A Humidity-Controlled Display Case

A cabinetmaker gets advice on appropriate details for a climate-controlled display case for musical instruments. October 8, 2005

I'm not sure if this would be called a humidor, but a client wants me to build a case for his acoustic instruments, where he is able to control the humidity. It is going to be a wood display case, made of cherry, with three glass sides and one wood side. He wants to maintain humidity between 40 and 50 percent. What would this do to the wood case itself, specifically the joints? To build a display case is a piece of cake, but Iím not sure how the wood will respond.

Forum Responses
(WOODnetWORK Forum)
From contributor A:
The consideration is that the interior environment will often be different from the exterior environment, but the interior remains stable. If you construct the cabinet from timber equilibrated to the required interior environment, you need to effectively seal the exterior surfaces to retain the stability of the piece. The other alternative is to seal the inner surfaces, but this could allow the cabinet to move more with seasonal changes, leading to a chance of leakage.

In the old days, such things were lead-lined with soldered joints!

From contributor B:
Build the case with good old frame and panel know-how. Let the panels float, and use good joinery, allowing for movement. You don't explain how the humidity level is to be maintained, but I would assume actively through humidifier and humidistat. Seal the door with silicone bead seals and rabbets, as found in window weather-stripping, and build them thicker than usual to stand up to the humidity differential between the inside and outside.

There is a level of cabinetmaking that makes solid wood bookcases for rare book collections, etc., with wood framed glass doors that seal out dust and air exchange. These doors are typically inset and have primary and secondary rabbets with the w-strip kerfed in around the perimeter and solid ball catches in two places for retention.

No amount of finishing will seal out moisture exchange, it will only slow it down. Think of the cabinet as being like an exterior door - the thickness, weather-seal, and construction details are what stand up to the differences in humidity.

Since the best environment for people and houses and wood is at 35% RH, I wonder if your client understands the cost of the little gain they will get.

From contributor C:
I would question the glass for the humidor. Any sunlight that can reach this box is going to change its atmosphere. It needs to be sealed off from all the elements.

From the original questioner:
I am going to use a UV glass. Also, this case will be opened quite a bit, at least once a day. This is being treated as a glorified instrument case with a small, Damp-it passive humidifier to maintain it between 40-50%. I may be making too big a deal out of this, but there's only one way to learn and the client is willing to be the guinea pig.

From Gene Wengert, forum technical advisor, Sawing and Drying Forum:
40% to 50% RH is 7 to 9% MC in the wood (or 7% to 9% EMC).

From the original questioner:
Thanks Gene. That makes me feel so much better about this project. The UV glass is to protect the instruments from the sun. Instruments consist of violin, mandolin and guitar.