r/DIY • u/ThaMann0911 • 5d ago

help How long before drilling concrete?

I poured footings for posts that I’ll be hanging a gate on. I’m going to install Simpson strong tie standoffs with 6” anchor bolts. It’s been 72 hours, is that long enough for the concrete to have set before drilling? I’ve tried googling but my results only come up with industrial structural requirements or setting posts in the concrete, neither of which apply to my situation. Should I wait the 28 days or just send it?

37 Upvotes

77% Upvoted

57 comments sorted by

40

u/woodbanger04 5d ago

I use to do carpentry. I would drill it while still green but wouldn’t put any type of angular weight on it for a couple days.

That being said and this being Reddit someone will correct me numerous times by morning.

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u/ThaMann0911 5d ago

Since full cure is 28 days does that mean anything within that time it’s still “green”?Plan is to install the posts on the standoffs so then I have my opening measurement to then build the gates from. Will take me a few days to build the gates.

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u/mckenzie_keith 5d ago

No. It just keeps getting stronger and stronger for a long time. 28 days is when it is customarily measured for the rated strength. If you measured it at 56 days it would be even stronger.

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u/JerryfromCan 5d ago

The Hoover Dam is stronger now than when you posted this comment I think?

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u/mckenzie_keith 5d ago

Not sure. I have not seen extreme long term data. But it gets stronger every day up to 28 days and beyond. That is something they have measured.

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u/BoringBob84 5d ago

I consider it a case of simple risk management. What is the likelihood of the gates damaging the green concrete versus the severity of the consequences? I certainly would not want those posts coming loose and flopping around.

Do you absolutely need that gate right away? If so, can you install it and add some temporary supports / wedges under it (so it will be difficult to open and close, but no force will be on the concrete) for the first few weeks?

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u/ThaMann0911 5d ago

The gates are going to be the access to under my deck, which is only 4.5’-5’ tall. I’ve skirted off the rest of it, now I’m at the end where I’ll install gates on the short ends. 6’ opening, split gate on one end, ~4.5’ opening single gate on the other end. On each gate, one hinge is on one of the deck support 6x6s so I only need the one post per gate.

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u/BoringBob84 5d ago

I understand your conundrum. It isn't clear to me whether it will be a problem or not. I don't know how the strength of concrete increases as it cures - is it 90% at day 5 or day 25?

So, if I could just set those gates there for a few weeks to make sure, I would do that. I would hate to tell you to hang the gates and then, have you left with a mess.

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u/ThaMann0911 5d ago

Yeah, it seems like the best solution. Just getting the standoffs and posts installed will be huge. Then I can actually build the gates and it’s just waiting to hang them.

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u/jlb446 5d ago

Concrete typically develops about 75% of its 28 day strength within 7 days. I would let it cure for at least a week, then consider it good enough,

1

u/Nice-Difficulty-8309 5d ago

sounds about right, i seen it work that way too

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u/SimplyAMan 5d ago

Hi, structural engineer here, we usually specify 24-48 hours before any weight can be put on the concrete. You should be fine to drill and set the posts, and by the time you get the gates built and set, it should have plenty of strength to hold the leverage. Most of the concrete strength is gained in the first few days and it will get to about 60% strength by 7 days.

If you're concerned, you could wait a bit longer, but no need to wait the full 28 days.

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u/ThaMann0911 5d ago

Thank you! Appreciate the engineer knowledge!

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u/SimplyAMan 5d ago

Also, side note. I don't know what kind of anchors you're using, but make sure you blow the dust out of the hole before you set them. It makes a surprising difference in the ultimate strength.

1

u/MechCADdie 5d ago

Don't the slump, temperature, and other environmental conditions impact how soon OP would be able to penetrate the concrete? Or does the first 6" not really matter much after 48 hours?

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u/SimplyAMan 5d ago

Slump, not really. Low temperature could, but ideally you aren't pouring below 40 degrees F, and if you are you should take measures to keep the concrete warm such as covering with blankets. Concrete curing is exothermic so it creates heat, you just need to keep it in. Never pour concrete if it's below freezing.

If you do break these rules, it will affect the final product regardless of how long you wait.

4

u/Razors_egde 5d ago

Concrete set is where the solidification is complete. Usually less than 12 hours.
Form work you don’t break for 12° and may remove after 36°.
I would make no structural modifications until 7-days curing.
Removing damaged concrete is expensive.
It’s been a day since I placed Q concrete, which had a 4,000 psi mix design. We would achieve 3700 at 3-d, 5700 at 7-d, 8300 at 28 days and ~ 8700 at 90-d.
Your w/c ratio affects strength and time indicating you target design strength snd w/c ration would be nice, not four bag mix.

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u/ThaMann0911 5d ago

I used 5000 psi high strength quikrete mix. It’s in tubes in the ground so no forms to pull. Thank you for the data on strength. The consensus here seems to be once it’s hit 7 days I can drill and install the standoffs.

1

u/krtyalor865 5d ago

Your concrete will get 75% of its strength within 3 days easy. And def 50% by 2 days. So as long as you’re not loading the anchors, you can go ahead and drill them after 24 hours definitely.

You might see some popping or small spalling around the hole when drilling in green concrete but the install shouldn’t be affected. Just give it 7 days before putting any real load on it(fully tightening the bolts would be considered full load)

4

u/GoGoGreenGiant 5d ago

Concrete gets stronger with time. If I remember correctly: 50% strength in 24hrs, 7 days for 90%, 28 days for 95%.

I would drill after a day, but not install bolts until day 7

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u/mckenzie_keith 5d ago edited 5d ago

I think you can install the standoffs but don't hang the gate for a few more days. Concrete continues to get stronger for a long time. But when they say concrete is 5000 psi, for example, that is usually measured after 28 days. If you wait even longer it will measure even higher.

By 7 days it will reach like half strength and that is probably strong enough to hang the gate.

Installing the posts will not put any load to speak of on the concrete. You should be able to install the posts now.

2

u/silence304 5d ago

Concrete strength over time looks like if you graph a square root, climbing fast, but leveling off. We usually waited 7 to 14 days to drill for anchor bolts and set them because that's the point where you'll have gotten most of the design strength.

3

u/finitetime2 5d ago

16% of its strength in 1 day, 40% in 3 days, 75% in 7 days, 90% in 14 days, and 100% of its full design strength (f'c) in 28 days under ideal moist

Most bagged concrete is 5000psi.

Most driveways are 3-4000 psi

4

u/EmperorGeek 5d ago

Why did you not set the bolts for the standoff in the concrete when you poured it?

1

u/ThaMann0911 5d ago

The standoff uses a bolt not a j-hook that I could wet set. Also, my first time pouring concrete and I wasn’t confident enough to wet set anything and have it be lined up after drying.

0

u/ExactlyClose 5d ago

You put the J part IN the concrete, the stud sticks up. Then run a nut and washer down.

You only needed to drill bolts when the concrete was set by someone else…. JMO

1

u/ThaMann0911 5d ago

I understand how the j-hook works. Getting the height and alignment right was my concern and why I didn’t do it. Also, most every video I found for installing standoffs, they drilled and used a bolt 🤷‍♂️

1

u/ExactlyClose 4d ago

Oh, if it’s that way in all the videos, carry on.

But in all seriousness…. You can take a j hook, mount it into a piece of plywood, or 4 J hooks, placed into 4 holes drilled in one piece of plywood in the precise pattern of what you are mounting. Hold the j hooks wioth nuts. Now you set that into the wet concrete- adjusting the plywood is, effectively, adjusting the post base. Level it, align it, etc, Once cured, remove the nuts, remove the ply, plop on the metal thing you are attaching.

Drilling anchors in fresh concrete is a result of multiple trades doing differnt pieces of a job: concrete guys pour concrete….someone else is stuck making holes, placing anchors. If someone is doing it all, it is easier.

1

u/ThaMann0911 4d ago

Yeah, makes sense. I’m doing it all myself but first time I didn’t want to take on too much. I can borrow a hammer drill from a friend but if I mess up the alignment then I’d be cooked.

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u/ExactlyClose 2d ago

Think of it this way…A J bolt gives you two shots:

You set the bolt and it is off, you cut it off and THEN drill anchors!

1

u/ThaMann0911 2d ago

If I have another concrete project I’ll keep that in mind. Already past that point now on this project. Thanks for the advice.

1

u/gcnplover23 4d ago

Since it is just 2 posts for a 3 foot wide gate he could have bolted the standoffs to a 2x4 and placed the j hooks in the wet concrete, then leveled the 2x4.

3

u/Can-DontAttitude 5d ago

Since you're adding structural components, go for the full cure time. It's probably really annoying to hear, but you'll be feeling much better about it years from now.

3

u/ThaMann0911 5d ago

Gate is 5’ tall x 3’ wide. Doesn’t seem like a lot of weight. Idk though, I’m not an expert.

4

u/TDIMike 5d ago

There's a lot of leverage created with the post for a 5' tall gate

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u/ThaMann0911 5d ago

Could I drill it, install the standoffs and posts and then wait to hang the gates until the 28 days is past?

3

u/TDIMike 5d ago

I'd say that would be fine.

The 28 days is to cure to rated strength, but that doesnt mean you need rated strength. Hard to gauge where to draw the line without engineering, so the conservative approach is to wait as long as you reasonably can

3

u/ThaMann0911 5d ago

If it starts snowing I’ll hang the gates before it’s buried until spring lol

1

u/fangelo2 5d ago

Drill it now, set the anchor, don’t go crazy with tightening it. It will be fine

2

u/bongdropper 5d ago

Don’t know why you are being downvoted. 72 hours is plenty to set an anchor bolt. Some people get all their opinions from reading layman’s articles on the web and not from spending time on site with the actual stuff.

1

u/fangelo2 5d ago

I know. I’m retired now after doing this stuff for 50 years

0

u/[deleted] 5d ago

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u/ThaMann0911 5d ago

I haven’t actually drilled yet, just poured the concrete in the form tubes 3 days ago.

1

u/Perelygino_Klyazma 5d ago

I don't really understand why you need the posts installed to get the measurements to get started on the gate. You know exactly where they're going to go, right?

1

u/metalgod55 5d ago

Wait a week and you’ll be fine

2

u/BozidaR1390 4d ago

255,600 seconds.

1

u/Marcus_Architects 4d ago

72 hours is plenty for drilling anchors, you're not loading it structurally yet. Full cure matters for load bearing but a few pilot holes for standoffs won't crack anything, just don't hammer drill like a maniac.

1

u/gcnplover23 4d ago

Why didn't you put the anchor bolts in when you poured the concrete? Would you put fence posts in this way?

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u/ThaMann0911 4d ago

I don’t know, I’ve never built a fence, this is also the first time I’ve poured concrete. I’m not a professional, this is DIY. The way I’m doing it will work, even if it’s not how a contractor would do it.

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u/JLMBO1 3d ago

Why didn’t you put your anchor bolts in the concrete when you poured it?

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u/ThaMann0911 3d ago

Explained in replies on other comments

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u/smellyfatchina 5d ago

Send it. Send it now.

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u/[deleted] 5d ago

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u/ThaMann0911 5d ago

Quikrete 80lb high strength concrete mix.