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Saunas hold a special fascination for me. It's almost unbelievable that so simple a thing -- a warm, dry room -- can do so much for you. It's not just the health and hygiene advantages, though these are real. If that's all there were to a sauna, there wouldn't be tens of millions of sauna users, worldwide.
I was introduced to saunas during a long trip through Europe in the late '60s, and the more I used them, the more convinced I became that the Europeans were onto something good. When my wife, Jaki, and I returned to the States, we knew that before long, we'd want a sauna of our own.
We bought some land in upstate New York, and built a small cottage, which was to be our temporary home while we constructed a full-scale, earth-sheltered home for our permanent residence. Saunas were incorporated into both house plans.
When we moved into the earth-sheltered home, the sauna space was still unfinished; we continued to use the cottage sauna. But after a while, we got the idea of building a freestanding sauna halfway between the two buildings, one that could be used by the occupants of either -- or both. By this plan, the indoor sauna's space could be given over to other uses: an extension of the kitchen at the cottage, and a utility room at the earth shelter. Best of all, a freestanding sauna would be a place where we could truly "escape" from the normal surroundings of the house, a special pleasure during the cabin-fever months of February and March.
Naturally, we wanted the new sauna to look good, be simple, and not cost too much. We also wanted to be able to do as much of the work ourselves as possible. Since both the cottage and the earth shelter featured "cordwood masonry" walls (more on this in a moment), we decided to build a cordwood sauna. To tie in with the underground house, we also elected to put a sod roof on the new building.
Cordwood Masonry
Cordwood masonry is an inexpensive building technique in which very short logs called log ends are placed widthwise in a wall (the length of the log ends establishes the thickness of the wall) and then mortared in place. Actually, there is very little physical bonding between wood and mortar, but because the mortar in a cordwood wall forms a precise cast of every log end, any loads applied to the wall are distributed without stress points, making the wall immensely strong in compression. Some cordwood masonry buildings in Canada have been standing for over a century, and are still in fine shape.
Because our sauna was to be of modest size (about 10 X 15 feet), we decided to build a post-and-beam framework, and to use the cordwood masonry as a solid filling between the framing members (see the illustration). This choice was somewhat arbitrary; we could have built a frameless cordwood structure instead, although the technique of building cordwood corners, or of eliminating corners in round cordwood buildings, is more difficult. As we had decided to use 8-inch-thick posts and beams, we used 8-inch-long log ends for the walls' cordwood infill.
Several factors affected our choice of what kind of cordwood to use: availability, the dryness of the wood, its insulation value, and the desired appearance of the finished wall. Dense hardwood with insulation values of less than R-1 per inch would not have been good for keeping the heat in our sauna, at least not at the 8-inch log-end length we were using. Softwoods have a higher intrinsic R-value, but the sauna's high heat could cause a problem with resinous softwoods such as pine: Bleeding of the sticky pitch can occur at high temperatures. We were left with a choice between cedar and poplar, both common in our part of New York. Although cedar is more expensive, we chose it for its better R-value, aroma, appearance, and resistance to rot and insects.
Any logs used in cordwood masonry should be thoroughly air-dried for one year if the logs are split, or for at least two years if they're unsplit. The idea is to have the wood reach and stay at its "ambient moisture content," which varies from wood to wood, but which is generally in the 10 -- 15 per cent range. In this condition, wood will expand and contract slightly as it absorbs and gives off small amounts of water vapor with changes in the weather, but it will always return to its original size. Because shrinkage cracks and gaps are minimal, your wall remains weather-tight.
Some kiln-dried wood, or wood that's been stored indoors for a very long time, can pose another problem: It may be too dry. We ran into this problem during construction of a round cordwood house during 1981. The overdry hardwood we used absorbed moisture from rain and swelled enough to tilt a wall out of plumb. An adjacent wall of very dry cedar did not experience this swelling pressure on its mortar joints. The lighter, airier cedar seemed to allow wood-fiber expansion into its own air spaces. Cedar log ends, then, can act as their own expansion joints.
For our sauna, we were lucky enough to obtain a load of 75-year-old split-rail cedar fencing cut to precise, 16-inch log-end lengths -- wood that had reached ambient moisture content decades ago. It was a simple matter to cut each piece in half with a chain saw. The new wood we thus exposed was smoother and lighter in color than the older, weathered surfaces, so we chose to use the fresh-cut ends to form the sauna's inner walls and the weathered ends for the outside.
Besides wood, the other major variable in a cordwood masonry wall is the mortar. The only mortar problem you're likely to run into is overly rapid drying -- the moisture being drawn off by the relatively dry log ends. This problem is easily prevented by the addition of wet sawdust to the mortar mix; the sawdust retains the moisture long enough to allow full hardening of the masonry. Our mortar "recipe," which has proven itself in a number of different buildings, is seven parts clean sand, five parts wet sawdust, three parts masonry cement, and one part lime.
Any strong foundation will support a cordwood wall: block, stone, gravel, slab, etc. We chose to build a foundation of reinforced concrete beams "floating" on a pad of sand for good drainage.
Next came the floors. The heated half of our building, the sauna proper, has a "sawdust concrete" floor (two parts sand, two parts sawdust, one part masonry cement) sloping to a center drain. The unheated, southern half (an open-air antechamber) is floored with 3-inch-thick slabs of elm set in sand.
We then erected the post- and-beam frame, and roofed the building to provide a sheltered workspace for the construction of the cordwood walls. Although our sod roof is more complex to build than ordinary roofs, I feel it was well worth it, considering its contribution to the aesthetics of the sauna. But if you prefer shingles or roll roofing, they'd be fine, too. Our 2 X 6-inch roof planking is covered by a layer of hardboard, a Bituthene waterproofing membrane, and an inch of extruded polystyrene insulation. Sand and then H inches of topsoil cover the polystyrene.
Building The Walls
If you can stack firewood, you can build a cordwood masonry wall. We began ours, naturally, at the bottom. First we laid two "beds" of mortar along the length of the "sill," or lower beam, that was to support our wall, dividing the sill into thirds: an inner mortar bed, an air space, and an outer Gourmet. Beating mortar bed (see the illustration). Next, we filled the air space with fiberglass insulation. This insulation provides an essential thermal break between the inner an outer mortar joints, and prevents a significant amount of heat from passing through the wall. When the insulation was in place, we laid log ends width-wise in the wall, so that the ends of each log were set in the mortar. We placed the logs a little less than an inch apart, and continued until the entire first "course," or layer, of logs was in place. Then we "mudded up" the second course (following the random ups and downs established by the first), insulated, and installed log ends to fit the spaces created by the first course. The wall was now virtually building itself, telling us where the next piece should go. We kept a good supply of split and small logs of different diameters on hand to help fill the odd spots.
When we'd used up our first batch of mortar, we started "pointing" or "raking" the lower courses. Pointing (so called because it's sometimes done with the point of a trowel) consists of using a tool to smooth and compress the outside surface of a mortar joint, both for the sake of appearance and for shedding water. We made an effective, no-cost pointing tool by bending the last inch of an old butter knife to about a '30-degree angle. The blunt, rounded edge is easier to use and more effective than a trowel.
Next, we mixed a new batch of mortar, and continued mudding, insulating, and stacking until the wall was finished. We left holes for windows, doors, chimney openings, and the like, by installing slightly oversized wooden forms in the wall, and then running the cordwood masonry around the form. We installed the windows, doors, etc., after the mortar had fully cured. At the same time, we added a small sauna stove and some homemade benches.
Performance and Cost
OK, we've built the thing, but does it work? The answer, I'm happy to say, is a resounding "Yes!" The first time I fired up our little (20-inch cube) plate-steel stove, I took it kind of easy with the fuel. It took an hour to bring the sauna's air to 165 F and Jaki and I enjoyed the very pleasant sauna. Two days later, with a starting internal and external temperature of 65 F, I fired the stove with a charge of scrap hardwood and left the damper open. Thirty-four minutes later, the sauna temperature was at 177 F. Success!
Now that we use it daily, we like to "season" the sauna before entering. Seasoning means heating the mass of the structure -- the cordwood, the stove's own mass, the concrete floor, and the inner mortar joint -- rather than merely heating the air. Once the entire building is warm, it tends to stay warm, and you can even shut down the stove altogether. If you go in the sauna too soon, the part of you facing the stove may he fine, while the other side of you is chilly -- wait a short while and you can bask in glorious, even warmth.
As for costs, see the materials list accompanying this article. We actually paid somewhat less than the figure shown in the materials list because many of these materials were already on hand, or were obtained for free. You may be able to do even better on the price. But even if you pay the full $1200 or so, you'll still have a bargain: only about $8 per square foot for sauna and antechamber. Figure on about 250 man-hours of labor.
Is it worth it? Well, I may be prejudiced, but out of the dozens of saunas I've sampled all over the world, including several that I've built myself, this one pleases me most.
For more details on the techniques of cordwood construction, see Cordwood Masonry Houses: A Practical Guide For The Owner-Builder, by Rob Roy (Sterling Publishing Co., 2 Park Avenue, New York, NY 10016; $7.95 plus $1.25 postage and handling).
MORE INFORMATION For information regarding the purchase, construction, or installation of spas and hot tubs, call or write the International Spa and Tub Institute: ISTI, Box 195,'31, Irvine, CA 9271,'3 (800/854-8112). They can send informative booklets, along with names of reputable spa and tub dealers in your area.
We haven't found a similar central source for sauna information, but two companies in particular seem to have a lot of information they're willing to share with consumers: Bruce Manufacturing, Box 213, Bruce Crossing, MI 49912 (906/ 827-3906), and Viking Leisure Products, Box 6298, San Jose, CA 95150 (408/294-4331). Bruce sells sauna stoves; Viking sells stoves, accessories, and complete pre-fab kits.
The following books also contain a wealth of information, especially for those interested in do-it-yourself spas, hot tubs, and saunas.
Build Your Own Hot Tub by Ed Miller and Steve Flamm $5.95 plus $.50 postage and handling Ten Speed Press P.O. Box 7123 Berkeley, CA 94707 (415) 845-8414
Hot Tubs, Spas and Home Saunas By Jack McDowell $3.95 (CA residents add state sales tax) Lane Publishing Company Menlo Park, CA 94025 (415) 321-3600
How To Build A Sauna by Carlton Hollander $5.95 plus $1.25 postage and handling Sterling Publishing Company 2 Park Avenue New York, NY 10016 (212) 532-7160
Sweat by Mikkel Aaland $7.95 plus $1.00 postage and handling Capra Press P.O. Box 2068 Santa Barbara, CA 93120 (805) 966-4590
The Sauna Is... by Bernhard Hillila $3. 00 Dr. Bernhard Hillila Valparaiso University Valparaiso, IN 46383 (219) 464-5000
Tubbing by John Silversmith $10.95 hardcover, $6.95 softcover (limited number available) plus $1.50 postage and handling (NY residents add 8% sales tax; NJ residents add 5%) Crown Publishers, Inc. Attn: Retail Sales One Park Avenue New York, NY 10016 (212) 532-9200
Rodale's New Shelter February 1982 pp. 33-35