Bolting to old concrete block walls?

[Stephen Tashiro]

In my 1941 vintage exterior concrete block walls, the typical expanding lead anchor and bolt is hard to use since the mortar in the joints crumbles when I drill. (I assume its best to put anchors in joints. I think I'd risk cracking the block if I drilled into its side.) Is there a better scheme of fastening a board to an old concrete wall?

I'm confident in how lead anchored bolts resist a downward force, but I don't think they resist a force trying to pull tem out of the wall well.

[Rich Engelhardt]

the mortar in the joints crumbles when I drill.

Use an air hammer to remove the old mortar and strike a new joint w/new mortar.
You can embed bolts in the new mortar.
Just take care not to disturb the other mortar joints other than the one you're working on.

You don't have to use an air hammer - but - using one turns a half hour job into a 30 second one.

My mother in law had one block in her foundation that had lost about a third of the mortar in the joint. I figured I was in for an afternoon of work this past Summer striking a new joint. Much to my disappointment, the whole job only took about a half hour from the time I fired up the compressor to the time I stuffed the new mortar in.
(You have to understand that doing work at my mother in law's means I get to go outside, drink beer and generally avoid the rest of my wife's work-alergic relatives - which is why it was a disappointment it went so quick )

[Dan Hintz]

I assume its best to put anchors in joints. I think I'd risk cracking the block if I drilled into its side.

Actually, you don't want the joint to crack as that can propagate, so it's better to put it in the block.

[Rod Sheridan]

In my 1941 vintage exterior concrete block walls, the typical expanding lead anchor and bolt is hard to use since the mortar in the joints crumbles when I drill. (I assume its best to put anchors in joints. I think I'd risk cracking the block if I drilled into its side.) Is there a better scheme of fastening a board to an old concrete wall?

I'm confident in how lead anchored bolts resist a downward force, but I don't think they resist a force trying to pull tem out of the wall well.

Toggle bolts in the hollow sections of the block...............Rod.

[Lee Schierer]

Tapcons into the block work well. Just be sure to drill eh hole 1/2" deeper than the bolt and to blow out any dust. Never in the mortar.

[Brian Effinger]

Stephen, what are you trying to bolt to the wall?

[Stephen Tashiro]

Stephen, what are you trying to bolt to the wall?

Essentially, I just want to bolt a 2x4 to it. There would be some simple bevel and flashing to make water run off the top of it. One one wall, I want to have hooks in the 2x4 to hang sections of lattice in the summer. I'll take them down in the winter. On other walls, I want to construct a narrow awning above some window, something that would only project about 12 inches out from the wall to keep water that runs down the wall from splashing so much on the exterior sill of the window - and perhaps to hang a bird feeder from.

I have used an air chisel on my walls to remove block at times. It works great for that except that the retainer springs on the tool break too easily. (I got some specialized retainer device that is supposed to fix that problem, but I haven't tried it yet. ) I find my air chisel too aggressive to use for "pointing" joints. An electric angle grinder with a thick disk works well, but it leaves places on the vertical joints that must be done by hand.

If I took out the old joint and put in concrete instead of mortar I would have confidence the bolts would be anchored, but the bags of mortax mix I've used don't harden to be very strong material.

I have a number of block that were removed from the wall. I've used these to experiment with drilling through the walls of the block and I don't like that process. These old block have a different "grain" than modern concrete block. They seem to be made with coarser particles and are not as homogeneous as modern block. I hope I don't have to install a new block everywhere I want a bolt!

[Phil Thien]

Toggle bolts in the hollow sections of the block...............Rod.

+1. I don't think you're going to get much stronger than this, if you're worried about pull-out resistance.

[Keith Westfall]

I find my air chisel too aggressive to use for "pointing" joints.

Turn the regulator down on your compressor...

[Dan Hintz]

Essentially, I just want to bolt a 2x4 to it.

Have you considered construction adhesive (comes in caulk tubes)? That stuff will break the brick before being ripped down, so I'd consider it stronger than toggle bolts, and since you're not drilling into the brick or mortar, no cracks.

[Phil Thien]

Have you considered construction adhesive (comes in caulk tubes)? That stuff will break the brick before being ripped down, so I'd consider it stronger than toggle bolts, and since you're not drilling into the brick or mortar, no cracks.

The previous owner of my home used construction adhesive to attach fir strips to the basement walls to hold panelling.

None of it held.

When I removed the dropped ceiling, I discovered it was the only thing holding the panelling against the walls.

Now, the job was 20 years old when I removed it. I'm sure it lasted some amount of time.

But I'm not longer as confident of construction adhesive as I once was.

[Dan Hintz]

I have no idea what type he used (or if he used it properly), but 3M (among others) guarantees their stuff... I'm telling you, it will hold a buffalo against the wall if you let it cure. I had to take a sledgehammer and chisel to one piece I put in the wrong spot on the floor

[Phil Thien]

I have no idea what type he used (or if he used it properly), but 3M (among others) guarantees their stuff... I'm telling you, it will hold a buffalo against the wall if you let it cure. I had to take a sledgehammer and chisel to one piece I put in the wrong spot on the floor

I have no idea what he used, either.

Perhaps it was junk, or mis-applied.

I can tell you that the bond broke at the wood, not the wall. I had to hand-scrape the old stuff off the wall, and it was a chore times two.

[Brian Effinger]

Essentially, I just want to bolt a 2x4 to it. There would be some simple bevel and flashing to make water run off the top of it. One one wall, I want to have hooks in the 2x4 to hang sections of lattice in the summer. I'll take them down in the winter. On other walls, I want to construct a narrow awning above some window, something that would only project about 12 inches out from the wall to keep water that runs down the wall from splashing so much on the exterior sill of the window - and perhaps to hang a bird feeder from.

If I took out the old joint and put in concrete instead of mortar I would have confidence the bolts would be anchored, but the bags of mortax mix I've used don't harden to be very strong material.

I have a number of block that were removed from the wall. I've used these to experiment with drilling through the walls of the block and I don't like that process. These old block have a different "grain" than modern concrete block. They seem to be made with coarser particles and are not as homogeneous as modern block. I hope I don't have to install a new block everywhere I want a bolt!

Sometime those old blocks are just crappy to work with. Could be real cinder blocks. In this case, the joints are the best place of attachment. For a mortar, use type M or type S. These are higher strength, and should be able to hold some light weight materials. It will be tedious work, though.

One other concern (at least for me) is your flashing. How that ties into the wall is critical. If water gets behind there, it will rot the wood, and destroy the mortar joint eventually.

[Bill Cunningham]

+1 for the adhesive.. The stuff they make now, is not the same stuff they made 20 years ago.. But I would also use pressure treated wood to eliminate the rot that will eventually happen..