How to Cut OSB
OSB, or oriented strand board, is a common building material used during the framing stage of construction. It is used as a roof and wall sheathing and as subfloor decking. Oriented strand board is manufactured from thousands of wood chips measuring 3 to 4 inches in length. The strands are oriented perpendicular to each other and bound together with a strong chemical adhesive. The board is molded into a sheet and baked under pressure. The resulting board is structurally strong and resistant to moisture. It is easy to cut, drill, nail, and screw. However, cutting the edge of a piece of OSB breaks the waterproof seal. For the best results, always reseal the freshly cut edges of an OSB sheet before installing it in your building.
WARNING: OSB is made of numerous wood chips, which means sawdust and splinters will likely start flying around when you're cutting it. Wear a face mask and safety glasses to protect yourself during this task.
Step 1 - Measure and Mark Wood
Determine how much OSB you need to finish the project you are working on. For most applications, you will only need thin square sheets. Screw these sheets into the joists or studs. At most, you will have to cut one or two edges to fit the remainder as you run rows of OSB sheets across the length of a wall. Measure the dimensions you need to fill and mark them on the sheets. Use a square and tape measure or a chalk line; you want to make a very straight cut. If you are working on a nontraditional or crafty project, you might wish to cut the oriented strand board on a curve or angle. This is also quite easy. Use a cardboard stencil or protractor to mark the wood.
Step 2 - Select Your Tool
Select the cutting tool which best meets your needs. If you are cutting a large number of thin boards you can use a chop saw. If you are only making one or two cuts, a hand saw is both convenient and portable. If you don’t need an exactly straight line, you can prop the sheet on sawhorses and cut it with a circular saw. For straight cuts, it is easier to feed the sheet of OSB through a table saw. For curves, use a router, jigsaw, or coping saw.
Step 3 - Cut the Boards
Cut the sheet of oriented strand board along the line which you marked. Use eye protection. Adjust the guide fences and blade guard on your saw as applicable. Because OSB is made with large particles it is subject to “tear-out.” Bits and pieces may fly into the air. The edges of the cut may be jagged and rough, so smooth them over with sandpaper or even a block plane.
Step 4 - Reseal the Edges
OSB manufacturers coat their product with a waterproof sealant after it is baked. Cutting open an edge exposes the core of the board to moisture and can weaken it. Paint the freshly cut sides with a waterproof exterior sealant. Let the board dry for at least 4 hours before the final installation.