At home DIY Dome WFO

[JJPT831]

Hello from NY! I've been lurking on a lot of sites and watching videos on the DIY ovens. I was very close to doing the perlite 5111 mix ,but after reading through multiple threads here on FB I decided to do the 3:1:1:1 no perlite recipe. I'm very new to using cement and doing anything like this. I don't have a carpentry bone in my body for anything that needs precision. I think most of you will see based on my progress pics.

For the inner dome recipe I used:

Dome size 85CM ball slightly over inflated

1. Pool Sand (based on brickwoodovens.com)
2. Hydrated lime
3. Hawthorn bond fire clay
4. SS refractory needles

I under estimated the amount of sand had to stop for about 7 hours until I could run to the store.

Questions

1. I under estimated the amount of sand and had to stop for about 7 hours until I could run to the store. After 7 hours I finished applying the mix to the entire dome. Would like to know thoughts on this age difference in layers. It clearly seemed to be fine when I applied the fresh mix to the somewhat hard base,but I'm curious if anyone did the same and experienced problems?

2. How long should I wait to remove the mold? The dome seems pretty hard,but I'm not in a rush because I still need to build a rolling trolley.

3. When should I apply the ceramic fiber blanket. How do I calculate how much I need?

4. I bought perlite because I was going to use it for the dome,but based on David S' suggestions on other topics I didn't. Now I have a lot of perlite. What mix can I use as a good insulator with perlite?

5. Is there a way to figure out how tall the chimney should be? If so what are some economical options? From what I understand I should stay away from galvanized steel.

6. Any tips of what type of cart plans work best. I'm thinking of a wood cart with large casters.


I know this is a winded post,but hopefully you guys have patience to help me through the process.

Disclaimer I KNOW this isn't the best looking dome out there,but it's literally the first think I have ever built. So I'm looking guidance on what I've already done and any tips you can give going forward.

[david s]

1. The 7 hr difference shouldnt make much difference to the next layer bonding to it and as you cant do anything about it now anyway, just put it behind you.
2. Anything made containing Portland cement should be damp cured for a min of a week to enhance strength, so cover it with wet hessian or old towels then wrap the whole thing up in plastic to retain as much moisture in there as possible. Then remould.
3. Again wait a min of a week to allow the water to dry out. Direct sun and wind will do a reasonable job of drying it, but cover if it looks like rain. Apply the blanket when the casting appears dry. Area of a sphere= 4 Pi x r2, but as its a hemisphere, divide by 2. The extra required for the entry is about the same as the area of the door so they cancel each other out. So just calculate the area of a hemisphere.
4. Use the perlite 10:1 as a secondary insulating layer over the blanket. It will provide a firm substrate for the final cement rendered outer shell, but drive the water out with gentle fires after the perlcrete has dried. You don’t mention the addition of any burnout fibres in your homebrew mix, so you must be sure to drive out the moisture very slowly. Proprietary castable refractory contains fibres in the mix which melt at 160 C providing mini pipes that help provide a pathway for moisture elimination. Homebrew does not contain these and they should be added.
5. Yes stay away from galv. It won’t last. Use stainless, for your sized oven it needs to be 6” (150 mm) diam and comes in lengths of around 900 mm. One length should be sufficient as it only has to get the smoke out of your face.
6. Timber is a poor choice IMO as it weathers and moves, steel or masonry are better. Although I have my mobile oven sitting on a timber trolley that rolls on and off my trailer. Any heavy brittle materials are subject to cracking if moved over bumps. The larger the wheels the better.

[JJPT831]

"2. Then remould." Are you suggesting adding another layer of the homebrew in addition to the ceramic fiibre layer and perlite?

"4. Use the perlite 10:1 " Just to be sure is this 10 parts perlite 1 part water? And would I add any Portland to this mix?

"You don’t mention the addition of any burnout fibres" I didn't add any to the dome mix.I only added stainless steel needles for strength. I must have missed that in my research. Should I add some to the perlite layer?

"6. Timber is a poor choice IMO" I know I hear you,but it's not my forever oven, so I'm not necessarily in it for the long haul. I plan on using pressure treated wood and constructing the cooking based out of firebrick. At the same time I'm also looking for a fabricator in my area to get an idea of cost for steel cart.


4 days curing so far with damp towels based on your suggestion.

[david s]

2. No I was referring to the inner layer casting done in separate batches with the 7 hr difference. Sorry I shouldn’nt have used the word “layers” there.
4. 10 parts vermiculite or perlite to 1 part Portland cement and 3 parts water.

too late for burnout fibres just go extra slow on the drying fires. They won’t be of assistance in the perlcrete layer as there will be plenty of air pockets.

Given that you haven’t got any burnout fibres in the inner casting, after it’s damp curing , I think you should allow the inner casting to dry in the sun and wind for a minimum of one week before proceeding with the insulation layers. And at this stage obviously cover it if it looks like rain.

[Nickp9000]

How much of the home brew mixture did you buy/use for each?

Trying to do a similar build, but want to figure out how much stuff to buy.

Thanks!

[JJPT831]

Nick I purchased 1 bag of portland @94 lbs(probably used half the bag or so) ,used about almost 2/12 bags of sand at 50lbs each, I purchased a 50lb bag of fire clay used about half or so,60lb bag of lime used about half or so. Used about 8lbs of the 10lbs of SS needles ordered from ebay. hope that helps. I haven't lifted my dome yet,but it seem pretty heavy.

[JJPT831]

Also guys just an update, I've taken a lot of time off from this project. I now had the chance to build the cart. using an idea from a website. No plans I just eyeballed what they did. I created 5 inch thick base concrete. The next step in the pictures are using a ceramic fiber board. My question would be can I create a perlcrete slab and lay my firebrick on top? CFB is very expensive for the size of my base (38x56) What are some substitutes that I can do? Would appreciate any input.

[JJPT831]

david s

This is where I'm at so far. I just added a 4 inch 5:1 perlite slab on top of the 6 inch concrete slab. I'll add photos of the perlite tomorrow. My questions are:

1: Can I add my firebricks right on top of the perlite? Or should I add CaSi board then FB?

2. Dependent on answer 1, If I proceed to put the bricks on top of the perlite slab should I add a clay and sand mixture like I have been seeing on other posts? Whats your take?

[david s]

1. Yes. 4” of 5:1 is the usual thickness of an underfloor vermicrete slab.
2. The sand/clay mixture is only a leveller in case the height of the bricks is uneven. Just sit them on top of the vermicrete slab unmortared. If you have a flat floor the leave them. If not remove them and use the levelling mix. I think it’s best to leave the mix dry so the bricks are free to move and make it easier to replace a brick down the track should one crack. Others prefer to add it wet and bed the bricks in.

[JJPT831]

1. Yes. 4” of 5:1 is the usual thickness of an underfloor vermicrete slab.
2. The sand/clay mixture is only a leveller in case the height of the bricks is uneven. Just sit them on top of the vermicrete slab unmortared. If you have a flat floor the leave them. If not remove them and use the levelling mix. I think it’s best to leave the mix dry so the bricks are free to move and make it easier to replace a brick down the track should one crack. Others prefer to add it wet and bed the bricks in.

Thanks. I ended up having to level the hearth with with the dry mixture. I finally moved the dome to the hearth, but it seems I have some major gaps on one side. It looks like the plywood I used to construct the dome must have slightly buckled due to the weight. As a result the left side of the dome doesn't sit flush with the hearth. I've tried shoving some of the dry mix to raise the bricks,but that'll just make one side higher than I need. What would be the best way to deal with the gaps? should i patch with the homebrew refractory? or is there another way to deal with this.

Also there are some voids within the dome. Possibly due to not vibrating after applying..not sure. should I be concerned and should I apply more HBO? the holes do not go thru to the outside at least not from what I see.

[david s]

Another disadvantage of using the gym ball over the sand mould, apart from having to lift the casting into place is the poor fitment at the base. You can use use some home brew to fill the gaps. Try to force it in hard. This is best done while the casting is still moist so you get a decent bond with the casting. If the casting is quite dry you may have to remoisten it and hold the moisture in for another week to allow the new home brew mix to cure. Likewise any voids can be filled with the same mix, but it is better, to fill the smaller holes, if you can sieve the sand so there’s no course grains in it.

[JJPT831]

I broke my foot back in august 2019 and have not had the chance to finish my oven. It's been sitting under a tarp. How can I waterproof the outside? Found this stuff at HD will it work? https://www.homedepot.com/p/Rapid-Se...0050/304671674