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We just got done compacting dirt, filling with 3/4" crushed stones and compacted it again ready to pour concrete. However, extremely heavy rain came.

These guys are telling me they really just need a couple of days to dry before pouring with concrete, but I just wanted to do some DD before I commit.

Firstly, has anything been ruined because of the rain timing? Will the heavy rain affect the integrity of the slab once it's in? Would I have to compact it again or start over?

Or does it actually benefit because the water might help settle the stones more? The dirt has a high clay content.

And how long should I wait until we pour concrete?

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  • How thick is the gravel base over the dirt? Is the gravel base compacted as well?
    – Jack
    Mar 18 at 3:47
  • Typically if the gravel is placed over any other type of dirt, I see no problem pouring right after the rain stops, it helps slow the drying out of the concrete making the slab stronger. If the gravel is just placed and not compacted and is too thin of a layer over the base, with all the rain, the clay may churn up into the surface. Not the end of the world, but not good, especially if it churns up while pouring the slab and the mud gets into the mix. But that depends on the answers to the questions above.
    – Jack
    Mar 18 at 3:52
  • @Jack The foundation wall is about 2 feet. I don't check the site everyday, but I think it's safe to assume the stone layer is at least 1.5 feet since they unloaded the stones last I checked. Don't think they added much dirt since. Mar 18 at 4:14
  • To confirm, the gravel is a continuous 1.5 ft. over the dirt base??
    – Jack
    Mar 18 at 4:18
  • @Jack Yes. I saw when unloaded the stones in a pile within the foundation walls. I'm assuming they haven't filled any more dirt at that point Mar 18 at 4:22
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If the gravel is that thick it would need to be compacted to keep it from settling over time. It should be done in stages (lifts). Add a layer, tamp that then add a layer and tamp that until it reaches the height needed. An engineer provides this type of info regarding how much gravel at a time for each lift. I know this is not what you asked, but it is good to know.

With that in mind, I do not understand why the wait on the pour since the gravel is so deep, and the contractor is just using that as an excuse. Perhaps it will put his schedule behind if he did your job the next day. He is most likely going to the other jobs he already had scheduled for the next few days until he gets a new opportunity to pour your slab

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  • If the subgrade is clayey soil with almost 18" of gravel fill, as long as there is no standing water, I don't see problem to pour the concrete right now. However, I suggest to make the concrete a little stiffer, since the base aggregates will not absorb the excess mixing water as anticipated, that might result in excessive bleeding water later.
    – r13
    Mar 18 at 18:08
  • Any concrete I have seen poured as a floor slab in a home has a layer of poly as a moisture barrier, it also help slow the cure of the concrete, which is a good thing.
    – Jack
    Mar 19 at 2:19
  • @Jack do you have an email for consultations? I have some questions that may be out of scope from the forums Mar 22 at 3:34

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