new build

[cannyfradock]

cec

Brilliant pictures.....and great progress. I love this pic...



I carried on from this stage ...as per Turkeys post. You look like you have a limited space at the rear for insulation. You could always drill and fix a piece of timber to take the insulation. In any case...if you can try to put a thermal blanket on the dome, then chicken wire, then the vermecrete layer........many people have difficulties laying this vermiculite, cement and water layer on. It is truly a pig to use. The best method I've found is to empty 2 or 3 100 ltr bags of vermiculite into an empty 1 ton ballast/sand jumbo bag......add about 1/2 to 1 bucket of water onto the vermiculite . Mix well and leave overnight to let the vermiculite suck the water in. The next day add the cement......and a bucket full of lime (if you have any left over) and use the handles of the jumbo bag to pull the mix over and over so the mixture is well mixed in. By soaking the vermiculite overnight you should be able to have a mix which binds together.......sometimes it's easier to use this stuff using marigold gloves and hands on......rather than a trowel. It does however form a solid crust when dry.

Really enjoying your build and hope the next stage goes OK.

Terry

[cec]

Do I really need to put a blanket over it , I'm just not so sure about having something soft under a render ,
You see when I've had a few beers I tend to fall over and I can see myself falling on my oven and cracking the outer render .
Could I not just double up the vermiculite ?
Oh if I must cover with a blanket could I not use ( don't laugh ) ........ Loft insulation ?

[samuraidave]

There are two types of loft insulation, rock wool and glass wool. One is fire resistant and one is fire proof. I have used loose vermiculite on my build and it works great. Vermicrete would be a great insulation layer, but the guys are saying that a thermal blanket would be a good move and they are the ones with the experience.

Good luck with whatever you choose.

Dave

[cec]

The loft insulation is glass wool ,

I've been looking at k rend for the outer render ( over the vermiculite render ) is this a good move ,
It says it's waterproof so should be ok as I'm not putting a roof over mine

[bookemdanno]

Wow, another fabulous build. Well done! What diameter dome you end up with?

I'd reckon that any insualtion is a bonus, regardless of the style. It's just whether you're happy with the results from it at the end. More insulation equals more retained heat over a longer period. It'd work with no insulation, but you'd have to keep it well fed with fire. Fire Blanky is the top spec, for heat resistance, with mineral wool a better insulator. Not so good on the high temp resistance tho. Check Rockwools webby for Tech Specs. Then Vermicrete is a lower thermal spec. There is a product called LECA which is Lightweight Expanded Clay Aggregate, which is used in floors. Also for hydroponics. It has a thermal R value similar to Vermiculite, but is small hard balls, so might be more workable with a small amount of sharp sand added to the mix. No-one has yet to try it though.
The Fire Blanky, Vermicrete and render is the tried and trusted method.
Anything else and you'd be breaking new boundaries!

[cec]

Collected my vermiculite tonight , bargain £5 eBay
Bookemdanno the dome has an id of 30" . I know it's not massive but I was very limited on width ,it will do I think , but watch this space , I may yet build a smoker house at the left of it now and try a bit of smoked fish , cheese , etc .

[turkey]

cec, you can always stay with just vermicrete but I believe compared to the proper blankets its not as good thermally so would need more thickness for the same result,

you could get proper refractory blanket as they also do rigidizer to set the blanket to a firm shell if required, however this is the expensive option.

as space is tight and if you are worried you could always just use vermicrete but after an even layer all over you could add more on top where it will loose more heat. It will make the top something like an egg rather than igloo but would help keep the heat in, keep the width down and also be cheap.

you are a few weeks ahead of me and facing similar space constraints so I am very interested how it turns out.

[cec]

I think I will just give it a good rendering with the vermiculite , maybe 2 lots , 2 x 2" layers

[wjw]

Wow...you've made more progress in three weeks than I've made in three months. Bravo!

Looks great.

Bill

[cannyfradock]

cec

I think the guys have just about answered your question on insulation. The general rule of thumb is...the more insulation the better. I asked the technical guys at the Cardiff branch of "Sheffield insulation" if rockwool was OK for our needs and they advised against it. I ended up buying a roll of the fire-stop insulation from them, that is used in the attic space of timber framed new terrace houses. Rather than use a thermal blanket which is'nt suitable you may be better off with your idea of just using vermiculite concrete. I also asked them about using k-rend and they said ....as long as the insulation layer/s stopped the majority of heat from leaving the chamber, it would work. I'm not sure if leaving out the blanket would work with k-rend? You could still try it (with chicken wire between the coats).........if it did crack you could always trowel on a layer of 2 part flexible tile adhesive (the stuff used in underfloor heating)

Since Jan 06 2010 we've shared 100's of WFO builds and I dont think that any 2 have been the same. Like someone mentioned...the worst scenario is having to use a little more fuel/wood and even when builds have small (or large) cracks appear in the render......they all function.

Terry

p.s.....the only big problems we've heard about is from people who have bought cheap modular ovens.

[bookemdanno]

FornoBravo Says Fire Blanky is more than twice as efficient than Vermicrete. So 3" FB no vermi, 1" FB with 3" Vermi, or 6" Vermi on its own.

Thanks for the Diameter info, i was just imagining my own requirements, and how the brickwook should work out.]

Cheers!

[veauifru]

Apr 25, 2012 9:33:22 GMT cannyfradock said:

I asked the technical guys at the Cardiff branch of "Sheffield insulation" if rockwool was OK for our needs and they advised against it. I ended up buying a roll of the fire-stop insulation from them,

I would be wary to take advice from people trying to sell you something else more expensive

[cannyfradock]

veauifru

Very wise words and quite true......and the thermal blanket would have been cheaper from Liam, but I'd already had my delivery from Liam so it was the cheapest option.

Terry

[cec]

I've been thinking about all this thermal mass stuff , does it really matter if I burn a bit more wood for let's say a 2 hour cooking window , ( thats a lot of pizzas ) , I will do meat joints when I get use to it and if it doesn't work I will change something .
Iv cooked full piglets on my old BBQ befor in about 4 hours and that's only got a 2/3 mm lid and not a scerick of insulation .
I've got about 2 ton of chopped wood at bottom of garden well seasoned ( 2 years ) so wood int a problem , but build cost is .
Has anyone done a befor and after with heat getting through bricks , I mean a with a laser heat thing ,
1st one with just a layer of vermicrete 2"
2nd one with 2 x 2" layers
3rd one with the full bag of mashings

I do like to get things right but I disagree with spending more money for the sake of 1 or 2 logs .

[tonyb]

I think I'm beginning to sound like an old broken record.

Rule No 1 - There is no single WFO design!

What we have is a collection of design ideas and rule of thumb guidance. Want to use ordinary bricks? Fine. Don't want to use ceramic blanket? Go ahead.Want to cut your firebricks into thirds instead of halves? Fantastic.

Each decision on design and material has consequences: price, mechanical strength, thermal performance etc.

Rule No 2 - Don't start thinking about materials or design until you are clear about how you are going to use the oven.

If its mainly pizza (a little bread and roasting) you probably need some ceramic material for the oven either firebrick or cast. How much insulation you use is a function of your cost (and value) of fuel.

If its mainly bread, particularly multiple batches, then you need plenty of thermal mass and insulation to provide a wide (time-wise) retained heat baking envelope.

I'm not aware of any proper analytical testing of varying degrees of insulation etc, its unlikely the results would be particularly transferable in any case. The best we can do as a forum is to make sure posters are aware of the pros and cons of a particular design or material, and for responders to say what worked and didn't work for them.