concrete patio questions

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Old 05-14-11, 09:37 AM
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concrete patio questions

Hello all,

I'm putting in a pretty large concrete patio (approximately 40' x 14', with a 14' length section being a right triangle). Have a few questions I would like to get feedback on. So far, planning on 5" thick slab with 1/2" rebar spaced 2' x 2'. Plans for use of it would be mainly outdoor living space, but occasionally I will use it to work on the family vehicles.

1) Live in San Diego, CA so freeze/thaw cycles are not an issue. Soil is heavy clay. I've already excavated the 5" and the soil underneath is heavily impacted, so there shouldn't be much in the way of settling. I am hoping to get away with not needing to put down a sand base as I'm trying to keep costs down. Think I can get away with this or am I asking for trouble?

2). Control Joints. Because of the size of the slab and the fact it goes against the house, I can't really use planking over the slab to use a control joint hand tool to put in control joints while the cement is wet. I plan on using my cement blade to simply cut some control joints. Currently, the plan is to cut 2 control joints across the width (approx at the 15' and 30' mark). My question is whether I need to do a lengthwise cut, or 14' wide is narrow enough that a cut like that is not needed.

3) Connection to the the house. The slab will be going up against the house. House is on a basic slab. Is there something I should place between the house slab and the new concrete? Did concrete for a summer many years ago and I recall some type of cellulose plastic used to protect against expansion/contraction.

Thanks for any advice you can give.
 
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Old 05-14-11, 04:24 PM
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The sand would be a good idea. It's not just for making a flat area for the slab to sit, it's also to let water migrate freely under the concrete. The cost of the sand can't be nearly what you're spending on the 5 inches of concrete and the rebar.
On a 40 x 14, I'd cut a joint lengthwise so the two halves are 7 x 40, then cut those crosswise every 6 feet 6 inches. It's a pain in the butt, but may save a lot of cracking. On a 5 inch thick slab, the joints need to be 1 and a quarter inches deep to be effective, and they need to be sawed as soon as possible, not two days later.
You need to put expansion joint material between the slab and the house or any other rigid structure it abuts. Closed cell poly foam is what I use, but you can get the old black cellulose fiber kind too.
 
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Old 05-14-11, 04:34 PM
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In San Diego. you will not have cold soil and the temperatures are moderate. sio I would cut as early as possible on the next day.

A "soft saw" blade would be good if you can find one to fit your saw.

Dick
 
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Old 05-14-11, 04:37 PM
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Amen, brutha. The sooner the better.
 
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Old 05-16-11, 07:45 AM
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Thanks for the help/information. That's a lot of control joint cuts, but the gf does hate cracks so well worth the initial annoyance.
 
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