I had a 20x20 concrete pad poured last Friday to add on to driveway to park 2 cars. The contractor says I cannot park the cars on the slab until today. It has been raining since Saturday and I have not been able to inspect the work. Is there anything I should look for when inspecting the work before I pay the guy ? How long is a reasonable time to allow the concrete to cure before determining the pad is OK.
OT - Concrete slab/pad question
- Thread starter BhamDawg91
- Start date
Stay off of it as long as you can, 1 week, 2 weeks is even better. Technically concrete cures for years. Hairline cracks are ok, bit major cracks are not. Concrete is going to crack. If it is 20x20, you should have control tool joints dividing the pad both ways to create a cross. Concrete drives need control joints every 10 feet and expansion joints every 20-30 feet. If no control joints it is going to crack for sure.
The is one down the middle but not cross. Not that it matters. It's actually a little bit smaller but I rounded up. It's more 18x20.
That 18' section will eventually get a crack once you start parking on it. Control joints are to control where the crack will be. It could could start in the middle or 2/3rd and go diangonal, who knows. I would request cutting across too. Needs to go about an inch deep too.
It reaches something like 90% hardness during the first 24 hrs, then another 5% in next 30 days and it theoretically never reached 100%, or that's at least what my MSU education taught me
Make sure the pad is draining properly...
The control joints should drain properly too. No pooling in the middle or else freeze/thaw cycles will have adverse effects. If it's at least 4" thick with some reinforcement in it... You could park an elephant on it by this point.
The control joints should drain properly too. No pooling in the middle or else freeze/thaw cycles will have adverse effects. If it's at least 4" thick with some reinforcement in it... You could park an elephant on it by this point.
You dont have to wait two weeks to park on it. I had a driveway poured last year that is about 60ft x about 40 ft and the guy that did it said I could park on it in two days. I drove on it in about three days with no problem and only has one crack between petitions that happened about two months ago due to the drought we had. Slab is four inches thick.
It is 4 inches thick. I believe I saw rebar before it was poured but I can't be 100% sure on that. It has a gradual slope that meets the existing driveway which runs off well. With all the rain we have had recently there is no pooling on the new pad.
Do what you have got to do...
But stay off of it as long as you reasonably can.
Best thing, was that it rained, best to keep it moist for a while.
Concrete essentially cures in 28 days. (and will cure in the bottom of the ocean)
Too fast is not the best for it.
Karls' advice.
But stay off of it as long as you reasonably can.
Best thing, was that it rained, best to keep it moist for a while.
Concrete essentially cures in 28 days. (and will cure in the bottom of the ocean)
Too fast is not the best for it.
Karls' advice.
Good rule of thumb regarding joints is to double your thickness in inches and that is how far your joints need to be laid out in feet. You can get all detailed as far as expansion and contraction joints, but no need on a driveway or sidewalk. I would say you need at least one saw-cut joint down the middle (splitting your 18' section into two 9' sections) and one or two saw-cuts cut transversely. Two might be excessive, but at least it will prevent cracking. You probably can get away with one. So in other words, 4 sections of concrete.
Also, go to Lowe's once it's cured out, and get you some joint sealer to put in the crack, to prevent water from getting in and weakening the ground underneath.
With all this rain lately, I would stay off it for a while!
There's a lot of variables, though - How well was the pad compacted? How wet was the pad when they poured? How well did the contractor position the rebar/mesh? How much water did he add for workability? How was the weather in the 24 hour span after the pour? If everything was ideal, two days would probably be fine. They never are. Better safe than sorry.
Concrete Slab
The recommended joint spacing for slabs less than 9 in. thick is 12.5 feet so, you definitely need to have the vendor come back and saw a transverse control joint about half the length of the slab. You can also match any existing joint lines in the existing driveway so they match up. You typically cut control joints to 1/4th of the slab thickness or 1 in. for your 4-in. slab. It is good that it has rained and kept the slab moist so that it doesn't cure too fast which will help minimize the potential for surface shrinkage cracks. The guys gave you good advice to stay off it as long as you can as the concrete is still curing, but it is about 95% cured at 28 days. I doubt they put rebar in your slab, it was probably welded wire reinforcement which is essentially cattle fencing. The wire doesn't do much but helps hold the cracks together after they are formed. In the future, you'd be better off to pour a 6-in. slab on grade for a little more money and better long-term performance. Four inches is the absolute minimum so I hope you don't have to traverse it with any heavy trucks like propane trucks or it will do some damage. Often, they don't do a great job preparing the subgrade and/or use 2x4's for forms, which leaves you with about a 3-in. slab in places.
The recommended joint spacing for slabs less than 9 in. thick is 12.5 feet so, you definitely need to have the vendor come back and saw a transverse control joint about half the length of the slab. You can also match any existing joint lines in the existing driveway so they match up. You typically cut control joints to 1/4th of the slab thickness or 1 in. for your 4-in. slab. It is good that it has rained and kept the slab moist so that it doesn't cure too fast which will help minimize the potential for surface shrinkage cracks. The guys gave you good advice to stay off it as long as you can as the concrete is still curing, but it is about 95% cured at 28 days. I doubt they put rebar in your slab, it was probably welded wire reinforcement which is essentially cattle fencing. The wire doesn't do much but helps hold the cracks together after they are formed. In the future, you'd be better off to pour a 6-in. slab on grade for a little more money and better long-term performance. Four inches is the absolute minimum so I hope you don't have to traverse it with any heavy trucks like propane trucks or it will do some damage. Often, they don't do a great job preparing the subgrade and/or use 2x4's for forms, which leaves you with about a 3-in. slab in places.
I work for an architect and we specify a 6" x 6" wire mesh for a 4" slab in most areas of Mississippi. Depending on who designed it there may be another grade beam in the center both ways. We usually specify a minimum 20 foot between grade beams in any slab. As stated earlier the concrete will crack in time and if it is outside eventually the top layer (called the cream) will wear off. Make sure that the contractor broom finished the slab so you have traction on it (especially important when we have ice storms).
