|PJ’s scarf joint.|
Dear Ken: I stumbled upon your site yesterday while searching Google for “how to paint crown molding.” You have done a fantastic job, as there is nothing else like your site on the web dedicated to molding. Well done, I love it.
Some background: I am putting up crown molding for the first time in my 550 square foot apartment just outside of New York City. The ceilings are concrete and the walls and corners are far from square, which has made this job quite challenging for a first timer. I have glued small wood triangles cut from a 2×3 board into the corners of the walls to act as anchors.
- Did you glue the two mating faces of the joint? If you did, excellent. If not, the joint will separate over time with changes in temperature and humidity, and you’ll just have to live with that unless you do the installation over again.
- Do you have a power miter saw or a manual miter box? If you have a power miter saw, then I highly recommend you remove the over-lapping molding and shave that 1/32 of an inch or so off to make it match. Doing the same thing using a manual miter box with a back saw would make it very difficult indeed.
My method for blending a scarf joint is the same for any type of molding, so you can apply them to your crown, which, I might add, you did an excellent job of matching the scarf joint with such a detailed crown molding.
Steps to Blending a Scarf Joint:
- Start with 80 grit sandpaper. Sand a piece of scrap molding first to see how the molding material behaves under such a course grit. MDF moldings are made from many different formulas, and the cheaper kinds tend to shred under a course grit sandpaper, so that’s what you’ll be looking for with your test sanding.
- Cut out manageable size pieces. With the 80 grit, sand back and forth about 6″ on either side of the joint. This is going to take some time to blend the bulk of the material down, but it can be done. You will sand away the primer, and that’s a good thing because it will help you concentrate your efforts.
- When you can barely feel the raised joint, then smear the whole joint with a fine coat of spackling and let it dry completely.
- When the spackling is completely dry, sand the whole joint again with finer sandpaper, like 150 grit. At this point you are not trying to sand the joint. Rather, you are only looking to see how much spackling is left — an indicator of how much molding material is left to remove.
- When you’ve blended the joint to perfection like in the picture rail post, you have to prime the sanded area (maybe even twice) sanding lightly between coats.
- The last step is to paint the crown and enjoy your perfect scarf joint!
Crown or picture rail molding — same technique.
“Stuff and smear.”
Sand about 2″ across both sides of the joint.
Perfection. This scarf joint will not show under your paint.
And finally, if you think you have the molding bug, I’d be happy to help you come up with a trim package for your small apartment, it would be a fun project!