Furniture Shipping and Tropical Moisture Issues

Shipping from the tropics to the temperate zone, how do people deal with humidity changes? Here are some thoughts and possible solutions. November 8, 2007

I am just starting out in the furniture making business. I have my first batch of furniture ready for export from my workshop in Indonesia to the UK.

We dried our oak in a custom-made kiln before fabrication, but I am very worried that whatever drying effects we might have produced in the kiln will be wiped out by the storage of our finished products in the tropical atmosphere!

I have read that some simple and cost effective precautions include heating the storage facility (same location as the workshop, so might get very hot for the people working there!) to ~10C above the morning low temp, and also insulating the finished products using thick plastic sheeting. I plan to do both of these things.

Are there any other simple and cost effective ways of ensuring that our finished products do not regain moisture from the air, while they are waiting for the container to arrive? We are going from a ~80% RH manufacture environment to a ~50% RH consumer environment. I see the risk associated with shrinkage due to water loss in my products to be the single biggest risk to my business at the moment. Can anybody advise what the maximum MC value I should except for shipping should be (considering that this is my very first batch, I am pretty desperate to get some positive cash flow at this point!). I'm thinking that MC greater than 12% will just be too risky to ship to the UK, with MC ideally at 9 or 10% to suit the UK's ~50% RH environment.

If the products do turn out to have MC greater than ~12%, and I decide that the risk of damage is too great, is there anything I can do with the finished products to get their MC back down (quickly!)? If I raised the storage temp by ~10C above morning low (equivalent to ~40% RH?), presumably the products would gradually reach equilibrium with that environment (~10% MC), but I guess that could take a long time? Could I dry the finished products in the kiln, on a low temp?

Forum Responses
(Furniture Making Forum)
12/17 #3: Storage & Drying in Tropical Env.

From contributor S:
Perhaps a dehumidifier set up in an old but airtight shipping container on site would work okay. Heat is already fairly good, as I recall from a holiday in Bali! From talking to exporters there, I think the biggest warping headaches come from teak, or whatever is used that is a low grade and badly dried timber. It is cheaper, but gives many problems. Some there are using recycled demolition teak, which is really stable. Please think of the orangutans before using wood from Sumatra. Java is all plantations, but their wood needs care.

From the original questioner:
Thanks for the advice! I'm typing this from the transit lounge of the Singapore airport, on my way out there, properly equipped with digital moisture meter, and extremely hopeful that the first batch won't be too wet!

What you say about poor quality timber and poor quality drying regimes seems to fit with what I'm hearing from my people there. And thanks for the storage container idea; that hadn't occurred to me before. I guess it would make a cheap and easy air-tight storage space, perfect for conditioning the air, as you say. Does anybody have advice on a safe maximum MC% that I should allow in pieces that I approve for export to the UK?

From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
I had a shop in Barbados that used plastic film and made a small room that they stored work in progress and finished work until they could get the furniture piece into a plastic bag. This room had a small home dehumidifier. Once the finished piece is in the bag, there is no way that moisture can enter or leave, so the MC is stable.

From contributor A:
I have experience with teakwood and mahogany that exported to the UK for MC 12% (the furniture, not the timber, out from kiln dried chamber), finished in PU, and they are okay, but you have to carefully select and check that all wood in the item is a similar MC. There are some problems if one part is MC 10% and another part is 13%, and this could happen in Semarang or Jepara especially if you got the furniture from a supplier. Also put a dehumidifier bag on the container before loading. It's helpful to absorb the humidity around container. Don't know if the items are rawframe.

From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
Regarding the use of a bag with a desiccant in it... A piece of furniture that weighs 20 pounds (that is, has 20 pounds of wood in it) will require 0.2 pounds of water to change by 1% MC. As we can usually tolerate a 2% MC change, then we are talking about 0.4 pounds of water or about 1/2 cup. Can a small bag absorb 1/2 cup of water? No way. Try it and see. The water, when absorbed, does not occupy less space, so the bag must be able to hold 1/2 cup of water volume-wise. In fact, wood is a better desiccant than these bags.

From contributor A:
The drybag for dehumidifier I use is 8 pieces at 1.4 kg for 40 ft container and hanging around corner. It's helpful for problems for exporting from Indonesia, especially in this rainy season there is very high humidity that can lead to other problems. As the container sweats, there is water vapour in the air condensing on the inside surfaces of the container when moving from tropical or temperate climates to cooler areas. This can attract fungi, molds, and mildew as the container voyages up to 2 weeks. Contributor S's ideas that he saw in Bali are right, but I use a sealed room instead of container and control the moisture to stock finish item.