Messing around with Tapcons and a concrete brick

This is a followup to my recent post on concrete fasteners. A large-scale furniture assembly project has been polished off and it’s about time to give anchoring our bookshelves to the walls a go.

Cordless rotary hammer drill: check (XRH06ZB 18V LXT® Lithium‑Ion Sub‑Compact Brushless Cordless 11/16″ SDS‑PLUS Rotary Hammer). Wall scanner: check (Bosch GMS 120-27). Carbide-tipped Makita masonry bits and an array of concrete fasteners (see the above-referenced previous entry for photos of those): check. But I wanted to get in some low-consequences practice at making holes and installing fasteners before tackling the actual task.

Concrete pavers are widely used in Hong Kong sidewalks, alongside clay brick pavers, so it seemed as though buying some locally ought to be relatively easy. While this doesn’t seem to be reflected in its Wikipedia article, one of HK’s locii for purchasing hand and power tools, DIY stuff, and building materials is Reclamation Street and the neighboring parallel thoroughfares. It had been a few years since I’d last made the slog out there and we walked by a few cafes that I don’t recall having seen in the past, so the area seems to be undergoing the local version of gentrification. It’s still plenty gritty, though, and still mostly chicken-coop-sized tool/DIY/construction shops. Unfortunately, it was a Sunday when S. and I made it out there and three quarters of the establishments were closed for business with their riot shutters bolted down.

Bulky, heavy things are tricky to order on Taobao, but I gave it a shot. My attempt to acquire some solid concrete blocks (larger than the bricks I eventually stumbled upon) got snarled in a back-and-forth with the vendor inside AliWangWang (the online chat system for buyers and sellers built into Taobao/Tmall), regarding shipping. I talked with just a few other concrete block purveyors but they, too, all wanted to charge a nominal shipping fee at order time and then I’d have had to meet the delivery guy and pay the actual shipping cost in cash on the spot.

That was where matters stood for a couple of days. It seemed I’d either have to head back to Reclamation street (or to one of the couple of other similar spots here) or I’d have to lump it and accept having to rendezvous with a courier in person and pay them an unknown amount for shipping. While running other errands in a residential area in a different part of HK, we walked by a dusty, out-of-place-seeming building materials shop on our way to having a perfectly acceptable dinner in a déclassé local-style restaurant. My roving eyes spotted a huge stack of what appeared to be concrete blocks caked in Martian-looking orange dirt. I bought four bricks on the spot, carried them away in a woven plastic sack, and they sat on the floor beneath our table during mealtime.

They’re roughly 9cm by 21cm and 6cm thick and, upon closer inspection once they’d been cleaned (having just four of them made a quick scrub with dish soap and a coarse-bristled brush do-able, so I did it), I began to suspect that they were not of paver-level quality. Concrete is, in its simplest form, made of three ingredients: cement, water, and aggregate (stone and sand). Peering closely at these blocks, I could see (in addition to small stones) bits of ceramic, glass, red-clay brick crumbs, and other stuff. They also seem to be more thoroughly riddled with small voids than I think is optimal. Since I’m not a masonry connoisseur, take my pronouncements with a suitably large grain of salt.

Yesterday (Monday), after skimming the relevant parts of the rotary hammer drill’s paper manual and installing the 1/4″ Makita 3-cutter bit from the set I’d gotten on Amazon, I dug out one of the bricks and used an orange wax pencil and a straightedge to draw a corners-to-corners “X” on one of its large faces and then perpendicular sets of parallel lines to help me gauge where to drill. My plan was to drill two clusters of four holes each, for four of both kinds of 1/4″ Tapcons I’d bought (once again, see that earlier post for images of these fasteners and their cartons). The all-410-stainless-steel Tapcons I’ve got are 2-1/4″ (5.715cm) long and the Tapcons with the 304SS heads and carbon-steel bodies are 1-3/4″ (4.445cm) long.

The manufacturer of these fasteners recommends drilling a hole 1/4″ (6.35mm) deeper than the length of fastener that’s going into the concrete (the anchor embedment). Anticipating that these bricks might be rather brittle, I tried to reduce the embedment and hence the necessary hole depth a bit by using the screws to affix scrap pieces of wood to the block. The bits of wood I had in mind for the job were 1cm (approximately 0.4″) thick and had been haphazardly spray-painted white. For the shorter fasteners, the ones with the non-stainless bodies and using one layer of wood spacer, the hole depth should have been: 1.75″ + 0.25″ – ~0.4″ = 1.6″ (slightly more than 4cm).

To keep the brick from shimmying around due to vibrations from the drill, I positioned a couple of Irwin quick-clamps, the sort with navy-blue plastic parts and rubbery yellow softjaws (visible at top-right and bottom-center through a layer of translucent plastic material) on two sides. To trap dust and debris, the brick was sitting at the bottom of a woven plastic sack.

I got the first four holes done without any apparent issues and snapped this photo:

Trying to go slightly deeper for the longer, all-stainless Tapcons didn’t go as smoothly. On the first of what would have been the second batch of four holes, the backside of the brick blew out. On the second attempt, the brick broke in half along a path that included the blown-out ruined hole. I settled for making yet another, shallower hole in the smaller chunk. Then, instead of four short, half-stainless Tapcons, I installed two of each kind of Tapcon and doubled up the wood-scrap spacers for the longer, all stainless screws. The next photo was taken at that point:

To the smaller nugget, I attached a 25 kN mountaineering bracket (atop an unpainted 2cm thick scrap of wood as a spacer) using one of the long, 410SS Tapcons:

Back to the four screws in the big chunk. Tightening one of the short Tapcons, I achieved one possible undesirable outcome of, I’m guessing at the cause, having bored a too-shallow hole. Ratcheting it down was taking more and more effort, as though it was bottoming out, but the head wasn’t quite flush against the wood. Suddenly, the resistance vanished. The brick had cracked but hadn’t (and still hasn’t) cleaved completely apart. That particular screw turns freely in its hole but doesn’t pull out when I tug on its head with “vampire” pliers. The remaining three fasteners remain firmly in place. Here are side-by-side images showing the crack as it appears on the fastener side and on the opposite face of the block:

The first couple of images embedded in this post are two of many close-ups of regions on the surface of the scrubbed bricks taken using a 200x “microscope” that clips over a smartphone camera. Out of curiosity, I used the same doodad to look at the inner wall of one of the unsuccessfully drilled holes that were split in half lengthwise, specifically of the half of one on the chunk that got the climbing bracket bolted onto it. The images to follow show the hole side under a bit of pinch-zoom but no “microscope” and the remainder show 200x views of the hole side surface from left-to right. Some of the rust-red and dark gray splotches that bound the hole at its ends are visible in first and last 200x-magnification images, respectively.

What struck me as interesting or notable from my first-ever use of a rotary hammer drill:

This was my first-ever use of a rotary hammer drill. Making the holes was much easier than I had expected. I used the 1/4″ 3-cutter drill bit from the Makita SDS-Plus set from Amazon.com. Would it have been even faster and smoother with a 4-cutter drill bit? I don’t know. I had an M6 (6mm = 0.23622″) 4-cutter, but didn’t try it. Is typical concrete sufficiently more robust than the material used for these bricks that drilling in a wall will be noticeably more difficult? At this point, I cannot say.

For installation, I used a ratchet fitted with the socket that matched the size of the outer-hex heads of the Tapcons. I don’t own a torque wrench and the installation instructions on the Tapcons’ boxes don’t say anything about how much installation torque should be used but Red Head’s online installation instructions [PDF] give a maximum installation torque value of 20 ft lbs (equivalent to 27.116 Nm). The hole seems not to have been deep enough but did I crack the big chunk of concrete by applying excessive torque when I was driving it in with my ratchet? Maybe a torque wrench set to 25Nm would have clicked and told me to stop cranking in time.

My 100mL pump bottle of Makita Hammer Bit Grease (part# 194683-7) remains unopened. After cleaning the base of the drill bit, I inserted it into the chuck and got it seated and saw some factory-injected grease splooge up around the shaft of the bit. The inside of the Makita XRH06ZB rotary hammer drill’s chuck had been pre-lubed.

Clearing the pulverized material from the hole is the most challenging aspect of drilling in concrete. I used a reasonably powerful handheld vacuum with a fingernail-sized snout and thought I’d emptied the drilled holes but they looked shallower than they ought to have looked, so I turned the brick hole-side-down over a garbage receptacle and thumped it gently with my other hand and got the rest of the concrete crumbs out. It seemed like a lot of material, easily as much as was sitting in the receptacle in my hand vac. Cleaning out the holes with compressed air would make a real mess. Maybe a bristle bottle brush could help. I don’t know.

Note: Context for this entry can be found in a previous post: Taladrado Rápido! Mayor Duración! (Faster Drilling! Longer Life!): Concrete Fasteners, Drills.