First time builder. Strange/stupid oven design, advice required.

[Hattori-Hanzo]

Yes planning to do around a 22" internal oven with a mix of fire bricks and homebrew mortar.

Just reread post 10 and saw David mentioned a 5-1 mix too. Not sure where I've got 6-1 from, must be getting confused with something else
Will save the money for the ceramic blanket.

I was planning to use a 25mm ceramic blanket over the dome with a vcrete mix over the top of that. what thickness vcrete layer would you recommend over the ceramic blanket bearing in mind I want to keep the outside diameter as small as possible.

Many thanks for your time.

[david s]

Vermicrete insulating slab copy.doc.zip

One of the disadvantages of vermicrete is the large amount of water required in the mix. A third of its volume is water and it can take months to dry. Although marine ply is weatherproof I wouldn’t, be placing it under a vermicrete slab. The usual material for supporting an oven is a concrete supporting slab. If your oven is small and suitably supported underneath you should be able to get away with less than 4”, perhaps 36 mm cement sheet would work better.

[Hattori-Hanzo]

Thanks for your input David.

I've found some 100% water proof cement boards, one is glass fibre reinforced at 12mm thick.
another is dense foam base board with cement outer, again fully water proof but a thickness of 10mm

I cant find any cement boards thicker than 12mm and the cost of 3 sheets to make up 36mm will be too high.

I could add one sheet of either cement board on top of my 36mm marine ply to protect it from the moisture in the vermiculite mix.
The underside of the marine ply would be coated with a bitumen paint to protect it.

[david s]

As your planned oven is pretty small a 100mm thick base is overkill, but as long as it’s well supported underneath you might get away with your plan. The finished oven will be heavier than you think. Once you’ve built and used it you will probably want to build another one with improvements learned from the first.

[Hattori-Hanzo]

Indeed, I think this project is going to have a steep learning curve, it certainly isn't going to follow tradition Pompeii oven builds but I'd like to at least try and build it semi properly within my criteria and budget. Fingers crossed it will be successful.

I'd love to build a full size Pompeii oven but I just don't have the room or funds.

I'm curious to feel the weight of a fire brick, my plans may have to change once they are delivered

Though with the way I'm planning to build the oven I should only need around 40 bricks, plus a load of home brew.

The other side is even if the oven is not entirely successful I enjoy making things and hopefully will pick up some new skills along the way which will aid me in building a proper oven if I'm ever fortunate enough to have the room for one in the future.

Watch this space i'll keep you updated with the failings....I mean results

[Hattori-Hanzo]

Lost a bit of information in the hack but it was about the use of rock wool over ceramic blanket.

In the end after some good advice from david s I've decided to use some 25mm ceramic blanket with a Vcrete mix over the top.

[Hattori-Hanzo]

If possible could a mod move this thread to the "Other oven types" sub forum.

I'll be updating this thread as I progress with the build.

Cheers.

[Hattori-Hanzo]

Another quick questions guys.

I've tried to select the best bricks for the floor of the oven but they are slightly uneven in thickness.

When I lay them on top of my calsil board which is nice and flat the tops of the bricks are not flat.

Is there something I can use on top of the calsil board to lay the bricks perfectly flat? I worried I'll chip the corner of a brick with the peel if they are left uneven.

Thanks.

[UtahBeehiver]

A dry mix of sand and fire clay laid with a 1/2" notched trowel (like laying thinset for ceramic tile). CaSi too water absorbent to use a sand/fire clay slurry. If the bricks are only slightly raised some builders have used a belt sander or a angle grinder with diamond cup. PS thread has been moved.

[Hattori-Hanzo]

Thanks Utah.

So a 50/50 mix of sand and powdered clay should do the trick.
The brick edges are not out by miles but I'd like to try and get them as flat as possible.
I did wonder about trying to use a diamond cutter to flatten the edges but feared I'd take the nice factory finish off the brick or is this not a problem?

For the sand and clay mix, I have some play pit sand which is nearly 100% dry. Would it be better to use this instead of builders sand which has a lot of moisture.
Thinking the casi board will prefer a dryer mix.

cheers.

[UtahBeehiver]

What ever sand you got. You just can't use the wet slurry because it sets too fast on the CaSi. As far as the factory finish on the floor, after a few fire you won't know what is factory or not from the ash.

[Hattori-Hanzo]

Okay Utah that's great.
Is there a maximum thickness to the sand/clay mix? guessing as thin as possible is best?

Oh and another question I've just remembered, I'm planning to set the floor bricks loose on top of the casi board just in case I ever need to replace one.
What can I use to fill the small gaps between the bricks?

Is the sand clay mix best or is it better to just let the gaps fill up with ash?

cheers.

[UtahBeehiver]

I mentioned a 1/2" notched trowel should be good but if you are only slightly out of level a 3/8" or 1/4" notched trowel will work too.. Sand/Fire clay are not really a good insulator so just enough to level the floor and no more. You do not need to add anything between floor bricks, just dry fit and close as possible, they just fill up with ash.

[Hattori-Hanzo]

Excellent thanks again for your help.

I've also just read a build where kitchen aluminium foil was used over the casi board as a water proof layer, he was using refractory mortar to lay his bricks but I might do the same to protect the casi board a little more.

cheers