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Episode 2 - Shakers

Waterproof Tent
by Mike Leahy

Waterproofing agents
What could we use to waterproof our tent?
Obtaining suitable materials
Fire risk
Insulating the tent
Positioning the tent
How did the tent fare?

The Challenge
Southern Alps We were sent up a mountain with only a sheet of cloth and a few natural materials to make a waterproof tent. Being on the rugged west coast of New Zealand's South Island, we were likely to come across freezing conditions or torrential rain.

What is the best way to waterproof cotton or other materials, and what's the science behind it?

Waterproofing the tent
Some molecules interact with or attract water molecules so that they can mix freely with them. Others don't, and they are the ones that we are looking for. Most waterproofing agents work because of their molecular structure, where the molecules on the surface of the material are arranged with their organic, non-polar, water-repellent ends (if they have polar and non-polar ends, that is) all facing outwards to repel water. Many liquids, oils and waxes would be expected to repel water.

Waterproofing the tentA tent would not be very waterproof if it had a flat roof, because water would build up on top and eventually leak through. We settled on a simple, tried-and-true 'ridge tent' design. Because the roof is at a steep angle, water should run off easily, while the triangular structure makes it strong without the need for high-tech materials. As a bonus, it's easy to build.

Preparing tent fabricModern tents are made from a range of advanced waterproof fabrics. Some tents are made of nylon with a polyurethane coating. Others claim to be made of a rip-stop nylon with DWR (durable water repellent). Modern coatings can make tents so waterproof that they can withstand a hydrostatic head of over 39 inches. Simply put, this means you could line up a column of water over three feet tall on top of the fabric and it still wouldn't leak.

Frames on modern tents are usually made of strong, lightweight, high-tech materials like carbon fiber, glass fiber, kevlar or aluminum. We Rough Scientists just have a sheet of cotton and a few sticks. Cotton does have a few inherent waterproofing properties; as it gets wet the fibers expand and close down the mesh of the weave. However, our sheet stands little chance against the west coast elements unless we do something to enhance it.

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Painting the tent What could we use to waterproof our tent?
We need to make the sheet waterproof by coating it with or soaking it in a substance that doesn't mix with water.

We considered each of the following:

Lanolin — a mixture of non-polar (neutral) ester molecules that don't mix readily with water.

Coal tar — a complex neutral mixture of between 300 and 10,000 organic compounds. It is essentially the same as creosote, which is used to waterproof fences.

Ash — likely to make a mess.

Flax — Ellen reckons it might work.

Beeswax — made up of neutral molecules that do not interact strongly with water molecules. Surfaces polished with beeswax certainly seem to repel water.

From this selection, we decided to try these out:

Lanolin — it's effective in keeping sheep dry, and hopefully us as well.

Coal tar — because tars and oils don't mix with water.

Flax — this should work in principle.

Beeswax — as waxes don't mix with water and should be easy to apply.

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mike making coal tarObtaining suitable materials
We used the following simple methods to obtain each of our materials:

Lanolin was scraped off the top of water in which we'd boiled some sheep's wool.

Coal tar was obtained by heating powdered coal over a fire in a metal container and collecting 'fractions' of the liquids evaporating from the heated coal. The liquid was collected by a pipe leading from the container into a series of bottles, where it condensed and was captured. This is called destructive distillation. The liquid we obtained was not a pure chemical but a complex mixture. It looked, and smelled, enough like creosote that I was convinced!

We found some beeswax in our kit box.

The sticky plant flax was taken from the fleshy flax leaves, just underneath the tough skin.

We tested small samples of cotton soaked in each of these treatments, and they all seemed at least partially waterproof.

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But what about the fire risk?

Would the tent be flammable?We experimented with the material samples and tested the flammability of each by lighting the material with matches. The results weren't good:

Lanolin - flammable
Coal tar - very flammable
Flax - not bad but will burn
Beeswax - quite flammable

Despite the disappointing fire safety results, we decided to continue with our experiment. We constructed our tent with panels of cotton coated with the different waterproofing substances to see which would be most effective in keeping us dry overnight.

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Tent construction Insulating the tent
The next challenge was to insulate the tent and prevent our body heat from being lost too quickly to the cold environment. We started by covering a simple wooden frame with heather and leaves, piling it on in several overlapping layers. Then we took some flax leaves and arranged them in a fan shape to make doors. The size and shape fitted the end of our bush tent's triangular entrances exactly. Finally, Ellen wove a few mats from flax leaves to insulate us from the cold ground and keep drafts out where the tent met the ground.

Pitching the tentWe also hoped we could heat the tent. Mikey B. suggested heating up large granite stones in the fire and placing them in the tent overnight. Granite doesn't split in the fire, and because the rocks we used were large they had a small surface area-to-volume ratio (the area of an object increases as a square, while the volume increases by a cube. This means that as an object becomes larger, its volume increases much more than its surface). As heat is stored within the volume of an object but lost from the surface, this means that large rocks take a lot longer to cool than smaller ones. The rocks were very hot when we went to bed and still warm at dawn.

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Tent in clearingPositioning the tent
There's little point in making a tent that is well insulated from the cold if we camp in a exposed area with lots of wind. Similarly, we don't want to be soaked by rivulets of water if it rains, and ant nests are an absolute no-no if we want to sleep well.

WWe didn't have much choice when it came to the site for our tent, because we had to put it on the only piece of clear ground available — a tiny landing site and the only place for a helicopter to land for miles. We also needed to be near a gold bearing 'reef' and close to water. The hollow that we were in only saw the sun for an hour or so a day, making the place very cold, with thick frost lying on the ground all day. However, we were sheltered, and had camped well away from potential flash floods or landslides. Not a textbook-perfect camping place, but with no wind we shouldn't feel too drafty.

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Kate trying out the tentHow did the tent fare?
Luckily for us it didn't rain in the night, but the treatments still needed to be tested. None of them did really well, and Kate got very wet helping us test them. Our results were as follows:

Lanolin - poor
Coal tar
- not so good
- in the end this worked best (the best not meaning much in this company)
Beeswax - worked well on the areas that we managed to treat, but leaked like a sieve elsewhere.

Overall the tent leaked the worst at the seams. We did try to make the material overlap, and the seams did run vertically to help water run off, but water still came in. Just goes to show that I'm no good at sewing. Perhaps we should have thought about glue!

Note about filming this challenge
The tent sequence was filmed on private land (not government land administered by New Zealand Department of Conservation) with the full knowledge and cooperation of the owners. The production team were advised by a member of the Westland District Council and accompanied by an experienced bushman.

The area where the vegetation was cut down is a landing site for helicopters for the owners to access their land (the vegetation is cut back regularly in this area to allow safe landing for helicopters).

The production team worked closely with the Department of Conservation in New Zealand to minimize any impact from filming.

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Photo: Rough Scientists at work
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