36" in Seattle

[kebwi]

Re: 36" in Seattle

Yes, we want the pad to extend far enough in front of the oven to stand on while working. That's what you mean by apron? I'm not sure I fully understand the joint you are describing. Sometimes I see construction joints described merely as a shallow gap of about a quarter inch width that extends about a quarter of the depth into the concrete, not all the way to the bottom, as in two separate pours. Are you suggesting two separate pours with a gap that extends all the way down to the gravel?

Some detail would help. I readily admit I don't know much about proper concrete foundations.

Thanks.

[Neil2]

Re: 36" in Seattle

A construction joint can be one cut into the concrete or it can be simply the joint between two pours. Your slab will have two different loadings, one where you stand and the rest supporting the weight of the oven. This will cause stress which will almost certainly crack the concrete. The construction joint ensures it will crack at a particular line instead of irregularly.

If your slab is 5 1/2 inches, you can build the entire form, place the rebar, and use a 2 x4 as a "bulkhead" to contain the first pour. The re bar can run under the bulkhead or you can notch the bottom part of the bulkhead to accommodate the rebar. The next day, remove the bulkhead and pour the other half.

Get a concrete edger (see picture) and use it on the edge of your slab and each side of the joint

[kebwi]

Re: 36" in Seattle

It sounds from your description like you don't think I need an actual gap along the joint, since I think you suggested pouring the second slab right up against the first slab. Is that correct?

I certainly want to do this right, but the frustrating thing about breaking the pour into separate jobs is that I intended to do the foundation with ready-mix. There's no point in having then come out a second time for the smaller slab since that's smaller than the hearth which I'll be doing on my own anyway.

The question then becomes, is there any point in using a ready-mix truck for the slab under the foundation or is it now small enough (with the separation you suggested) that I should just go ahead and do it myself. I just don't have many friends I can lean on for this type of work, and I only have one wife.

That'll take some thought. I'll have to determine the best way to proceed.

Thanks for the input. I'll take it under heavy consideration.

[Neil2]

Re: 36" in Seattle

"I think you suggested pouring the second slab right up against the first slab. Is that correct?"

Correct.

This is the simplest way to ensure a construction joint. If you are going to do it in one pour, you can also use the edging tool and a 2x4 to tool in a double sided joint. This will create a stress line and should control the crack to that location. (Take a look at the sidewalk in front of your house - if you look closely you will see the crack in the tooled joint),

It is just an aesthetic issue and will not affect the structural strength of your slab.

[kebwi]

Re: 36" in Seattle

Cut the straight boards for the foundation form today from 2x6s. There are two places where I will curve the form with masonite. Grinding rebar is ridiculous loads of fun btw. After all my worries about rebar, everything worked out. I pipe-bend the 1/2" 20' rebar (barely with my 160lbs) in the Home Depot parking lot to get it on my roof rack. Then at home I cut it up with the grinder, which is a cinch.

On a side-note, do most people put the handle of an angle-grinder on their "handed" side or the other side? I've tried it both ways for this project (and also used angle grinders at a rock-climbing gym a few years ago), and still haven't decided on my preference. Thoughts?

[kebwi]

Re: 36" in Seattle

@Neil2: I warming up to the idea of doing the foundation myself over two days, using your suggestion of pouring the main foundation one day, framed off tightly around the building's footprint, then following up the second day with the extended chef's slab (in the diagram, both red and green are concrete). My calculations put the main foundation at 37 60lb bags if poured 5" and the extended slab at 16-22 60lb bags if poured somewhere between 3.5" and 5", which leads to this post's question...

Do you think it would be okay to pour the main slab to 5" but raise the gravel in the "extra" slab an inch and only pour it to 3.5" to 4"? The rebar and mesh (mesh not shown) will actually connect the two slabs into a single piece even though the concrete won't be bonded along the seam.

What do you think?

[papavino]

Re: 36" in Seattle

I would think it would be okay to raise the gravel and only pour a 3.5 or 4 inch slab for the chef's slab. It's not going to be supporting the weight of the oven, so unless you weigh 6000 lbs, I think you'll be alright. Why not buy 80 lb bags of concrete and save some dough? With the amount in a slab, that money adds up.

[kebwi]

Re: 36" in Seattle

Home Depot and Lowes both currently sell 60 lb bags for $1.98 ($.033/lb) and 80 lb bags $3.48 ($.0435/lb). I think the 60 lb bags were just recently marked down from $2.98 ($.0497/lb), so the discrepancy is recent and perhaps temporary.

Therefore, I gotta stock-pile like mad!!!

[papavino]

Re: 36" in Seattle

That's a good deal, then. I wish they had been running the sale when I built mine. Buy! Buy! Buy! Buy more than you need. Because even though your calculations tell you you need X, you'll really need X+Y bags. And you can return any unopened bags.

[Neil2]

Re: 36" in Seattle

Yes, the apron can be thinner.

Looking at your plan, I would also put a tooled construction joint between the two sections of apron. Maybe at a 45 degree angle through the "thin" section of apron.

[kebwi]

Re: 36" in Seattle

Yeah, I had a similar thought actually, just to keep the concrete patches semi-rectangular to encourage rational cracking. Thanks though.

[Dino_Pizza]

Re: 36" in Seattle

Ya, I agree with Papavino, pouring the thinner slab after with the rebar connection is fine. BTW: your Meshworks drawings are great!

I was lucky enough to have a friend donate prebent rebar and I did a lot of tying rebar pieces with rebar wire to connect them as well as overlapping the rebar in the brick cells and filling most with concrete. (see me picasa web album folder on the foundation).

Also, although it was a pain, I used construction string (you've seen the pink and yellow stuff at HD) and tied them to wood stakes 2 feet from the slab pour, so that after I floated my slab, I put the strings back up and they intersected at the 4 corners that marked the middle of the 1st block cell in each corner, then slipped a piece of rebar into the wet cement so I would have at least 4 pieces of rebar sticking up out of the slab. When cured (5 days later) I then I dropped my corner blocks over those rebar and filled those cells with concrete. Ideally, you should use a "J" hooked rebar, pre bent, but a straight pieces stuck into the we cement is better than non.

Since you are in earthquake country, your attention to good rebar reinforcement is a wise idea. Good luck on your build, it's good to see someone put so much attention and thought into it and it will make for a well made oven.

[kebwi]

Re: 36" in Seattle

Thanks, Meshwork is a nice tool. It's pretty dated, and unfortunately, the last version that was ever produced is lacking some fundamental features, but I don't really want to spring for more modern commercial software...too expensive.

I planned on stringing the foundation to mark the wall and then preinstalling the vertical rebar. Thanks for the push though. Actually, what I was *really* planning on doing was putting little wooden plugs in the foundation instead of the rebar itself, then pulling them out to reveal a hole I could drop the vertical rebar into so it would stay centered in the core when I fill concrete around it, but maybe embedding the rebar directly in the foundation is just as good an idea...except that some of my vertical rebar might come up, cross to the next core, then go down again, which obviously won't work if I embed the rebar in advance.

Whatever, it'll all work out...assuming the Seattle autumn rains doesn't prevent me from pouring the foundation entirely until next spring. Uuuuuuuuuuugh. My plan was to do the major foundation pour this coming weekend. The forecast is sketchy at best.

[kebwi]

Re: 36" in Seattle

The foundation is finally ready to go. Gravel is filled and level, form is nailed, masonite curves are done. You'll notice in the photos that I chiseled out the forms to make a lip for the masonite. Its curved tension holds it in place without any nails, but I put some in anyway so the concrete wouldn't spring them out while pouring.

I already have plastic purchased for the vapor layer and a pile of rebar and mesh cut up and bent, ready to go.

The big day is Saturday. The wife and a friend are lined up to help. I hope to get that damn foundation over and done with this weekend so I can move on to the next stage. It seems like this has taken forever...and it's not even done yet.

[kebwi]

Re: 36" in Seattle

Here's a dreadful shot of the vermiculite I got my hands on, possibly laced with rockwool; I haven't bothered to look yet since it was free anyway.

The other shot is one box (of two) of the bulk fiber I got. It is InsWool HP, obviously intended for the first dome insulation layer, a blanket surrogate in effect. I'm thinking I can hold it in place with chicken wire despite its unwoven consistency. The guy I bought it from, who is a glass blower, said this stuff will dry out if it gets wet and regain its full value. In fact, he suggested that the best way to install it was to intentionally soak it, then pack it on relatively densely while wet. I have been weary of intentionally compacting insulation since such behavior violates my intuition about how insulation fundamentally works, but other discussions on FB about 6# vs. 8# blankets have suggested that packing and compressing insulation is actually a good thing to do. Do people concur on this? Each box is 24"x18"x12", 25lbs. I think two boxes should be sufficient for a 36" oven.