New build in Barnet

[kaneabel]

So I took advantage of the Easter break to get started on my 90 cm Pompeii oven. I am a complete novice at this kind of thing so will be depending a lot on advice from this forum.

The site I have selected had some  crazy paving set on cement and sand and I spent most part of the last three days smashing my way through with a sledgehammer. Must say that was hard work - was not expecting it to take so long!!

This has left me with a slight problem which it would appreciate some advice on:

My garden gently slopes down from the house; the oven will be set diagonally on the left corner at the rear. (See picture). The crazy paving covered roughly half the site. The other half had lawn. In removing the crazy paving I had to dig deeper than I would have liked. That combined with the sloping garden has meant that the rear of the site has been dug quite deep while the front is not that deep. I would like the foundation to be a little above ground. Can I level off using gravel. This would mean a much thicker level of gravel at the rear as compared to the front? Secondly(this I suspect might be a silly novice question), can my timber form rest on the gravel or is gravel only filled on the inside of the form?

While digging I encountered a fair a amount of root from the tree standing right behind. Once I concrete over, will this cause any issue?

I am hoping to pour next weekend - thanks for all your help!

[chas]

Difficult to be 100% without looking in the hole clasping a glass of IPA, but generally it's better to have a level base to pour concrete over - compact the gravel fill as much as poss (or use some of that smashed stuff) and put your form down on that levelled surface. The top of the shuttering's now level too. As for roots causing trouble... well, they do sometimes, but was there any evidence of 'heave' before you lifted the paving? If not, then probably no problem.

Chas

[rivergirl]

If it's a pine , you might have more chance of a branch breaking than root damage. Like Chas I think I could be more help standing over the hole with a glass of left or wine in my hand . But seriously. We had a giant of one by the side of our house. With no evidence of root damage. I have just taken one out her but only because it was smack bang in the middle of the proposed kitchen.

[cobblerdave]

G'day 
i built a slab on a fall. Not directly parallel to the boundaries but facing the house so the slsb is at 45 degrees to the slope of the ground




Front right hand corner is only 200 mm deep. Back corner left is more like 600 deep. Middle of slab is only 75 mm
thick. 
I dug into the ground 300 mm in from the edge of the slab. Then the inside of this 300 mm outside trench I mounded up sand to get to within 75 mm of top of boxing. Boxed to level. And pour.
The resulting slab has a thick outer edge of cement where the weight will be and a thin centre thickness were thickness isn't required. Upside down cup shape if you like. Uses less concrete whilst following the contour of the ground and remaining strong in the places it needs.
Good trick I learnt doing this one was to use a battery drill and chip board screws to hold your boxing together. You can't knock anything out of plumb like you can with hammer and nails. You leave the heads protruding 10 mm and tape the ends so concrete can't get in the screw heads. Easy to put together and pull apart.
If anything is unclear please just ask remember there's no stupid questions when I'm discribing things from the outside of the planet!
Regards dave

[kaneabel]

Chas, Rivergirl, Dave,

Thanks for your responses. I will dig up the shallow end a bit more and then level it off with gravel- most likely the smashed up concrete. Couple of follow up questions: how small does the gravel pieces need to be? I suspect I might have to spend quite some time breaking down the concrete pieces further. Secondly, any tips on how to level off the gravel - don't want to spend any money on getting a compactor or anything fancy like that.

Cheers,
Kaneabel

[chas]

You're just trying to achieve a cohesive, stable layer that will let the concrete pad take the strain without itself sinking or cracking across and in effect reduce the thickness of the concrete for economy - so, pieces of various sizes that will knit together are required: can be anything, really, down to concrete 'dust'. And for this small area, any heavy 'pounder' will do: builders merchants sell an iron pole with a square lump on the end for about £15/20, but a heavy lump of wood or log somehow fixed to a pole will do, or even (and most probably) your sledgehammer, pounded up and down to compact and reduce the rubble. A few old mis-shapen soft bricks among the concrete will help make the process easier. Conventionally, you put about 6" of this 'consolidated hardcore' under concrete - but you could make your concrete 6" thicker instead!

Chas

[kaneabel]

Hello all,

I made some more progress with the foundation. It is all levelled and gravelled - ready for the concrete on Friday. I am thinking about dropping the rebar to save some money. Considering my foundation will be 8 inches thick, i think I will be alright. Any views on potential issues?

Kaneabel

[cobblerdave]

G'day
The steel is important . I didn't say what steel. Be a bit inventive and repurpose a bit. It can be sa bit rusty as well but not big flacky bits as the cement will stop the rust.
The neighbours garden shed slab has lengths of steel water pipe and the steel mesh out of old bed. As long as you wire it together and prop it up on old bricks and rocks etc so when the concretes poured its in the middle of the concrete. That's important you can't have bits poking out or to near the surface as the steel will rust and wreak your project. The cement stops the rust. The steel makes the slab strong and whole to stop cracking into sections
Regards dave

[kaneabel]

Hello all,

I poured the concrete foundation today. Here are a few pics by way of update.

Thanks for the help so far. I suspect, I am going to need a lot more going forward. Here are my latest question:

- I was originally planning to build the base with blocks as per the Forno Bravo plans. However, I have a few bricks lying around so will probably go down the brick route. Would a wall of single-brick thickness be strong enough or would I need two deep? I have seen a few members use blocks first and then a layer of bricks on the outside - is that for strength or just aesthetics?

Progress will probably be slow over the next couple of weeks. Lets see - will keep you all updated.

Regards,

Kaneabel

[chas]

"single brick" thickness will be ok - you'll probably be forming a 'U' shape which aids stability and single-brick walling is often found, stable, at heights beyond the metre or so you'll be going. It's what I did, and while I can't talk for the brick and block brigade, I'd guess you're right - it's probably aesthetics. Just keep it upright and you'll be OK.

Chas

[kaneabel]

Hello all,

Now that summer is here - I have restarted on the oven. Aim is to finish this summer but we will se how it goes. The next step is to pour concrete slab for the hearth and I am busy tempting some friends with bribes of whiskey to come and give me a hand.

Quick question: I have built the timber frame for the concrete slab. For the base rather than use plywood, I am planning to use hardiebacker boards to avoid too much carpentry. Does anyone have any experience of using this? I am concerned if the 12mm boards will collapse under the weight of the concrete, but would prefer these to plywood if they are safe to use.

Thanks in advance.

[kaneabel]

<sub>Hello all,

With the hearth poured and cured, I am ready to begin the actual oven build. I am about to order bricks etc as per the attached for my 36" oven. Does this seem alright? I must say this is quite a bit over my budget, particularly once you add 20% VAT and £70 delivery. This list has been created on kilnlinings. Anybody aware of better prices/discounts?</sub>

[bento]

Hi kaneabel,

Kilnlinings has a 10% discount code - a quick search on this forum shows it might be 'KLWOF10' at checkout.

As crazy as it sounds, I can't remember the size of my oven, so much as happened since I began, but I am pretty certain it is also a 36".

I ordered the following from kilnlinings:

1 x Fire Clay bag (Approx 25kg)
160 x Fire bricks 42GD - 230 x 114 x 76mm
1 x LBP HT Blanket 1200GD - 3.66M - 610 x 50mm (Density 128kg)

For me I found the following:

Using a homebrew ratio of 5:1:1:1 for the first few courses and then 4:1:1:1, this was enough fire clay for the dome, a complete render, and a little left over - although some use a 3:1:1:1 ratio, so may be a little tighter. The fire clay I received wasn't as fine as I thought it would be, I don't expect this to be an issue?!?

I sat my dome on the firebrick floor and also used firebrick for my entire arch and chimney base - I was probably about 10 or 15 short, having probably wasted a couple due to mishaps and bought 30 more smaller ones from ebay.

3.66m of 50mm fire blanket wasn't enough for me (covered about two thirds), and I bought another 6m of 25mm blanket off ebay which I doubled-up and fitted in the gaps - I used most of this, with the remainder I will use to make a door.

[kinley]

I've just finished my dome-insulation and had the first firing last night (thread will follow once it's rendered). I had followed the forno bravo list and found the quantities OTT. Kilnlinings have the cheapest bricks I found anywhere. I built a 36" (915mm) internal with firebricks for the floor, dome and entrance (i.e. everything). I used 135 114x230x64 bricks with 9 of the 25mm bricks. One bag of fireclay is enough. The 3.66m roll was just enough (4m would have been perfect). I used 6 bags of vermiculite but I suspect I have 125mm of vermicrete which is more than enough. Don't buy £20 worth of chicken wire - scavenge some off cuts: my local agricultural merchant sold me what I needed for £4 (and they had 100l vermiculite for £16). I used 3 50mm calsil boards and have enough left over to line the door.

Look on ebay/gumtree and hoover up left over firebricks from others building. I got 80 at <£1 a brick this way. This also allowed me to fit the rest in the car saving the (hefty) delivery fee. Can't fault Kilnlinings service though. I got a 'seconds' single skin 6" flue from ebay for £21 and it works brilliantly. I was £550 all in for the dome.

[kaneabel]

Thanks for the replies.

I finally went with Kilnlinings. The bricks arrived yesterday and I am ready to go. As I am mocking up my dome, I am wondering if I should go for the angle iron or the arch for the oven opening. Any advice on pros and cons? Also, I have read about thermal gap at a few places but am not sure I fully understand. Do I need to plan for it in my design?

also,

- does the soldier course go on top of the insulation board or on to the concrete base?
- how do I bond the the cooking surface bricks to the he insulation board or is weight enough?

thanks,