By Brett Miller, NWFA Vice President of Education & Certification
As a professional flooring installer, you understand sanding wood floors is not a DIY project. It requires specialized tools, each of which has a specific function and requires professional training.
Drum and belt sanders, also called big machines, are large, heavy, walk-behind sanding machines designed for high production. Drum and belt sanders are all similar, the difference being the way that the sandpaper is attached.
On a drum sander, a sheet of sandpaper is wrapped around the drum and secured by a diagonal slot on the drum. A drum sander typically cuts slightly heavier on the left side and feathers on the right side.
A belt sander employs a continuous belt of abrasive. Belt sander users should be always sand from the left side of the room to the right. This is because of the wheel configuration; the right wheel is located directly behind the drum and the left wheel is offset. As you sand left to right, the left wheel is always on a freshly sanded surface leaving a much flatter floor.
Both types of machines are available in widths of 8, 10 or 12 inches. They are used for sanding wood over large, open areas, as well as removing old stain or finish.
Wheels of both sanders must be inspected prior to sanding as debris or filler stuck to the wheels will translate to the flooring surface. Do not store big machines on their wheels for long periods of time to avoid creating flat spots or warped wheels. Storage dollies or travel bases are available for most units.
Edgers, also called spinners, are small circular sanding machines designed for areas big machines can’t reach, such as around the perimeter of the room, in closets, on stairs, and in other small areas. These hand-held rotary-disc floor sanding machines are used to remove material, flatten the floor, and minimize scratch patterns. Two wheels on the housing hold most of the machine’s weight; each is adjustable to vary the depth and angle of cut. The edger pad is set to hold the sandpaper disc at a slight angle to the floor.
The offset edger, also called a toekick or duckbill sander, drives a disc offset from the motor, with a belt-and-pulley arrangement. This configuration allows reaching under difficult areas like cabinet toe kicks and radiators. Some edgers can be set to cut on the left, right, or near center of the leading edge of the paper, somewhere between 11 and 1 o’clock. Follow the manufacturer’s recommendations for setting the edger. Never store these edgers upright on their pads as this can cause flat spots which translate to vibration that will transfer to the floor.
Buffers (rotary sanding machines) use circular sanding paper, screens, pads, or polishing brushes. Sizes varying from 13” to 22” in diameter; however, most common buffers in the wood flooring industry are 16” to 18” machines. They are walk-behind machines that abrade in a circular pattern, cutting between 3 and 6 o’clock.
Buffers for floor sanding run at low speeds of around 175 RPM and are used for final sanding, abrading between finish coats, and low-speed buffing. Some models are designed for dedicated use as either sanders or polishers. Be sure to match the machine with your main application.
The primary use of these machines is to blend the field with the edges in the final sanding process. This machine is also used to employ mechanical abrasion between finish coats. The buffer can also employ a hard plate driver. Hard plating is a process often used to flatten a floor and to minimize dishing out of soft grain, multi-directional floors or floors containing multiple species by using a sanding disk, without a driving or backing pad.
Multi-disc (planetary) sanders are often used for fine-finish sanding and for flattening floors. They may have three or more perimeter discs that rotate in one direction around a main disc, which rotates in the opposite direction. This allows for no particular sanding direction to be followed during the final sanding process.
These sanders are designed to utilize abrasive types from medium to extra fine grit. No abrasive grit should be skipped when using multi-disc or planetary sander machines. Some multi-disc driver attachments are also available for buffer/rotary sanding machines.
Oscillating machines move in an elliptical pattern. Oscillating machines provide a less aggressive cut than big machines, but with more random abrasion patterns.
Harder-to-reach places require the use of hand scrapers, sanding blocks, and random orbital sanders. Hand scraping of areas not reached by the edger should be completed before final surface preparation. Scrape in the direction of the grain whenever possible. Follow this by hand-sanding with a sanding block to help blend in the scraping marks with the rest of the floor.
Never sharpen the scraper on the floor to avoid discoloration from the metal shavings. Hand-held random orbital sanders can also be used with the same grit abrasive as the final sanding abrasive, in order to assist in the final detail of the perimeter of the floor.
Most standard sanding machines have dust-collection systems attached. This performs two functions: it collects large dust particles and also filters the air that passes through by catching the smaller particles on the inside of the bag. The key to keeping such machines performing optimally is permitting air flow through the system. That means the bag should be emptied often and turned inside out and blown/vacuumed frequently, as well.
For best results, the bag should be emptied before the dust reaches the full line – usually about one-third of the bag. If it isn’t emptied by then, the dust-collection system will not function properly and can cause the machine to over-heat.
All systems must be emptied daily and disposed of safely in a proper disposal container. Contact local agencies for guidelines and directives on proper disposal at here.
Sandpaper is another important wood flooring tool. It is made up of three general components: the backing, the adhesive bond, and the abrasive mineral (or grain).
The backing is the base for the abrasive minerals to be bonded to. In the wood flooring industry, backings are typically made up of paper, cloth, or screen mesh. The type of backing used dictates the intended use of the abrasive.
The adhesive bond is the binding agent used to adhere the minerals to the backing. These adhesives are designed to withstand the high temperatures and pressure produced in the sanding process.
The abrasive minerals or grains can be comprised of different man-made materials. The most common minerals used in our industry are silicon carbide, zirconia alumina, ceramic alumina, and aluminum oxide. Silicon carbide is a sharp, brittle mineral. This mineral may dull relatively quickly on some floors, but tends to leave a very fine scratch pattern. It is typically intended for sanding finishes and intercoat abrasion.
Zirconia alumina is a sharp, highly viscous mineral. These minerals are designed to fracture in small pieces leaving very sharp edges. Ceramic alumina is a long and sharp viscous mineral. These minerals are designed to micro-fracture into small pieces leaving extremely sharp edges. These minerals typically are intended for finish and material removal.
Aluminum oxide is a blocky, cubic-shaped mineral. These minerals typically fracture into larger pieces, maintaining sharp edges. These minerals commonly are used with extra fine abrasives often designed for intercoat abrasion or a first sanding on factory finished floors.
Temperature and humidity can affect the performance of the sandpaper, so they should be stored between 60-80°F and 30-50% RH. Abrasives should be stored in original packaging away from potential sources of moisture.
There is no one-size-fits-all grit sequence that is right for every job. That’s because there are a wide variety of circumstances that may dictate grit sequence. The abrasive grade (or grit) provides information about the size of mineral used on the paper. The grit number directly corresponds with the number and size of minerals per inch. The larger the number, the smaller the mineral.
Choosing the appropriate grit sequence for the job will dictate the process to achieve the necessary results. The grit chosen for the initial sanding will be determined by several conditions including: existing coatings, degree of unevenness, species, and overall condition of the flooring.
In general, the following steps should be followed:
- Start with the finest grit that will remove existing coatings and flatten the floor.
- Do not skip more than one grit during the sanding process. Doing so can result in a rough surface, or premature wear of the finish.
- It is recommended to not skip grit sequence with fine and extra fine abrasive selections.
- Set the drum pressure to coincide with the abrasive choice. Finer grits require less pressure settings on the big machine; coarser grits require heavier pressure settings.
- Load the sanding machine with the proper sequence of sandpaper. Skip no more than one grit following the abrasive selected for the first cut. The second cut abrasive removes the deep scratches created by the first cut. All subsequent cuts remove scratches created by prior cuts, with the appropriate abrasive leaving shallower scratches that should result in a surface that appears smooth.
- When the final sanding sequence with the belt or drum sander ends at a medium grit, a multi-head or planetary sander must be used to follow the abrasive grit sequence to fine or extra fine grits to achieve the desired end result.
The key to any successful flooring installation is having the proper tools available, and the training necessary to use them correctly. The National Wood Flooring Association provides detailed training for wood flooring professionals of all skill levels. For more information, contact the NWFA at (800) 422-4556 (USA and Canada), (636) 519-9663 (international), or www.nwfa.org.