garage footings and stem walls

i am about to begin construction of a new garage. my plans call out for footing/stem wall construction. i have never done any foundation work before, but i'd like to do the forming/steel work myself and have a few questions.
1. are separate pours required/recommended for the footings and stem walls, or can they be done at the same time?
2. is it recommended to compact the footing trench and also put gravel under the footings?
3. for a 6" high footing, is simply using 2 x 6 boards somehow staked into place acceptable?
4. for the stem walls, do you cut the plywood to the height of your stemwall and control the height by slaking off excess as the forms fill? also, how do you secure the forms to the footing to keep them in place and plumb?
any other advice for a first timer would be welcome. if there is a book or website out there that explains all this, please refer me to it!
thanks!
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While we are on the subject, can someone tell me what a stem wall is?
Is that just another footing placed in the middle areas of the total perimeter, to give me support to the slab, or to major interior walls ?
Thanks !!
--James--
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it might be possible to pour footings and walls in one fell swoop, but most everyone would use two pours. pour the footings, then you have a good base for your stemwalls.

where i'm from, footings sit on undisturbed native soil.

yes, 2x6's are fine for a 6" footing. you could even use a 2x4 and dig out 2 1/2 inches. stake them with wood stakes or buy steel stakes depending on your soil type. use a spreader across the top if you feel you need the extra strength.

yes, cut the plywood to the height of your stemwall. you should snap a line and nail a 2x ledger to the footing on each side of your wall.
wall forms can be braced with 2x kickers down to the ground held in place by double 2x stakes.
you don't mention how you will support the plywood. will you use snap ties and walers? there are a number of ways to do this, but you need to be prepared for a great deal of pressure on the forms from the wet concrete. a blowout is big, big trouble. also, you need a plan for placing rebar. usually vertical dowels are required. these can be drilled in after the footings are poured in some areas, though other jurisdictions will require you to have the verticals in place before the footings are poured. horizontals can be tied in when you are forming the stemwalls.

fine homebuilding put out a book on foundations that is pretty good.

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We poured our own garage foundation a few years ago. I had no experience in this area, and only did it myself because we couldn't find a contractor who would take the job. It took a couple of months of work, but it was really satisfying to do it ourselves, and the foundation turned out great.

There was an article in Fine Homebuilding a while back about doing a single pour, but I think most people would prefer doing separate pours. I personally poured the footings first, then did the walls. Much easier for an amateur.

Usually you'll want to dig down to undisturbed soil and pour directly on the ground. If you have to pour your foundation on fill for some reason, you'll probably need to check with your building department for what is required in your area. They may require pilings or special compaction before setting the forms.

Yes, you can just dig out an extra 1/2" inside the footing forms.
However, unless your site is already fairly level, you may need a variety of form sizes. I ended up using a combination of 2x6's, 2x8's, and a couple of 2x10's to accomodate dips in the excavated site. Mostly due to sloppy excavation work. Pile dirt against the outside of the forms to keep concrete from oozing out under the forms.
I used 2x2 wood spreaders to tie the inner and outer forms together at the correct distance.

We wanted 2' high stem walls, so I built 2'x8' wall forms out of 3/4" plywood and a 2x4@24" OC framework. I leveled the forms on the footings, then screeded the concrete along the top of the forms.
We reused the forms to pour our house foundation, then I sold them to a farmer who used them to build structures for his animals.

I left my footing forms in place while I poured the walls, and just screwed the wall forms to the tops of the footing forms. The footing forms were already staked and braced with dirt on the outside. I did add a few concrete nails into the footings to add a little extra support.
As for the tops of the forms, I installed 2x2 spreaders to keep the forms tied together at the right distance. Then I installed diagonal braces every 8' on the inside and outside of the forms. These attached to stakes driven in the ground to keep the forms from tilting or shifting as the concrete was poured.
I wanted a little extra insurance, so I bolted the inner and outer forms together every 8' or so. I installed a short piece of PVC pipe as a spreader, then passed the bolt through that, with big washers on each side of the form. The pipe let the bolt come out easily, and the PVC is easy to tap out and patch the hole with grout after the pour. They make special form ties for this kind of thing, but the bolt approach worked fine for me.

My favorite books are no longer in print, but your local library should have plenty of books showing how to do concrete work. You could also check out Fine Homebuilding magazine, and the books offered by Taunton press.
When you get to the framing stage, one of my favorite books is "graphic guide to frame construction". It's more of a reference manual than a how- to guide, but I liked it a lot.
Also, different areas have different requirements (soil types, seismic risks, etc.), so check with your building department to see what is needed in your area. They'll have requirements for footing sizes, the size and locations of rebar, etc. We had to install special tie downs in the foundation walls on each side of the garage doors to keep the building on the foundation in case of an earthquake.
When you are pouring your concrete, take a long stick and "jab" up and down along the inside and outside of the forms. This will work out air bubbles that may form as the concrete is being poured, so you don't end up with voids when the forms are stripped. This is especially important around doorway openings, foundation vents, etc.
The pour itself goes FAST, usually less than an hour per pour. But, you'll work harder in that half hour than you did all week! :) According to code, you should also leave the forms on a full week before stripping the forms. And, cover the concrete with plastic to protect from rain and keep evaporation to a minimum.
We used a company with trucks that mix the concrete on-site. If these are available in your area, I highly recommend them. You only pay for the concrete you need, you don't have waste to dispose of, and they can usually provide a little extra if your calculations were off a bit.
Basically, just do your research, take your time, and do a good job. The rest of the building depends on the foundation, so you don't want to cut corners here.
Compared to the rest of the building, the foundation takes a lot of time and work. You spend a lot of time building the forms, only to tear them down again after the pour. It's a great feeling when you finally get "out of the dirt" and start framing!
Anthony
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