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I want to fasten some boards to my basement walls to act as mounting backers. The walls are natural stone, Diabase if that's important. They can be damp at times. The boards will bear some weight, I'll be hanging stuff on them, and using plastic spacers to prevent the boards touching the walls and to account for the uneven stone surface.

Can I use Tapcon™ concrete screws? Their docs list all kinds of masonry but not stone. That would be ideal because without anchors I don't have to drill large holes.

If I need to use anchors can I use use metal lag shields? Regular plastic masonry anchors? Again, everywhere I see specs, they spec all kinds of masonry but not stone.

I have hung some lightweight things on these walls with plastic anchors, but that proves nothing, there's no test of how effective the anchors are when all they are holding is EG a light switch. A few heavier things were hung by pros using powder-driven fasteners. I'd go there if it's my only option, I guess that would be fun if I can learn to do it safely.

isherwood
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jay613
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  • Do you need them to be readily removable? – Matthew Apr 13 '23 at 23:52
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    Will the fasteners need to hold all the weight, or will the boards sit on the floor? Tapcons should work to hold the boards to the wall, not sure of their weight holding capacity. – crip659 Apr 13 '23 at 23:52
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    I have been remarkably unimpressed with Tapcons - They might work for you. Or not. I think in my area there's way too much granite as aggregate in concrete for the wimpy things and they either snap, or shear the threads off, far more often than they go in and hold. With limestone aggregates I think they stand a chance. But looking up diabase I see it described as very hard and tough, so I'm betting against Tapcons in that. – Ecnerwal Apr 13 '23 at 23:52
  • @Matthew they do not need to be easily removeable but it would be a small benefit if they are. – jay613 Apr 14 '23 at 13:34
  • @crip659 The boards will not sit on the floor. The *purpose* of the boards is to make it easier to hang things on the wall using wood screws. – jay613 Apr 14 '23 at 13:37
  • Tapcon weight carrying capacity is pretty good, varying with size used of course. See the manufacturers' specs – keshlam Apr 14 '23 at 13:49
  • Is the stone wall a monolithic stone face? Or built up of individual stones? If individual stones, I would be concerned about pull-out forces weakening the wall. A pile of stones has high compressive strength, but low shear/pull-out strength. – longneck Apr 14 '23 at 15:28
  • @longneck It's made of very large stones cemented/pointed together. It's a basement foundation, not a cave. :) There will not be massive pullout forces, mostly shear. I would have to try very, very hard to create pullout forces that were greater than the soil and hydraulic forces the walls are already encountering, and I'd have to make my anchors very, very strong to literally pull a stone out of the wall. I think I'd have to be quite purposeful to destroy the wall this way. I'm more concerned with just my stuff not falling off the wall. – jay613 Apr 14 '23 at 17:26
  • there are all sorts of stones, what stone are we talking about? – njzk2 Apr 15 '23 at 22:19

5 Answers5

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You should consider using a chemical stud anchor. If you've ever been to something built inside a cave you've probably seen these.

A chemical stud uses an epoxy to hold a fastener into the material. They're great for natural stone because they don't rely on wedge points within material and the epoxy should fill in the void completely to prevent water intrusion.

The fasteners will be permanently attached to the stone but it will likely be a threaded rod which allows you to readily remove whatever you attached to it and also to finely adjust the spacing away from the uneven surface.

Matthew
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  • Tempting answer. And I like the cave reference. I *have* noticed that. But wow that stuff is expensive! – jay613 Apr 14 '23 at 15:09
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    Consider that you may only need minimal numbers of them. For example if I were putting up shelves I would only use two chemical anchors per vertical attachment. A vertical board attached to the anchors, then my shelving or whatever else attached to the mounted board – Matthew Apr 14 '23 at 17:10
  • I used anchors like this for an earthquake retrofit. The anchors are a bit expensive but the epoxy, the gun to squirt it into the holes and the mixing tips for the gun were very steep. You need those even if you only do one or two holes. I would guess one set was $150-200 five or ten years ago. I was doing a bunch so could amortize it. – Ross Millikan Apr 15 '23 at 02:56
  • @jay613 it may be possible to hire the expensive parts for far less than the cost of buying them. Do all the prep work you can before, do the rental for one day and then return the mixing gun. You'll pay well under the purchase cost. – Criggie Apr 15 '23 at 23:16
  • There is an anchoring epoxy that comes in a gun-style tube with two special mixing spouts. Each spout is single use, IE, it can be used only until the mixed epoxy inside it solidifies. So the whole tube is good for two installation sessions. It requires a high quality silicone gun with a "high leverage" trigger. IE you can't use a cheapo gun. So, this is an option that costs a lot more than some plastic anchors but a lot less than the special kit referenced by @RossMillikan. – jay613 Apr 15 '23 at 23:22
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Here's a partial answer: Tapcon's customer support answered my question saying that they are not for use in stone, only concrete, block and brick.

jay613
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Tapcon™ screws, as their name implies, work by cutting (tapping) a thread into a predrilled hole in concrete. I wouldn't expect that to work well, if at all, in a less granular material, but I have no experience with diabase; on average it seems to be about one Mohs step harder than (equally average) concrete. Try it and see?

If you can drill a hole at all, I'd consider either one of the expanding anchor types -- including traditional lead anchors-- where driving the screw squashes the anchor firmly against its surroundings, or one of the epoxy bolt setting systems.

Exactly what makes sense will depend on what stresses you expect this to take, in which directions.

keshlam
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  • Given the comments from you and Ecnerwal about tapcons, I think I will not spend time experimenting with them. I'll buy a decent 1/2 inch masonry bit and experiment with anchors and 1/4 inch lag screws. Starting with the anchors I already have, which happen to be plastic. – jay613 Apr 14 '23 at 13:43
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If they are available in your area, Fischer has some universal plugs:

https://www.fischer-international.com/en/products/standard-fixings/plastic-fixings/universal-plug-ux

which are specified as suitable for natural stone too (see the list of building materials in that page under "Application and Approval").

Lorenzo Donati support Ukraine
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  • These look nice. Sold under a different brand name in the US with non-metric sizes but NOT sold in the larger sizes EG 1/4 inch. However I will in future try their Duopower line for drywall, according to some youtube reviews they significantly outperform the spiral self-tapping ones that I use. – jay613 Apr 15 '23 at 14:11
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Drive Pin Anchors

aka Hammer Drive Pin Anchor Set

I've never been able to shear them, but must be drilled out to remove.

enter image description here

From https://www.grainger.com/product/11K342

Criggie
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BZZZzzz...
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  • Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers [in the help center](/help/how-to-answer). – Community Apr 15 '23 at 11:58
  • I don't see how these could be used for the application I've described: Mounting wooden boards with standoffs on an uneven surface. I will have as much as two inches of the fastener protruding from the wall. These may be good for close-mounting a thin object, EG a metal brackets on a uniform surface. – jay613 Apr 15 '23 at 14:14
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    Use these to install metal hangers and attach the wood to the hangers. – longneck Apr 16 '23 at 00:13