Nailing Crown to Ceiling

I am finishing out the ceiling of a study with stained white oak. The ceiling has four beams laid out like a tic-tac-toe pattern. I am going to cover the beams with 3/4" plywood. I will put 1/4 ply on the ceiling inside each of 9 squares of the tic-tac-toe pattern (I will attach the 1/4' sheeting with brad nails and construction adhesive). I am then going to put crown inside each of the nine squares. Since I have 3/4" ply on the beams, I will have a good nailing surface for the bottom edge of the crown. If I shoot a finish nail through the crown into the ceiling it will only have sheetrock and 1/4" ply to hold it. Will that be sufficient to hold the crown or will I need to install a backer strip or go into the attic and install blocking? Note that the maximum length of any one piece of crown is 48", so the mitered ends will somewhat lock things in place.
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On 22 Jan 2004 08:07:35 -0800, snipped-for-privacy@swri.org (Kent) wrote:

the nails into the beam will be plenty.
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1/4 ply and sheetrock will be enough to hold since the top of the crown will be relatively undisturbed. Don't shoot your nails straight in, shoot them at different angles. This will help hold the crown tight against the ceiling and will help prevent it from popping out if you have to stress it any.
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One thing to think about... I have had crown molding warp away from the ceiling when I have not secured it. If your molding is any kind of hardwood, you will also face this, especially as the wood "seasons" ion the room and dries completely over the next several months. Remember you are finishing only the face, and the back of the unsealed molding may cause it to misbehave.
If it is a smaller crown, the bottom only solution of nailing to he plywood will be great as you may actually go as much as half way up the molding. But if is the larger stuff (4" and 6") now favored for that type of detail you will definitely have trouble with the upper parts, sometimes just getting the original fit to be acceptable.
However, your solution is easy and you are prepared for the big molding. Shoot the bottom of the molding into the plywood, then take your 18ga. brad nailer and shoot a brad at an acute angle into the 1/4" plywood ceiling/sheetrock on 8" centers. The plywood/sheetrock will hold these brads fine, and thus the molding. Then you will have no problems as it is now secured top and bottom, and these 18ga. nail holes are so small they are a breeze to fill and will not be visible on the ceiling from the floor.
Robert
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On 22 Jan 2004 08:07:35 -0800, snipped-for-privacy@swri.org (Kent) wrote:

I've done a number of coffered ceilings, one of which is shown at:
http://home.comcast.net/~tjwatson1/page2.htm
That one only has wallboard in the fields, rather than ply. I'd caution you to be careful when using 1/4" ply and construction/pannelling adhesive. If you don't squeeze the lines of the adhesive out they will read through as ridges in the 1/4" ply and the ply will look wavy over time. When I've done it I've use 1/2", which doesn't show the ridges and provides more substantial nailing for the upper edge of the crown. If you are committed to the 1/4", I'd think about running over the adhesive with a notched trowel and putting a dead man or two against the panel face while it sets up
Except in the cheapest work, I've always ripped out triangular blocking to go behind the crown molding as a nailer. You should be able to get a good bite on the 3/4" ply by using construction adhesive and common/box nails into the ply (or screws). Crown can twist and the good nailing afforded by the blocking/nailer is well worth the minimal time and expense, as you will not be able to caulk the joint line at the ceiling and have things look nice. It doesn't have to be ripped to the exact inside face of the crown. It just has to provide something solid to nail into ( I prefer finish screws). You'll like having that blocking to nail to when you get a cope that doesn't want to lay down just right and needs a bit of persuasion.
Good luck.
Thomas J. Watson-Cabinetmaker (ret) Real Email is: tjwatson1ATcomcastDOTnet Website: http://home.comcast.net/~tjwatson1
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