Square Buff Sander Sandpaper: 12×18 Size Guide

The Square Buff takes 12 inch by 18 inch sheets. The machine sold under that name is the American Sanders OBS-18, rented at Home Depot under code 07014A, and its manufacturer lists the pad as 12” x 18” with an 18-inch sanding path on every variant including the dust-control OBS-18DC.

Before you order anything, understand one thing about this machine that no product listing explains: the abrasive never touches the sander. A floor pad grips the machine’s driver by hook-and-loop, and the sheet attaches to the pad. Three layers, and the middle one is the part renters forget to ask for at the counter.

Machine specifications

Specification	Value
Pad size	12” × 18”
Sanding path	18 inches
Models	OBS-18, OBS-18DC (dust control)
Home Depot rental code	07014A
Motor	1 hp
Orbits per minute	3,600
Orbit diameter	1/4 inch
Weight	about 125 lbs
Abrasive attachment	sheet to floor pad, pad to driver by hook-and-loop

Specifications from the American Sanders OBS-18 product page, read August 2026. Confirm your machine at the rental desk; the manual is usually attached to the handle.

The three-layer stack

Working from the machine down:

1. The driver plate on the machine has a hook-and-loop grip face.
2. A floor pad presses onto that face and stays there. The manual calls for replacing it once it mats down to 3/8 inch or thinner.
3. The abrasive sheet attaches to the pad, not to the machine.

Two consequences. If the rental counter hands you a machine with no pad, you cannot use it, so check before you leave. And if you try to stick a sheet directly onto the driver, you foul the grip face and the next renter inherits the problem.

Screens are the exception. A screen is not stuck to anything. You lay it on the floor and lower the machine onto it, letting the pad hold it by friction. Screens are for screening between finish coats, not for cutting old finish off.

Two backings, and the difference is counterintuitive

This is where readers waste money.

PSA sheets carry a pressure-sensitive adhesive under a release film. Peel the film, press the sheet to the pad. Virginia Abrasives sells these as its 12×18 PSA line.

Cling-back sheets have no film and no adhesive. The back is lightly abraded so it grips the pad on contact. Virginia Abrasives QuickSand works this way, and so does the Mercer 418 series, whose own listing states that the “backside of sheet has enough grain on it to adhere to a sanding pad.”

Both hold. But the OEM manual describes peeling a film, so a first-time renter who buys cling-back sheets goes looking for a liner that does not exist and concludes the product is faulty. Read the backing type on the listing before you order, and expect whichever one you bought.

Grit sequence

The manufacturer’s guidance for this machine is a coarse initial cut at 20 to 36 grit and final cuts at 60 to 80 grit. In practice the job decides:

Job	Grits	Notes
Screen-and-recoat over sound finish	120 then 150 screens	No bare wood exposed. This is the machine’s best use.
Between coats of polyurethane	220 screen, light pass	Knock down raised grain only.
Light bare-wood finishing after the drum	80 then 100 sheets	Follows the drum and edger, blends both scratch patterns.
Heavy old finish removal	20 to 36 sheets	Slow. A drum sander is the right tool for a full room.

Match this to the drum work. If you ran 36, 60, 80, 100 on a rental drum sander and matched grits on the edger, the Square Buff comes last to blend the drum’s straight-line pattern with the edger’s semicircles. Skipping that blend is the most common cause of visible ghosting under finish. The full progression is in our grit chart.

How many sheets to buy

For a 500 square foot floor:

Use	Sheets or screens	Notes
Screen-and-recoat	4 to 6	Two at the cut grit, two to four at finish, one spare
Between coats	2 to 3	220 grit, light pressure
Bare-wood blending after the drum	4 to 6	Add one per grit on species harder than red oak

Scale roughly linearly. Old finish eats abrasive faster than bare wood, so add 25 percent if the existing coating is thick or gummy. For per-square-foot math on the drum and edger side, use our sheet calculator.

Sheets sell in packs of 20, which is more than one job needs. That is fine if you refinish regularly and over-buying if this is a one-time weekend rental. For a single room, buy the smallest pack you can find or ask the rental counter what they sell loose.

Name collisions that cost money

Four things get called the same machine and are not:

• Square Buff, SquarBuff, OBS-18. These are the same machine. Abrasive catalogs spell it inconsistently.
• Square Scrub is a different manufacturer’s machine. It appears alongside the Square Buff in some abrasive fitment lists, and it takes larger sheets. Do not read a Square Scrub fitment as covering your OBS-18.
• 12×24 sheets exist and do not fit this machine. Some catalogs list a Clarke American Sanders Square Buff against 12×24 abrasive. The OBS-18 pad is 12×18 on every variant per the manufacturer. If you order 12×24 you get paper six inches too long.
• The EZ Sand and the OBS-18 are both American Sanders orbitals. The EZ Sand uses three 7-inch hook-and-loop pads and is a different consumable entirely.

Common problems

Sheet slides off mid-pass

The pad is worn or glazed. A matted pad below 3/8 inch no longer grips. Swap the pad, not the sheet.

Swirl marks under finish

Too much pressure or dwelling in one spot. This machine has a 1/4 inch orbit and works by staying in motion. Let its 125 pounds do the cutting. For the wider diagnosis of drum and edger marks, see our problem guide.

Screen flops and cuts unevenly

Normal on a screen that is not held by a pad above it. Confirm the floor pad is on the machine, then lower it squarely onto the screen rather than dragging it into position.

Machine leaves a haze rather than cutting

Wrong tool for the job. If the finish is thick and intact, you are asking an orbital finisher to do drum work. Strip with a drum sander first.

Species note

The OBS-18 is a finishing machine, so species matters less here than on the drum, where hardness drives sheet life directly. On harder species than red oak (Janka 1,290), such as hard maple (1,450) or hickory (1,820), add one sheet per grit and expect a slower cut. Softer species, such as pine (690), load the abrasive faster rather than wearing it out. The full species table is in our drum sheet guide.

Where this machine fits

The Square Buff is the third machine in a refinish, not the first. Drum sander for the field, edger for the perimeter, then this to blend. For a dedicated screen-and-recoat with no bare wood involved, it can be the only machine you rent. If you are choosing between this and a Bona FlexiSand, the FlexiSand is a 16-inch rotary buffer and this is a rectangular orbital, so the Square Buff reaches square into corners while the FlexiSand does not.

Right size, a pad on the machine, and the backing type you expected. That is most of the job.

Matt.