Fitting Log to Pedestal
As protection against water wicking up from below, I seal the bottom end of the log with torch-down roofing. To do this, use a torch to heat a piece of roofing material that’s slightly larger than the base of the log. Then, while wearing gloves, adhere the hot membrane to the bottom of the log. When it cools, trim it with a utility knife to match the bottom of the log and slit it at the plunge cut.
The log post attaches to the HD-10A with 5/8-inch-diameter through-bolts, so the next challenge is to drill the bolt holes. First I use a level to orient the log so that the plunge cut is horizontal. Then, using the same technique as before, I draw a plumb line from the center of the plunge cut to the upward face of the log. I draw a matching line on the other end of the log and snap a new line down its length. The bolt holes fall on this line. I measure the heights of the holes in the HD-10A and transfer the measurements to the new chalk line.
The next step takes two people. One carpenter drills the hole while the other guides the 11/16-inch auger bit with a layout square and a torpedo level. After the holes are drilled, we slip the log over the HD-10A to make sure they align. The bolts should be about 1 inch longer than the diameter of the log so there’s room for the nut and washer. We plumb the post and brace it from two directions.
Joining Post to Beam
As mentioned above, beams either sit on top of the posts or in pockets. Pockets can be cut so the beam runs through, or the beam end can be hidden in a blind pocket.
Pocket cuts require two parallel cuts for the sides and a plunge cut at the bottom. To be safe, we work from scaffolding, first running a string line from post to post down the length of the deck to represent one side of the beam. We mark that side on the tops of the posts, then measure to mark the other side. From these lines, we draw plumb lines down the sides of the posts, mark the bottom, and use the chain saw to cut the pocket.
Blind pockets are laid out and cut in much the same way, but the side cuts and the bottom plunge cut don’t go all the way through. Also, you’ll need to make a blind cut from above to end the pocket.
After test fitting the beam in the pocket, it’s a good idea to bevel the remaining flat parts of the log’s top to shed water. I fasten the beam to the pocket using FastenMaster’s LedgerLok screws. You could also use bolts or lags.
If the beams sit on top of the posts, I attach them with 4-inch-long pieces of 4-inch-by-1/4-inch powder-coated angle iron with two holes on each leg for lag screws. The angle brackets attach to the bottom side of the beam and to the side of the post to transfer lateral loads. (All these connections are engineered.)
Because large timbers and logs are usually not pressure-treated, I use a three-prong approach to prevent rot: preservative, sealing, and covering.
I prefer to use borate wood preservatives, which are nontoxic and easy to apply. Two brands that I’ve used are Timbor (Borax, 760/876-4775, borax.com) and Bora-Care (Nisus Corp., 800/264-0870, nisuscorp.com). Timbor comes in a powder and must be mixed with hot water. Bora-Care comes in liquid form. You apply them with either a sprayer or a brush.
For severe exposures, like the windy side of a house in a moist climate, I also use Impel Rods (Wood Care Systems, 800/ 827-3480, ewoodcare.com). I insert them into holes — drilled in the log at vulnerable areas, such as the top and bottom where end grain can wick in moisture — and plug the holes. These crystalline borate rods, which come in 1/8-inch to 1/2-inch diameters, sit inside the wood until moisture dissolves them. The dissolved borates then move within the wood toward the highest concentration of moisture, inhibiting the growth of fungus and rot.
Because borate products are water soluble, they need to be sealed into the wood. I use One Time (Bond Distributing, 866/663-8463, onetimewood.com), which is an acrylate resin that soaks deep into the wood and cures with sunlight. Over the past 12 years, I’ve tested numerous stains and preservatives, and One Time is the best I’ve found. While its initial cost of about $75 a gallon may seem high, the manufacturer guarantees that it will last seven years. This beats the annual or biannual reapplication required with most other sealers.
Finally, you need to provide a barrier to shed the water from the tops of the timbers and posts. I find that torch-down roofing gives the best results. Again, I use the torch to melt the roofing to the top of the wood, both the beams and the posts. Torch-down roofing membrane comes in 18-inch-wide and 36-inch-wide rolls. Using a utility knife, I cut the membrane into long strips 2 inches wider than the beam. After adhering it to the top of the beam, I trim the membrane so that 1/2 inch overhangs each edge of the beam; this provides a drip edge to direct the water away.
This three-pronged approach to preventing rot has satisfied every building department I’ve dealt with, although some have required an engineer’s report. The engineer I use has gladly provided the documentation.
Kim Katwijk is a deck builder in Olympia, Wash. Linda Katwijk co-authored this article, which was reprinted with permission from Professional Deck Builder magazine.
Safe Plunge Cuts
Plunge cutting with a chain saw requires caution. If the top of the bar contacts anything while the chain is spinning, it will kick back at the operator, which could result in a serious injury.
Start the cut with the bar at 45 degrees to the base of the log and the bottom of the bar tip contacting the wood. While maintaining downward pressure to avoid kickback, slowly raise the saw as you push in. Keep pushing down and inward, stopping the plunge when its about 2 inches deeper than the height of the anchor. The finished cut shouldn’t be much higher than the width of the bar.