How long before drilling fresh concrete?

Ultradog MN

Well-known Member
Location
Twin Cities
Question for the brain trust:
Had a slab poured this week and want to
start framing. The contractor set a couple
of j bolts in the wrong location.
I plan to cut them off and drill for quick
bolts after the he wall is up. Just
wondering how long I should wait. This is
for anchoring the bottom plate around the
perimeter of the slab. I have a good Hilti
hammer drill.
Any concrete men here?
Thanks.
 
I agree with sms, drill it now but don't tighten the bolts for a week if you can wait that long. It all depends on the quality of the concrete too.
 
Technically, you need to wait the 28 days to achieve the full value of the expansion bolt or sleeve anchor, but at 7 days the concrete should be a 1/4 of it's compressive strength, 14 days 1/2 and so on. If you crank down on these, concrete will spall and you will have zero value on that fastener. I have done the testing on these many times, let that concrete achieve some strength first, just enough to avoid spalling. Given it's a sill plate, would seem you'll have a lot of pull out forces, but would be nice to know you have the fastener value needed for the load, given it is what holds the framing to the foundation.
 
This article gives some info. Looks like a week is safe for load bearingif you can wait that long. I agree with others that you can drill before that, but you are talking about near slab edge so be careful not to split a piece off.
Concrete cure
 
Drilling holes wouldn't be a problem. It's the anchor which is putting pressure outwards which could cause the concrete to crack. Depending on how the weather is were you are it could take a month for the concrete to fully cure and develop it's full strength. You might just stick the sill plate down with liquid nails and let it sit for a while and drill the hole for the anchor through the wood.
 
Out of curiosity, two misplaced J-bolts out of how many total around the perimeter? Also, I suspect that maybe the actual location (middle of a long wall, next to a door, etc) of the two you cut off might have some bearing on how important those two anchors are in the overall design (not saying though that a guy should pass on finishing up what you want to do).
 
Epoxy anchors will cost more and you will have to wait the full 28 days for the concrete to achieve its design strength. This cannot be guessed at, you have to follow the manufacturers instructions and the concrete strength must match what fastener manufacturer calls for to achieve the values they show in their fastener charts.
 
Put in one or two to keep the sill from shifting but wait with the nuts and the other anchors Till you need to finish the inside of the wall.
 
I say 7 days if it?s possible. A 7 day break usually is about 80-90% of the design strength. If you can weight longer to tighten them it?s better. Epoxy and anchor aren?t spendy. Fastenal carries Red/Head brand which performs well. Just make sure to clean the dirt out of the drilled hole.
 
Used to see this all the time, with a variety of materials, most of which call for the full compressive strength of the concrete to be achieved 1st. They don't want to wait the month and did not plan initially to have to wait. In this case, an embedded item was mis-located by mistake or otherwise. Hate to sound rude, but the ship has sailed, messing with green concrete is always a mistake. This is still a structural connection with forces applied, maybe just wind loads and lift, but still. It would have been far better to get those sill connection rods located correctly or, wait until the concrete has reached its full strength. Problem here is, I am sure Jerry will want to start framing, which buries the fasteners. So, if you want to tighten them later, the access may not be there. It's a mistake that will cost you a month on the schedule and a very simple rule was missed when constructing with concrete. It happens and people want to imagine ways around it when there really is not a safe way to. Always know your materials and with concrete, plan ahead so that month of curing time does not affect your production schedule. In this case, it delays the start of framing. Fastener manufacturer instructions will usually call for the concrete to be at full strength. I've never seen it different to date in a long spanning career in the construction industry.
 
it is always a good idea to make a couple of test cylinders when you pour concrete--the smaller ones are less than a dollar apiece and then you always have a resource to go to for unexpected problems if they arise. A testing outfit could test them for you, but i have seen setups with a hydraulic press test cylinders also
 
oh and i forgot--there are devices to measure the strength of concrete after it has set--although not as accurate as testing cylinders they do give you an idea of the strength--one is called a Swiss Hammer.
 
I disagree, the only way you can prove strength is actually 80-90% is breaking test cylinders at 7 days which may indicate that the concrete has reached a 1/4 of its full compressive strength and is rising to meet the full design strength. The material is going to vary widely and some will get stronger sooner, but YOU DON'T KNOW THAT until it's proven. He does not have 4 test cylinders and is paying for an inspection service to do the 7,14,21, & 28 day breaks. You cannot guess at this stuff and expect real results.
 
Another is a windsor probe, and it's actually good enough for a P.E. to sign off on a T.R. 1 form for city of ny d.o.b. controlled inspections
 

UD I've always been told to wait 7 days before building on new concrete.
When we poured my shop floor I waited 7 days, then put 2 coats of concrete sealer on, one coat per day, gave the sealer 3 days to dry and then started building, total of 12 days.
Bolt alignment for the plates was good but additional anchors where needed in a couple of locations, after the walls where up, trusses set and outer metal installed we drilled and installed to final anchors.
All told it was 3-4 weeks before those last anchors where drilled and installed.

If you can drill yours in later I don't see a problem.

I do recommend a good coat of concrete sealer to help protect the surface finish and water proof the concrete.
 
Drill today where you need the anchors. Set ready rod in the holes with Por Rock quick setting grout. Great stuff and does not shrink. (like 20 minutes and is stressible in an hour. Jim
 
I have seen contractors set the walls on a slab after a week using cement nails. After the roof was on go back and drill thru the plate and put in the anchors in a couple weeks or more.
 
the grout does gain strength quickly--but the concrete around it has not developed strength so under stress the grout can pull out in a lump and take the concrete with it--have seen this a few times on bridge beam anchor bolts when tightened down too soon.
 
True it is. My intent is to offer an alternative that will work. Stressing it before the base pour is cured for 24 hrs at least (remember it is an anchor bolt, and will just barely squeeze a washer under the nut.) Jim
 
Wow.
Lots of help!
I guess there's no real hurry to drill and install the quick bolts as I could just drill through the bottom plate and into the concrete later.
Thanks guys.
 
I did not read all the comments so maybe someone has mentioned this. Keep the slab wet for as long as possible. Wet it down every time you walk by it. Water lets the concrete to cure slower. You will be doing yourself a favor.
 
When we built our shop I started setting the walls the next morning, and I had the shingles on and the door in
within a week, and the floor is fine. I probably waited a few days to tighten the J-bolt anchors.
 
(quoted from post at 06:27:20 07/14/18) I disagree, the only way you can prove strength is actually 80-90% is breaking test cylinders at 7 days which may indicate that the concrete has reached a 1/4 of its full compressive strength and is rising to meet the full design strength. The material is going to vary widely and some will get stronger sooner, but YOU DON'T KNOW THAT until it's proven. He does not have 4 test cylinders and is paying for an inspection service to do the 7,14,21, & 28 day breaks. You cannot guess at this stuff and expect real results.

I disagree too. Concrete strength is not a straight line. You get well over half strength at 3 days and 75% at 7 days, of the 28 day strength. It continues to gain strength for many years after 28 days, but at a slower and slower rate.

I've always loaded after three days (light loads, framing, etc. and never had a problem.
 
I like that having built my house and numerous buildings....but not a contractor nor expert! Crete is still sorta soft, so drilling is easy. Come back when it's hard and glue in your anchoring devices. Also like nailing sole plate (initially) so you can get on with the framing and coming back to fill in the holes with anchors and glue. Much better than fighting "J" anchors as part of the pour process....get a better finishing job on the crete too not having to work around the "stobs" and framing out works faster too.

Since 3 days to start framing puts your plate on the slab quickly, you can drill through both and have everything ready for your anchors when the time comes.

Not an expert but keeping it wet helps to make a good pour. Even the highway department here, when doing bridges, cover and wet. I have seen slabs and driveways where the top ⅛", the finishing surface, separates from the main slab after 15ish years. Usually see it on driveways and in subdivisions where you know they don't cover or keep them wet.

On getting the plate wet, I wouldn't worry about that, especially if using treated wood which is the norm these days (I used 15# felt paper 40 years ago), or even untreated.....how many houses/buildings have been successfully built and occupied for who knows how long that got soaked in rain/snow in the process of being built......my house for one. Built it in Aug and Sept, thinking Aug would be a dry month to get it weathered it......wrong....rained on me 3 times before I got it weathered in and it got soaked good....still good to go.
 

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