New build - 1.2M dome

[jonv]

Thanks. At the moment I am thinking of fixing it to some 1/2" ply that I've cut to cover the hearth bricks, putting the pivot point an inch or so above the hearth. To compensate I'll cut a course of 'half soldiers' at the right height and angle to put me back onto a hemisphere with the IT. If that makes sense.

[Gulf]

Great looking IT! In your case (with the arch bricks) that should do just fine. Like 99.9 % of ITs there will be some difference between the horizontal length and the vertical length. As long as you are aware of that and take that into consideration when you mount it at or probably below the finished floor level, all is good .

[jonv]

Surprised how few places stock 3/8 UNC stud and connectors here (or even good old whitworth)... anyway, connectors arrived today so I could put my IT together. Once again I have borrowed an idea I saw somewhere on the forum - using a tripod ball joint - but can't remember where; thanks whoever it was

My bracket isn't at right angles, because I have a pile of arch bricks for the dome. The tripod ball joint could be bigger, but I was trying to minimise the added height above the floor - it's all metal and seems to work ok, and for a couple of quid I'm not complaining.

I have a quick release clamp thing to go with it too, if needed.

[jonv]

You might be right - a bit of further research suggests that backer boards might not deteriorate in wet conditions but are not waterproof. My mistake. Might just spread some of that thick black waterproofing gunk over the concrete.

[Gulf]

I'm not sure about the backer board. But, I think that glazed ceramic or porcelain tile would work just fine.

[jonv]

Just a thought... what about putting a layer of tile backer boards on top of the concrete? In a 6mm sheet it would have no impact on the working height but would lift the boards clear of the concrete for both rising damp and seepage. They're supposed to be waterproof for use in wet rooms and such...

[david s]

Yes you can use that or a concrete sealer you can paint on. The type used for sealing bathrooms prior to tiling is very good. Borrow or hire a decent sized electrohammer drill and it will go through the concrete in around 10 secs.

[jonv]

Thanks for your reply. It's not especially wet - south of England - just unpredictable - hence the big party tent which we need for example at our midsummer celebrations - 50:50 rain in the last four years!

So I could definitely try to drill a couple of holes in the slab, though that concrete will be tough. You would recommend using a membrane? Do I need to look for anything particular or is regular damp proof material ok in your opinion?

[david s]

You are probably over worrying the issue. Ovens in Italy are usually out in the open without a membrane to stop rising damp and without fancy high tech insulation. How wet are your conditions?
I like to drill or cast a hole or two through the supporting slab and the membrane, if you use one, to allow moisture in the form of steam to escape when firing. The membrane will still prevent rising damp

[jonv]

That sounds like the ideal thing for the job. Bit late for my build now; I should have asked before :/

So, what would you recommend I do now?

[david s]

There's no such thing as too wordy - I like words

I thought about adding a waterproofer to the concrete but I understood (at least from those I looked at in our local builders merchants) that they weaken it and are best avoided for structural work. Perhaps there are some that don't. No idea to what extent this may be anyway and I suspect it would have been fine.

I have been putting off the final decision on the covering of the dome although leaning towards an igloo style. Will definitely add a waterproofer to the render if I go down that route, as well as applying sealer afterwards.

My OH has decreed that the oven will be fired weekly, nominally on Friday evenings, so in theory shouldn't sit idle for too long... Yeah right, we'll see how long that lasts!

The reasoning behind a waterproof membrane under the insulation layer is to prevent rising damp. Unfortunately it also helps to hold moisture in the insulation slowing it's drying. should it become wet. Instead of using a membrane I use a product, called Xypex, added to the supporting slab which both increases the strength of the concrete and makes it waterproof.

[jonv]

Is it appropriate to stick a damp proof membrane under the insulation, or not suitable?

[jonv]

There's no such thing as too wordy - I like words

I thought about adding a waterproofer to the concrete but I understood (at least from those I looked at in our local builders merchants) that they weaken it and are best avoided for structural work. Perhaps there are some that don't. No idea to what extent this may be anyway and I suspect it would have been fine.

I have been putting off the final decision on the covering of the dome although leaning towards an igloo style. Will definitely add a waterproofer to the render if I go down that route, as well as applying sealer afterwards.

My OH has decreed that the oven will be fired weekly, nominally on Friday evenings, so in theory shouldn't sit idle for too long... Yeah right, we'll see how long that lasts!

[SableSprings]

Your sealer will probably be all you'll need to stop wicking from the concrete oven pad...however, water will very probably find its way into your insulation base by simply seeping in on top of the sealer from the edges and seams. Russell's (UtahBeehiver) solution was to use a layer of foamglas between the concrete and the ceramic insulation board. The foamglas does not absorb water easily and basically raises your vulnerable ceramic board above the possible water seepage. There are also products that make concrete "waterproof" (Xypex is one that's highly recommended--they have a web site www.xypex.com that's pretty informative). I don't know how you plan to enclose the oven and top insulation...and that is going to be important for you. Stucco with a water resistant base works well for many folks, you just need to be planning on doing regular maintenance to fill/cover cracks that always will develop over time. David S has noted that putting Xypex in your concrete is pretty effective...so putting Xypex in a cement "overcoat" of the oven (imitating stucco ) might be a little longer lasting...but then the old saying is "There are two kinds of concrete, one that's cracked and one that's going to crack." Please don't get paranoid about the water angle, just realize that exposed ovens need a little more attention. I guess using a product like Xypex in your stucco would be another option to increase the waterproofing effectiveness.

I suspect that if you simply threw a tarp over the exposed oven when it was not in use, you'd be in pretty good shape. And if you are using your oven often, the minor water seeps will take a long time to become anything other than minor. In your wet/damp climate, any cover you can give your oven will be good...and in worst case, the insulation gets wet if the oven sits for a while in the rain and you need to do another oven curing when pizza and baking season return to your household.

Hope that helps a bit...and doesn't come across as too negative or like a scare tactic. Sorry, I'm always too wordy.

Plenty of Pompeii ovens in use where the sun don't shine all the time..., so relax and continue your build as the fall embraces us.

[jonv]

Thanks for that. Perhaps it was your build - I've looked through so many I can't remember where I pinched various good ideas from

I put a couple of coats of sealer on the concrete - does it need something more than this?

My roof won't cover the whole of the oven - it will just overlap the front, hopefully lining up so that the flue can be supported on the end of the roof structure. Most of the oven will be exposed to the weather after the build is complete.