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Posted by jb on April 29th, 2002 12:31 PM
In reply to Installing crown molding by Bruce Rich on April 28th, 2002 07:25 PM [Go to top of thread]

If we are JUST talking about "skarf" (sp?) joints, where it is an endgrain to endgrain angle butt joint then you shouldn't be getting a lot of separation for any reason, especially from moisture expansion and contraction cycles. The wood fibers are like straws, all in the same direction. They expand and contract mostly in WIDTH, not end to end. The amount of end to end movement is very small for kiln-dried stock. There can be SOME shinking end-to-end and this would be made as bad as possible if the stock was wet or swelled excessively just before installation. Even in those cases though, usually a good carpenters glue will hold the joint together. Any cracks that normally develop on scarf joints can be filled with a good vinyl adhesive calk like phenoseal.

The main exception that I have seen to everything I have written above is for pre-primed, finger jointed mouldings. I recently installed a large, fancy, 45* crown molding that later developed decent sized cracks at the scarf joints, much to my embarassment - since I had fitted the pieces almost perfectly and thoroughly glued and tacked the ends together as I always have. I summized (sp?) that the scrappy little pieces of pine that they join together for these cheap moldings are not always put in with the grain facing exactly the same way. I have noticed that these finger jointed moldings can shinks end-to-end over 1/8" over 20 feet. I would still use the moldings again because they can be VERY cheap and save you a lot of money. Plus, being pre-primed they don't need as many layers of paint and we know how much carpenters hate to paint...

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