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HopefulHomemaker
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# Posted: 1 Jul 2012 11:24pm
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We're doing 12 foundation grade lumber posts for our 16x20 cabin with 16x8 porch. We were planning to just set a block in a 4' hole, set the post on it, pour in a bag of dry quikcrete, and backfill. This is what has been used by a builder in the same town, so we know it'll pass the permitting process. Now we're just trying to work out timing. How long would we have to leave those to set before we could start building the rest of the house? If we mix and pour concrete rather than using dry, will it make the process any faster?
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MtnDon
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# Posted: 2 Jul 2012 12:03am - Edited by: MtnDon
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Mixing concrete with the proper amount of water results in concrete that will have the designed strength. Concrete mix poured into a hole dry, is a shortcut that can result in inferior (weak) concrete. We're talking about the very foundation for the foundation here. If you've gone to the trouble of obtaining genuine foundation grade pier material why mess around with a footing that may never develop the strength it should have.
If you are dropping a concrete block in the hole and filling the cores with concrete, where is the rebar? A concrete footing requires rebar to pass under IRC. If your location passes footings without rebar they are being sloppy, IMO.
If too much water is used when the water evaporates it leaves little spaces behind. If too little water is used the concrete will not hydrate properly and will not cure properly. Concrete cures, not dries. Ideally the concrete is kept wet once it reaches its initial set. That's the reason concrete contractors spray drives and roads with a curing membrane. If kept moist for 28 days, then and only then will maximum rated strength be reached. If the concrete is rated for 4000 psi that is the rating after a proper 28 day cure. After a week it may have only half it's strength; after 3 days maybe a third. And that is only if kept moist or wet.
Oncethe cement in the concrete is wet if the concrete dries out before the 28 days passes the chemical curing stops and rewetting will not reactivate the curing. With a footing the soil moisture will often be sufficient to keep the concrete moist enough for a full cure. But I would not count on the soil being able to supply all the moisture a dry mix requires. Not to mention the mixture will not be properly mixed. Sort of like tossing the eggs and water into the dry cake mix ingredients and expecting it to come out of the oven looking like it should.
So anyhow, once the concrete is mixed and placed in the hole with the rebar placed about mid level, try to let it sit at least a couple of days before dropping the piers in. At that point the concrete is still "green" and it can be cracked if shocked. So build gently, don't drop the piers in on the green concrete. Place the piers. Then pack the dirt back in the whole placing the dirt back in what are called "lifts" Maybe 6 inches of fill to a lift. Then tamp. Another lift... etc.
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HopefulHomemaker
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# Posted: 2 Jul 2012 07:08pm
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Ok, I'll share this with husband as well. But the short version is, roughly three days before we start building?
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