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 . . .

For crying out loud we run traffic on 3250 PSI concrete. We build bridge decks with 3750 PSI concrete.

Matt you could form it yourself, get some HD-50 in 50 lb bags and make it yourself. You can mix HD-50, place it and be driving on it in a few hours.

That's what I'm thinking too........




Casey

Keeping them in precisely the correct place is the trick.

also, it was poured today, along with the outside stuff, from a pre-mix order,delivered.

I'll have to move the safe from house 1 to house 2 when the time is right.

right now, looking at 15 day placement, 19 day anchor install. kosher?

in 28 days you have the specified strength, but NOT the ultimate strength. It cures for a LONG time. You can generally drive on it after 7 days.

I just poured a 9 yd slab and missed a couple of anchor bolts. I drilled and put Red-heads in after 4 days and used an impact to tighten them. They held fine.

As for moisture releasing, once it is gray, you have most of the moisture out. If it is still green, it is still wet. Depends on your climate and how you treated it after the pour. If you have kept water on it for days, it will dry slower but cure much harder and stronger. If it is warm and sunny, it will dry in 5-6 days.

My main slab is 18" thick (to support my lathe) and the approach is only 4" thick. The 4" stuff was dry in 4 days, the 18" stuff took all of 7 days.

We often started framing on a slab the 2nd day after it was poured. We tightened the anchor bolts with a rachet and I have never seen one pull out- just don't get carried away.

Its gonna be hard to place a heavy safe over a few bolts. Anything over two bolts would turn out to be a serious job! For instance, if there are four bolts to be placed in the concrete, they better be exactly the same dimensions as the pre drilled holes in the safe, and you would need some kind of lift or crane to lower it directly over the bolts without damaging the threads or the bolts themselves.

I think he plans on drilling into the slab to put anchors in them and then bolting the safe down instead of leaving the bolts and nuts sticking out from the safe floor.

otter---proper sidewalk mix is 4000psi---- not for strength but to withstand the elements better. Web

Making the spacing for anchor bolts is pretty simple work with a plywood jig you build to fit whatever spacing you have on the safe. Stick your bolts thru the holes in the safe, place plywood up against bolts, smack with big hammer, drill holes in plywood where marks are. Build you a jig to hold the plywood level with the floor/concrete and bolt your anchor bolts to the plywood at the right depth..pour concrete and stick the jig down into the conrete etc....math is way overated lol. Same way we do it on everything from a 4" column to a 8' diameter smokestack with a circular pattern.

However picking up a safe and setting it down on anchor bolts inside a house isn't going to be super easy.

Drill it would be my choice.

That's interesting on 3250 psi concrete. We can't even pour a curb or fill a pan stair here with less than 4k. The only bridge we did with a concrete deck required a lot more. We failed two test pours in a row before the concrete people got it right, but it was a swing bridge - maybe that's why.

Here they are finishing the base for UtahLefty's safe:

Concrete never stops curing, for something of that weight I would defiantly wait a few weeks. If he put rebar in the little slab if it cracks it won't be a major deal, if he didn't put rebar in it, wait a little longer, if it cracks that crack will really open up on you.

Good luck, Matt!

2 weeks is a really, really safe bet. He's covering his ass.

When we pour concret, it's 7 days before we can drive on a standard mix.

geez we frame the day after the pour and I'm shooting hilti pins into a a deck the 3rd day. Its a 1200 Lb safe folks, he's not driving a 100K Lb truck over it.

Your thinking too much about this.


ML

So what safe are you going to put on the slab ?

I guess that was kinda my point. When we pour a bridge, we can drive equipment on it after 7 days, without doing breaks.

You can put you safe on it after 24 hours. If you want to be really safe, wait a few days before you drill the holes in for the bolts.

For highway use, 30 days before use is a good benchmark. It might be longer for your application (anchoring a safe) since the concrete and moisture within, might cause the safe's metal bottom to rust.

If you can put something between the concrete and safe to stop the cold from transfering to safe. Will help inside moisture control. Plastic sheet against slab and a 1/2 plywood spacer.Keep safe at room temp so moisture doesn't form inside. You should be able to drill thru the safe floor holes, ply and concrete and install red heads. the bolts can even be angled so they won't pull out if someone tries to lift by prying. 7 days is plenty up to 90% cured.

Again, 7 days is considered the min. for loading/drilling/stressing etc.. We build on them and backfill against them (carefully) after 7 days. 7 days if it were mine, keep plastic over it the first 6.

I'd say as soon as this thread dies, you should be good to go.

He should be good by now and it's still going!!!. If you are that worried about moisture, you can put a piece of tyvek down or even plastic. to keep it off the safe. The bolts are NOT an issue. They are ready to drill 3 days later.

As far as setting anchor bolts, There are better ways now. Most projects are engineered both ways.

In my slab, I used coupler nuts with tape over them. I can finish right over the top. This speeds up the finishing and makes a much cleaner job.

One the concrete is dried enough (12 hours or so) I simply flaked the skim of concrete off the taped areas and screwed a stud into the coupler nut. Now I have all the advantages of an anchor bolt with the convenience of nothing in the way of finishing.

This really wouldn't work for a gun safe but for walls it works fine.

Anchor bolts on a gun vault don't have to be torqued down, just snugged up so it doesn't walk off- it's not being vibrated or bumped around...

Exactly.

Maybe 10 days depending.


I would also drill into the slab, like Dennis said 3-4 days. Hopefully the rebar was placed so you don't hit it with the bit.

I would be more worried about moisture under the safe than any strength issues. A slab on a slab has great lateral strength, it also bleeds out more on top because up is the only way for the moisture to go.


Of course you might as well wait the full 14 days just in case some freak thing happens later on with the slab.

You are partially correct. We specify 3250 PSI in 28 days for Class B concrete and usually end up with 4000 PSI. We consider that ultimate strength. Yes it does continue to develop strength as time goes by until all the cement/water has hydrated.

In Wyoming wind? Not a chance.

Not that kind of swing bridge. Like a drawbridge that pivots side to side on a big bearing about 1/3 of the way across instead of up and down, balanced with a big weight box. It's made to go across bayous that only ocasionally need opening to let the shrimp fleet up in the bayou during hurricanes etc...

Damn thing had a girders about 12' tall. Pretty much like any other bridge just built heavy enough to support itself on that one big bearing instead of both ends.

Looks like this.

it''s not green anymore. kind of an ashy-gray. is that good or bad ? (grin)

Tear it out and start over.....

As most of these guys have said (tzone, Sam, etc.) you'd be perfectly fine going ahead to do it at 7 days, though if your contractor says 2 weeks, you might as well just wait the two weeks in case some freak accident occurs. That way if it would be something your contractor did, he can't turn it around on you for not waiting the two weeks he specified.

Sam does bring up a great point about the rebar, and hopefully you won't run into any issues there while drilling.

shouldn't - the general anchor location was marked and avoided when setting the rebar.

thanks to all.

Famous last works in construction - "Does this mean to avoid this or does it mean to stick it here?".

I recieved approvals on several mix-designs, for three different wind farms on Tuesday of this week. We poured several "mud mats" yesterday, and the bases for the towers will start on Saturday. I'm betting there will be towers standing on that concrete in two weeks.

I hope that puts things in perspective.>grin<

Did you hear about the unfortunate collision between a prison bus and a concrete truck?

Motorists were cautioned to be on the lookout for hardened criminals...LOL

GEEZ!

There is a lot of good general info here. You shouldn't have to worry about concrete strength for a slab on slab issue, especially considering the weight of the safe you'll be putting on the slab.

The only comment I'd make at this point is that in lieu of a typical red-head type anchor bolt, look into the Titen HD Concrete screw made by Simpson. Typical expansion bolts have to remain in the concrete, even after you are done with them (if, for exapmle you moved the safe elsewhere). You have to just cut the top of the anchor bolt off flush with the slab. The Titen HD is a self-tapping screw that can be removed easily, and re-used if necessary. I'm a Structural Engineer who designs concrete structures for a living, and the Titen is a fantastic product.

Never....never ....admit that around here....you just painted a target on your back for Les!

We did a McDonalds where those were specified. I agree, they are good, just very pricey. When I say "Red heads" I am using it as a generic term for anchor bolt that is install AFTER concrete has cured. I don't even know what brand I have.

I got no beef with that, but when I say my mixs will exceed specifications - and am willing to prove it using ACI standards - please don't tell me I don't have enough cementicious materials. >sigh<

Test cylinders, I've made enough to sink a carrier.

I had the locksmith over yesterday, scoping out the move (out of one basement and into the other). I gather he's got an "L" shaped sled and winch system for extracting safes out of basements.

When I moved the smaller one (only a 600#er), I discovered two of the anchor bolts were spinning when I went to loosen the nuts. I managed to wedge the safe up enough to get a sawz-all blade under to cut them off.

I'm going to remove the bolts on the bigger one this weekend and expect to have to do the same.

At the new location, sawz-all access will be blocked on three sides by concrete walls - it might be a permanent install....

Use the screws... they work REALLY good, maybe 5 bucks a piece here at the lumber yard. ANd then you can remove them later if needed much easier.

I'm thinkin' it should be about ready......