jt7157 said:
I'm getting ready to pour a concrete porch. It will be eight feet wide and five inches inches thick at the house and four inches thick at its end. My main concern is cracking. I will use steel re bar in a grid on two foot centers. I plan to use the concrete with the fiber mixed in the recipe. Are there any other additives that will help with cracks? I guess my question is this: what is the best recipe to help prevent cracking, especially those annoying hairline cracks? Thanks in advance.
I don't know the size of your pad other than the 8' dimension. If I did, I could suggest saw joints in the top to make control joints for cracks.
Are you doweling the pad to the house foundation? This can keep the slab from sinking into the "overdig" around your house foundation. (How many times do you see a slab sunken near the house or a sidewalk poured near a foundation that tilts towards the wall instead of away from it?) I usually compact the soil from the foundation out about 3 feet since this soil is usually soft for up to 30 years after the house is built. I take a small sledge hammer and punch holes into the block of the house and allow my rebar rods to stick into the cells in the hollow block. Then right at the start of the pour, I get shovel-fulls of wet concrete and pack it into the open cells of the block to secure the rebar and close up the holes I created. If you have a poured concrete foundation, drill the holes into the wall w/ a hammer drill , then epoxy the rebar into the holes you drilled.
Try to keep your rebar in the lower 2" of the slab, not the upper 2"
Make sure you have good drainage under your 4" thick stone bed. Drainage should roll away from the slab to let water out from under the stone. It helps to tamp the stone to get rid of any soft spots, too. That way if you have a freeze, it won't heave the pad.
Try to mist (not too much, no puddles) the concrete frequently during the curing process to keep the surface from spalling/shaling.
That's about all you can do. the only gaurantee you can give a customer about exterior concrete is that it might crack someday. It's at the mercy of the earth underneath, the water from the heavens and freezing in the winter.
Good luck.
