Dome stayed up this time!

[KISS4me]

Have just finished my dome Mk II after an initial collapse. Thanks to forum advice this version looks more like an dome and importantly has stayed up!

It ain't pretty (trapezoids etc. are out of my league) but will hopefully do the job. See photos attached.

I have two decisions to make now, and would appreciate any comments/opinions :
1. By building a chimney does it add to efficiency/ease of use, or is it mainly aesthetics on an outdoor oven?
2. Undecided about how to finish the dome. My choice is to either use layers of sand and cement render OR use a thermal blanket and chicken wire before the render finish.

Cheers Steve

[nissanneill]

Re: Dome stayed up this time!

Goes to show what that Aussie inginuity can do when you get the right advice.
Well done mate!
Now you can dry it out and start to enjoy thr fruits of your labours.

Neill

[maver]

Re: Dome stayed up this time!

Looks good - it's going to work fine for you. If you can use a thermal blanket you should, sand is a poor insulator as has been described here many times in the past. Chimney? Should help with draw to develop better convection in the oven, but you would not be the first oven to go without. There may be a minor safety feature in having a chimney - it keeps you away from the hot gasses exiting the oven - if you don't use a chimney please remember that the upper few inches of your oven opening are a danger zone when the oven is in use.

[nissanneill]

Re: Dome stayed up this time!

Steve,
I used a 25mm themal blanket on my 40" Pompeii. Cut it to size and nailed it in postion with galvanised clouts just enough to hold it in position. Then covered it with chicken wire and then plastered it with 3 layers of vermiculite cement. A little difficult to apply and hold on the vertical sections but made it a little stickier with the addition of a little fireclay. Now, after 6 hours of fierce fire for pizzas and 2 hours cooking the same, the top of my oven is COLD. I topped off the third layer with a render which I intend to mosaic tile to complete the oven and also to make it totally waterproof.
See the progress pics on:
http://www.fornobravo.com/forum/f21/...10-a-2119.html

All the best with your decission.

Neill

[Bacterium]

Re: Dome stayed up this time!

good work Kiss4me....go the insulation

After much thought about insulation "I bit the bullet"........ so I'm currently insulating mine - thermal blanket is on and vermiculite (actually used perlite) is underway (gee its a bit tricky getting it to stick on the steep sided parts)

got my blanket for about AUS$120.......600mm x 7.2m roll which is 25mm thick...... had some left over

[Hendo]

Re: Dome stayed up this time!

Steve,

Great job and congratulations after the minor set-back. I think I would have just given up or called in the brickie. Pizze just around the corner now!

And it sure looks prettier than mine ? have just laid the floor and started cutting the bricks for the ?floor ring? today when the rain came ?

Would agree with others to include the blanket insulation and perlite/vermiculite concrete before rendering (this from a man who is yet to get to this stage though!) There are numerous references on this forum to the importance of insulation all around the oven, and it makes sense ? both for minimising heat-up time and retaining all that heat.

Damon, Neill,

As a matter of interest, where did you get your blankets, and what product did you use? There seem to be two different products available here ? one that is a blend of Silica fibres and either Calcium/Magnesium Oxide fibres (like Insulfrax & Superwool 607), or Alumina fibres (like Cerablanket). They all seem to offer similar thicknesses, densities, widths and roll lengths. At this stage I?m leaning towards two ??, ?? or even 1? layers of 96kg/m3 density blanket, criss-crossed over the dome.

Cheers, Paul.

[KISS4me]

Re: Dome stayed up this time!

Thanks for postive feedback.

I am now convinced that I need to use a blanket.
Have not sourced the material yet, so I cannot help you with this Paul.
Neill's advice on how to insulate with 25mm blanket (galv clout sheet on, followed by chicken wire and perlite mix, finished off with render) sounds achievable.

Also convinced that a short chimney is worth the effort.

Will post progress report.

Cheers Steve

[james]

Re: Dome stayed up this time!

When you buy a full roll of ceramic fiber insulation -- use the whole thing. Just put the extra on top of the dome, or in the area between the top of the dome and the vent. It gets hot there, and more is always better.
James

[nissanneill]

Re: Dome stayed up this time!

Steve,
I don't feel comfortable suggesting that we buy materials from another supplier especially when such a fabulous forum provided by Forno Bravo is being used by us to achieve our builds. However, since they are not here in Australia and freight will put a higher cost on the products, contact a company called Thermal Ceramics:
Thermal Ceramics - A World Force In Heat Management
They are an international company and the lady that I have been dealing with in Adelaide is so helpful and switched on, it was an absolute pleasure doing business with them.
They have everything that you will need but they no longer carry nor make fire bricks.
I bought their 25mm thermal blanket 610mm wide by 7.??metres for Aus$77 + GST. They also have a 50mm blanket for the same price but only half the length. I decided against that as I wanted a hard surface which will be tiled to ensure waterproofing a little later.
I only put a single layer of the 25mm blanket on but have around 1 metre left over which I plan on using some for my doors. I also used the corner offcuts to pack in around behind my lights to protect the wiring from the heat. It works well.
If you tack it on with the galvanised clouts, position them into the softer mortar but don't hammer them all the way home. I only tapped the heads flush with the blanket top. The chichen wire can be distorted and squashed in ares where it is too wide, just keep it thin so that your steel cement trowel doesn't catch on raised wire which will cause the vermiculite to fall out. I found it easier to put some vermiculite cement on a brickies trowel and then push it off onto the dome but just below the areas where it is holding on.
It is quite difficult to get the vermiculite cenent to stick to the blanket, however if you start at the easy top section and work your way down and around but ensure that you keep dragging your trowel upwards and onto the area that has gone on OK. If you change your direction, it will simply fall away and get you rather frustrated. It was on the second layer that I included around 50% as much Fireclay as cement into the mix which makes it a little more stickier. The mix I used was 5 vermiculite:1 portland cement:1/2 fireclay. Remenber that fireclay is also a good absorber of heat so i wouldn't use it all the way through the vermiculite layer as it will reduce the isulating properties. I only used it through necessity on the vertical areas and only on the second and third applications, ie after the blanket and the first vermiculite layer.
Don't try to make the layer greater than 25mm as it simply will fall off on the vertical areas, but if you keep it around the 1" mark, you will ensure that an even 3" or 75mm will be all over the dome. I put the second and third layers onto very fresh previous layers to ensure better adhesion, rather than waiting a week between layers. It only takes around an hour for each layer so one in the morning and one in the afternoon and then again next day wil see a good dome covering. It took 3 bags of vermiculite for the dome insulation which is also available from Thermal Ceramics (Aus$26+/100 litre bag). The final layer was plaster sand 3:1 portland cement and this went on easily in a 1/2 - 3/4" layer which will waterproof the dome and a great base to glue the ceramic tiles onto.
If you want, do as James suggested and use the last bit of blanket over the dome top - vent area, where you have the hottest fire.
If you want any other help please feel free to contact me direct email or through the forum. I am more than happy to help you (or anyone else).
Good luck.
Neill

[Bacterium]

Re: Dome stayed up this time!

Neil, thats a good price on the thermal blanket(approx.$85 including GST).....your about $35 in in front of me ....AUS prices that is.
I got mine from Avero (previously called Alphacon). He was able to get all the stuff - blanket, firebricks/blocks, clays and other heatproof coatings.

Vermiculite/perlite was about the same, I got it from the local landscape supplier.


Couple more things on applying the thermal blanket.
The 1inch thick stuff was a bit bulky to work with so had to be patient to shape it. I just laid it on and where there were any joins I over lapped it and put wide strips of blanket over them. This actually helped it all hold in place, so I could then carefully put chicken wire over the whole lot (large single sheet). Then I carefully stretched/pulled the wire past the blanket and used masonary nails into the brick edges (below the blanket) to secure the wire. I suppose the trick is not to compress the blanket as that would reduce the thickness and potentially reduce it's thermal capability.

I have most of my perlite on now and when thats done I was thinking of adding another layer of chicken wire over the top of that. Hopefully this will help my render (stucco) coats to stick on nicely.

At the time.....because I hadn't decided on my exact method of insulation I actually cured my oven at the dome only stage (I had a chicken wire/mortar capping on it) and then used it for about 2 months. This was kind of a good thing as I noticed how much heat actually being lost.
I'm guessing I don't need to recure it as the blanket/vermiculite layers will keep the heat away from the outer render (stucco) coat as it undergoes its own curing.


......I'm going to do part 2 thread of my oven progress soon. Hendo I'll try and put the details of things like what type of blanket I used etc......stay tuned Redgum Roarer Part 2..........sorry kiss4me - hope you don't feel like I'm hijacking your thread.

[nissanneill]

Re: Dome stayed up this time!

Damon,
it sounds like you are back on track.
I didn't overlap my blanket, simply butted it close together, mainly to ensure a nice smooth semi spherical dome.
You can use a second layer of chicken wire and if putting insulation cement (vermiculite cement) over the blanket. you will need to do this if you want it to stay in place. Once you get the first layer on, it is much easier to apply the second and subsequent layers. You won't need to use anymore wire after the insulation layers are on. The final water proofing plaster/render/stucco layer will bond beatifully to the vermiculite layers and water proof it or as a good base for tiling of painting as required.
Phone Fiona at Thermal Ceramics
10-14 Toogood Avenue
Beverley S.A. 5009 Australia
Tel: +61 (8) 8243 5300
she will organise whatever you need. A very knowledgable lady and rather pleasant on the eye as well.

Neill

[CanuckJim]

Re: Dome stayed up this time!

Oz and all,

Had a thought. We've been dealing with the Portland/vermic mixture for so long that maybe we should step back a bit and consider. Straight Portland does not have a lot of inherent stick to it and is quite rigid. Let's at least consider using a vermic/Type S or vermic/Type N mixture. Type N is good for vertical surfaces and will provide the needed stick, so will Type S, but less so. In an insulating layer, rigidity is less of an issue than stickiness.

Addtional thoughts? Uno?

Jim

[RTflorida]

Re: Dome stayed up this time!

Jim, I took your advice and used the Type N over my perlcrete insulation before doing my mosaic tile....your 110% correct on its sticky nature. I've used Type S many times but this was the first for the N....very good adhesion on vertical surfaces. Good advice.

Never mentioned this before, but I actually ran out of portland when pouring my vermiculete hearth slab. I had 1 1/2 bags of Type S leftover from another project and used it to finish the insulating slab (glad I had it, didn't want to risk wasting 45 minutes running to HD in the middle of the pour)....other than being a slightly different color grey, you could not tell the difference from the portland area.

RT

[KISS4me]

Re: Dome stayed up this time!

Good advice Neill and Damon. I reckon I better check Google Earth to see just how many domes are appearing in backyards around Adelaide.

The discussion on cement beyond Portland is beyond my realm of interest although I have supplies of both Portland and White cement (Brighton lite) and have wondered if they have the same qualities under heat and as an outside render.

Cheers
Steve

[nissanneill]

Re: Dome stayed up this time!

Steve,
my understanding of Brighton lite cement is the same as portland cement only that is an off white cement rather than grey.
There are two basic types of cement, general purpose and Blended cement. The latter has a percentage (around 25%) of flyash in it to 'extend' it but also improves the workability of the mix and improves strength over time.
Brighton lite is a specially manufactured Off White Portland cement that has revolutionised the development of architectural concrete.
Neill