NOFMA Tip Sheet: How to Fasten a Solid Wood Floor -- Flawlessly
For the general field of the floor, nail on the tongue side of the piece. This is also called blind-nailing, and simply means hiding the fastener by driving the fastener at a 45-degree angle just above the tongue.
For the edge of the floor, where you start your runs, and where you end up on your finishing runs, you nail through the face of the board at a 90-degree angle. This is called face-nailing. Here, you can either hand-drive or tool-drive the fasteners.
For the last runs it's OK to face-nail three runs or two runs and a rip up to the wall line. More than that is not considered good installation technique. You also want to identify the location of the joist so you can face-nail into it.
Additionally, follow the same nailing interval if you're hand-nailing those last few runs. You need to continue to follow your regular fastening interval, or schedule.
Regardless of the subfloor type or length of board, use a minimum of two fasteners per board. And make sure you place a fastener within 1 inch to 3 inches from the end of the board.
Finally, use the right number of fasteners. NOFMA specifications recommend a nailing interval, or frequency, keyed to the type of flooring. For strip flooring (less than 4 inches width) nail, staple or cleat every 10 to 12 inches. For planks (4 inches or greater width), use an 8-inch interval. These formulas should also be used for face nailing over a slab. For face nailing over joists 16 inches on center, it is OK to nail into joists and at the ends of flooring.
The Right Fasteners
Fasteners come in two basic categories: hand-driven and machine-driven. Hand-driven fasteners include nails and screws. Nails are generally 6d, 7d and 8d casing nails. They should be galvanized to prevent staining and provide extra grip. The rougher the nail, the better it holds. For this reason, use a nail that's not only galvanized but also offers the extra grabbing power of a ring shank or twisted (helical) screw type.
You can also use trim screws. These are unique in that they're small, similar in size to an 8d casing nail. They feature a small head that takes a No. 1 square drive bit. If you really want to position and hold a particular board in place, using a trim screw can accomplish that better than any of the fasteners.
Machine-driven fasteners include cleats and staples. Both use some mechanical device to drive the fastener. These include cleat drivers that require muscle power and/or air to drive the cleat. Cleat drivers can work both for blind-nailing and face-nailing. For driving staples, only air tools are available.
Air-driven tools have evolved as the implement of choice by the everyday installer for driving both cleats and staples. They're popular because they work fast and they do the "heavy lifting" of punching the fasteners through the wood.
A word of caution: Do not mix fasteners - cleats and staples - when blind-nailing in the field. Since the fasteners hold differently, the areas will perform differently through seasonal changes in heat and humidity, and can result in a costly call-back. What's more, the line of the boards can be affected, resulting in out-of-line runs.
Match Fastener Length to Subfloor Type
Choosing the right length of fastener for the job is another important step. The length of the fastener is dictated by the subfloor type, whether it's a slab or a joist system. With slabs, the minimum subfloor thickness is 3/4-inch plywood. So for slabs, you would typically blind-nail using a 1-1/2-inch fastener, which does not go completely through the plywood. You can use a longer fastener, but it would require that you tilt the machine at a greater angle - about 60 degrees for a 2-inch cleat.
You do not want the fastener to penetrate the bottom of the subfloor material for two reasons. First, you don't want the fastener to punch a hole in the vapor retarder. Second, you don't want the fastener to hit the concrete and seat incorrectly in the tongue of the board. Otherwise, it will interfere with the tongue and groove fitting of the floor board.
With joist systems, you typically use 2-inch fasteners. When blind-nailing the field over subflooring, you don't need to locate and nail into the joist. There's just not enough nail length to reach the joist. For 5/8-inch subflooring, however, nailing into joists adds to the holding power of the fastener.
The other exception to nailing into the joists or supports is when you're starting or finishing a run. Then you do want to face-nail down through the subfloor and into the joists. This is because, when you're driving straight down and through, nails are long enough to grab the joist. Typically, you also may be using a longer fastener, like an 8d 21/2-inch casing nail or 2-5/8-inch trim screw. That's plenty long to reach and grab the joist.
Take extra care fastening a wood floor above a radiant floor-heat system. Of course, you don't want to penetrate the heat tubes. This is particularly an issue with radiant heat systems that employ sleeper supports. The tubes cross the 2-by-4s, either where they are notched or in a space at the end of the 2-by-4. Be sure the location of the tube is marked so you can avoid hitting it.
Cleats vs. Staples
I have no bias for or against staples or cleats. Today they are used about equally. Staples typically cost less because they're easier to make. The manufacturing process takes wire, cuts to length, forms into a staple and collates the staples into a clip.
A cleat is made from a piece of sheet metal.
Some situations favor one fastener over another. For example, cleats allow the board to move in its own space. Where significant seasonal moisture changes occur, tests have shown that this movement results in fewer permanent gaps than with staples.
Staples hold differently than cleats. They have two legs with a crown across the top. So when a staple is driven through a tongue, it has a much greater bearing force on the board. Too much force can split the tongue where it intersects at the board. A fractured tongue means poor fastening to the subfloor. Too much force and poor fastening or over-driving can tilt the board and lead to problems like uneven boards, excessive movement and noise. To avoid this problem, make sure you've set the shooting power of the stapler appropriately.
Overdriving tends not to happen as much with cleats. A cleat is a single-leg fastener. It penetrates in only one place. It holds well, but not with the death-grip of a staple. Also, the single-leg cleat tends not to fracture the tongue as much as a staple can.
That said, problems like tongue fractures are not the fault of staples per se. It's more of an issue with the setup and operation of the tools. Adjusted and applied properly, a stapler gives excellent performance.
Use Factory-approved Supplies
We discourage using off-brand substitutes for fasteners, particularly for staples.
Use the manufacturer's recommended staple or cleat - most often their own brand. There are off-brand and generic fasteners that cost less. But cheaper fasteners won't make up for a bad fastening job. In cleats and staples, as in life, you get what you pay for.
Get it Right the First Time, Every Time
You'll do a great job of installing a wood floor with the right materials, tools and techniques. Just remember that it's worth getting it right the first time. You not only make another customer happy, but you avoid expensive call-backs. You lessen the risk of contract disputes. And you build your bottom line while you build your reputation. FCI
Here are a few additional wood-floor installation tips:
• For the new ACQ treated plywood and sleepers often used in costal areas, use stainless-steel fasteners or triple-dipped galvanized nails and screws to avoid corrosion issues. Borax treated products do not have the same issue with corrosion of fasteners.
• Fasten boards at toe-kicks. Particularly for retrofit situations where you have cabinets in place with a toe-kick, it's tough to nail boards in that toe-kick space. One way around this is to drill a hole through the bottom of the cabinet, above the toe-kick. That allows you to fit a drive bit inside the cabinet and drive a screw into the last floor board run below the toe-kick.
• Pre-drill for face-nailing and hand blind-nailing. If you pre-drill a pilot hole, it's easier to drive your screw and nails. This also keeps the board from splitting.
• Bend nail for closer blind-nailing. If you've already got a drilled hole in your flooring and you're getting really close to the wall, you can actually bend the nail straight. This allows you to get even closer with the hammer without having to face-nail. Typically, the nail is on a 45-degree angle toward the wall. You pre-drill the hole, set the nail in the hole, bend it, and then you drive it straight down. The nail follows the path of the pilot hole at a 45-degree angle, yet you hammer the nail straight down.
• Face-nail into open grain, fill and scratch filler to mimic grain. In order to camouflage your face nails, face-nail in the coarse or open-grain part of the wood. Next, insert filler in the hole you've made with the face nail. Then, take a knife and scratch the filler to simulate the grain and hide the nail head and hole.
• Place face-grain plug over screw. If you have to use a wood screw to make a repair, install the fastener, and then place a wooden plug of the same species in the hole. If you use a face-grain plug, you can match the grain to the plug to hide it.
• Use a slip tongue and blind-nail at reversals. Any time you have to reverse the direction of your floor, you don't want to show face-nailing at the reversal. If you're butting two grooved edges up against one another, some contractors will nail both grooved edges. That's unacceptable and unsightly, with the rows of nail holes showing. Instead, take a spline or slip tongue, glue that in the groove, and then nail that like it was a tongue-and-groove combination.
• Set nails. If you hand-drive or mechanically drive a nail, the nail should be set below the surface of the wood with a punch. This is only for face-nailing.