Homemade anchor-bolt holders
Wanting to minimize the chances that I’ll mess up the last stage of my house build where what I do gets set in stone, I’ve been reading up on the most foolproof ways to set anchor bolts exactly where they should be in the bond beam of an 8″ masonry stem wall. A great article at http://www.finehomebuilding.com/2002/07/01/precise-location-of-foundation-bolts describes several techniques that the author considers superior to inserting the bolts by hand after the concrete is poured, and my idea is a slight modification of one of his.
I would make each anchor-bolt holder by drilling a 1/2″ hole in the middle of a foot-long piece of 2×3 or 2×4 that would sit perpendicular across the top of the stem wall. I would drive two pairs of nails 8″ apart in the wood so that the nails angle slightly inward on the underside. When I push the wood onto the concrete blocks, the nails will pinch the outside surfaces of the blocks enough to keep the wood in place. A nut will hold the bolt at the right height, as the wood is the same thickness as my sill plate, and the bolt should be held plumb by the 1-1/2″ vertical hole it runs through. I could also tie a lower part of the bolt to the horizontal rebar in the bond beam if necessary.
I’m sure this will seem like more trouble than it’s worth to many, but I live in a dry, hot climate where the grout in my bond beam might start to set quickly, so I don’t mind putting in the extra time to avoid having to rush to set the anchor bolts during a short window of time, even with help.
Am I overlooking anything that might go wrong with this technique?
Would tying a lower part of each bolt to the horizontal rebar add any significant benefit?
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Replies
Jeff,
If you want to make a jig that holds the anchor bolts in the correct position I would do as you suggest but not place it until the concrete bond beam has been levelled. otherwise this will become a lot harder and there is a good chance of voids or an irregular surface around the bolts.
I can't help but feel my answers to your last enquiry have caused you to worry unnecessarily. If you place the bolts a bit too early you will quickly see they are tilting and can wait a bit. If they are a bit off plumb or a bit off the centre of where your sill plate will go that isn't a big deal.
Tying them to the rebar won't do much structurally. If you want to upgrade their holding power you can use more of them, use a longer bolt, or use square seismic washers to secure the sill plate.
Thank you, Malcolm. Yes, I was a little worried about leveling underneath the 2xs. Putting them in place after the grout is poured and leveled, as you suggest, sounds like the best idea. I made a test holder today, starting with just one nail at each end, and it held really tight. I had to tap it with a hammer to get it on, but it took only a few seconds. I was thinking about tying to the rebar only to help the bolts stay aligned, but given how tightly the holder stayed in place, I don't think it's necessary.
No, you didn't make me worry about placing the bolts any more than I would have anyway; I'm just extremely wary of making mistakes with concrete, as they would be so hard to correct. It is good to know that some slight misplacements won't be a big deal.
I may have a hard time getting anyone to come help me for such a short amount of time. If I have a pump operator filling the bond beam and reinforced cores, my holders with bolts and nuts inserted ready to go, and the spots where each holder with bolt will go marked on the interior side of the stem wall largely enough that some grout spillage won't cover the marks, do you think I'll have ample time to level the grout and place the holders by myself before the concrete has set too much?
Jeff,
Don't forget, if the worst did happen and the bolts didn't all get set, you can drill and insert them afterwards using Simpson epoxy approved for the purpose.
Thanks, Malcolm. I'll ask the readymix company how quickly the grout sets around here this time of year.
Jeff,
If you want to use a jig to hold your anchor bolts, go ahead. Done correctly, that method works, and you end up with accurate placement of the bolts.
Malcolm's method also works -- but his method can result in slightly weaker concrete near the bolts. Inserting the bolts displaces the large aggregate in the mix, and the displaced aggregate is replaced by watery grout. I'm not saying this is a big problem -- it usually isn't -- but seismic engineers care.
Thank you, Martin. My bolt holders grab the sides of the concrete blocks tightly enough that I could set them 1" above their final positions before the grout is poured so that I can see and reach under the wood with a trowel to make sure the grout is solid and smooth and then tap them down the last inch once everything looks good. Would moving the bolts only the last inch after the grout is poured alleviate the displacement enough--or would it be better to set the holders all the way down before the pour and then just reach under the wood with a trowel to smooth the grout and eliminate any voids sight-unseen?
Jeff,
I hope you will come back and describe how the pour went. It would be useful both to describe the process for other's facing the same task, and also for experienced posters to understand what parts of the work first time builders find difficult.
Again, good luck with your build!
Will do, Malcolm. I generally only ask questions here when I can't find answers anywhere else after exhaustive searching; therefore, discussions such as this one should provide information other builders like me will be very glad to find. It may be a week or more before I do the pour.
The grout pour went quite well. I was glad that I set all of my anchor-bolt holders in place beforehand, as the bolts all ended up at the exact depth and placement I wanted, and I had plenty of time to level and consolidate the grout without any help. The anchor-bolt holders were easy to make and set, and they held onto the wall tightly even with the pump hose bumping against them. One of the blocks that I had left with a marginally tight grip got raised up 1/4" during the pour; I tapped it back down with a hammer while the grout was still quite wet, and I gave each other block a tap just to make sure as I went around leveling.
As I went around, I also poked under each 2x4 with my finishing trowel to make sure grout had filled in where I couldn't see. When I removed the 2x4s, two had superficial defects in the grout underneath, dips around 1/2" deep and 1" square, probably the result of my not poking my trowel into those spots sufficiently. Underneath the rest, the grout had formed a nice, smooth surface flush with the surrounding block.
A finishing trowel seemed much better than my Philadelphia trowel for leveling the grout, because of its straight edge and ability to push quite a lot grout along the top of the wall.
I ordered a little more grout than I thought I would need, so I dug some rectangular holes in the dirt nearby to act as forms for blocks to be made out of the excess. Between the grout excess and the footing excess, I will have enough blocks to make little walkways to each of my doors.
Thanks again, Malcolm and Martin, for your advice.