Does a container floor have any effect on the relative humidity in a shipping container?

By: Pakarada Premtitikul
General Manager
InterDry (Thailand) Co., Ltd.

Container Floor Tests

Speed of achieving a hygroscopic equilibrium.

In this experiment, a piece of plywood, used for container flooring at MSC, was conditioned at 23 ° C and 50% relative humidity. The piece of wood was placed in a climate test cabinet at 45 ° C and 75% RH where the wood absorbs moisture. Every day the wood was weighed and the moisture content of the wood was determined. With this procedure we have more knowledge about the speed at which wood reaches its hygroscopic balance.

The wood was protected with tape in places where in reality it is not subjected to the internal container air. Following pictures show how the wood was protected.

The tested piece of wood top and bottom.

The initial mass of the wood was 3259g. Following graphs show the results of the test. The first chart shows the mass of absorbed moisture per day. The second chart shows the increase in the moisture content of wood per day.

Absorbed moisture per day

Increase in the moisture content of wood

Unfortunately, the hygroscopic equilibrium had not been reached before the trial was stopped. The moisture content remained almost constant after 3 days. Yet the wood continued absorbing moisture. Since it is plywood, that means that once the moisture content of the top layer remains constant, the moisture will move to the lower layers of wood.

Comparison of the climate of two containers at MSC.

In order to see the difference between climate change and the change in the moisture content of the container floor in a container with a desiccant and a container without desiccant, the following experiment was made.

Two containers at MSC were used for this test. One container (container U6472633 MSC) was provided with desiccant and the other container (U1089745 MSC) was left as it was. The ventilation holes in the two containers were sealed with tape.

A data logger was used in both containers to measure the changing climatic conditions. In container U6472633 MSC a probe was placed near the ceiling and a probe on the floor. In container U1089745 MSC a probe was mounted on the ceiling and a probe on the outside of the door to measure the outdoor conditions. Following figure shows the positions of the probes of logger 56,844 in container MSC U6472633 and logger 56,845 in container U1089745.

Before the container doors were closed, the moisture content of the floors were measured. Following figure shows the moisture content of the container floor at various locations in the two containers before the start of the trial.

The test was performed over a period of 28 days at the port of Antwerp, and below are the results of the data loggers.


Data logger 56844:

The purple curve and the green curve are respectively the relative humidity near the ceiling and the relative humidity near the container floor.

It can clearly be seen that fluctuations in relative humidity in the vicinity of the ceiling are much higher than those in the vicinity of the floor.

The purple curve shows maxima of 85% and 90% and minima of 30% and 40%. The green curve shows maxima of 70% and 75% and minima of 55% and 60%.

The blue curve and red curve are respectively the temperature near the ceiling and the temperature near the floor.

The fluctuations near the ceiling were slightly larger than those near the floor. The minima of both are roughly equal at about 10° C. The maximum temperature at the ceiling was about 40 ° C and at the floor approximately 30° C.


Data logger 56845:

The purple curve and the green curve are respectively the relative humidity near the ceiling and the relative humidity outside the container.

The fluctuations of relative humidity are not comparable because outside the container it was sometimes larger and sometimes smaller.

The blue curve and red curve are respectively the temperature near the ceiling and the temperature outside the container. Minima are comparable, but the maxima showed extreme differences. The maximum temperature at the ceiling was about 40 ° C and outside about 30 ° C.

For a better comparison between the climate of both containers, the temperature changes and changes in the relative humidity near the ceiling are shown in the figure below.


The temperature and relative humidity within containers MSC U6472633 and MSC U1089745 and outside.

The temperatures were almost exactly the same. The relative humidity, however, showed some differences. The relative humidity in the container with the desiccant showed smaller maxima.

The explanation lies in the fact that an amount of moisture was absorbed by the desiccant resulting in less moisture in the air, resulting in a lower relative humidity.

After weighing the desiccant, it was discovered that a total of 4.465 kg of moisture was absorbed. Since the air in a container itself contains little moisture, this must have been moisture from the floor. The desiccant always causes a lower relative humidity in the air so the floor was looking for a new hygroscopic equilibrium. Therefore, the moisture of the floor in the container with desiccant should have dropped as well. Next figure shows that this indeed is correct.

The moisture content of the container floor in MSC U6472633 decreased 2 to 5%, while the moisture content in container MSC U1089745 remained constant.

Climate control inside a container is a very difficult task.

There are so many variables to be taken into consideration that it is practically impossible to determine a precise figure on the number of desiccant needed within a container.

Nevertheless, significant conclusions can be made such as the fact that a container floor is one of the main sources of humidity.

Desiccant always absorb more at higher temperatures and higher relative humidity. High relative humidity provides a high absorption capacity, while a high temperature results in faster moisture absorption.
If the packing unit increases in mass, the rate of absorption decreases, but the active absorption time increases.

When comparing the different desiccant products two main groups are distinguished by their absorption properties, namely the rapid absorbers and those with a long effective absorption time. If a rapid moisture-absorption is desired, for example for a shorter sea voyage, the first group of desiccants holds perhaps the greatest advantage. If a constant fluid intake is desired, the second group is the most desirable.

As the products that continue to absorb also the ones that absorb the most, fewer units are needed for this type of desiccant which is a big advantage. It should be noted that the desiccants with faster absorption, are the clay based desiccants. The desiccants that ultimately absorb the most are the desiccant based on salt.
From the test at MSC can be concluded that desiccants work. Products succeed in absorbing the moisture from the wood to bring down the relative humidity in the air. Because the relative humidity is lower, a new hygroscopic equilibrium needs to be created. In the MSC container was that new hygroscopic equilibrium was created by the wooden floor expelling moisture.

Finally, it should be noted that the choice of desiccant is not easy, but it is determined by a diverse range of interacting conditions such as type of cargo to be shipped, the length of the voyage, the sea route, the season the container is transported and so on.

Related articles

Desiccant use at home, warehouse or boat.

Advice on solving humidity problems

Excess humidity at home can cause the appearance of mould, mildew, fungus and all kinds of nastiness that endangers your and your family’s health.

In order to solve the humidity problems in a room, bathroom, store room, etc. first of all you need to find out the cause of the excess humidity:

If the humidity comes from outside, caused by a leak or by defective insulation, our products will help to reduce the level of ambient humidity, but will not solve the problem for good. The best thing to do is to consult an insulation specialist so as to solve the root of the problem.

If the problem is due to excess ambient humidity in the room because of poor ventilation or condensation, our product can solve your problems.

How does it work?

Put the product anywhere in the room and leave it to work. The desiccant will activate automatically, absorbing the excess humidity. Once the desiccant has stopped absorbing, put in a refill. How long the product lasts depends on the temperature and level of humidity in the room.

It works without electricity or batteries.

Nordic Power Desiccant regulates the level of ambient humidity to bring it down to the recommended optimum level of 45-50%, without drying out the atmosphere, absorbing only the excess humidity.

Is it toxic? Can I use it in a child’s bedroom?

All Nordic products are non-toxic. They can be used without any problem in any room in the house, whether inside a wardrobe, in bathrooms or in store rooms – even in bedrooms. They are also very popular for use on a boat or yacht.

The desiccant contained in the product is calcium chloride, hygroscopic salts which are non-toxic and environmentally friendly.

Finding and Identifying Basement Mold


Basement mould is a term refers to the types of fungus that grow in basements under certain conditions. Basement mould is harmless in small quantities, but as it grow, it becomes more and more of a health hazard. Some will cause certain types of allergic reactions while others are outright poisonous. If left untreated, the basement mould will keep growing, eventually spreading through the entire building. This is why you must find the mold before the problem gets out of hand. Once you find it, you will need to be able to identify it—otherwise, you won’t be able to figure out how to get rid of it.

Finding Basement Mould

One of the easiest ways to identify the mould is by it’s stench. However, this is only true for some types of basement mould, others may not start to smell until their growth reaches a certain stage. That is why you may want to take a more proactive approach and check the spots where the mould is most likely to emerge. That way, you will have a better chance of spotting it while it is still at manageable size.

Basement mould needs a wet environment in order to grow. It will grow near the pipes and along the walls. The mould feeds on common household materials such as plywood, drywall, furring strips and carpet padding, as well as dust and cellulose in carpets themselves. Try to check any parts of the basement that are hospitable to mould at least once every week. Be sure to bring a flashlight with you—you may not be able to get adequate illumination without it.

If your basement suffers any sort of flooding, the walls will become infested with mould spores, which will remain dormant until they come in contact with water. The spores can remain dormant for a long time. Just because the mould didn’t develop after the flood doesn’t mean it won’t become an issue several years down the line.

Mould Safety

If you find a patch of mould, try not to inhale too deeply and don’t touch the mould with any part of your body. If it gets on your clothing or your tools, wash it immediately. You can identify the mould by sight, so there is no reason why you should be touching the mould in the first place.

Identifying Basement Moulds

Basement mould can be identified based on a number of factors. First, there is colour. Basement mould comes in a variety of colours that range from light gray to black. They may have  green, blue and/or brown tinges. If the mould is closer to black, it is either the Stachybotrys or Cladosporium molds. If it’s closer to light grey, it is either Aspergillus or Fusarium moulds.

To figure out which type of dark mould and you have, look at the texture. If the basement mould looks slimy, it is probably Strachybotrys. Otherwise, it’s Cladosporium.

To figure out what kind of light coloured mould you have, look at the growth pattern. If the mold grows in disjoint circular patches, it is most likely to be Aspergillus. Otherwise, it’s Fusarium.

The Next Step

If possible, try to get the mould tested in a lab. While the factors described above are usually fairly good indicators, only the professional analysis will be able to tell for sure. If the mold patches are small, you may be able to remove it yourself. However, if the patches are fairly large, you will need professional help.