thickened edge Garage slab questions?

Old 11-22-15, 07:46 PM
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Question thickened edge Garage slab questions?

I'm getting ready to pour the floor for my 32 wide x 44 deep garage. It will be a thickened edge slab. I live where there's snow and slush for about 5 months a year. Thinking of adding floor drains; Maybe two to the front stalls?

1. Will they only lead to cracks in my floor?
2. Are they worth the hassle? Will water have to squeegeed anyway?
3. wheres the best placement, center of stalls or near corners?

4. I'm also planing to pour (in a second pour) a knee wall that will form the bottom foot of my garage walls. Should I put rebar inside my first pour (the slab) that will extend up (to act as anchor bolts) inside the wall pour?

Thank You.
Old 11-23-15, 03:21 AM
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The biggest thing you have to consider is your local code for the floor drains. A few years ago I considered floor drains when I was going to replace my garage floor. The only way I could put in floor drains without a vented flammable waste trap (very expensive), was to have no trap in the drain and daylight the drain pipe outside. It's a fire hazard thing.

1. With or without floor drains, you will get cracks. A fact of life is that concrete cracks. Talk to your concrete guy about control joints. My rule of thumb was no more than 10' (or so) between CJ's.
2. You will want to slope the floor to the drains. The absolute minimum would be 1/8" per foot; experience tells me that even good concrete guys have trouble getting 1/8" without some birdbaths that have to be squeegeed.
3. Placement is more a matter of personal preference and how much total slope you can tolerate. I personally like the drains under the vehicle.
4 Definitely add rebar, it's cheap! Without a sketch and dimensions, it's hard for me to say where the rebar should go; generally, rebar should go where the concrete is in tension.
Old 11-23-15, 07:28 AM
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Don't forget to consult your local building codes. They will specify the size of footers needed. How deep they should be and if and how much rebar or other reinforcement is needed.

If doing you knee walls as a separate pour it's a good idea to have at least rebar protruding from the slab pour to help hold the two pours together. Sometimes a key slot is formed into the slab to provide further engagement between the two pours. Then on the top of your knee wall you can embed threaded anchors to attach your sill plate.

Another way to do it is to pour your wall and footer first. Then pour your floor slab inside.
Old 11-23-15, 12:40 PM
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I was going to post almost exactly what Pilot Dane posted as far as recommendations go so I won't repeat what you said.

I would however recommend that you use the alternative he suggested and for the footings and wall in one pour and then put the interior slab as a 2nd one.
Old 11-25-15, 07:09 PM
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The biggest problem with pouring walls before the slab is that you then will need to use temporary screed rails adjacent to the walls in order to strike-off the fluid concrete--pulling the rails as you go and filling in the voids, all while bending over the walls (from the outside) for a lot of hand-finishing. Hand-finishing while standing on my head has never been very rewarding, or even enjoyable.

An alternative is having a finisher wearing tall rubber boots and very talented using his darby, finishing concrete to grade lines established by the top of expansion joints nailed to the walls, all while standing in and working his way out of the wet mud.

If it was mine (and the local code allowed it), I'd pour the slab first, contiguous with footings and stemwalls, then build the kneewalls on top after the slab had cured enough not to be easily damaged. Pouring half the slab at a time (a 16'-wide slab is plenty challenging to properly place and finish).
Old 11-26-15, 10:26 AM
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Wouldn't it be less messing around to pour your floor and footings then put a row of block for your walls to sit on? That's what I had done on my garage 26 years ago and it's still there.
Old 11-26-15, 01:56 PM
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What Baldwin said seems to be the most common thing I see. Pour your thickened edge slab (size of the footing will depend on how many stories and what the building is used for). stick vertical rebar around the slab a few inches out and run a row of cinder blocks on top of the slab after. Usually, it is only one or two rows, the idea being that you keep the wood walls off the garage floor so any water on the floor does not get into the walls and damage them.

To answer the other questions, floor drains should go in the center of the garage bays, and will not lead to any additional cracks if the floor is prepped correctly. They are not much hassle to install and will be a lot less hassle than cleaning up a big puddle on your floor from a bunch of melted snow.

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