How to Cut LP® Moulding
Learning how to cut LP® Moulding is quite simple since it’s made of polystyrene. And once you do it once or twice, it’s intuitive. There are three basic types of cuts: Splicing, Mitering, and Coping.
Quick Tips
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Measure twice.
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Test-cut your angles with throw-away pieces.
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If needed, lubricate saw blades with candle wax or furniture polish.
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Measure it again, just for good luck.
Splicing Moulding
For long wall length, splice, or join mouldings.
For inside and outside corners on crown moulding, position the moulding upside down and face up in the miter box. You will be placing the moulding so the ceiling-side will be flat against the bottom of the miter box and the wall-side will be flat against the vertical back fence. Make the cut at 45°.
Mitering Moulding
Mitering is the quickest and easiest way to cut and join mouldings at corners where it is important for the mouldings to appear as though they have joined without a seam. With mitering, the ends to be joined on each of the two pieces of wood are cut at an angle equal to half that of the corner angle. For example: miter cuts at a 90-degree corner would each be at 45 degrees.
- Measure the length needed to cut the shortest side of the moulding.
- Set the miter box at the correct angle. In all cases the number of degrees will be exactly half of the total corner angle. (The instructions that come with your miter box will show you how to set the angles - simple miter boxes may be limited to 45 or 90-degree cuts, while power miter saws may have more options.)
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For a standard corner door or window casings, position the moulding at the bottom of the miter box, face up.
- For chair rail and baseboard mouldings, place the mouldings in the miter box as you would on the wall, with the flat side against the back of the miter box. For crown moulding, see instructions below.
- Cut the wood at a 45-degree angle using a hand or power miter saw and assemble at the outside corner. It is often better to cut a sample piece as a test.
Mitering Door and Window Casing
- Position door and window casings on the bottom, face up, in the miter box.
- Use the exact measurement from corner to corner and add 1/8" to 1/4", to allow for clearance.
- Cut from that point out, for your 45° angle.
How to Miter Cut a Return
When moulding ends mid-wall, rather than into another piece of moulding, like in a chair rail that ends mid-wall or bottom-only window casings, it requires at least one “return.” A return gives the moulding a smooth ending and hides the unfinished, cut end (known as the “endbrains”).
- Measure and mark the end of the moulding that needs a mitered return.
- Position the piece vertically in the miter box, with the good face toward you.
- Depending on whether you are cutting a right or left end, make the appropriate 45-degree cut, angled toward the back of the moulding.
- Using a second piece of moulding, make the first cut for the mitered return piece by cutting a miter in exactly the opposite cutting direction as the first piece.
- Cut the fragile wedge-shaped return by carefully making a 90-degree cut on the moulding where the miter cut meets the back.
- Apply carpenter's glue to the wedge and adhere it to the mitered end of the moulding.
Coping Moulding
Coping is an alternative to mitering corners in which the moulding profile, or shape, is duplicated to fit tightly against the face of the adjoining moulding. Cope moulding sections that meet at inside corners for a perfect fit.
- For inside crown moulding, position the moulding upside down and face up in the miter box.
- Place the moulding so the ceiling-side will be flat against the bottom of the miter box and the wall-side will be flat against the vertical back fence.
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Make the cut at 45°.
- Use a pencil to highlight the profile edge.
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Cut along the profile edge with a coping saw.
- Smooth the edge with sandpaper or a file.
- Run a bead of adhesive along the cut surface and install moulding with the coped edge butted firmly against the first piece.
The Pros Know
Test your Angles
Because few walls and corners are perfectly square and flat, test-cut your miter angles with throw-away pieces of moulding. Then adjust your angle if necessary.