Sometimes in the winter season, you really have to pull out all the stops to keep warm. The following technique might be a bit much too work for a cool spring evening, but in the dead of winter in the great outdoors, a nice warm bed is worth the trouble.
So how does this hot rock mattress work? The heat of a fire is collected into enough stones to build a mattress, and the heat is then buffered so that it comes out slowly over a 6 to 8-hour period.
Now the hard work begins. You have to first build the thing and maintain a big fire.
This type of heated bed is best used in a dry location with easy to dig soil and abundance of dry rocks and firewood – in conditions that have a very low risk of causing a wildfire. However, you may be able to adapt this technique to many different climates and terrains.
After you pick the location, start digging a wide, shallow trench a little wider and taller than your body. I’ll usually dig down 4 to 6 inches over this entire area, and bring the dirt all to one side of the trench. This creates a reflecting wall for the fire, and keeps it handy for the upcoming refill.
Next, lay flat stones in the entire trench. This is the rock part of the hot rock mattress. It’s OK if the rocks are a bit thicker than the trench is deep, as long as you have enough dirt to cover them all with 3 to 4 inches of soil after the firing.
Safety warning: Make sure you gather rocks from a high and dry location, as waterlogged rocks can explode when they heat up in a fire. The steam builds pressure in the rock causing it to blow up like a grenade.
Now comes the fire needed to heat the rocks up. Burn a good-sized fire over all the rocks for 2 to 3 hours. After the rocks have been heated through, rake all the coals off to the side (I like to create a new fire from this). Quickly cover the hot rocks with 3 to 4 inches of soil and let the moisture steam out of the dirt for 10 to 15 minutes. My final trick is to cover the soil with a few inches of leaves or other type of vegetation to help insulate the hot rocks and dirt. Top it off with your normal outdoor bedding and hit the rack.
This bed might feel too hot at first, but as it cools, you’ll have many hours of comfort in an otherwise freezing cold night. Yes, it’s a lot of work. But I’ve never regretted that work during those frigid campouts.
Let us know if you’ve tried this, or if you remember the scene in Jeremiah Johnson where he burned his pants using a similar technique. Enjoy at your own risk.