Is it really OK to pound concrete anchor bolts in place?
I just had my 3′ high foundation walls poured today. Between using a super-plasticizer and delaying over an hour to start inserting the anchor bolts, the concrete was already setting quite a bit.
Half-way through, it started taking them nearly 15 seconds of intense manual effort to sink a bolt to its proper depth. Then they’d spend a full 60 seconds pulling the bolt up and down in the hole! They insisted that this will properly consolidate the concrete around it.
Then they started using a hammer to insert bolts as the concrete continued to harden! They followed this up with their standard policy of jerking the bolts up and down in the holes for a prolonged period before sealing the hole in the surface with more concrete.
I even have videos of them doing this! When I repeatedly stated that I didn’t believe this procedure would anchor the bolts securely, he insisted that he’s been doing this for years, everyone does it, and he guarantees it’s just fine.
I’m convinced that the bolts are not embedded properly. I believe that all that motion of the bolt in hardening concrete just forces water and fines into the hole, and pushes larger aggregate aside. Which could significantly weaken the anchor.
I don’t want to accept this quality of work, but I don’t know if I can insist that this be corrected. Prior to starting my home, I could not find any local contractor willing to fix the bolts on the forms prior to the pour.
Is there any way I can prove that this is not adequate quality work? Do I need to consult an engineer? Is there something specific in the code regarding this issue? Or am I just making a big deal out of this? Thanks.
Replies
Debra, it's certainly not best practice, especially if you're in a high-wind or seismic zone. You're right that their jerking motion is likely causing the space around the bolt to fill with fines, and may also leave some voids. Both reduce the strength, but it's hard to say by how much.
The simplest fix is probably to have the contractor add Simpson Titen HD screws, or similar, which are concrete anchors installed after the concrete has cured.
I have seen contractors take a piece of wood with tiny holes in it. The wood is treated in diesel fuel so it doesn't stick to the concrete. The wood is placed on top of the poured concrete and the anchor bolts are dropped in the drilled holes in the wood and a washer/nut prevents the anchor bolt from sinking. Once the concrete is cured, they simply loosen the nuts and remove the wood board. The anchors are set into the concrete with no issues.
I have also seen them do the above but for a wood top plate on an ICF wall. They place a pink foam under the wood top plate to protect the wood and prevent moisture transmission from the curing concrete. The difference is the wood top plate is left in place and not removed.
Ideally you have four guys on a pour. One works the pump, one vibrates the concrete or taps the forms, one screeds the top, and one sets the bolts. If someone gets behind, one of the others helps them for a bit. You are doing something wrong if you are a contractor and can't set the bolts in the right locations at the right time.
This group was 3 guys. First, one poured while the other two worked the vibrator. Second, they all screed the surface and smoothed the top to a very fine level with hand tools. Only then did they finally start inserting the anchor bolts. Stupid!