New build - 1.2M dome

[agrasyuk]

that is a great build. I am also interested to see how your grill /smoker comes out.

would anyone like to chime in on dry-stacked CMU blocks vs. buttered with mortar?

[jonv]

The party tent should solve the problem of building in the British Autumn weather

[UtahBeehiver]

That has to be one of the fanciest construction tent I have seen on the forum. Even better than some finished structures.....,LOL.

[jonv]

Spent quite a while this week reviewing dimensions and getting things more or less straight in my head, adjusting a few things from the plan when we laid everything out and could see what it looked like.

The hearth has dried out nicely. Had a bit of fun removing the forms underneath, and a smack on the head from one of the supports, but if all looks ok. Today I marked out and cut the insulation layer - 2 layers of 2" calsil. I had no idea what that stuff would be like. Easy to cut but otherwise a horrible material.

I cut the boards so the joints overlapped and it's roughly in the right position - will adjust tomorrow when the light is better. I decided to allow about 4.5" of board outside of where the firebricks will be. I didn't like the idea of the bricks sitting right on the edge of the board. The insulation blanket will fill that space later.

Now I can start to lay out the hearth bricks and mark for cutting and I'll feel like I'm finally building this thing

[staestc]

That really is a hell of nice tent! Build is coming along nicely. Now is where it gets fun!

[SableSprings]

Looking Good Jonv! This would be a time to consider putting a moisture barrier between the concrete top slab and the insulation board. Since you're ultimately going to build a roofed structure over the oven, then it won't be an issue in the future...but if you won't have that spiffy tent covering it all winter...a piece of plastic would be inexpensive insurance again extra drying/curing time in the spring. Lots of discussion on the forum about how quickly that insulation board will suck up water if given the chance...

RE: your post #11, I had used the form tension wires for an "odd shape free form" form up in Canada at Hihium Lake doing the top platform base for a CasaG90 install...don't know if it was my posts you remembered, but glad it was something you were able to use...

RE: your post #13, My oven cooking floor is just the standard firebrick thickness (2.5"-3") and has performed well for me and my bread bakes. I do 15-20 loaves per firing (usually in batches of 5-10). Each batch of baguettes takes about 15 minutes to finish baking at 575-585F.

p.s. Agrasyuk - buttering the CMU blocks with mortar vs filling alternate cores...definitely more time/work mortaring than dry stacking (IMHO), can't imagine with the top slab weight and rebar tie-ins that there is any strength/mechanical advantage to the "buttering" method over the dry stack & core fill (IMHO). One thing that does come up however is that by mortaring the CMUs individually in place you do add some height (and length) to the stack--1/4" per mortar join. Measure a block-multiply that by # blocks of oven stand, plan on that length/height...butter the CMUs and the structure length/height will be longer & higher than you planned...just a thought

[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.

[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]

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!

[jonv]

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

[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]

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]

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]

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]

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.