How to Avoid Warping of a T-14 Post & Other Tips on Post Construction-- Ken Kostka, Purple Martin Preservation Alliance
After my newly-installed T-14 post warped noticeably over a period of five months, I was determined to prevent this from happening again. After corresponding with several other people whose post also warped, and after consulting my brother Stan, a master carpenter, I've put together a list of ways to help prevent warping of the T-14 laminated wooden post. This is intended to be a supplement to the T-14 Plan Book.
1. Buy the lumber well ahead of time to let it dry, if possible. Boards sold at lumberyards are kiln-dried but can still have a high-moisture content due to shipping/storing conditions, and the weather. If you store them for a few months in a warm, dry place, like the eaves of a barn in summer or a heated basement in winter, they’ll be thoroughly dried, reducing the chance of warping after assembly. If a fully-dried board is screwed to a moisture-laden board, the "wet" board may bow them both as it dries and shrinks. All the lumber should be thoroughly dried before being assembled into the laminated post. However, some people recommend assembling the pole before the lumber dries out, to avoid warping while the lumber is drying. If you choose to do that, assemble (glue and screw) the pole, then allow it to dry and just paint the outer surfaces. Don't forget the endgrain!
2. Take your time choosing
the lumber, especially the 2” x 6”s. Don’t allow yourself
to be rushed at the lumberyard. Explain that these board are for a "special
project" and need to be straight, as dry as possible, because the T-14 will
slide up and down the pole assembled from these boards. If the pole warps
after being assembled, it won't look good, but more importantly, the house
would slide up and down properly, causing a major headache. Take this tipsheet and the T-14 plan book
when going to buy the lumber; they will help explain to the yardworker why you
need better than average boards. Buy grade 1 lumber if possible. Make sure the boards are straight and
have regular grain. Check for “warp,” which is a generic term and refers
generally to any and all deflections from straight in any direction. “Twist”
refers to deflection where the end cross sections are out of parallel. “Bow”
refers to deflection along the face lengthwise. “Crown” refers to deflection
along the edge lengthwise “Cupping” refers to deflection along the face
widthwise. Avoid boards which have a significant amount of any type of warp, but
reject outright any boards that are twisted. Bowing is the most noticeable type
of warping; a bowed board placed face down on a flat surface will “rock” like a
rocking chair. If in doubt about the bow or crown of a board, stretch a stringline along the length. The
dimensions of lumber at lumberyards is not precise. Try to get boards that are
as close as possible to 5&1/2 inches in width (which is the width that they
should be). An eighth of an inch wider (5&5/8") is OK, but the T-14 is designed
to slide up and down a pole that is 6 inches wide; you want to allow for
some play and avoid a tight fit that will cause the house to get stuck when
going up and down.
3. Paint/seal all the boards with deck sealer or oil-based primer & paint before assembly, especially the end grain. Even though you'll be using treated lumber, further sealing all surfaces will further reduce the chance of warp and preserve the section of the post that is underground. Consider using a paint that is similar to the color of the wood so that any paint rubbed off by the raising and lowering the house is not as noticeable. Consider painting the outer surfaces of the underground section with roofing tar or motor oil to further protect it. After the pole is glued and screwed together, paint all exposed surfaces; don't forget the endgrain!
4. Oppose bowed and cupped boards to cancel out warp.. Every board will have a tendency to bow (and to a lesser extent, cup) in one direction or another. Oppose the bows and cups (ends-touching-ends & edges-touching edges) so that any gaps are on the inside before glueing, clamping, and screwing the boards together. Remember, your goal is to end up with a solid, straight 4" x 6" post. (See #2 above for warp terminology)
5. Glue both sides of the 1” x 6”. Put a complete and even spread of waterproof glue/construction adhesive (like Liquid Nails for treated wood) on both sides of the 1” x 6” before clamping and screwing the boards together. One rule of thumb when laminating (sandwiching) materials that are not stable (like wood) is to equalize the glue bond on both sides. This large surface area created by the glue bond should help eliminate warping. Make sure the glue and paint are compatible; some glues may say they only work on bare wood surfaces.
Clamp boards together before
Driving in the drywall screws will not close gaps created when slightly bowed
or warped boards are placed face-to-face for assembly; therefore, it is
important to attach clamps to squeeze shut all the gaps before driving in the
screws. Otherwise, you’ll end up with gaps in the assembled post, making it
prone to warping. These clamps should run the length of the post. Don't clamp
any tighter than is necessary; if you overtighten, too much of the glue will be
squeezed out. You can use scrap wood to keep the clamps from "biting" into the
post boards. Also, I recommend pre-drilling the holes for the drywall screws,
and placing 2 screws every 8 inches, instead of every 16 inches, as recommended
in the manual.
7. Miscellaneous. When finishing the surface of the concrete at the post base, be sure it has a slope away from the post in all directions to shed rain. Seal any cracks that develop between concrete and post with some type of sealant like silicone or cold patch tar and check it every season. Reseal if necessary during the dry summer season. Bowing is likely to be less noticeable in 16 ft. boards than in 20 ft. boards. If your martin house is well out in the open, as it should be, height is not critical and 16 ft. boards will usually suffice. Douglas Fir is a closed-cell wood that is much better at resisting warp. Assuming it is available and affordable, it would be better than pine. File a small (3/8" wide) notch in the center of the 1" x 6" just below the pulley, on both sides. This will keep the cable centered and prevent it from riding in the crack between the 1" x 6" and the 2" x 6", which tends to occur.
If you follow all of these tips, I believe the chances of your T-14 post warping significantly, if at all, will be greatly reduced. Any additional input and advice is welcomed. Please e-mail email@example.com. Thanks to Doren Claire, Gerald Kaufman, Stan Kostka, Joe Kostka.