Do my crates need to be lined?

[Rick]

My problem has to do with whether or not to line crates?...

I'm producing three travel crates for a collection of (50+) framed, etchings.

My supplier could not get MDO (after 10 days wait) and I substituted a paint-grade plywood (3/4" maple veneer). I knew there would be disadvantages to not using MDO, but I could not wait longer to begin the project.

My question is whether or not to line the crates, and, if so, with what?

The body of the crates are the mentioned plywood, with 1x4 poplar as binding/battens and 2 inch ethafoam on inner surfaces. Joints are fairly tight: air-nailed, glued and screwed. The crates are to be used as travel crates (and storage), so I'd like to get this right.

All the works are framed, behind glass (not plex) with backs sealed in paper (Not that it pertains here, but all the works will be fitted vertically).

My question: If the crates can be stored with lids ajar (or removed)--do I still need to line them? And, if so--what lining would you recommend? Is there anything suitable that is cheaper than Marvelseal?

Thanks for any help!
Rick

[T. Ashley McGrew]

We were talking about lining in terms of climate (Rh) and off-gassing but really the practice originated as a very realistic response to a danger encountered shipping art work. Originally lining crates was specified as an extra layer of protection against water damage from leaks. This goes back far enough that it originally applied to use in non-plywood crates made with individual planks of wood nailed side by side so it was essential. It's use was continued after the adoption of the use of plywood for a very good reason.
When a crate is damaged that doesn't mean that it falls apart into a pile of fragments like a cartoon or something. In fact the most dangerous aspect of damage is that it may be all but invisible. What normally happens is that the corner joins are broken open but with the panels still held in place by mechanical fasteners this failure may not be visible without very close inspection. The tradional use of asphalt-coated waterproof paper was supposed to counteract this compromise of the crates seal. Asphalt coated paper has fallen largely into dis-use because some versions of the paper were really nasty in terms of off gassing.

There is a more modern alternative that offers some of the better qualities of other products. Rather than the extraordinarily effective but expensive and challenging to work with Marvelseal or the similarly expensive Tyvek that acts as less of an effective barrier there is another product that behaves much like the old asphaltic paper liner. It is a plastic coated craft paper That results in a similar appearance and effect on the inside of the crate to what you get with MDO. It is easier to deal with than some other materials but it still takes some work to use. This paper can be applied with either doublesided tape which is a bit of a reach for most, or simply held in place watered-down wood glue put on the panels with a paint roller. By having the paper have consistent contact between the non-plastic-coated side of the paper and the plywood you create a solid surface to glue your foam blocks onto (it looks pretty nice too). Here is a link to one version of this product -

http://www.uline.com/BL_1957/Poly-Coated-Kraft?keywords=plastic

It is worth noting that any liner needs to be flexible in the corners though so it won't tear if the corner of the crate gets "cracked open". I am attaching a couple of illustrations that show the adhesion "gaps" in the collar. Marvelseal is what is shown but the same idea applies to other liners.

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Other solutions can include lining the crate with plastic which is then stapled with the resulting punctures being sealed over with tape. Obviously this doesn't provide a good surface for glueing foam to but it can be used if your foam is instead glued to a removable substrate like Fomecor or Coroplast.

Possibly the most stripped-down approach to minimizing water damage due to a compromised join in your crate is a high quality silicone caulk which is allowed plenty of time to cure with the crate left open. This can help with minor cracking but not if the crate takes a really serious hit.

Finally there is another school of thought that says you can use the same silicone as a primary adhesive in the corners resulting in a "flexible" join and thereby minimize the likelihood of a broken join. Critics of this approach point out that the problem is that you end up with exactly what you are shooting for - a flexible join. They assert that the first level of protection that you seek is in fact a rigid shell - not a flexible one.
Since I've just about worn out this topic I would like to mention one thing. Any lining material you employ shouldn't be used to interupt wood to wood glue joins in the corners. Their use there turns what should be a "wood to wood" join to a "wood to liner to wood" join with the liner representing the weakest link (often significantly weaker). This is the only thing I don't like about MDO (even then it should be mentioned that the built-in liner is way stronger than those you are likely to apply yourself).
I am attaching an illustration for that as well.


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[T. Ashley McGrew]

Ok I just noticed that like an idiot I didn't address all your questions. Going back a bit - to start off with yes it is a sound standard practice to line crates. If you can assure that the crates will be properly stored then your major concern is just that you maintain a good seal to protect against potential leaks. A framed/glazed WOP that is wrapped and sealed should have adequate protection against off-gassing if they will be exposed to only to normal shipping times. The only thing to really be aware of is that it is by no means unheard of for traveling exhibitions to have venues cancelled which can result in objects being left inside their crates for 3 months or more. That isn't really a great situation (and a good case for the extreme (marvel seal solution).
Nomex - this has tradionally come in two forms the most common is soft, somewhat fuzzy and was traditionally used to cover pads or line cavity packs in both crates and for storage. This version is very porous. There is also a more obscure form which is a crate liner and that looks very much like parchment paper. I frankly don't know how effective a vapor barrier that is.

When it comes to expense, it is worth comparing sources on products like marvelseal. In 2011 I helped a museum re examine their procurement practices. During the process sources for Marvelseal varied from $2.29 per square foot to $ .12 per square foot. Contact me directly if your numbers vary too much from mine.