New Build on this side of the Pond

[underpendle]

Just a thought. if the reasoning behind not mortaring the dome to the hearth is expansion. would the same be achieved by laying the first course on newspaper? and hence giving the dome a more stable base.
I have no experience of ovens whats so ever so forgive the daft observations but with a well insulated build, I would have thought the expansion of the dome and hearth would be very similar, the coefficient of expansion obviously the same using the same materials.
I plan on 100mm 28kg blanket immediately over the fire brick, and then a vermicrete mix on that. To the rear of the oven this void will be completely filled. I plan to build on this area as part of the flue. initially with a vermicrete mix, but then also some structural concrete.

Suppose what I'm getting at is how much will this lot move?

S

[david s]

Unfortunately the rate of expansion is not the same because the oven gets hotter in the crown of the dome than lower down at the base because heat rises. This causes a different rate of expansion. Because the expansion is directly proportional to the temperature there can be a huge difference in expansion. This problem is exacerbated when the oven is new, during the stage when you must drive the water out slowly. The top will dry first and consequently the temperature there will rise even higher while the bottom is still wet and its temperature is held down. This is why it is recommended to allow the oven to cool to ambient and you can begin again.

[SableSprings]

... A question if I may, when you say your dome i set on the floor, I assume you mean laid on a similar sand/clay mix?. I had considered this but was erring toward laying on home-brew?

Simon, I first laid out my hearth (cooking floor) level and then put my first chain of the dome on the perimeter of the hearth. (My brother-in-law is pretty experienced at brick work so he showed me how to set and level the cooking floor.) The first chain was only lightly mortared in place, since the second chain really set everything solid. As you can see in the pictures, we didn't have to cut hearth perimeter bricks...just needed to make sure every brick of the dome's first chain was sitting solidly on a hearth brick.

As David S explained so well in his post above, that initial curing process and consequent firings move things around in different ways. I'm positive that my light mortar bond between the base dome and the hearth bricks was broken well before my curing process was done.

[underpendle]

Cheers Guys.

Think I'm going to go with this then. Unless someone sees an obvious disadvantage. I'm planning to lay the hearth bricks loose but bed my first course on home brew, laid directly on the hearth but with a layer of newspaper put down first. My reasoning being that the dome will then have a solid base but the two should be able to expand/contract independently. Had a quick search for some coefficient data but couldn't see anything readily.

Im considering taking the arris of the hearth brick before I lay them, maybe 2mm? I'm sure I've read somewhere that someone did this but a forum search doesn't turn anything up. Have any of you tried this?

S

[SableSprings]

Cheers Guys.

Think I'm going to go with this then. Unless someone sees an obvious disadvantage. I'm planning to lay the hearth bricks loose but bed my first course on home brew, laid directly on the hearth but with a layer of newspaper put down first. My reasoning being that the dome will then have a solid base but the two should be able to expand/contract independently. Had a quick search for some coefficient data but couldn't see anything readily.

Im considering taking the arris of the hearth brick before I lay them, maybe 2mm? I'm sure I've read somewhere that someone did this but a forum search doesn't turn anything up. Have any of you tried this?

S

I'm not sure I understand this correctly...I'm thinking (hoping) you mean to lay down newspaper on the perimeter of the cooking floor and then mortar the base dome bricks together (sides only) on top of the newspaper. My first reading of your post made me think you were going to lay newspaper on top of your cooking floor perimeter and then lay down a layer of homebrew. Then you'd plan to bed the base chain bricks in that layer of homebrew...I don't see that laying down a layer of home brew on the newspaper and then setting (bedding) the first chain on top of that has any advantage...in fact, if your cooking hearth floor is level, adding a base layer of homebrew to bed the first chain of bricks will introduce "leveling issues". Hopefully, I just was misreading this and you are not putting an extra layer of homebrew down on the newspaper... With the newspaper layer, there will be no "stick" between the hearth and the base dome chain...so no point in putting homebrew on the downside of the dome bricks. The little bit of mortar that will naturally settle down from the side joints will be the only bonding material that touches the newspaper...newspaper will keep your cooking floor bricks clean from splattered mortar but I'm not sure of it's value under the dome chain.

As to "taking the arris of the hearth bricks" ...I don't know what that means... ???

[JRPizza]

I laid my dome bricks on top of the hearth, and used a layer of newspaper to keep the mortar between the first course from sticking to the hearth bricks. I don't know if it was necessary, but I saw it suggested in a few threads and it seemed like a good thing. No mortar between the first course and hearth was used.
I think by arris you are talking about doing an "edge break" or chamfer/radius on the edges of your hearth bricks. Might be a good way to prevent catching on your peel and pots, but I just laid mine in a herringbone pattern and tried to pick bricks that fit well with their surrounding siblings.

[underpendle]

Thanks again for the reply.

The arris of a brick is the edge where two faces meet. So I think what JR describes as an edge break is the same thing. If I get finished at a reasonable time I'll do a couple tonight and post a pic. My idea of what is a reasonable time to run a grinder and wifey's ain't always the same:-)

Mike. Yes I had planned on bedding the bottom course. Reading your post I think you are advising just laying direct on the hearth brick? I don't have any problem with that other than the potential for creating point loads. the fire brick I have are pretty reasonable so I think I'd be getting a reasonable contact area with no bed at all. Sorry if I'm labouring the point, but I'm not not used to dry laying anything, always use a bed to effectively spread the load.. Hence my idea of the newspaper.

Cheers
S

[SableSprings]

Simon, JR - thanks for the explanation of arris. It's a new term for me...I initially did a Google search and only looked at the first results page which references an American Telecommunications company .

Simon, yes indeed I was advising just laying direct on the hearth brick. I had used a very thin mortar layer to set my base chain but realized as I set the second chain that it didn't serve any purpose for my dome build's stability or strength. Going by the forum builds (JRPizza's is a great example - link to his build in post #51 above. Go to his second page and look at the pics in posts 17, 23, & 24), I'd say the percentage of direct/dry lays on the first chain is pretty high and no one's reporting problems with that method. My bricks seemed to set nicely on top of the hearth bricks and I never considered point loads. If I had any irregularities, the thin mortar layer took them out of play. The reality is, which ever method you're comfortable is fine.

As to the arris rounding, I simply used the herringbone pattern like JR did and haven't had any problems with a peel catching. I'm sure that choosing bricks carefully and leveling to minimize exposed edges is all you need. Rounding the arris will create little furrows that will hold a bit of ash...so you might have a little more difficulty "cleaning the floor" before putting a pizza in...not to mention adding a bit more work to your build. Again, whatever you're comfortable with is the way to go as these are all pretty minor issues in the overall big picture of the build.

[underpendle]

Cheers Mike.

Just about managed a bit of a play tonight. Took the arris off a couple of cuts and I think OK? an additional advantage being that this would decrease the chances of spalling. As you point out also a place for ash to hide. I'll ponder this for a while. A doddle to do, just tickled them with the grinder, recon I'd have the whole floor done in less than an hour.

Set the floor out, I also have used a herringbone pattern and freehanded a few cuts and the first arch/dome brick, angles a bit out, was losing the light by then so gave up for the eve. I have projected my arch 30mm from the dome inner circumference. I recon to have drawn this out on auto cad and seems to work ok, think I may dry build the arch though before I commit.

[SableSprings]

Looking great Simon!

I'm sure you've thought of this, but when you lay out the herringbone pattern set the front bricks so that you are cutting off the "little triangles" instead of needing to cut little triangles out to fit (like I had to on my hearth entry--first picture of post #48 above ). I believe that tip came from David S and I think it's a terrific detail/technique for setting in the cooking floor!

The arris beveling looks great...I think I may have been imagining a far deeper rounding (based on my skill level, I'm sure it would not have looked as clean as yours does). If you use the blow tube or peel slap method to clean off the ash I suspect it will work A-OK. I also never thought about spalling on the edges of my hearth bricks...so far I haven't seen any problems on mine, but definitely an interesting note for future builders to consider.

[underpendle]

Yes I'd clocked that, think it may have been on your thread I'd seen it. I hope to make some progress this week, will post any progress I make. Feel like i'm swimming up stream with work at the moment so not sure how much that will be. I'm trying to get the rest of the house a bit more finished for Xmas, wifey keeps talking about the sitting room. She doesn't seem to think an oven is as important as the front room!! Cant think why:-)

S

[Gulf]

Simon, Mike,

I did the herringbone pattern to keep the peel from catching. Over the last year or so, I have started noticing something with my floor brick. The corners (arris) are becoming slightly beveled. Wether it is spalling, sliding cast iron pots, or the "peel slap", it is happening. In my case. it might be a combination of all the above.

Mike, Have you looked real closely at your floor brick lately. (I have to use reading glasses to do that ) I'll try to get a pic of mine as soon as I can.

[underpendle]

Got the hearth laid this eve. Went with the idea of taking the arris of prior to laying, only took about 20mins.

I smeared the CaSi with Marg before then using a mix of sand and fire clay. I mixed with water using a whisk to about the consistency you use to lay block. `Wetted the fire brick prior laying. Then went over the whole lot with a board and rubber mallet. Think I'm pretty happy with the result, will look at tomorrow when daylight. Option of going over with belt sander before starting the dome if required but I think it'll be OK.

Mike following on from our discussion re laying the first course, I'm erring toward using the same mix for laying the first course with Home brew to motar the vertical joints. I had a little mix left over so I have stuck? a couple of bits of scrap together will see how they are in the morn, I'm thinking they will have formed a loose bond which will shear relatively easily,

Cheers S

[SableSprings]

That hearth looks great Simon! Don't think you'll need the belt sander. Good idea using the mix with a "loose bond" for the first course. Again, don't use very much since you don't want loose pieces coming out onto the cooking floor . Incidentally, I'm starting to really like the idea of smoothing the arris a bit during the build (see below) -- thanks for bringing this up.

Simon, Mike,

I did the herringbone pattern to keep the peel from catching. Over the last year or so, I have started noticing something with my floor brick. The corners (arris) are becoming slightly beveled. Wether it is spalling, sliding cast iron pots, or the "peel slap", it is happening. In my case. it might be a combination of all the above.

Mike, Have you looked real closely at your floor brick lately. (I have to use reading glasses to do that ) I'll try to get a pic of mine as soon as I can.

Joe, I've attached a couple pictures I just took of my hearth bricks (sorry the lighting's so crappy)...interesting that my bricks now appear to look like Simon's "de-arrised" hearth bricks. As you said, could be from several different mechanical actions...certainly isn't hurting anything, but it's very interesting. I also think that the simple expansion of each floor brick during firing creates a space between them when they cool...sort of like birds on a wire all sitting 2 wing widths apart. Each brick simply pushes out and the result is even gaps throughout the cooking floor bricks...actually it's very cool! If I do another oven or help someone in their build, I'm leaning toward using Simon's technique with the hearth bricks. Looks like that + the herringbone pattern will definitely keep any peel from catching even if the bricks lose a little of their level.

[underpendle]

Got a bit of time to play this aft so set up the arch. Started too taper it but ran out of time, hope to get this finished tomorrow aft if I'm home in time.
I've dropped a bit of a bo....ock. I'm a tad short with my CaSi board at one point. Don't know quite how Ive managed that but there you go, thats what comes of doing it in the dark I suppose. Anyway easy enough to sort I can nick some from where the landing is going. I'm planning on a complete thermal break here with a piece of thin stainless to prevent any damp ingress. Utah beehiver I think suggested this?

My question is whats the norm for insulating under the landing? In my opinion which is of course based on zero experience i would have thought thermalite would be fine here, it's not really doing anything. Would the recommendation be to cut the insulation off plumb with the front of the hearth and run the stainless to the deck or leave some in? Any thoughts?

Don't really want to have to buy another sheet of CaSi If I can avoid it. Its the shipping that kills it. However not the end of the world If I need to.


Cheers S