Replies

1. 
   Eric_M._Borgman | Apr 13, 2001 07:04pm | #1

   *
   What is the design strength (psi)? High early strength or regular mix? Footing thickness? Wall height? Footing reinforced or not? Ambient temperature? Cold slows curing.

   Most of our jobs we pour reinforced footing on day one. Wall rebar and forms day two. Pour walls day three. Subgrade is usually 2000 pounds per square foot bearing.

   Eric

1. 
   Mike_Maines_ | Apr 14, 2001 02:23am | #2

   *Most concrete contractors are always in a hurry to strip their forms and get to the next job....after one day regular concrete only has 10% of its design strength...50% after a week...90% after a month. Strip the forms after a day or two and the walls will crack. Assume the same for footings. Leave the forms on for a week, keep covered with plastic or burlap, wet down twice a day, and you'll have a MUCH stronger foundation.But if you can't see it from my house....Mike

1. 
   Gabe_Martel | Apr 14, 2001 04:14am | #3

   *Leave the forms on for a week and two things will happen.One, when you strip the forms, you will leave a lot of the forms behind.Two, your foundation will cost you three times as much.Footings one day, form the walls the next and pour on the third, strip after 24 hours and protect.Gabe

1. 
   Johnnie_Browne | Apr 14, 2001 03:26pm | #4

   *I have never really thought about is but around here it is pour one day, next day strip forms and begin the wall. I know alot of contractors that will pour dry(3-4 slump) so they can have 100% of strength in seven days. Most small houses call for 2500 psi and builder buy 3000 so in three days it is around 2200 to 2500, but that depends on the crew.I do not know many contractors that will pay a crew for a week till the concrete cures. The big crew will pour about 10 houses in a week so it will cure.

1. 
   Ryan_C | Apr 14, 2001 06:17pm | #5

   *I've left forms on for too long before and had a nightmare getting them free. Release Agents or not, strip forms as soon as the concrete is solid. As long as the concrete isn't allowed to dry out, it will continue to cure for several days (actually three weeks but the first few days are the important ones).I feel comfortable working on concrete two days after it's been poured.

2. 
   Mike_Willms | Apr 15, 2001 05:57am | #6

   *Concrete design strength is lost by overwatering (adding water to transit truck on site), or improper curing techniques. Keep forms on 24hrs min. The longer the forms are left on and the damper the concrete is kept, the closer to design strength it will be. 2000psi concrete can deteriorate to 700psi by adding water and stripping under 24hrs. The other option (better option) is to use higher strength material. If 4350psi concrete isn't allowed to cure properly, it might drop to 2000psi...which is what you want minimum. I pay $30/metre more for 4350psi, small investment. Call me crazy.

3. 
   Mike_Maines_ | Apr 15, 2001 06:31am | #7

   *You can strip forms after 24 hrs, and people also say "concrete will crack no matter what you do." You can do what most everyone does, strip forms early and expect the concrete to crack. Or you can use lots of release oil on clean forms (2 coats), leave the forms on for several days, keep a dry mix (low slump) damp for the duration, and you'll have a foundation that won't crack.What's yer hurry?Mike

4. 
   CaseyR_ | Apr 17, 2001 04:16am | #8

   *A related question: Is there anything that can be used as a release agent besides the form oil that will allow the reuse of the lumber used for the forms with a minimum of concrete residue? Would it work to cover the ply with plastic sheeting and then put the form oil on the plastic? The concrete will be covered, so a few wrinkles left in the wall from plastic sheeting would be an esthetic problem.

5. 
   Eric_M._Borgman | Apr 17, 2001 04:44am | #9

   *Casey,If you want to reuse your forms, buy FormPly plywood or a similar product. It's more expensive than regular ply, but it is coated for a good release and reusablility. If you want, I can look up a link.EricPS The plastic idea sounds like a pain in the *ss.

6. 
   CaseyR_ | Apr 17, 2001 08:22pm | #10

   *Thanks, Eric. I think I have used formply. My rememberance is that it is a paper covered plywood that gives a good, smooth finish but that it still needs to be oiled for release. Since I want to reuse the concrete forms as part of the structure of an out-building, I would like to minimize the mess of oil as well as the added flammability of oil soaked paper.I did a quick search on Google and came up with a number of hits of places that carry it, but no real technical info on the product.

7. 
   Mike_Maines_ | Apr 18, 2001 03:39am | #11

   *Casey, the plastic thing might work, just use a very heavy grade, attach it well (roll the top edge several times around a piece of strapping and nail this to the outside of the form). Dad used to keep used motor oil around for all sorts of uses, including lubing concrete forms, preserving timbers, staining timbers, oiling our bikes...but I don't think it's PC anymore.Mike

8. 
   Mike_Smith | Apr 18, 2001 05:10am | #12

   *casey.. if you are going to use snap-ties .. you can forget about lining the forms with poly......the form oil will be minimal in the reuse of the ply for your structure...b but hey, whadda i no ?

9. 
   Jerry | Apr 18, 2001 05:54am | #13

   *I'll just reiterate what Mike said('cause I was thinking the same thing). Commercially available form oil is pretty benign stuff these days and won't be a problem for reuse (unless you want something to stick to it). Just keep in mind you will have a bunch of holes in your plywood.Jerry

2. 
   greg_scott | Apr 18, 2001 05:54am | #14

   *
   Could some please tell mee how long footings must set before the walls can be poured? Also, how long before framing can start after walls are poured?

   Thank you!