New Build on this side of the Pond

[SableSprings]

I'm only just starting my own build so I might have misunderstood many things, but I thought some folk cut the floor bricks to fit inside the dome, with a little bit of a gap, to allow for expansion of the floor? That's my plan, anyway, although there seem to be plenty of builds with the dome sat on the floor bricks - haven't read of any problems with this...

Jonv: There are advantages and disadvantages to each style of dome/cooking floor placement. The bottom line is that either method works well...do what fits best with your plans and comfort level as DeeJayoh noted. My build put the dome on the cooking floor and I've had no problems. As you have mentioned, there are plenty of builds done this way but just as many done with the floor bricks cut and set "inside" of the dome.

UnderPendle: Consider some prep or utility carts to roll under your cast span/cantilever. As a sidenote, my cast span (with ash drop ) made me a bit nervous when I was planning it...nobody would give me an opinion on it working or not. Your span/cantilever is much bigger than mine but it sounds like you've got solid engineering on your side. If it was me (because I'm chicken), I'd be putting a steel post on either side--back 30 cm or so from the edges--and then running some solar LED holiday lights on the posts to make the oven look like it was floating (and to ease my non-engineering mind).

Watching with interest and admiration...

[underpendle]

Hi Mike
Considered an ash drop but decided against in the end, Ive grown uo with solid fuel open fires as our heating and know how much a warm flue can effect draw.(we've only just moved here its our first house with proper central heating!!!) I wanted the ability to light my fire directly under the flue, which for me is the obvious place to put the shoot. Bit late to change my mind now. Just been looking at your photos and I don't think our spans are too diff. I'd guesstimate yours is prob a touch longer, but does look like you have some angle iron at the front? How thick is your slab?. May well end up with something like you suggest just keeping my options open at the moment. Looking forward to this project but also have a lot on with the rest of the house.

[SableSprings]

I just laid a piece of angle iron in across the front inside of my form before the top slab pour. It really was as much to get rid of the scrap metal as it was to provide any actual reinforcement to the span. I hoped it would add something (again, being a chicken on my first span...). My top slab is just 4" thick with "normal" rebar reinforcement...normal meaning I didn't have any experience with what I was doing.

Yes, these projects are always dynamic. I suspect there are very few builds that end up exactly as the initial plans were set up...and the options being left open is always best

And I know what you mean about the house stuff...we just got home from a long trip to Canada and my list of house chores is pretty daunting right now...but it's more fun doing a little catch-up with the forum as I ease into them

[underpendle]

Just Getting ready to order my building materials. A quick question if I may.

I have planned on 100 CaSi Board under a 75mm hearth. Although my finished oven will be covered, it will be open to the elements to some degree and I'm thinking about water wicking into the Boards. I was thinking about building on a Ridid 25mm PU(Celotex) board as a DPM. Is this considered acceptable, if so this leads to the next question being can I substitute 50mm CaSi with 70mm Celotex. i.e 70mm Celotex, 50mm CaSi, 75mm Hearth. Would think the U value of Celotex, 0.21W/mK would be equal or greater than CaSi. Compressive strength OK at >175KPa.

Cheers S

[Gulf]

Forget about the Celotex. If it is made across the pond like it is here, it is made of natural fiber, it will eventually deturiate.

[underpendle]

thanks Gulf.

[underpendle]

Just Taken delivery of Fire Brick etc. Unfortunately Ive missed ordering the CaSi board!!! my mistake, just wondering what users opinions are of making the hearth a bit thicker, 114 instead of 76mm and putting 100/150mm of thermalite airated block under for insulation? I'm away this weekend anyway so can't do a lot but keen to start and not to keen on paying another £70 delivery!!!!

[cobblerdave]

G'day
Most ovens use 35 mm hearth for faster heat up time. Full brick at 76 mm takes a bit longer to heat but has and advantage of longer cooking times. 115 mm is pretty thick and you might consider it suitable if you require really long cooking times i.e. multiple loads of bread. If you have are on you first oven consider 35 mm or 76mm giving you a more all rounder oven .
Thermolite is called hebel here and I have 50 mm under my Heath and does me. 150 mm sounds better to me. You can't overdo insulation but you can overdo the mass.
Regards dave

[underpendle]

Cheers Dave, Thanks for the feedback.

Would you consider Thermalite/Hebel to be an equivalent of CaSi? Can put a Thermalite layer in for a fraction of the price of CaSi. The bricks as delivered have some damage. Ive contacted the supplier and hope for some recompense. This may be a free delivery? Maybe some money back. Spending a lot of time/money on this and don't want to spoil the job for the sake of a few quid. However it is a consideration.

Yes first oven. Ive bought 76mm so thats what it'll be. Want the ability to bake bread so think this is for the best, Im only building 800mm ID so not big by the standers on here but hope it'll serve all our purposes.

S

[underpendle]

Just checked with my local merchant they have 140mm Thermalite in stock. Just to qualify Ive purchased 100mm of blanket to insulate the dome which IMHO is where its needed most. Will prob get some vermicrete/vermiculite in there as well.

S

[jonv]

£70 seems a bit steep for delivery. I found calsil varied rather a lot in price - got mine for £15+vat for sheets of 1000 x 500 x 50, which I thought was pretty good...

[underpendle]

Cheers Jon, where from?

[underpendle]

This may complicate matters. Would appreciate some input from the experts:-)

Just found CaSi Board at my Local merchants. Not sure price till the morning but will be a sight cheaper than I was expecting and no Delivery!!

8x4 sheets but only 12mm. I can obviously use muti layers but am I losing the effective U Value with every joint? My gut says Id need to somehow bond these to be effective and would the then plyboard be comparable to the afore mentioned thermalite?

I could go with say 100mm thermalite, 25-50mm CaSi, then the hearth. Or multiples there off.

Am I over thinking this?

The obvious advantage other than price to using thermalite is they can easily be laid on sand and cement, before placing the hearth on fire clay. Also building directly onto the block would again be easy.

Any advice gratefully received

Cheers

S

[jonv]

I got mine - along with fire bricks, aluminate cement, and aggregates - from Intocast (http://www.intocast.co.uk/).

I found Jim Allen there to be most helpful - and very patient with my indecision!

[jonv]

I'm sure some of the experienced builders will have more to say on the subject, but, for what it's worth, I don't see why you couldn't put a layer of calsil on top of thermalite blocks with good effect. Calsil is a significantly more effective insulator, but if you put an inch or two with the blocks I would think it would do a good job. Personally, I wouldn't want to put the hearth bricks directly onto thermalite blocks without a layer of proper insulation between as I would not be comfortable that they would be entirely happy with the temperature, but that's just my feeling.

BTW - as I understand it, calsil comes in different grades - it is worth making sure that this really is the right product. Some don't appear to have such a high temperature rating, presumably due to some of the other stuff that is added to the product...