About to start build.

[daimo]

Hello, I'm daimo and I've been wanting to build a pizza oven for several years. With Covid downtime and having finished tiling the bathroom floor I'm up for a new challenge.

I've been researching construction and where to find the cheapest materials for a few weeks now and about ready to push the button but thought it would be good to get some advice before I go down the wrong path.

I'm a roofer so have good construction knowledge and have lots of building materials down our yard, price is KEY and would prefer to upcycle where possible.

Plan
- 1mx1m base due to space constraints
- Planning to build permanent plinth/stand but want the oven to be transportable on it own base as follows:

-1mx1m wood frame clad with timber 22.5-25cm hight
-Plywood or OSB base with 60mm layer of hardcore/vermiculite mix
- 10-20mm sand to smooth layer
-60mm layer of beer bottles gap filled with sand
- 30mm sand
- 64mm 40% alumina fire bricks dry laid in oven area with normal bricks outside oven area

Dome
Was thinking about going the whole vermiculite/excercise ball route but my research has concluded the vermiculite layer is the insulation layer and necessarily a good refractory layer/appropriate layer for the fire flame to lick. I light of this and the fact I have tons of sand to make a dome former, I was thinking about heatproof screed so need input on this design.

- Sand/newspaper former
- layer of heatrpoof screed c25-30mm
- layer of 25-50mm vermiculite/non-refactory cement (will the screed be enough to protect the normal cement in the mix or would I need ceramic blanket between as I don't want the added expense of buying refractory cement?)
- 25mm ceramic blanket
- normal sand, sharp and cement render as I'm guessing the vermiculite and blanket layer will be insulating enough to not need refractory cement?

- hoping to make the entrance chamber/arch from a normal bricks and normal cement mortar and terracotta 4-6" inch chimney pot/flue I should have in the yard.

With all shipping and taxes this currently sits around £210 as I have all the base/arch materials and keen to keep the price sub £250.

Fire away with any advice or flaws in my design.

Thanks in advance.

[downunderdave]

Apr 30, 2020 12:59:34 GMT daimo said:

Hello, I'm daimo and I've been wanting to build a pizza oven for several years. With Covid downtime and having finished tiling the bathroom floor I'm up for a new challenge.

I've been researching construction and where to find the cheapest materials for a few weeks now and about ready to push the button but thought it would be good to get some advice before I go down the wrong path.

I'm a roofer so have good construction knowledge and have lots of building materials down our yard, price is KEY and would prefer to upcycle where possible.

Plan
- 1mx1m base due to space constraints
- Planning to build permanent plinth/stand but want the oven to be transportable on it own base as follows:

-1mx1m wood frame clad with timber 22.5-25cm hight
-Plywood or OSB base with 60mm layer of hardcore/vermiculite mix
- 10-20mm sand to smooth layer
-60mm layer of beer bottles gap filled with sand
- 30mm sand
- 64mm 40% alumina fire bricks dry laid in oven area with normal bricks outside oven area

Dome
Was thinking about going the whole vermiculite/excercise ball route but my research has concluded the vermiculite layer is the insulation layer and necessarily a good refractory layer/appropriate layer for the fire flame to lick. I light of this and the fact I have tons of sand to make a dome former, I was thinking about heatproof screed so need input on this design.

- Sand/newspaper former
- layer of heatrpoof screed c25-30mm
- layer of 25-50mm vermiculite/non-refactory cement (will the screed be enough to protect the normal cement in the mix or would I need ceramic blanket between as I don't want the added expense of buying refractory cement?)
- 25mm ceramic blanket
- normal sand, sharp and cement render as I'm guessing the vermiculite and blanket layer will be insulating enough to not need refractory cement?

- hoping to make the entrance chamber/arch from a normal bricks and normal cement mortar and terracotta 4-6" inch chimney pot/flue I should have in the yard.

With all shipping and taxes this currently sits around £210 as I have all the base/arch materials and keen to keep the price sub £250.

Fire away with any advice or flaws in my design.

Thanks in advance.

The inner dense dome needs to be at least 50 mm thick for both adequate strength and sufficient thermal mass to balance with your floor bricks. You can use a castable refractory, but it is expensive. A cheaper alternative is to use the homebrew mix, but you need to add the burnout fibres to reduce the possibility of steam spalling during the water elimination stage. A proprietary dense castable refractory usually has these already in the mix. If using the homebrew you should add the burnout fibres and the casting should be damp cured for a week. Thereafter another week should be left for it to dry before covering with insulation.

[daimo]

Thanks. I was thinking about the refractory layer last night and was scared the screed would crack under firing/drying as it's expensive stuff and could only really afford 40kgs of the stuff.

I was doing some reading on the forum yesterday and did come across the homebrew mix. Could you please tell me the ingredients, ratios, cheapest place to purchase and quantities.

I take it I can then proceed with my intended layers of vermiculite, ceramic blanket and render?

[oblertone]

Homebrew is a mixture of Sand/Cement/Lime/Clay in the ration 3-1-1-1 by volume. The first three can be had at any builders yard, the powdered clay can be more tricky but kiln Linings (amongst others) can supply it, as can potters etc. 

The only flaw in your plan I can see would be the use of a terracotta chimney section for the flue. This will be subject to intense heat rather than the cooled exhaust gases from a fire which have travelled up a chimney or metal flue; I'm not saying you can't use it, but expect it to crack if you do.

ps - As a roofer you may have access to clay tiles which I used to create the arch entry to my oven (see link below) from #30 for the arch.

[daimo]

Hello, thanks for the advice.

Should I use builders sand or a fine sharp?
I gather I need hydrated lime over quicklime as that reacts with water?
Normal Portland cement or is it worth buying some refractory/alumina cement?
Will something like a HV powdered ball clay from Clayman supplies do? What clays provide the least Shrinkage?

is the sand element the grog in the mix and is this the element which reduces shrinkage? I see some people use crushed fire bricks as grog. I gather this improves the refractory properties of the mix but if I swapped out 1 part sand for 1 part crushed fire brick would I increase the likelihood of shrinkage?
I can't see your link.

[downunderdave]

May 1, 2020 22:10:24 GMT daimo said:

Hello, thanks for the advice.

Should I use builders sand or a fine sharp?
I gather I need hydrated lime over quicklime as that reacts with water?
Normal Portland cement or is it worth buying some refractory/alumina cement?
Will something like a HV powdered ball clay from Clayman supplies do? What clays provide the least Shrinkage?

is the sand element the grog in the mix and is this the element which reduces shrinkage? I see some people use crushed fire bricks as grog. I gather this improves the refractory properties of the mix but if I swapped out 1 part sand for 1 part crushed fire brick would I increase the likelihood of shrinkage?
I can't see your link.

The fine sharp sand will make the mix more workable although either will do. Sand can turn to glass at around 1200C , but as our ovens only go to around half that, it is not a problem, sand is a cheaper option than grog.. shrinkage will be the same. The powdered clay will add the refractory properties required. Use hydrated lime and Portland cement. Do not replace the Portland cement with calcium aluminate cement because when married with lime it is further accelerated and it’s working time is already very low..

[oblertone]

Link might not display if you're using a phone, try this:

www.fornobravo.com/forum/f6/mobile-pompeii-not-purists-20752.html

[daimo]

Thanks, Dave.

I understand the homebrew mix is a trade off between economy and performance. I don't mind spending a bit more money modifying the mix if it increases performance.

How would a mix of:

Sharp: Sharp: FB grog: Powdered clay: Alumina cement

Perform against:

Sharp: Sharp: Sharp: Powdered clay: Portland cement: Lime

Would my proposed mix have poor workability as removing the the 1 part lime increases the grog portion of the mix (sharp/FB grog) to 60% and I've read increasing the grog portion over 50% can destroy the plastic qualities of the clay? If so, can my mix be modified or does anyone have a better recipe? Apart from the fire bricks and the vermiculite insulation layer I pretty much have everything so don't mind spending c£100 on the refractory layer if the homebrew mix can be improved up to this figure (internal diameter 700mm)?

OB, great idea, we have thousands of reclaimed/new clays at our yard. Enjoyed reading your build.

[downunderdave]

Yes, that mix sounds a lot better, but I don’t know how it would work and neither will you until it’s tried and tested. Qualities like shrinkage and workability are guesswork until tried. Another alternative is to use a proprietary dense castable refractory which will have had years of testing and also will include the burnout fibres that you will need to add if you make your own mix. The mix should be able to pass the “ball up” test. Ie make a ball around the size of a cricket ball and toss it 2 ft into the air. If the consistency is ok you should be able to catch it intact.
Ther is another consideration re calcium aluminate mixed in that they begin to react as soon as you add water and sometimes will be hardening before you’ve had time to place it all. Being very temperature dependent, chilled water can extend working time. The upside is that it reaches full strength in 24 hrs so no extended damp curing required, although I always keep it damp for 2 days. The homebrew requires damp curing for at least a week.

Regarding the clay, for our required temperatures any powdered clay is ok, bricklayers clay from builders supplies or ball clay from a potters wholesale supplier. Avoid bentonite because of the extremely small particle size it has high shrinkage.

[daimo]

When you talk about proprietary castables, are you talking about the castable concretes the likes of kiln linings sell? If so, aren't these like a wet mix concrete poured into a mold and not formable round a dome shaped former?

Also when you talk about ball clays, is this a type of clay or the state the clay comes in? Does ball clay come powdered and the ball part refers to its type or does it mean it comes in a lump like the modelling clay you used at school? I take it I'm after a powdered clay?

So, if you've got sharp, normal cement, alumina cement, powdered clay, fire brick grog and lime at your disposal, how would you make your homebrew for longevity?

[downunderdave]

May 3, 2020 14:05:01 GMT daimo said:

When you talk about proprietary castables, are you talking about the castable concretes the likes of kiln linings sell? If so, aren't these like a wet mix concrete poured into a mold and not formable round a dome shaped former?

Also when you talk about ball clays, is this a type of clay or the state the clay comes in? Does ball clay come powdered and the ball part refers to its type or does it mean it comes in a lump like the modelling clay you used at school? I take it I'm after a powdered clay?

So, if you've got sharp, normal cement, alumina cement, powdered clay, fire brick grog and lime at your disposal, how would you make your homebrew for longevity?

Refractory suppliers have many different castable products. contact them, tell them what you are doing and they will advise the most suitable product. You need a dense castable though, not an insulating one. The product I use is both gunnable (spray) and trowel-able.

Ball clay refers to the method of crushing it up. It is put through a ball mill and comes out powdered.

3:1:1:1 by volume sand, portland cement, hydrated lime, powdered clay.

Making your own castable with calcium aluminate cement is an unknown/untested recipe. Do not mix lime with calcium aluminate cement as it will accelerate the already short pot life of a mix that contains calcium aluminate cement. If making your own mix do add the fine polypropylene burnout fibres.

[daimo]

So I've just spoke to someone at castree kilns and they weren't very optimistic about homebrew.

I asked them about their 1400c dense castable and it can be troweled. As my main concern is durability I'm happy to use a dense castable over a homebrew mix as the cost isn't extornionate.

A few questions:

1. Is the Clayman supplies pizza dome calculator transferrable for dense castable as it calculates c70kg of clay for for a dome of 700mm dia./50mm thick or do I need more?

2. The guy at castree thinks I can do away with the vermiculite layer and go dense castable > 50mm ceramic blanket > render to achieve pizza oven temperature. Do you guys agree?

3. I could save c£20 from making the hearth out of dense castable instead of firebrick. What are the pros and cons of this? Is it too hard to work with to get the smooth surface you need for the peel?

[downunderdave]

May 4, 2020 16:02:11 GMT daimo said:

So I've just spoke to someone at castree kilns and they weren't very optimistic about homebrew.

I asked them about their 1400c dense castable and it can be troweled. As my main concern is durability I'm happy to use a dense castable over a homebrew mix as the cost isn't extornionate.

A few questions:

1. Is the Clayman supplies pizza dome calculator transferrable for dense castable as it calculates c70kg of clay for for a dome of 700mm dia./50mm thick or do I need more?

2. The guy at castree thinks I can do away with the vermiculite layer and go dense castable > 50mm ceramic blanket > render to achieve pizza oven temperature. Do you guys agree?

3. I could save c£20 from making the hearth out of dense castable instead of firebrick. What are the pros and cons of this? Is it too hard to work with to get the smooth surface you need for the peel?

Home-brew will work for the dome but is not suitable for the floor. Neither is un-sintered castable. It may be rated to 1400 C but it needs to be evenly, slowly and carefully fired to over 1000C for this. You won't be able to do this in your oven. The best solution for the floor is loose laid firebrick.
Some folk have rendered directly on to the blanket, but as it's springy it is difficult to render against as well as compressing the blanket at the top where the weight will squash it down reducing its insulation value. As it's also a bit lumpy a 10:1 vermicrete or perlcrete about an inch and a half thick over the complete dome provides a firm substrate to work against, restoring the perfect hemispherical form covering the lumps and bum[s of the blanket, as well as providing additional insulation. Allow about a week for it to dry though as it contains lots of water. Get a bit more castable than you'd think because its volume reduces around 20% once you mix it with water. Don't mix too much in one go as it goes off really fast. If it's a hot day use chilled water.

[oblertone]

Make the floor from storage heater blocks, loads on eBay and even Freecycle (when it's back up and running).

[daimo]

I've looked at storage bricks but eBay is a bit dry down here in Surrey, I either have to travel 100mi for cheap bricks or take 3 pack heater bricks for £25 so proper clay fire bricks @ £2.10 is still the best option.

Dave, you've made several ovens and looking at your website had commercial success. How should I build my oven with the materials at my disposal listed?

- hardcore
- ceramic fibre board
- fire bricks
- dense castable over sand dome former
- 25mm ceramic blanket (as you recommended vermiculite layer figured can reduce the thickness as easier to apply layers on thinner blanket and vermiculite will provide lost insulation)
- vermiculite/cement mix
- render