Crating materials

Hello! I am a bit new at this (crate building to museum standards). I work at a university gallery, and my boss has recently asked that I build crates for an exhibition of framed photographs by Ed Westcott. I'm a very comfortable woodworker, however, I'm not certain about the specific materials needed for the crate.

Specifically, what type of exterior grade plywood is commonly used, and at what thickness? These crates will be small-ish in size, at no more than 48"Lx25"Wx30"H. I don't want to overbuild, but I don't want to underbuild, either. He mentioned MDO . . . does the fiber coating provide any particular advantages over normal exterior grade plywood?

Part of my design issues have to do with creating a thick enough edge that some sort of threaded insert or tapped plate could be mounted into it. Then, the lid can be affixed with a bolt, instead of screws into wood (which seem to last about three uses, on the crates we get some shows in, before they strip out entirely).

I planned on coating the exterior of the crate in gloss polyurethane. Is it recommended that the interior be coated as well? Is poly the appropriate product, or will it offgas and damage work?

Finally, I have laid in a good stock of 1" and 2" thick ethafoam, which I planned to use as runners along the floor of the crate on which the photographs can ride, as well as on the lid, to secure them from the top.

I have also read of various weatherstripping/adhesive-backed foam products to be used as a moisture barrier where the lid attaches to the crate. Any types to avoid?

Thanks so much for your time! Any information you can provide is much appreciated!

Very best,

Benjamin Wooten

Hi Benjamin! The plywood to use depends on how well insulated you want the artworks to be. Exterior-grade such as ACX is quite adequate for crating and shipping artworks if temperature and moisture protection aren't a concern, and they won't be used for long-term storage. MDO provides excellent moisture resistance, due to a thin layer of plastic laminated under the paper surface. I recommend double-sided MDO for the best protection, as it has this laminate under each face.

For plywood thickness, I would generally recommend 1/2" in most cases. Oversized crate walls or unusually heavy artworks can sometimes make 3/4" or thicker stock a better choice. But the crates you are describing are quite small and relatively light, so you could even go with 3/8".

The wall edge thickness that you need for durable construction, and securing the crate's lid, is provided by solid wood battens. These are most commonly 1x4 stock in the wood of your choice. #2 Pine is lightweight, and does the job. I recommend looking closely at crate designs featured on art handling company websites. Most of them show examples of their crating styles. PACIN also offers a publication on crating techniques here. A common practice is to assemble battens all around the edges of each crate wall before you put the walls together, with the dual purpose of strengthening the structure and providing thicker surfaces for the joins.

Bolt closures for the lid is a standard practice in crates that will be used more than once. However, the life of screw closures can be extended by using new screws each time the lid is closed, and moving the holes as well. Of course, old screw holes would somewhat defeat the purpose of an insulated crate, but only slightly if they were used only once. They can also be filled and/or partially blocked by your lid gasket.

Use heat treated lumber as a general rule. If you are shipping internationally, the crate will need to be labeled clearly with an IPPC "Bug Stamp" on all sides to clear customs.

There are various ways to pack framed flatworks that are safe to wrap in plastic, including slotting the foam or stacking them in separate trays with foam wells that lift each piece off the face of the piece behind it. A minimum of 2" cushioning on every side is recommended. Temperature fluctuations can be mitigated by lining the crate interior with 2" of extruded EPS. Not the pebbly expanded EPS, but the solid variety rated for thermal insulation. It comes in blue, pink or green, depending on the manufacturer. This lining would go in first, and your foam bumpers for cushioning would be attached to the EPS.

I use water-based lacquers for exterior paint. It does provide a modest first line of resistance to moisture, but MDO construction is still recommended if moisture is a concern. Don't paint the interior. It can off-gas, as you suggested.

To seal the lid, I use an open-cell neoprene sponge in the form of an adhesive tape at 3/4" wide by 1/4" thick.

Best wishes,
Chris

Excellent information, thank you Chris!

Regarding bolt closures . . . is there a commercial source you recommend? Or, are they simply threaded inserts a-la McMaster-Carr?

This is just one option, but I happen to use Masterpak's bolt plates. A single closure includes top plate, bolt and threaded receiver plate. The steel plates are simple, and you could fabricate closures of your own design in house with a cold saw, drill press and a few custom jigs.

Great! Got those, and the MDO is on order . . . speaking of this: To seal the lid, I use an open-cell neoprene sponge in the form of an adhesive tape at 3/4" wide by 1/4" thick. . . . who supplies it? Thanks a bunch!

BEN

Ok, I found some at (of all places) a foam tape outlet! :)

Hi Chris. Do you have a good source for the 3/4" Wide by 1/4" thick Adhesive tape to seal the lid? I can only seem to find it in 3/16" (thick) which does not work for me.
Thanks,

John

I Found it from another post on this forum. Thanks. http://www.mcmaster.com/#neoprene-foam/=ncyio2