42" build in McPherson KS

[slschoming]

UtahBeehiver Yeah, I think Saturday was sort of my last hurrah before winter, though we usually get a couple warmer weeks during winter that I might be able to take advantage of... However, I will be taking a break to rethink my oven size...

I think I may be able to increase my dome size a little bit now that I have the overhanging hearth. I will be using 9 inch firebrick (split) for the dome. I am trying to get an idea of my overall final "dome wall" width so I can decide how much extra I really can expand. Is 2 inches of FB blanket a common/adequate amount of insulation? I keep reading that you can't over insulate, but I am just curious what is the most common insulation width on the dome. Maybe 2 inches of blanket and then 2 inches of vermicrete?

[UtahBeehiver]

2" of ceramic blanket is your minimum amount, if you add 2" of 8-10 to 1 p/crete then you are golden, skim coat with render and then final coat of choice.I cannot recall if you are enclosing or not. If you were, I would do 2" of ceramic blanket then fill the enclosure with dry perlite or vermiculite.

[slschoming]

UtahBeehiver I am hoping to build an external brick dome around the oven, similar to cobblerdave's oven.

So with 2" of ceramic blanket being the bare minimum around the dome, does the same go for 4" of vermicrete under the floor? should I be increasing my floor insulation as well?

[david s]

Glue some insect screen over the holes before you lay up the vermicrete. This will prevent it falling through the holes.

[slschoming]

Glue some insect screen over the holes before you lay up the vermicrete. This will prevent it falling through the holes.

Thanks for the tip, I was planning to put insect screen on the BOTTOM of the tube to keep bugs out, but hadn't thought yet about how to keep the vermicrete from going down the holes. I blocked the tops off by stuffing wads of paper towel before I poured the hearth but I knew that wasn't going to work for the vermicrete layer since I can't punch through from the bottom again.

[slschoming]

Removed my forms. My edges didn't come out very clean in a few spots. Can this be filled in with something?

[SableSprings]

The gaps in the concrete edges (along the forms) are fairly common...that's why you see folks tapping the forms during and just after a pour. The tapping settles the concrete and the air gaps get filled in. The issue is very minor in terms of your slab strength and utility. I tiled the outside of my foundation stand and simply filled in the rough spots along the top edges of the platform top with mortar or thinset...which ever was handy at the time. I suspect you had planned to finish the outside of the CMUs and it could be covered up at that time. Otherwise, simply make up a batch of mortar and fill/smooth out those areas. Relax, it's looking good (and very normal!)

[slschoming]

thanks SableSprings. In places where the hearth is flush with the CMU wall I plan to stucco so it looks like a continuous wall and I will pour a countertop on top of that. On the side where the hearth juts out from the CMU wall (the oven side) I haven't decided if I will pour a countertop or if I will try to stain/polish/finish the hearth itself to give it more of a two-tiered look.

[slschoming]

I was trying to describe the final product to my wife and she told me to just draw a picture.. Here's a very rough sketch of what I'm going for..

[slschoming]

I removed all my supports and popped out my weep holes... I guess I was a little deeper than I meant to be and it didn't pop out as cleanly as I hoped but it should do the trick.

I won't be able to work this weekend, but I have a couple questions for future work days...

david s You seem to be the expert of the crown method. I plan to build some sort of mound between the weep holes to direct water. Would standard mortar work for this or do you have a better suggestion?

UtahBeehiver As nice days present themselves over the winter months will I be able to do a course here and there, or should I be holding off on the dome until spring? I have never done any masonry before this project, but I am anxious to get going on the dome. However, I don't want to compromise the strength of my dome. Say I have a nice afternoon of 50 degrees but it's supposed to freeze overnight... would that be undesirable conditions for laying a course of my dome?

[david s]

The slight depression created around the weep holes should work to your advantage, rather like a drain in a shower base. Re mounding the supporting slab it’s probably more important to have the supporting slab sloping down slightly from outside the outer shell so water is discouraged from entering there in the first place. It is far easier to form the supporting slab in this way when pouring and forming it. I gues you could build up a topping layer though.

[SableSprings]

As David noted above, making a slight slab "dome" to keep casual water moving away from the base of the oven is best done at the time of the pour. Your weep holes will work great to allow exit points for moisture. Instead of trying to add a concrete topping layer now, I would suggest putting sheets of glass or porcelain tiles between the slab and the insulation board. Here's a thread link explaining the concept and if you go to post #19 in that same thread, there are some good photos showing the tile layout. You can often find excess/discontinued pattern tile sheets at garage sales and in the clearance sections of large hardware stores (Home Depot, Menards, Bunnings, etc.) at give-away prices...or in a friend's storage shed that does a lot of handy-man chores (and who might like a future pizza party invitation )

https://community.fornobravo.com/for...444#post407444

If you lay the tile sheets with the mesh base up, the support for the insulation board is better and the channeling to the drain holes is more open.

[slschoming]

SableSprings I was planning to use vermicrete rather than insulation board. I still have scraps of hardiebacker board.. Do you see any issues with maybe putting a layer of hardiebacker on top of sheets of scrap tile and then pouring the vermicrete layer on that?

[SableSprings]

The advantage of having the tile scraps between the top foundation slab (hearth) and the insulation layer is simply creating a draining system/water barrier gap to keep water from seeping up into your insulation. It doesn't matter whether it's board or vermicrete, so I don't see any issue with the slab-tile sheets-hardiebacker-vermicrete-leveling sand/fireclay-cooking floor order. Since you said scraps of hardibacker, I assume there will be some small gaps between pieces that will help water drain out of the vermicrete down to your weep holes through the channels between individual tile pieces. Just make sure that you don't position any gaps directly over a weep hole (to avoid a possible plug forming--probably not an issue since your weep holes have a nice "collection basin" that popped out of the concrete). The hardibacker I've used has a slightly depressed grid system on one side...if your backer board does also, put the grid side up.

I assume you are planning to lay your cooking floor inside the dome (most do that rather than setting the dome footprint on the cooking floor bricks). Either way make sure your lower layers are wide enough to act as the insulation base for the entire footprint of the heated oven components.

Where are you located? It helps sometimes to know the build's general climate area when answering questions.

[slschoming]

SableSprings Thanks for the info. I am located in the middle of Kansas.We're to the point now where we occasionally freeze overnight. Daily highs ranging between 45 and 60 F. I was wondering if I should be calling it quits for the winter, or if I still have some workable weekends. I was also curious if it would be out of the question to do an occasional course of my dome on warmer days in the winter or if I should be planning to wait for the spring.