I recently poured an ICF basement wall.  The home owner wants to backfill his basement this weekend.  I have not poured the floor yet and I know that I have to before he can backfill.  His house was moved off the crawlspace and this basement put in.  My question is how long should I wait to get the building mover back to move the house onto the walls?  Thank you.

Definitely do NOT backfill the walls until the basement slab is poured. Normally, you would want the floor system in place to brace the top of the walls before backfilling. Since that won't be possible in your case, I would strongly suggest temporary bracing on the inside of the walls until the house is back in place and secured to the walls.
Ideally, you should wait 4+ weeks after pouring the walls before allowing a house to be rolled onto them. This allows the concrete to reach its maximum strength before you apply any unusual forces to it. I have set modulars using a crane after 2 weeks. with no problems, but it probably wasn't the best idea.

Design strength for concrete is based on 28 day strength. Typically you reach 75% of this strength after 7 days. This is based on normal curing and no additives (such as fly ash, etc). Fly Ash slows the curing process down.

If you can wait the full 28 days, that is best. Minimum 7 - 10 days is typical since maximum design loads are not reached right away (full hydrostatic pressure).

W1K,

You are getting some good answers here but they all seem to leave out some very specific questions that need answered before anyone can make a determination as to when you can set the house on it an backfill. I will list some questions that you can answer to help make a determination or you can ask your engineer of record to tell you when to backfill and set the house on the new foundation or read your general notes on the plans.

1. How was your basement walls designed? Cantilevered unrestrained retaining walls or as fully restrained retaining walls? This can be determined by looking at the footing and the placement of wall on the footing. If your footing is very thick and 4', 5', or 6' wide and the wall sits significantly closer to one edge than this is probably a cantilevered retaining wall and can take the load of the back fill once the footing is keyed into place with the basement slab or fill.

2. What is the design strength of your concrete in your plans? They should have a reference to the footings, walls, and floors.

3. What was your mix design of your concrete? Did you add water to your concrete on site or did you use supplemental plasticizer to wet up you mix? If you added water, how much?

4. What has been the average temperature in your area from now to 2 days before you poured?

There are many factors that affect the curing of concrete. Wes is correct that fly ash or slag can retard the mix's curing time. An example on one of my recent project we were pouring a "Green" concrete mix design that was about 40% slag, 10% fly ash, and 50% cement. It is a 6 sack mix with other chemicals in it and the 2 day break on this mix was 800 psi, the 7 day break on this mix was 3400 psi, the 28 day break on this mix was almost 7000 psi. The same day on the same project we needed the concrete to cure to 2500 psi in two days behind the weld plates that were installed so we would be able to start installing to floor system after the weekend. By removing the fly ash and slag and using 100% cement the 2 day break was 3400 psi, the 7 day break was 4200 psi and the 28 day break was 6200 psi.

So you can see that concrete has a lot more science to it than just wait 28 days and it reaches 75% strength in 7 days. Although waiting 28 days without hard facts and figures from concrete crush tests is a safe and conservative approach and 7 days is a good thumbnail if you don't add a lot of water to the mix, or you don't have high amounts of non-cement additives.

If you are new at this and/or uneducated on building science. By all means take the conservative approach. The last thing you need to do is collapse a basement you just poured before you even get the house on top of it.

ICF Contractor

The owner may need the property to set up a bigger construction project. The benefits from house moving as compared to the costs of demolishing, and the relative losses thus incurred are eliminated.You able to hire a new building mover.

Source :
www.wolfehousebuildingmovers.com