Home Forums Hunting & Shooting Hunter's Campfire Concrete pad for safe, drying time?

Quick question(s):

For a concrete pad poured to locate a gun safe upon, how long to let it set up prior to:

a.) drilling anchor bolts

b.) installing the safe (not wanting moisture to wick up into the safe)

contractor doing the out-doors concrete work who poured it says 2 weeks...

2 weeks...

I would follow the recommendation of the contractor

2 weeks.

I'm not trying to skate on the minimum....any compelling reason to wait longer?

Curing concrete can give up moisture for a very long time. You can check it after a couple of weeks by putting a piece of plastic over it, and see if any moisture is accumulating on the plastic. IIRC, on one job we used a heat lamp shining through the plastic to accelerate the evaporation. If there are any doubts about it still giving out water vapor, you might set the safe on a couple of pieces of furring strip for a while. I know that messes up the idea of anchoring it down. but I wouldn't want the bottom of the safe wet, either.
A moisture barrier between the safe and the concrete might be worthwhile, if you could get the safe in place without tearing the barrier.

Myron

There are many variables in a concrete mix-design. Ultimate strength, and pozzolin content(fly ash) would be my concerns in your instance. Let's assume the concrete contains at or near the maximum levels of pozzolins - this is done to reduce cost - which delays the ultimate strength.

With that assumtion, you should have 'bout 70% of ultimate strength at seven, to fourteen days, and you'd be fine drilling and installing anchors. Less, or no pozzolins would allow the work to be performed sooner. If the pad is covered, or a curing agent has been applied - so much the better.

Your contractor seems to have a handle on it.

In 28 days you have ultimate strength. You have about 80% in 7 - 14 days depending on the mix.

Oops didn't read Mako's post sorry.

This is good information.
+1

You might want to have the contractor put in a moisture barrier (thick sheet plastic) before he pours the cement in the form. If he doesn't, the concrete will constantly draw moisture from the ground.
Then put another moisture barrier between the slab and the safe such as a 1/8" to 1/4" rubber mat. You can drill through it and set your anchor bolts still.

But yeah, two weeks curing will do.

For a product that runs like mud and dumped out of a truck, Concrete is actually a very precision product. There are many other ingredients that can be added to the mix to add air, quick strength, early hardening and several other properties.
Without a substantial vapor barrier you will always have moisture in the concrete especially if it is on the ground.
28 days is considered the time of obtaining max strength, but the concrete can be worked on and used prior to that time depending on what you are doing. A safe will have little effect on the slab. It just isn't going to be heavy enough to damage the slab. Moisture will be your biggest problem.

Why drill for the bolts? Just set them in place when you pour.

Matt,

Are you making an elevated pad on already placed concrete or placing this on the ground.

In my expert opinion I'd say 2 weeks. My experience = 0

We should have an answer after 3 or so pages.

I don't know might be more....I've only worked with the stuff for 28 years and I am still learning....

If I were pouring a concrete slab for myself for a safe. It would be at least 4"thick with #9 ga. wire mesh and 4000 psi concrete Mix. The width and length of the slab would be at least 1 ft more that the size of the base of the safe. I would keep it covered and moist for at least 7 days. Quick drying of concrete is a no no . Drilling for anchor bolts can be done in under 7 days. Placing the safe would depend on the weight of the safe. A safe of 1000 lbs could be placed after 7 days -- Web

to answer a couple questions:

a.) 5000 psi mix (according to the contractor, no drying agents (salts, etc))

b.) 6" slab on 4" existing concrete floor, tied with 6 xx length pieces of rebar anchored into the existing floor

c.) 5" larger than safe footrprint

d.) it's a secondary install - pre-drilled holes in the safe. easier to re-drill the holes in the concrete than do the math to get the bolt placing exactly right

Consensus seems to be min of 7 days, that's my opinion also. In my past life, we did vertical slipform structures (as opposed to highways and such) and routinely had 7 day breaks of 4000 psi mix in the 5500 psi range and 28 day breaks of nearly 8000 psi. I'm sure the mix design had something to do with it, but most mix designs will exceed their advertized design strength. Just don't use "sidewalk" mix.

BTW, UL - concrete doesn't "dry", it "hydrates" . . . it'll get hard under water . . .