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Old 04-11-2011, 06:44 PM   #1
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cement porch


We are going to pour a cement porch - 20 ft long, 4 1/2 ft wide, 4 1/2 in thick. It will be partially over an existing cement walkway. will we need crack lines (I've never seen crack lines in porches)? and will we need to use rebar?
Thank you for any comment.

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Old 04-11-2011, 08:28 PM   #2
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Originally Posted by debd View Post
We are going to pour a cement porch - 20 ft long, 4 1/2 ft wide, 4 1/2 in thick. It will be partially over an existing cement walkway. will we need crack lines (I've never seen crack lines in porches)? and will we need to use rebar?
Thank you for any comment.
I have two concrete porches. One 8X13 and has never cracked. The other 5X6, cracked in two places.
I suspect that frost was able to heave the smaller porch, which cause the pad to crack.
These porches are about 60 years old.

Make sure that the walls are on footings that are below the frost line and use a reinforcing mat in the pad and then you should not have to cut crack lines.

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Old 04-11-2011, 09:02 PM   #3
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you may have never seen jnts ( crk lines ) in con crete porches HOWEVER you've seen crack'd conc porches, right ?

20' porch can be divided into 4 sections 5' long meaning 3 contraction jnts are needed UNLESS jomama &/OR dick disagree be particularly careful of ANY underlying jnts,,, that may defeat any good advice you might get

Last edited by stadry; 04-12-2011 at 04:49 AM.
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Old 04-12-2011, 05:00 AM   #4
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hes. One 8X13 and has never cracked. The othethe crks in the 5X6 slab are probably NOT due to tension but early loading or a base problem,,, the 8x13 slab may have crk'd at the 6 1/2' area but didn't so you got lucky,,, an experienced finisher would have placed a contraction jnt on that line to CONTROL a crk.

its rate to see reinforcing mesh OR steel in 4" slabs & is not recommended bue to the difficulty of placing it properly - at the exact vertical midpoint +/- 5%,,, that's roughly .1" w/NO more tolerance,,, not impossible w/auto screeding equipment but HIGHLY unlikely after the conc jabonies finish walking back & forth even aci doesn't recommend it,,, save your $ on the fiber, too,,, not worth it

conc experiences its greatest stress while hydrating/curing,,, tension can cause crks while it cures & shrinks,,, IF your slab's elevated, rebar will add FLEXURAL strength but no compressive strength,,, for a 4" slab-on-grade, steel or wire mesh helps hold the broken pcs together when it does crk
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Old 04-12-2011, 09:35 AM   #5
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hes. One 8X13 and has never cracked. The othethe crks in the 5X6 slab are probably NOT due to tension but early loading or a base problem
It was a base problem! The foundation was constructed by digging a trench 24' deep and placing a form up 24"' There was no footing.
In this area. footings are required down at the 48" level. I know this because I had to underpin the large deck, so as to build a roof.
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