What order do the base layers go in?

[WoodywWun]

New to the forum so I'm going to ask the stupidest question first!

During lock-down I'm constructing a wood-fired oven in the garden to replace oven cooked pizza and a poor BBQ. I've watched loads of YouTube videos and got some good but divers information on various techniques.

I've got a brick-walled stand/base in construction and I'm planning the next stage. My proposal is to have a 75 mm thick refractory concrete base, a 75mm Vermiculite concrete base and a 75 mm cooking layer made of reclaimed bricks (which I already have).

The daft question that only someone new to this could ask is what order do the two concrete base layers come in? I'm guessing that the refractory concrete base goes under the Vermiculite base? Even I can work out that the cooking layer goes on top of both!

Have I got the thicknesses of these layers sufficient? Is there any other cost-effective way of adding to this set-up or maybe doing it completely differently? I'm not intending using mortar between the cooking layer bricks but do I need a fire-proof mortar layer under them? Any suggestions for the proportions of the mixes for the two layers? Can I put chicken wire in either or both concrete layers to strengthen them or is this a no-no?

I'm going to construct a dome-shaped oven, again made of reclaimed clay brick, on the concrete base, held together with refractory concrete and with fire-proof mortar used carefully inside to plug any gaps.

Any tips, links ideas would be gratefully received!

[UtahBeehiver]

I suggest you download the cheap/free eplans from Forno Bravo. It will give you a good baseline for design and construction. Do read them and study before you get too far along with your build. They come back to the forum and ask questions that are not covered or unclear from the eplans. There are a lot of YouTube videos out there, some good, soom okay, many just plain not in the best interest of a builder.

[WoodywWun]

Many thanks for the reply.

I've downloaded the Pompeii eplan, which is very helpful. Reading through, I see that once the concrete hearth is poured and starts to cure, that FB Board can then be laid on top (over the whole area of the hearth). Later, using the Vermiculite concrete mix as an alternative insulation layer there is a picture of this pour being limited to the area under the oven. Could the FB board option work in the same way i.e. limiting it to the area under the oven and the area outside the FB Board/dome being made up to the correct height with standard concrete?

I see that my original idea to cover the entire hearth slab with fire bricks (Actually reclaimed standard clay building bricks turned frog down.) to create my cooking surface is not shown. Is the whole area not covered to keep costs down or would doing it this way somehow create a source of heat loss by conduction?

I understand that proper fire bricks are the best but are standard, clay bricks significantly poorer as a cheaper alternative? I was proposing to use them to build the dome as well.

The idea of constructing the cooking surface to fit inside the dome is one that I might look at.

Any further comment or ideas would be received, gratefully!

[UtahBeehiver]

The plans are a good baseline but dated. More current options are found on the forum. How you are doing your oven, enclosed or not enclosed? You really only need insulation under the floor and dome walls and some do the oven entry. The floor gets the most abuse so clay bricks of unknown refractory properties is a crap shoot, may work, may not so caveat emptor. Cutting to fit floor inside dome wall require a lot of work and the school of thought is you can remove a damaged floor brick if needed. That said, I have only seen one or two builds out of hundreds that require a damaged floor brick replacement. CaSi board is the most efficient floor insulation but also the most costly, 2" CaSi (min recommended) requires 4" 5 to 1 vcrete .

[Chach]

I am a big believer in using the correct materials for their intended purpose. These structures and ovens will provide a lifetime of joy and use, but if inferior materials are used or if you are using the wrong product for the job you will either have an improper working or unsatisfactory working oven. You can also have an oven that can fail prematurely structurally. Bottom line in my opinion is that these projects take commitment of time and body abuse to build so you should reward yourself by using materials that will give you the most successful outcome because that's what you deserve for taking on this type of project.

Ricky

[WoodywWun]

Thanks for your posts. The oven is in the garden so I guess that makes it "not enclosed." I did a search on the forum but no new plans popped up, unfortunately. I'm trying to source fire bricks locally here in the UK but builders' merchants don't seem to stock them. Delivery is understandably expensive online.

[WoodywWun]

...OK "enclosed" means you've built an extra structure around the oven. I've just spotted it in the glossary!

[UtahBeehiver]

Go the the Forno Bravo store site and look under "Resources" the plans are there. There are several UK builds going on now and one the the builders listed where he found materials including fire brick. Some UK builders have had used heater storage bricks for the floor. If budget is an issue you may want to consider a homebrew cast dome. I think there is at least 3 UK builders doing one right now. PS Avoid the YouTube videos promoting vcrete domes and gym balls forms. Not in your best interest. I just notice you said you downloaded the eplans in post # 3 so I don't know what you mean about "new" plans

[Hattori-Hanzo]

I'm new to WFO builds myself and am currently in the process of building a smaller oven.

I can offer a little advice from the research I've done so far but clarification from one of the veterans will confirm my post.

As I understand red clay bricks can handle the heat of a wood fired oven no problem however they can be much more susceptible to thermal shock (going from cold to very hot quickly) which can cause the bricks to fracture and crack.
The more the oven is used the greater the risk of a brick failing.

You can save some money on refractory mortar by making your own "home brew"
This consists of 1 part Portland cement, 1 part powdered clay, 1 part hydrated lime, 3 parts sand.
This mix can be used for laying bricks and filling.

You can also use this mix to "cast" an oven over a mould negating the need for bricks all together, other than for the cooking floor.
Casting a dome can be an easier and cheaper option if fire bricks are out of budget.

For insulation under the cooking floor calcium silicate board is recommended but can be expensive.
A cheaper alternative is a 5 to 1 mix of Portland cement and vermiculite.

Ceramic blanket is recommended for insulating the dome of the oven with a 8 to 1 mix of cement and vermiculite over the top.

You need to go to a refractory supplier for fire bricks as most builders merchants don't stock them.
If you're lucky enough to live close to one you can save on delivery which can be expensive as they weigh a lot.

Here are some suppliers I've found which will deliver.

https://www.castreekilns.co.uk/

https://www.kilnlinings.co.uk/index....te=common/home

https://shop.vitcas.com/products/fire-bricks.html



If you want to go for home brew, powdered clay from these.

https://www.bathpotters.co.uk/powdered-fireclay

https://www.valentineclays.co.uk/product/aa-fireclay

https://www.bluematchbox.co.uk/raw-m...=0&sort=lowest


You should be able to find hydrated lime in any builders suppliers.

[Chach]

I'm new to WFO builds myself and am currently in the process of building a smaller oven.

I can offer a little advice from the research I've done so far but clarification from one of the veterans will confirm my post.

As I understand red clay bricks can handle the heat of a wood fired oven no problem however they can be much more susceptible to thermal shock (going from cold to very hot quickly) which can cause the bricks to fracture and crack.
The more the oven is used the greater the risk of a brick failing.

You can save some money on refractory mortar by making your own "home brew"
This consists of 1 part Portland cement, 1 part powdered clay, 1 part hydrated lime, 3 parts sand.
This mix can be used for laying bricks and filling.

You can also use this mix to "cast" an oven over a mould negating the need for bricks all together, other than for the cooking floor.
Casting a dome can be an easier and cheaper option if fire bricks are out of budget.

For insulation under the cooking floor calcium silicate board is recommended but can be expensive.
A cheaper alternative is a 5 to 1 mix of Portland cement and vermiculite.

Ceramic blanket is recommended for insulating the dome of the oven with a 8 to 1 mix of cement and vermiculite over the top.

You need to go to a refractory supplier for fire bricks as most builders merchants don't stock them.
If you're lucky enough to live close to one you can save on delivery which can be expensive as they weigh a lot.

Here are some suppliers I've found which will deliver.

https://www.castreekilns.co.uk/

https://www.kilnlinings.co.uk/index....te=common/home

https://shop.vitcas.com/products/fire-bricks.html



If you want to go for home brew, powdered clay from these.

https://www.bathpotters.co.uk/powdered-fireclay

https://www.valentineclays.co.uk/product/aa-fireclay

https://www.bluematchbox.co.uk/raw-m...=0&sort=lowest


You should be able to find hydrated lime in any builders suppliers.

I'd say you pretty much said it all..Good research this should help our UK friends.

Ricky

[WoodywWun]

Go the the Forno Bravo store site and look under "Resources" the plans are there. There are several UK builds going on now and one the the builders listed where he found materials including fire brick. Some UK builders have had used heater storage bricks for the floor. If budget is an issue you may want to consider a homebrew cast dome. I think there is at least 3 UK builders doing one right now. PS Avoid the YouTube videos promoting vcrete domes and gym balls forms. Not in your best interest. I just notice you said you downloaded the eplans in post # 3 so I don't know what you mean about "new" plans

Thanks for the reply UtahBeehiver and sorry for causing confusion. It was just that you said the downloadable plans were a bit dated and that there may be more on the form.

[WoodywWun]

Thanks for the advice and links Hattori-Hanzo. I'll check all the links out as well. Fire bricks seem to come in various thicknesses, the thinnest (so the cheapest!) are 32mm (1,1/4") which I guess is thick enough?

[Hattori-Hanzo]

I think the most common thickness is 64mm for the cooking floor and dome.
Fire bricks are slightly larger than house bricks at 230x114x64mm. You can also get them in 230x114x76

42% alumina content is classed as medium duty which is standard for WFO.
I think 64% alumina is heavy duty and not so recommended, I believe they are also harder to cut.
Insulation and vermiculite bricks are to be avoided for floor and dome construction as they are not suitable.

A common practice is to cut the fire bricks in half when building the dome, this saves on cost and weight. For this reason 32mm are not used for the dome as far as I know.
You could possibly use them for the floor though again they might be too thin.


I should add you will need to add polypropylene fibres and stainless steel reinforcement needles to the home brew but I'm not sure on the quantity needed?
The fibres are easy to come by and aid in moisture removal when drying the oven.
The stainless needles are harder to come by in small quantities. These help to strengthen the mixture when cured.

[WoodywWun]

Thanks for all of the excellent posts. I'm on my way with the oven stand and will be casting the concrete top to this soon and I'm intending to do a fairly standard concrete mix with a coarse ballast/sand mix and chicken wire in it for strength.. Probably about 75 mm (3") thick. Over this will be the insulating layer, restricted to the vicinity of the dome. I'm just costing a calcium silicate board at the moment and will go for this if I can afford it or a vermiculite concrete if I can't. I'd go for a similar 75 mm thickness for this? I'll make up the depth of the concrete outside of the dome with a standard mix but probably finish it with a layer of upturned clay house bricks to make it look good.

I'll probably go to the expense of decent fire bricks for the cooking floor. However, the cast dome idea sounds good in place of bricks. I've got enough clay bricks to do the dome but can someone tell me which is best, heat-wise, moulded dome or standard 1/2 house, clay bricks?

Ceramic blanket over the dome and then a vermiculite layer over this. How thick? The finish with a "weather-proof" standard concrete final layer?

I have space for about a 900 mm (36") diameter "high" dome. Any idea of how many standard 1/2 house bricks or fire-bricks (probably out of budget) for the dome?

Any help, figures or suggestions would be great!

[UtahBeehiver]

As I mentioned before, clay bricks may or may not work. There have been some UK builds as well as one in Christchurch done with repurposed red clay bricks (old ship ballast), IE Bookemdanno did one, but I have not seen a followup. Typically house bricks will not work. A lot of interest lately in homebrew cast ovens. You have to decide.

I do not believe chicken wire will provide any structural strength to the oven hearth, Rebar is the typical concrete reinforcment. A min of 50 mm of CaSi board floor insulation is recommended which means a 5 to 1 vcrete requires 100 mm thickness to be equivalent.

Most all of this info is on the forum.