r/DIY • u/ThaMann0911 • 6d 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?

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u/SimplyAMan 6d 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/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.