Tagged: s are sold.
8 November 2018 at 4:05 pm #553094
I’m looking for help on a very specific problem. I’m making a wall-hung bookshelf. So, it will be supported entirely by fasteners in the wall with no support from the floor and no connection to the ceiling.
The walls do not have studs. Instead, there is 1950’s wallboard on 3/4″ furring strips and the furring strips are on cement block. The shelves must go in a very specific location, are about 30″ wide, and the furring strip spacing is approximately 15″ on center, although the shelf will be in the vicinity of a window and a corner, so things may be oddly spaced, especially since it is junky 1950’s US construction. The point is that you cannot count on there being any more than two furring strips behind the shelf and they may not be centered. Actually, you could end up with only one strip.
My estimate is that the shelf plus load will be about 210 lb. If I later add doors, that will be yet more. Let’s just call it 400 lb.
So, how to hang this thing? I’m going to build the shelf, so it can be designed with hanging in mind. Right now, I’m thinking of a French cleat, but I’m really not even sure about the fasteners. If you hit a furring strip, the best you can get is 3/4″ of wood for the fastener, and that’s not enough, I think. If you try to use a drywall anchor, you’ve got about 5/8″ of drywall and a 3/4″ gap behind it before the anchor would be impeded by the block. Maybe, but seems on the edge.
I know from prior experience that this block will *not* take tapcons, but they *will* take cut nails and AJs. So, I’m thinking of attaching a French cleat with cut nails. The problem is that there’s about 1.5″ of drywall and air gap before I hit the wall, so even with a 4″ cut nail (the largest I see), I’m wondering if it will hold. Construction adhesive would help, but this needs to be reversible by just patching a few holes.
Any ideas? Big toggle bolts?
8 November 2018 at 4:32 pm #553097
- This topic was modified 9 months, 1 week ago by Ed.
400 lbs? I personally would not attempt based on the restrictions you cite.8 November 2018 at 4:35 pm #553098
@sdbeggs what would you guess as the limit for total weight, shelf plus load, under these circumstances?8 November 2018 at 4:51 pm #553099
Just found some info from a toggle manufacturer, which says 75 lb allowable load per fastener in 1/2″ wallboard (shear) and 140 lb allowable load per fastener in block. Not sure how to degrade these numbers for my circumstance, though. I should have more strength than the simple wallboard number if the toggle goes through the block, but not as much as the stated block number because the load is held away from the block by the wallboard and furring strips and because it is old block.
But, if I go with the lower number, 75, and put two at the top of the shelf and two at the bottom, that’s 300 lb.
Maybe it’s doable?
8 November 2018 at 5:17 pm #553101
- This reply was modified 9 months, 1 week ago by Ed.
A cleat supported by toggle at 8 inch intervals could support 200 lbs assuming a 36 inch shelf but that is not been personally tested, it’s just an estimate. Take it with a grain of salt.
Another point is I would never trust a load where a gap exists as you describe. The gap would put a tear down stress on the wall board at shelf attach point. I’m not sure 8m using the correct terminology I hope it’s understood.8 November 2018 at 7:07 pm #553103
I wouldn’t depend on any system that depends on fastening to the furring strips, which themselves are probably fastened with now rusty cut nails. And i’d Heed the advise that you avoid any system that cantilevers the screws unsupported.
So I’d use something like the TAPCON series of fasteners that are tailored for all different applications in concrete or cinder/cement block screwed through the furring strips into the block. Block walls are somewhat weaker than solid concrete and depend on the type of block.
TAPCON fasteners are screwed into holes drilled with tungsten tipped concrete drill bits sized for the screw sizes ( most easily with a hammer drill) . 1/4” screws are rated for 700 lb pullout in concrete and 900 lb. in shear. Keep in mind that an engineer will usually specify loads 1/4 of rated strength.
For 3/16” or 1/4” screws I’d use the TAPCON supplied bits perfectly sized to the screws. Larger sizes use standard ANSI concrete bits. The largest I’ve used are 1/2” and they are quite secure in concrete, being rated to 7,414 lbs in pullout and almost 12,000 lbs in shear ( in concrete) they are often used to secure machinery.
TAPCON bits come in blue coated, 410 stainless, and zinc plated, depending on moisture and treated lumber conditions. They come in hex head and #3 Phillips flathead ( maybe other heads).
There are competing structural fasteners ( Headlox , Simpson), but I’ve only used then in wood, not into block.
Keep in mind your limiting factor will be the condition and type of the concrete block wall. If it is crumbly, all bets are off.
You will also get a bit help if you also use construction adhesive between the shelves and the wall surface.
The technical pdf does include structural ratings for lightweight and heavyweight concrete block, including mention of the 1/4 safety factor.8 November 2018 at 7:08 pm #553104
@sdbeggs yes, that gap is exactly what worries me and for exactly the reason you give. Thanks for your replies.8 November 2018 at 7:43 pm #553107
@lorenzojose, unfortunately, I know tapcons will not work in this particular block from experience. Cut nails and AJs, yes, but not tapcons. Sometimes they bite, but just as often they don’t.8 November 2018 at 9:53 pm #553108
Too bad. That’s the one issue with an otherwise easy solution. Good fastening requires good substrate.
Another solution in questionable hollow block is an epoxy system with sleeves to contain the epoxy like the ones Simpson offers.
They are a bit more tedious, however.8 November 2018 at 10:08 pm #553109
If I’m understanding you, I think you’re saying to assure the anchoring of the furring strips to the block and then fasten the shelf or shelf-ledger to the furring strips?
If so, couldn’t we kill two birds with one stone? Drill through the shelf ledger, the wallboard, the furring strip, and the block and then install a toggle bolt? There’d be no gap and the bolt would pull everything together.
The furring strip needs to be in the right place, though, and if happens to be over the cross-web in the block, we’re out of luck or need to move to the epoxy.9 November 2018 at 12:10 am #553110
I’m saying to drill through the furring strips into the block to avoid the cantilever, ignoring whatever fasteners were used originally for the furring strips. They aren’t dependable. I also don’t think the 5/8 -3/4” strips are enough wood to hold the fasteners rated for your needs.
So, yes, just like you describe in the second paragraph of your question.
The epoxy with sleeves will work whether you hit a web or a hollow in the block. The sleeves contain the epoxy enough so that in will hold in a solid area and mushroom slightly into the void. In both cases, some of the epoxy works its way through the web of the sleeves. Before sleeves were developed, we used to use some cheesecloth to contain the epoxy, but the sleeves are much quicker. If by chance you hit a solid web, then a sleeve isn’t necessary. Just clean out and fill the hole with epoxy and install the fastener.
And when you get the epoxy, pick up a bottle brush sized to whatever hole you drill. They are usually available where the epoxy syringes are sold. In order to meet the rating specs, the hole must be free of dust so the epoxy adheres to the concrete. You can also use a pice of tubeing to blow the dust out. Wear eye protection.
The downside of the system is that you are installing threaded rods, then screwing and tightening nut on after the epoxy cures when you install the cabinet. You will have to figure a way to hide the rod and nut or use something like an acorn nut that is decorative.9 November 2018 at 11:56 am #553115
Seems like the gap is generally accepted as an issue, which I agree with.
I would, like Larry fix to structure, like the blockwork.
I would use a PAR timber spacer the depth of the cavity and cladding, cut out of the cladding the exact size of the spacer, fix the spacer to the blockwork with countersunk fittings. Then plane the surface flush with the wall and fit the french cleat to that.
If the back of the shelf is open, the spacer just needs to have an equal or smaller size as the cleat and you wont see it at all.
ReUser11 November 2018 at 10:17 pm #553161
You could, if permissible, layout the size of the cabinet on the wall and then cut the drywall about 2” smaller all around. Install plywood over the block with construction adhesive and mechanical fasteners. You could then reinstall the drywall. Attach the cleats and hang the cabinet. If you ever remove the cabinet it would be easy to tape and finish the wall.
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