36" Pompeii Build Redux - This Time In CA

[rsandler]

Picked up the inevitable Harbor Freight brick saw yesterday (I sold mine from the last build to make room for woodworking tools) and the rest of the ingredients for home-brew mortar. Besides getting the saw set up and generally organizing my workspace, I also went and ground down both the exposed rebar and all the exposed PVC from my weep holes.

Anyone have thoughts on when I can remove the bottom supports for my raised slab, given the shorter spans from the H-shape block stand? "When to remove the forms" is a question that's asked all over the place on the forum, and I feel like I've seen answers all over the place as well. I've left the side forms on to help with moisture retention for the first week, and plan to take those off tomorrow once it's been a full week. Less sure about the bottom forms. Would be nice to at least pull out the supports from the cast lintels (almost two weeks now since those were poured) so I can get underneath and make sure my weep holes go all the way through before I put insulation down.

[MarkJerling]

7 days is fine for a small slab. 14 days is preferred for larger slabs.

[rsandler]

Some people have leg days; for me, today was a jig day :-P. Spent most of the day in the garage making jigs for the oven.

First picture is the arch form, nothing fancy there.

Second is the Indispensible tool. I re-used the castor from my original IT (held onto that thing for 11+ years, go figure), but used an offset design that I saw somewhere around forum. The wood block in the pivot extends exactly 1.25" above the pivot point, so the tool should hit my dome bricks in the center of the 2.5" brick height. What I liked about this design is it should make it easy to get purchase for a clamp to hold the bricks in--I recall on my first oven, the clamp could only ever apply pressure toward the top of the brick, which would often push it out of alignment if I didn't orient the clamp just right.

Original plan was to anchor the IT to a sheet of plywood that would also protect the floor. Had this great plan of how I was going to build the cover/anchor out of two sheets for easy removal, and use my circle-cutting jig on the bandsaw to get a perfect shape. In the end, my circle cutting jig slipped, cut the circle 2 inches too small, and I didn't feel like going back to HD for more plywood. So, plan B: fake brick in the center of the floor, with a lower pivot point and a lower dome ceiling. The pivot is still a little above the floor, but at this height the IT should line up almost perfectly with the top of the half-soldier course.

Third picture is my brick-cutting jig for dome bricks. Because the new HF brick saw has a bevel adjustment, I just needed an angled fence, and to get the cutting surface higher so that I can raise the blade above the sliding table's fence, and avoid cutting that. Put one coat of spar urethane to keep the plywood from warping or delaminating; I'll put at least two more on before it's time to start cutting.

Also laid out my floor pattern, though I need to set it up again and mark where to cut the edge bricks, probably with my shiny new IT.

[rsandler]

My insulation is supposed to arrive at the local Distribution International location tomorrow, so getting ready to start placing it. The former owners of our new house left us a bunch of bricks and tiles and things, including a bunch of small clay tiles. Decided to use those to keep the insulation off the slab and allow room for drainage.

Two questions:

1. My suspended slab is not very flat, and undulates a bit. Consequence of having the tubes for weep holes sticking out during the pour and not being able to screed well. Using the tubes was definitely a mistake; should have just planned to drill holes with a masonry bit. Anyway, should I try something with self-leveling concrete, set the clay tiles in sand or mortar or something to level them, or just leave it as is as long as the insulation is level and doesn't wobble?

2. Do the gaps between my elevation tile look reasonable? Not sure how much the CalSil can safely span with the weigh of the oven on top. Between the size of the tiles and the placement of the weep holes, some are spaced as much as 2" apart. I guess probably most important to avoid gaps around the perimeter, since the middle only needs to support the floor bricks?

[Giovanni Rossi]

My bottom layer of insulation is FOAMGLAS. From handling it, the surface will deform up to a point and then stop. The CaSi board I used had a much more rigid surface. I would think it could span 2", but the engineers / more experienced builders should weigh in. Sounds like the number of tiles is limited, so I think your idea to have tighter joints under the dome is prudent.

Those tiles look thicker than most others have used. While not an issue on its own, I just want to remind others that all of these early decisions impact the final height of your floor.

As far as the level issue, I wanted to start as level as possible so I didn't have to adjust while laying the dome. It wouldn't be too difficult to true up your slab with an angle grinder.

For future builders reading this thread: I'm glad I placed the drainage tubes before pouring the slab. Just position the top 1/8-1/4" below the top of the slab. Stuff the top of the tube with some waterproof material (I used polyester fill). After the slab is cured, you can then run a rod up from the bottom and pop the core out.

[SableSprings]

The tiles you have are just clay...they will wick the moisture up into your insulation. You need to have porcelain or glass tiles that are impervious to water. That's why the mosaic tile sheets are recommended...not only are they a block to the moisture, but the spacing on a sheet of tiles is perfect. Flipped over, so the mesh backing on the tile squares/sheets is up, provides great support for the insulation above. The mesh is also adequate to keep particles of vermicrete or perlcrete from dropping through and blocking the channels (if you go for that insulation type). Lots of places have orphaned sheets of mosaic tiles for very cheap...they certainly don't need to match each other!

As Giovanni noted above, placing the drain hole tubing just below the expected top surface of the slab pour is the way to go. After the forms are removed, a piece of rebar or steel bar can be used from below to pop off the top cap of concrete. This has the advantages of allowing you to screed the top of your pour and creating a little collection funnel around the weep hole when it's cleared from below. Sorry that your setup didn't allow for a good leveling experience...but the drilling method would not have been pleasant either...especially if you hit a piece of rebar...

Can't tell how uneven your hearth surface is but the CalSil will accommodate a little unevenness.

[rsandler]

Hmm, thanks for the warning. I'll see if I can track down some less porous tiles. I wasn't bothered by the thickness--I'm actually hoping to get my oven deck a bit higher on this build, since I found I was leaning down a lot on my previous one. But if they aren't doing anything useful, I should look for something else, or skip them. I'm getting the newer Thermo 1200 CalSil, which is supposedly water resistant.

Good tips on the weep holes; wish I'd known/thought of that ahead of time. Oh well!

FWIW, I had to drill out my tubes because they got filled with concrete, and drilled another hole at a low point in the slab where there was no tube, and didn't find it that hard. But, I was lucky and didn't hit rebar either!

I will say more generally that I'm struggling not to overthink/over-optimize. Lots of great advice on the forum since my first build (and stuff I missed on my first build), and there's a temptation to try to do every little thing to improve performance. At the same time, my oven in DC worked great for me for over a decade...

[AJH]

What floor height are you shooting for in the oven and what was your previous height? I'm about 6' tall and am looking at 46" for the floor height... I did a mock up with some cardboard and a broom and felt like that was comfortable for working a peel.
Are you doing the floor with 2.5 inch brick or laying them on their sides for a 4.5 inch thick floor?

[rsandler]

What floor height are you shooting for in the oven and what was your previous height? I'm about 6' tall and am looking at 46" for the floor height... I did a mock up with some cardboard and a broom and felt like that was comfortable for working a peel.
Are you doing the floor with 2.5 inch brick or laying them on their sides for a 4.5 inch thick floor?

My old oven was 40.75" above the foundation. I was scratching my head about the math of that--a stand 4 blocks high is 30.5", normal suspended slab is 3.5", I had 4" calsil and a 2.5" thick floor, which comes to 40.5". Sounds like my normal level of incompetent masonry there :-P.

Anyway, for this oven I figured adding another 2" would be plenty, but 2.5" with tiles wouldn't hurt either. Might have skipped both if it hadn't worked out to get extra CalSil. Mind you, I'm a sight shorter than you at 5'7", so my 40.75" oven was maybe just a little shorter than ideal. Once I get the insulation (tomorrow, apparently!) I'll mock it up with my floor bricks and make sure it's not too high.

[rsandler]

Progress! The insulation arrived from DI this morning. Ran out to the Big Orange Store for a few extra things, including some cheap glass mosaic tiles that were on clearance. Got the insulation all set, and placed the wood block with my IT so the pivot point will be centered. Took the angle grinder to the worst of the high points, such that the CalSil lies more or less flat. Some have a bit of a wobble, but they flex enough that the weight of the bricks should keep everything steady. Just placing a couple test bricks caused them to settle in place.

That was all I had time and light for today. Hoping to start laying/cutting my floor tomorrow. Probably going to skip the sand/clay/water floor setting mix, but I'll see how flat things are directly on the CalSil.

[david s]

If you mix water with the clay/sand mix it will simply be absorbed into the cal oil board making string the bricks extremely difficult and the water will have to be removed anyhow. You are better off leaving it dry. If there's no difference in height in the floor bricks you may not even need a levelling mix.

[rsandler]

Got the floor laid and mostly cut this afternoon; needed a couple little triangles to fill in around the edges but didn't have time. Didn't use the leveling mix, as the floor was acceptably flat without for the most part. There's a couple small ridges, and a couple that wobble a bit. Might just let it be, or might pull the wobblies and put a little dry sand/clay mix down under them. Probably will hit the ridges with the angle grinder after I get the soldier course to hold the floor in place.

Aside: The new model HF brick saw is pretty nice; cuts well even with the included blade, pump puts out enough water that the dust is minimal, the rubbery table holds bricks in place at arbitrary angles remarkably well, which helped a lot in cutting the floor edge bricks. The pump is so powerful, it goes through a ton of water! I extended the water tub to run the pump out of a 5-gallon bucket (having destroyed the pump on my first saw running it out of the discharge tray), and I need to refill the bucket every 20 cuts or so, it pumps so fast. I'd need to empty the water try nearly as often, so some kind of auto-refill mechanism won't help much. I guess I get an automatic reminder to take breaks!

Hope to get the soldier course and start my entry arch over the weekend. Exciting stuff :-)

[AJH]

Progressing at breakneck speed!
Looks like you decided on 6 inches of CalSil board under the floor =) Do you still have enough for a decent insulated door?
What did you end up for a floor height with that?

[rsandler]

Progressing at breakneck speed!
Looks like you decided on 6 inches of CalSil board under the floor =) Do you still have enough for a decent insulated door?
What did you end up for a floor height with that?

With my floor bricks already picked out, this part came together really fast, actually. Makes it look like there's something there other than the world's smallest bomb shelter :-).

This arrangement of CalSil boards uses 5 per layer; since they come 9 to a box, I've got an extra 3. Plenty for a door.

Floor seems to be at about 43" above my slab. I think that will be good, but since I don't have an established patio around the foundation, I can fudge when we put in pavers if need be.

Work on the arch is going much more slowly; may finish today but the soldier course is looking unlikely (or maybe I'll just do the first couple arch bricks and go mortar the soldiers? not sure). Took me all morning to get the arch bricks tapered, and I haven't started cutting them to match the curve of the dome. The perennial problem with a 10" brick saw--you can't cut a brick on the 4.5" side. I figured I could raise the blade and just cut the maximum cut depth, leaving the outside of the brick un-tapered (no one sees that part of the joint anyway). But the pivot point for the motor actually gets a little lower when you raise the blade, so you still hit the mount trying to cut a full brick. Ultimately decided to rip the arch bricks to ~4" width before tapering. Which was fine, just tedious and time consuming. Looking forward to getting back to cutting bricks on the 2.5" dimension :-P.

[rsandler]

Well, the arch and soldier course took a lot longer than I planned--all the rest of Sunday, plus long shifts Monday and Tuesday afternoons after work. If I was still working East coast hours and commuting (or just couldn't spend every evening making progress, I think it would have taken a week or two. I was trying to make sure that the arch bricks extend all the way to the interior surface of the dome, but that mean a lot of fiddly cuts. I also learned from my old oven that it's really important to keep the reveal on the outside of the entry arch plumb and in plane so that the door seals well, and either had to fiddle or re-do a couple arch bricks that were out of true.

On the other hand, I also learned from my last build and from my woodworking exploits in years since, that there are parts of any project that no one will ever see, and those parts don't need to look pretty :-P. So although the inner-facing surface of my arch is very scraggly, no one will ever know once it's bricked over .

Not sure if I'll start cutting bricks for the first course today, or pause and clean up the work site a bit. I was so eager to lay down insulation and bricks when the CalSil arrived, the lumber from the slab framing is mostly strewn about the yard...