Post Installed Anchors to CMU
Post Installed Anchors to CMU
(OP)
I posted this in the fastening group but didn't get any useful tips, maybe someone here has some experience with this:
I need to attach plates to an existing cmu wall, my loads are in the 400#-600# range per anchor in tension and about 150# shear. These plates will support cantilever tubes so I want to have a good factor of safety in there. I have some questions about how people typically handle the following:
- Most likely the anchors will hit a mix of solid and hollow cells. If I go with Hilti they recommend a different anchor for each condition - do you spec both and make the contractor switch back and forth? Powers recommends the same epoxy for both hollow and solid cells, this seems less likely to contractor mix up.
- Most anchors are shown as not applicable at or near the mortar joint, I can't really control the location of these anchors. Do you typically deal with this by adding additional anchors assuming that some will be ineffective?
thanks
I need to attach plates to an existing cmu wall, my loads are in the 400#-600# range per anchor in tension and about 150# shear. These plates will support cantilever tubes so I want to have a good factor of safety in there. I have some questions about how people typically handle the following:
- Most likely the anchors will hit a mix of solid and hollow cells. If I go with Hilti they recommend a different anchor for each condition - do you spec both and make the contractor switch back and forth? Powers recommends the same epoxy for both hollow and solid cells, this seems less likely to contractor mix up.
- Most anchors are shown as not applicable at or near the mortar joint, I can't really control the location of these anchors. Do you typically deal with this by adding additional anchors assuming that some will be ineffective?
thanks






RE: Post Installed Anchors to CMU
RE: Post Installed Anchors to CMU
Ordinarily you'd try to avoid grouting existing cells, as it is a pain to do; but in application critical situations, you may be justified in requiring it and not having to worry about ungrouted cells.
RE: Post Installed Anchors to CMU
thanks
RE: Post Installed Anchors to CMU
Sawcut the face shell and grout. Have done it many times before.
RE: Post Installed Anchors to CMU
RE: Post Installed Anchors to CMU
kikflip - The anchors into hollow cells use the screen tube insert so they 'mushroom' on the backside and become almost like a mechanical anchor. I've used them before and never had an issue. Although since this is a cantilever I agree that it's a bit more risky.
RE: Post Installed Anchors to CMU
RE: Post Installed Anchors to CMU
RE: Post Installed Anchors to CMU
You break out the face shell then push down some pieces of empty grout bags to block out the cell cavity below. That's how I see the masonry guys do it.
I would normally thru bolt a cantilever connection and still grout 2-3 blocks above and below the connection.
RE: Post Installed Anchors to CMU
I would never anchor anything structural to hollow block, maybe a flat screen TV using tap cons or something. Take a hammer to a hollow face shell once and you will have a good feel for it.
I am sure you are doing something architectural, but anyway to add a small angled tube brace for truss action to reduce this to smaller axial forces?
RE: Post Installed Anchors to CMU
a2fmk - I can't add kickers due to arch and I don't have access to the backside so no through bolting.
This is actually a stair, the treads are cantilevering off of the existing block wall. It's a residential stair and is only 2'-6". I've designed it for 350# live load at the tip (3') or the equivalent of 700# at midspan. I have a continuous deep stringer bolted flat to the wall and I'm assuming that only one anchor resists the tension while in reality I have one per cell so even if one isn't up to strength I will be engaging several through the stringer. Since this is a stair and a cantilever I want to have a lot of extra capacity in there which is why I was so concerned with the hollow cells. I'll have them grout and possibly even add rebar. Thanks.
RE: Post Installed Anchors to CMU
RE: Post Installed Anchors to CMU
This will allow the loads to be distributed to the entire masonry wall.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: Post Installed Anchors to CMU
concretemasonry - thanks, good tip.
So my plan is to grout any hollow cells that we find. Do people agree with using chemical anchors to grouted cells? Any reason to use mechanical instead? How long after grouting is it safe to start installing anchors?
thanks again.
RE: Post Installed Anchors to CMU
You are bolting a channel stringer at every cell to the wall? If the spacing were further out, you may need to consider the torsion you are putting into the channel, but then again it is braced to the wall and sounds like you are only "spanning" it 8". Otherwise I may suggest using an HSS for that member.
RE: Post Installed Anchors to CMU
RE: Post Installed Anchors to CMU
RE: Post Installed Anchors to CMU
Just use the Hilti HY-20. It can be used in hollow or grout filled cmu. Just assume the loading for the hollow cmu. It will be conservative. Use the 3/8" HIT-A anchor with a short screen tube. I've tested these anchors and (assuming the CMU is new/good) you will easily get the loads you're looking for. If you're going into old or "cinder" blocks it's a different story. Always insist the installer is trained or know's what they are doing or else you might as well put mud in the holes.
Small mechanical sleeve (not wedge) anchors might work if the CMU is good.
RE: Post Installed Anchors to CMU
This is a building from the mid 80's so I don't know how great the cmu will be. I'm going to have a pull test done on a few anchors to get a feel for what I'm dealing with.
Hokie66 - You are saying to embed a bolt and leave the threaded portion out? I like it... but I doubt they'll get them in the right spot.
RE: Post Installed Anchors to CMU
RE: Post Installed Anchors to CMU
It's from experience that I know you can use HY-20 in solid masonry. Typically the masonry is the weakest element anyway. If you don't feel comfortable with HY 20 you can use HY-150 max. Hilti actually has test data in their tech guide that gives capacities in CMU. HY 150 MAX was designed so it can be installed into holes that are up to 1/4" larger than the threaded anchor rod. So if they hit a solid cmu you could essentially eliminate the rod (assuming the installer is competent). You could always just use the screen tube anyway in case the installer can't tell if it's solid or not. The holding mechanism will be bond instead of keying in solid holes. Cleaning the holes is obviously important here.
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RE: Post Installed Anchors to CMU
Thanks!
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