Flinting the hedgehog

[Thomobigands]

Just to add to this, I took good advice from others on a removable chimney that still works well. I don't even need anything to seal it because it's a good fit which seals itself when hot and then allows me to disconnect once cooled and everything contracts back. Sealed it with high temp sealant, bricked around it, vermicrete in between and homebrew on top, which has cracked a bit but didn't affect anything so no sleep lost.

[wolvisfamily]

Hi Thomobigands,
Good to hear from you, because I followed your thread with great interest. When you say " it's a good fit" I think I'm being a bit dense and not understanding precisely between what and what? I'll go back to your thread to check.
I'm hoping to have a stubby 500 mil stove flue fixed and insulated inside an approx 600 mm clay chimney pot , with the option of inserting another 1000 mm length of steel flue tube in the top as and when necessary. Again, sort of based on advice from the forum. Can't wait to actually get cooking!

[Thomobigands]

If you have a look at my separate chimney thread it should explain things.

ukwoodfiredovenforum.proboards.com/thread/2944/chim-chimney

I discounted the use of any kind clay pot etc myself as I was worried it would crack.

Any questions about what I did, just ask and if you need, I can probably send you the eBay links to the enameled flue and stainless steel joint section, which is used to connect and dismount the main chimney. It slides on when cold but then when heated, becomes stuck with the expansion! Hence its a good seal. Then once it cools, it frees itself again.

[Thomobigands]

How are you getting on with the build? Looks like you are not too far off now.

Are you going to add a second two pillars and arch to the entrance? I hadn't planned to originally but ended up doing so with 20 odd reclaimed bricks. I read that it gives more support to the single pillars to stop the arch pushing them out. I also thought it would protect the fire bricks from the rain a bit so they don't soak up as much water. Finally although it seems counter productive to add weight to the first arch, it means more mortar on the top of the first arch, thus reducing the failure points if that makes sense. That was my theory anyway. Plus it makes the front of the oven look like more of a feature.

I used homebrew for the second arch. Probably unnecessary but it was a last opportunity to wear the mask and goggles to scare the neighbours so I took it.

[wolvisfamily]

Hi, we are at a stage where it feels that we are almost finished, but have a few tricky things to figure out, none of which should actually interfere with the use of the oven. We still haven't cranked it up to full heat yet. I need to get my sourdough pizza dough recipe in place before then. I've had two loaves out of it with a live fire, but not yet tried clearing the ashes out and shutting the door.
We've got most of the perlite concrete on, with just a few patches where it needs to be bulked up to make the dome a little less misshapen (all these new "skills"). Good question about the second pillars and arch. I was intending to, following your build, but actually like the simplicity of what is there and wonder whether I can get away with protecting the firebrick some other way

, i.e. some sort of liquid treatment. Then we have to sort out what is happening all around the base and the apron in front. And then whether or not we are going ahead and flinting the whole thing. The debate has gone both ways; aesthetically it might look a bit odd because it will then bulge out beyond the concrete platform base, which was dictated by the narrow space available between the structure and the grass bank. So we might have to build that out too....We might even settle for putting some K rend on now for the winter and start flinting in the spring. I do want to use it over the winter if at all possible. You get the picture. In short: so near and yet so far.

[oblertone]

A slow roast turkey that's been boned, rolled and sewn into a meat 'football' is a thing of wonder; plus your main oven remains free for other goodliness !

[Thomobigands]

That sounds good! I seem to recall a post about waterproof treatment for firebricks, if you decided to go down that route.

Looking good though and with the bulk of the build done before winter.

[wolvisfamily]

Hallo again after a long cold absence.

First use of the oven after the winter, with the chimney mounted, and I'm wondering whether to add more Perlite concrete insulation. In the last firing the exterior was steaming and registering 50-60 degrees centigrade at the top of the exterior of the dome. The issue of waterproofing remains. K rend tell me that they only guarantee there product up to 35 degrees. I've got no space to build a brick enclosure, and my wife, ultimate arbiter of all things related to garden design likes the "snail/hedgehog shape" . Maybe we go back to the laborious, and no doubt tricky process of flinting it, or we find a waterproofing solution for the very fragile surface currently in situ. Anyone got any thoughts/suggestions?
Many thanks.

[wolvisfamily]

Just registered Thomobigands response from November. So sorry to have missed it. I'd be very interested in what you have found out about waterproofing bricks or the Perlite/concrete shell! Apologies for not having registered your response.

[devontiger]

wf what insulation have you got over the dome?
Normally when the dome gets hot it shoes lack of insulation.

I have a cheapy from e-b, & very little insulation.
I have added silica board to the base, & next week adding an insulation blanket to the dome, & re render over.

[jagnut]

Apr 26, 2018 13:51:55 GMT wolvisfamily said:

Hallo again after a long cold absence.

First use of the oven after the winter, with the chimney mounted, and I'm wondering whether to add more Perlite concrete insulation. In the last firing the exterior was steaming and registering 50-60 degrees centigrade at the top of the exterior of the dome. The issue of waterproofing remains. K rend tell me that they only guarantee there product up to 35 degrees. I've got no space to build a brick enclosure, and my wife, ultimate arbiter of all things related to garden design likes the "snail/hedgehog shape" . Maybe we go back to the laborious, and no doubt tricky process of flinting it, or we find a waterproofing solution for the very fragile surface currently in situ. Anyone got any thoughts/suggestions?
Many thanks.

Hi wolvisfamily check my build you will have no troble with k render just make sure that you insulation is fully dried out before applying. 

[downunderdave]

Apr 26, 2018 17:41:38 GMT jagnut said:

Apr 26, 2018 13:51:55 GMT wolvisfamily said:

Hallo again after a long cold absence.

First use of the oven after the winter, with the chimney mounted, and I'm wondering whether to add more Perlite concrete insulation. In the last firing the exterior was steaming and registering 50-60 degrees centigrade at the top of the exterior of the dome. The issue of waterproofing remains. K rend tell me that they only guarantee there product up to 35 degrees. I've got no space to build a brick enclosure, and my wife, ultimate arbiter of all things related to garden design likes the "snail/hedgehog shape" . Maybe we go back to the laborious, and no doubt tricky process of flinting it, or we find a waterproofing solution for the very fragile surface currently in situ. Anyone got any thoughts/suggestions?
Many thanks.

Hi wolvisfamily check my build you will have no troble with k render just make sure that you insulation is fully dried out before applying. 

Moist insulation won’t work too well. The remedy is long slow fires. Try to keep the fire going all day. If you see visible steam then you are going at it too hard, back off, or the expanding steam is likely to crack the vermicrete layer. A cement render is the usual solution. You need go no thicker than around 15 mm. I use random added AR glass fibre reinforcement but many use chicken wire.

[Thomobigands]

Hi, no problem I wasn't offended!

My second arch certainly keeps the rain from the firebricks so that has to be a good thing. I didn't opt for any other waterproofing in the end.

The shell of my oven is tarmac one coat render and has performed well. Couple of cracks over time but as someone else said- if you have no cracks in your oven, you are either not using it or you are lying about having cracks in your oven!

[wolvisfamily]

Thanks everybody, It looks like I may have to build a second arch to keep my firebrick arch dry, and then look at what is the best render solution. Absolutely see that I need to get it truly dried out before I can take that step, and that will depend on the Great British Weather. I think we've got lazy because it kind of works already. This was our last proper session, on Christmas Eve. But now we need to get it right, and try to protect it from the elements with something other than a lash up of tarpaulin.