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Post by Thomobigands on Mar 16, 2017 14:19:33 GMT
Hi,
Currently in the middle of building a 36inch Pompeii oven – only up to plinth level so far but hoping to crack on now. Currently about to order bricks and other items through Kilnlinings but I wonder if any of you would be able to plug the gaps in my knowledge before I order. I have separated the questions so feel free to comment on one or all of them!
Mortar:
Big debate on this I see! I like the ease of airset from a tub (do I add water to the Kilnlinings stuff or is it literally ready to go in the tubs?) but understand the limits of this re joint thickness, heat curing etc. My conclusion so far is to perhaps use pre mix air set to bond the bricks, filling in the wider gaps at the back of the dome bricks with refractory concrete/castable. The alternative is homebrew, which I can presumably use exclusively as long as I try and keep it away from the very inside of the oven? Following on from this, at what point in the landing do you stop using the airset ie if the very front of the landing doesn’t get hot enough to cure the mortar, it wont ever set? But then you don’t want to use standard mortar too far into the oven! Do you all just avoid this problem by using home brew? Have never worked with Lime before so all the warnings scare me a bit!
Entrance:
I intend to use refractory castable to pour an entrance arch. Does anyone know how to mix this up please? Any idea how much I will need and/or what else I need to mix it with? I am also thinking of pouring it into the wooden form, around my ceramic chimney to join the two in one go – bad idea?
Sorry, lots of questions but any help, gratefully received.
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Post by dave36 on Mar 16, 2017 18:46:05 GMT
Hi, Currently in the middle of building a 36inch Pompeii oven – only up to plinth level so far but hoping to crack on now. Currently about to order bricks and other items through Kilnlinings but I wonder if any of you would be able to plug the gaps in my knowledge before I order. I have separated the questions so feel free to comment on one or all of them! Fire brick cutting: Planning on purchasing a small hand-held angle grinder but have never used one before. How easy is it to create some of the intricate triangles and keystones needed for parts of the build? I cant see how I can hold such small pieces steady safely whilst making the cuts by hand – any thoughts, tips? Mortar: Big debate on this I see! I like the ease of airset from a tub (do I add water to the Kilnlinings stuff or is it literally ready to go in the tubs?) but understand the limits of this re joint thickness, heat curing etc. My conclusion so far is to perhaps use pre mix air set to bond the bricks, filling in the wider gaps at the back of the dome bricks with refractory concrete/castable. The alternative is homebrew, which I can presumably use exclusively as long as I try and keep it away from the very inside of the oven? Following on from this, at what point in the landing do you stop using the airset ie if the very front of the landing doesn’t get hot enough to cure the mortar, it wont ever set? But then you don’t want to use standard mortar too far into the oven! Do you all just avoid this problem by using home brew? Have never worked with Lime before so all the warnings scare me a bit! Entrance: I intend to use refractory castable to pour an entrance arch. Does anyone know how to mix this up please? Any idea how much I will need and/or what else I need to mix it with? I am also thinking of pouring it into the wooden form, around my ceramic chimney to join the two in one go – bad idea? Sorry, lots of questions but any help, gratefully received. I can chip in on only one of these... cutting bricks - I found the fire bricks tough to cut. Bolster and hammer is doable (and for those better at DIY than me, am sure it's easier than I found). I tried and didn't get a great finish, but depending on how you're cutting may not matter (rough edges on outside are fine as get covered by insulation / render etc) In the end I used a diamond cutting disc (255mm) on sliding compound mitre saw (one designed to accommodate brick cutting) which works well (after a quick brick soak) BUT brick dust is not good for you. See downunderdave's comments on my build post for more details of the health risk (I did the cutting outside, with a mask and holding my breath whilst cutting!). A 255mm blade will (just) cut through a standard 60-64mm fire brick, rather than having to flip it to cut all the way through). Sorry, this is becoming a ramble - in short - I'd recommend a sliding mitre saw with a diamond disc and look after your health. It's a smoot cut, so no concerns re your fingers. |
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Post by Thomobigands on Mar 16, 2017 18:59:21 GMT
Thanks! Am thinking I might hack away with a bolster and chisel for the dome-as you say, most cuts can be hidden. Then my finances will only stretch to a small angle grinder so will have to do the more detailed cuts with this. Note what you say about health though. Thanks for the advice.
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Post by downunderdave on Mar 16, 2017 20:38:37 GMT
The homebrew mortar is suitable for the whole lot. Some builders like to lay the edges of the bricks together on the inside so there's no gap at all. Because it works ok for large joints, unlike the air set, you can use it to backfill from the outside.
Regarding lime, just don't get any in your eyes. The lime is also tough on your hands, use a good barrier cream first and if you still have problems with dry flaking skin, use rubber gloves. Handle the stuff with your trowel (that's what it's for) rather than your hands. If using an angle grinder and diamond blade get a 5" one rather than a 4" because it has a deeper cut, and wear a respirator.
Castable refractory only needs the addition of water. Quantity you require depends on your design, but as you want the thermal mass in the dome it is preferable to keep the entry and its arch lighter and therefore thinner, because it acts like a heat sink.i'd be surprised if you'd need more than one bag.
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Post by Thomobigands on Mar 16, 2017 21:02:45 GMT
Thanks for the reply downunderdave. I like the fact the homebrew will do everything so that is the way I am going to go I think and I'll just have to be careful with the Lime.
See what you are saying about the entry arch acting like a heat sink - I hadnt thought of this but makes sense. I think I'll scale down my plans of casting a large, eyecatching entry arch for perhaps a simply slab type design.
I dont suppose you know what the mix ratio will be for the castable refractory and water? I have seen some posts talking of adding an activator?
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Post by downunderdave on Mar 17, 2017 19:42:32 GMT
I dont suppose you know what the mix ratio will be for the castable refractory and water? I have seen some posts talking of adding an activator? I just add water until it comes to a stiff mix. I've not heard of any other activators, but there are accelerants or retarders that you can add. I've found if you use the manufacturers recommendation for water addition it's still too dry. Others have also reported the same result. Start by mixing up a small batch as the stuff goes off very fast. I use chilled water in hot weather to give me more working time. It achieves full strength in 24 hrs so no need to damp cure for a week. |
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Post by Thomobigands on Mar 18, 2017 7:17:36 GMT
Thanks downunderdave, although doing a bit more research I am going off the idea of casting my entrance as people are saying that the refractory castable needs to be fired to complete the process. I imagine that it will get warm/hot during eventual use but not nearly the same as firing it. I wonder if I should just give brick arch building a go like most people do.
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Post by downunderdave on Mar 18, 2017 9:00:49 GMT
Thanks downunderdave, although doing a bit more research I am going off the idea of casting my entrance as people are saying that the refractory castable needs to be fired to complete the process. I imagine that it will get warm/hot during eventual use but not nearly the same as firing it. I wonder if I should just give brick arch building a go like most people do. Castable refractory relies on a chemical bond from the calcium aluminate cement unfired. When fired to over 1000C it becomes even harder and relies then on the chemical bond of the materials in much th same way as fired clay. Commercial WFO's that are cast from castable refractory are generally unfired and are perfectly serviceable. Because they rarely exceed 550 C they are never truly sintered or "fired". Casting is way quicker and will also allow you to produce a much lighter/thinner entrance which will be less of a heat sink which sucks heat from the inner oven. It also allows you to do compound curves with ease, something that's very difficult with bricks for the flue gallery. Others may have different views, but you're the boss. Dave |
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