mm289
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Post by mm289 on Sept 6, 2019 9:06:18 GMT
Cheers Dave, I guess my question on the moisture is if the dome is sealed from above where does the moisture get in? Is it just absorbed into the dome from the inside and moisture in the air?
I presume when people are puttingvents in the outer shell it is some sort of shielded vent to stop rain coming in but allow moisture out?
Cheers,
MM
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Post by downunderdave on Sept 7, 2019 8:00:35 GMT
I guess it depends on the weather conditions in your area. We live in the tropics and during our wet season, even if there has been no rain, there is sufficient moisture in the air to dampen the inner oven and insulation layers. Rain can often enter via the door and accumulate under the floor bricks. Around the flue pipe and also sometimes through a crack where the outer render meets the supporting slab.
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sean
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Post by sean on Sept 8, 2019 11:16:47 GMT
Hi Sean, I am just going to cement render it. It seems there are many opinions on render composotion so my plan is scratch coat will be 4:1 sand:cement with the sand being a 50:50 mix of sharp and plastering with plasticiser in. Top coat will be 5:1 (weaker) with the same sand mix but waterproofer added. I will then be painting the render white with Sandtex or similar to mimic a lime rendered wall.
TBH doing it in lime would be easier but it wouldn't be as waterproof as the lime is designed to breath IE let moisture in and out, which wouldn't really work in this application.
Cheers,
MM
Hi MM thanks for the reply, i was going to use Victus heat proof render/cement but i am liking your idea, i am guessing by the time the oven has has all its insulation material on the cement is not going to get any real heat that will create cracks and it needs to be waterproof especially up here in Scotland. I have just had the garden walls rendered with a material called stonecast (i think) the builders left 2 bags of it in the garage and my plan was to use that but they advised its not suitable and recomnded the Victus stuff I however was away at the time with work and my father in law passed on the message and i dont think he told the builders about the extra the layers of insulation to be added to the dome.
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mm289
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Post by mm289 on Sept 11, 2019 12:11:42 GMT
I guess time will tell how the render works - I would be very conscious of Dave's comments as he has seen a lot more ovens than me but I will feedback on here how it goes when heated up. So did some more work at the weekend including finishing off the brick facade on the front. Really pleased with how it has come out - will look a bit tidier once the lime has gone off a bit and I can brush the mortar joins.
With the fascia finished I could now prep for render. I had already decided I wanted a flat surface level with the oven floor so needed to infill this area to support tiles or render. I had the broken piece of dome left over from the original delivery so broke this up and used as an infill. My very flaky theory is it will be "insulative" to a degree around the oven base and isn't anywhere near as heavy as trying to infill with concrete or similar. I then poured some kiln dried sand to fill all the gaps and give me a solid surface.
So then on with the first coat of render. As mentioned elsewhere I have gone with a 4:1 mix of sand to cement with the sand being a 50:50 mix of sharp and plastering. This base coat has some plasticiser added and also the dome coat has some fibres mixed in to aid strength.
I also rendered over the infill area to create a base to lay tiles on at the front. These will only go half way back around the oven, the small flat areas on the rear two corners will be rendered with a small slope to encourage water to run off. All floated and scratched ready for top coat.
As you may have noticed I had a change of plan regarding the chimney. I had purchased the steel chimney with the kit which you can see on eralier photos. I was concerned about how I would render this and was reading a couple of other posts on here at the time. I also noticed when I did my test fire that this got very hot and potentially could be a hazard if anyone touched it. I had thought about getting a clay chimney pot and using this as an outer liner so that you couldn't touch the steel one.
This had the advantage that as it is wider that the flue opening and wouldn't be touching the steel flue it would get nowhere near as hot and would probably be OK to render up to with less risk of all the render cracking. So that is what i did as can be seen in the pics.
Now I am thinking this looks much nicer that the steel one so am seriously considering leaving it like this and not fitting the steel flue.......?
This also means that there is an area of the dome material that is open to the air (the flue and also about 15mm band where the chimney is wider than this opening). This would allow the dome to "breath" to a degree and could act as an area that any moisture could vent through.....
Worst case is I just slot the steel flue in as it is an interference fit anyway if the clay chimney on its own doesn't work.
Cheers,
MM
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mm289
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Post by mm289 on Sept 11, 2019 12:20:42 GMT
Had a day off work yesterday so managed to finish the render. I would suggest it is easy to underestimate how much work is involved in building a pizza oven!! The oven and dome itself is easy'ish - its all the construction of the base and the finshing that takes ages So, a pretty much full day later and we have a rendered oven
The top coat render was done at between 5 and 6:1 sand to cement. This time I went with a bit more plastering sand so the rations were 2:1 plastering to sharp. Instead of plastciser I added a waterproofer/plasticiser to try and give the top coat a bit more waterproof properties.
Whole lot was floated then sponged to get a nice smooth finish, again really please with the result.
Will give it a few days to dry out properly then will get brave and test it with a few warming fires and see what happens. Once I have done that i will then pain, lay the tiles and make the door for the storage area. Never know, might actualy get to eat some pizza soon
Cheers,
MM
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Post by downunderdave on Sept 11, 2019 18:56:38 GMT
The strength of anything made with Portland cement can be enhanced substantially if moisture is held in it for at least a week. This can be achieved by covering the whole thing. I actually wrap the whole oven in cling wrap. I know you must be keen to crack on, get some fires happening and start cooking, but taking things slow at this stage is far better in the long run.
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mm289
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Post by mm289 on Sept 13, 2019 8:45:54 GMT
Noted Dave, I do have it covered at present and the temps here are quite mild so will leave it at least 4-5 days before I think of firing Cheers,
MM
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mm289
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Post by mm289 on Sept 15, 2019 19:21:23 GMT
So whilst waiting foir the dome to dry out a bit I started on the frame for the storage area door. Nice sunny day yesterday so was quite pleasant working outside. Cut a couple of bits of studwork to size for the sides and made up a infill panel for the arch. Doors will get made out of bead and butt when I get some and mounted with external hinges like the doors in the farmhouse.
Also took the opprtunity to put some fire cement into the inside of the dome where the pieces meet, and also on the underside of the dome door arch.
Then today laid the tiles to the front of the dome. These are heavy old floor tiles so will be interesting to see how they hold up to the weather. Might well seal them once they are grouted in.
And finally this evening lighted my first small warming fire. Dome external temp hardly moved maybe plus 1.5 degrees, but it was only a gentle fire. Will maybe do another one tomorrow if I get a chance
Cheers,
MM
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Post by oblertone on Sept 16, 2019 11:21:09 GMT
Slow and steady does it for 'curing' fires; it's also important to let the oven cool completely between firings as this helps the moisture migrate to where you can drive it out.
Also consider making a removable wooden door for the very outer lip, this prevents cats making nests and goes some way to keeping moisture out.
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mm289
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Post by mm289 on Sept 16, 2019 17:02:56 GMT
Cheers oblertone, I have a steel door for the oven, would the wood door be in addition to that?
Thanks,
MM
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Post by oblertone on Sept 16, 2019 19:05:34 GMT
It all depends where the steel door is going. If it's to be placed inside your entry arch to separate the oven from the flue then that's fine, if however it's going to be decorative and close off the outer arch then it'll do just as well as a wooden one but might get in the way when the oven is in use.
I use a steel insulated one to close off the oven, and a wooden door to close the outer arch (when cold). The use of a wooden inner door is not recommended.
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Post by downunderdave on Sept 16, 2019 19:43:14 GMT
It all depends where the steel door is going. If it's to be placed inside your entry arch to separate the oven from the flue then that's fine, if however it's going to be decorative and close off the outer arch then it'll do just as well as a wooden one but might get in the way when the oven is in use. I use a steel insulated one to close off the oven, and a wooden door to close the outer arch (when cold). The use of a wooden inner door is not recommended. I use a wooden inner door for my ovens because it’s traditional and looks good. But it has a one inch insulating panel also. To reduce conduction the panel stands off the wooden face slightly by beads of high temp silicon. Even so, the wood will burn if the door is placed in position after a pizza cook up and left until morning. I recommend it not be placed if the temperature exceeds 300 C which is higher than you need for baking and roasting anyhow. The disadvantage of steel or other metals is that they are very conductive making them dangerously hot unless very thick insulation is used which then makes them unwieldy.
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Post by webbm00 on Sept 16, 2019 21:00:31 GMT
It all depends where the steel door is going. If it's to be placed inside your entry arch to separate the oven from the flue then that's fine, if however it's going to be decorative and close off the outer arch then it'll do just as well as a wooden one but might get in the way when the oven is in use. I use a steel insulated one to close off the oven, and a wooden door to close the outer arch (when cold). The use of a wooden inner door is not recommended. You can't close off the flue in these ovens as it's inside the dome. The best you can do is a flue damper
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mm289
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Post by mm289 on Sept 16, 2019 22:17:49 GMT
Cheers guys, the steel insulated door sits inside the brick arch at the entry to the dome and as webbm00 says closes the front of the oven but doesn't close off the flue. The steel chimney has a damper, although at the moment with my clay chimney I am just using a clay lid as a damper on this.
So the theory would be, lid on top of flue and door in archway should close off the oven, albeit their is a small gap around the steel door.
Cheers,
MM
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mm289
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Post by mm289 on Sept 17, 2019 20:44:45 GMT
2nd fire lit tonight, warmed it up to about 200deg - was interesting how easily I could control the heat with the door. One hairline crack eminating from the chimney and going down 1 side of the dome - think this is probably where the clay chimney has expanded more than the render can cope with. Apart from that all OK so far...... Cheers, MM
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