Fishing Weir Stakes: Waterlogged Wood Conservation

In 1995, Dale Knobloch, the founder of Preservation Solutions, was approached by the head archaeologist for the Maine State Museum, with a challenge to develop a better method of stabilizing waterlogged wood.

In 1996 over six hundred fishing weir stakes were discovered in Sebasticook Lake in Newport, Maine when the lake was drained. They carbon date to 5,000 – 7,000 years old showing that the site was in use for over 2,000 years. The museum was kind enough to trust Preservation Solutions with 5 stakes to experiment with. After treating various pieces of waterlogged 19th century ship timbers from a local river in Maine, we felt confident in treating the fishing weir stakes.

The stakes were made from various native woods such as Larch and Hemlock. They were first soaked in a mild solution of bleach (sodium hypochlorite) for several days to kill bacteria. Next, the wood was completely submerged in SP-11 for 30 days, then removed to dry in a cool, unheated room with a relative humidity of 55%. After 3 months of controlled drying, the wood showed no signs of cracking or checking. The stakes looked natural and were dry to the touch with no noticeable weight gain.

The museum then provided Preservation Solutions with another cut piece of weir stake to treat. It had been stored in a freezer and because of the high percentage of water in the piece the freezing caused the water to expand and the wood to crack open. This piece was treated with SP-11 like the others and after it had dried, it was impossible to detect the crack.

Several other weir stakes were sent to a conservation lab in Maine and treated with polyethylene glycol, PEG. Because of the difficulty in getting the PEG to penetrate, the stakes were then sent to a pressure treatment facility in Alabama to be put under pressure in a PEG solution. From that point, they were sent to another lab to be freeze dried.

The head archaeologist at the Maine State Museum noted the following results between the 2 treatment methods of the weir stakes:

  • The SP-11 soaked into the wood much quicker than the PEG.
  • Unlike PEG, the SP-11 did not need to be heated to penetrate the wood.
  • The surface of the PEG treated wood remained waxy and crystallized while the SP-11 treated wood had a smoother, dryer surface.
  • The PEG treated stake was heavier than the SP-11 treated wood.
  • A huge benefit of using SP-11 was that there is no additional treatment procedure needed.
Weir stakes

Photos of fishing weir stakes taken September 2014, 17 years after being treated with SP-11. The wood has been stored in a cool area, but not humidity controlled and still shows no signs of cracking, checking or shrinkage. The surface is dry to the touch.