BLOG 4. OLD IDEAS DIE HARD—WHY YOU NEED AN INTERIOR GROUNDCLOTH, by Cliff Jacobson
Old ideas die hard, and when it comes to camping, the hardest to die is that you should place a plastic groundcloth UNDER the floor of your tent. This is dead wrong, and akin to pitching the tent on a slab of concrete. Rainwater will flow between the impervious groundsheet and floor, pool there, and be pressure wicked by body weight into the sleeping
compartment. Then, you’ll really have a sponge party!
We had Flooded ground on campsite at Ham Lake
Photo above: Interior groundcloth in this tent saved the day!
For decades I’ve advised people to put the waterproof plastic groundsheet INSIDE the tent, not outside as recommended by tent makers and so-called experts. I’ve hammered on this in my books because an inside groundsheet is the most important thing you can do to stay dry in a heavy rain where flowing groundwater floods your tent. The one exception to this rule is in winter where the groundcloth goes under the floor to keep the floor from freezing to the ground.
Here’s some advice on picking a campsite from an old time camping book (not mine):
“Pitch your tent on high ground, with sloping topography all around. The area should be free of rocks and sharp vegetation that might puncture the tent floor. The campsite should be open enough to allow a gentle breeze to blow the bugs away. There should be a supply of fresh water nearby. Face your tent east so you’ll arise with the morning sun.”
Have you ever seen a place like this? In your dreams maybe, but seldom in the BWCA. You are allowed to camp only at those little red dots on your Boundary Waters map. Pitching your tent anywhere else is illegal. The rocky, hilly nature of the BWCA prohibits constructing idealistic campsites. The result is that you take what you can get which is often a low site that will flood in heavy rain. If you have a site like this, you’d best have a plastic groundcloth INSIDE your tent. Make the plastic sheet large enough so that it flows well up the sidewalls of the tent, all around. This way, when flowing groundwater gets into your tent (and it will if it rains hard enough and long enough—no matter what kind of tent you have), it will be trapped between the plastic and floor and you’ll stay dry.
What about using a second groundcloth under the floor to prevent punctures from rocks and sticks? Bad idea, here’s why:
1. You are essentially pitching your tent on a slab of concrete, i.e. a non-porous surface. Heavy rain water will pool between the plastic sheet and tent bottom and pressure wick into the tent. Yes, the interior groundcloth will (hopefully) keep the water confined and out-of-contact with your sleeping bag. But, the exterior groundcloth will push more water into the tent than would be if it wasn’t there and the water had been allowed to absorb into the soil.
2. A second, outer groundcloth is just one more thing to carry—more bulk, more weight and something you don’t need.
3. If it’s raining hard and blowing bloody murder when you pitch your tent, the exterior groundsheet may be blown about your camp—you may have to run to catch it! In any case, it will be a hassle to keep it in place while you pitch your tent on top.
4. Contrary to popular belief, a layer of plastic under your tent will not discourage tears or holes in the tent floor. Why? Because most holes develop like a “green stick break”. Explanation: When you bend a green stick it compresses on the bottom and elongates on top. The break first occurs on the elongation (top) side. The waterproof coating is on the INSIDE of your tent floor. As a sharp stick begins to force its way upward through the coated nylon floor, the undersurface (non-coated side) of the nylon compresses and the upper surface (coated side) elongates. When the elongation becomes large enough, the top coating breaks and the stick pokes through the floor. To prevent this, beef up the elongation surface (top surface), not the compression side. An interior groundcloth does exactly that.
We discovered this phenomenon years ago when we began using woodstrip solo canoes in tough rapids. Adding extra layers of fiberglass to the bottom of our boats added a lot of extra weight and not much security. Then one day we began looking at the breaks and observed that they were always “green stick” breaks—that is, the strips always broke inward. So we responded by adding a football-shaped reinforcing layer of fiberglass (and later Kevlar) to the inside hull. This largely solved the problem. By comparison, my five Cannondale Aroostook tents (no longer manufactured) have been used in commercial outfitting on rugged Canadian canoe trips for 35 years. Trips have lasted from one to four weeks. That’s more than two years of continuous service for each tent. We have always used an interior groundcloth in these tents. Damage? Only one tent got a hole in the floor. I might add that the interior waterproof coatings on these tents was long gone when I sold them at a garage sale a few years ago. After 35 years of heavy use only one tent had a hole in the floor!
The idea that the groundcloth goes under the tent got started in the 1950’s when few tents had floors. You set a poncho or separate tarp inside the tent then placed your sleeping bag on top. The best tents had “snow flaps”—wide flaps sewn to the perimeter. In summer, you turned the flaps inside and set your poncho or tarp on top. In winter, the flaps were turned out and snow was piled upon them to secure the tent.
If you’ve ever pitched a floorless tent you know it isn’t easy. Since there’s no floor to establish the shape, the tent usually goes up cockeyed. Getting it straight means pulling stakes, moving them around, looking at the tent then setting the stakes again. When I was a Boy Scout in the 1950’s, we took great pride in “getting it right” the first time around. But we were Boy Scouts and it was no big deal. But casual campers didn’t have the patience for this sort of thing. And that’s why manufacturers first put floors in tents—to make them easier to pitch, not to keep out water. Any water that gets inside a floored tent stays inside, and that’s why you need an interior groundcloth to keep that water away from you.
With this, I rest my case!