Reinforcing Door Stiles with Steel

Is steel reinforcement a practical idea to prevent a wood door from warping? Here's a discussion. August 22, 2014

We've been asked to make a mahogany slab door for a client. The design calls for a tall, narrow glass detail set about 6" from the lock edge and 6" from top and bottom. I would be making a ladder core with 1/4" skins on all faces and edges. I am concerned about stability on the lock side. I'll ask for a redesign to allow for larger top and bottom rails but am wondering whether a piece of steel running top to bottom inside the door would prevent bowing. Has anyone used this method?

Forum Responses
(Architectural Woodworking Forum)
From Contributor O:
I laid steel into the edge of one paired door set-up once. It was a lot of work, and I have never done it since. Those doors were thin, and I thought I was supposed to do whatever the customer wanted. The stile can get its strength from increasing thickness. I will not warrant an exterior door at 8' or over unless it is 2-1/4" thick, and 3" at 10' or over. How thick are you planning? The 1/4" skins sound thin - what happens when they move?

From the original questioner:
The door is 2 1/4", so basically a 1 3/4" stave core type construction with the 1/4" on the outside.

From Contributor O:
I assume the construction method you plan is familiar and has been successful for you in the past. It sounds as if you are building a stile and rail door, with stave cores faced with 1/4". That all sounds fine. You should have no flimsiness with 2-1/4" thickness unless it is extraordinarily tall. There is nothing unusual about a 6" stile and 6" top and bottom rails. Just use some nice long tenons, and cope and stick if possible. It is okay to trust wood. From your use of the word slab I assumed a flush type door. In our area slab means flush door, and door only, no frame, etc.

From contributor R:
Interior or exterior door? Wood moves, steel doesn't. Well steel does move, but very, very little. Steel rusts, wood doesn't rust but it rots. So trap moisture between the steel and the wood on an exterior door, and you get rust stains first, then rot. I wouldn't do it.

From contributor A:
If you are hell bent on reinforcing the door I would rip the stile in half and glue it back together with a 1/4" x 13/4" pultruded carbon fiber flat in the middle. Then bury it under the thick veneers. The stiffness would be off the charts. Yes, you can mix carbon with wood. It is done all the time. The cost of carbon strip and tube has come done quickly. The cost of the carbon should be easily offset by the minimal labor compared to other methods. Carbon is used extensively to reinforce wood masts, booms, kayaks, and other watercraft. In my opinion Contributor O is correct in saying that you should be fine with the 2 1/4" style.

From contributor W:
Iíve built plenty of exterior doors and Iíve always used a triple lamination for my stile and rails and Iíve never had warpage. If you want you can allow for deep "3/4 width of stile" tenons using the center lamination as the tenon/mortice. I guess you could use the 1/4" skins but Iíd still laminate the core.

From Gene Wengert, forum technical advisor:
A steel rod is used in large windows to prevent warping, which would potentially break the glass. It is easy, but does add weight. It works well indeed, so I suspect it will work well a door.