of the thermalites, I'll use the dust mixed with Portland to bed them on, and some dry under the firebricks to level them.
                              I could pass the larger bits through again but I think I'll get mostly dust.
                              I've got three more sacks to do but I don't think I'll end up with enough of a useable size to do the amount of insulation I want so I'll probably end up getting some perlite as well.

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