SP-11 Waterlogged Wood Treatment
In 1995, 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 and preserving waterlogged wood. Using his background in leather and wood treatment preservation, and 2 years of testing a formula for waterlogged wood conservation was conceived. Thus, SP-11 Waterlogged Wood Treatment was developed.
SP-11 has been used and tested on waterlogged wooden artifacts for more than 25 years with highly successful results.
What is Waterlogged Wood and Why it Must be Treated?
Waterlogged wood is a wooden object that has been found in underwater or excavated archaeological sites. The wood artifacts have often endured in the ground sometimes for centuries. They are found in areas such as bogs, bottom of lakes, oceans, rivers and glaciers.
Excavated wood is wood that is found buried in the ground in damp soil, such as sunken river boats and over time the river has dried up or changed course. This excavated wood in most cases retains a high percentage of moisture and can be treated the same way as waterlogged wood.
Since water soaks in and fills the cell walls of archaeological waterlogged wood, when removed from the water and dried, the tangential shrinkage can be 50-75% compared to 5-10% shrinkage in freshly cut wood. When left to dry on its own, this leads to radical shrinkage and degradation of the wood. Thus, a conservation treatment must be used to preserve the shape of these archaeological artifacts.
Past Treatment Methods
There have been many conservation methods to date including, but not limited to:
- Polyethylene Glycol, PEG
- Freeze Drying
- Alcohol Treatment
All of these treatments have drawbacks and concerns of their own including the lengthy time it takes to impregnate the wood plus the treatments can involve a many step process and often include several types of treatments combined. The most commonly used method has been the use of PEG, Polyethylene Glycol. However, there are some major drawbacks in using PEG to treat waterlogged or excavated wood:
- It is difficult to get it to penetrate and may require the use of heat elements.
- The penetration time is lengthy (can take several years or longer and often starts with a diluted solution).
- PEG adds significant weight to the wood and can darken it considerably.
- SP-11 is safe to use on wood that contains iron, such as nails, where PEG will eat the iron.
- It is hygroscopic making the wood sticky under humid conditions and requiring artifacts to be stored or displayed in climate controlled areas.
Preserving Waterlogged Wood with SP-11
SP-11 is a formulation of non-toxic modified polymers with a high grade, high flash mineral solvent that contains no sulphur and has a very slow evaporation rate. Being water soluble, SP-11 penetrates the wood quickly and displaces the water. It coats the wood cells and capillary tubes to prevent them from shrinking as the moisture leaves during drying. SP-11 is formulated specifically to compensate for the very high percentage of water in these waterlogged wooden artifacts.
When the treated wood is completely dry, a thin coat of SP-11 is left on the wood cell walls. See the photos below showing treated cross sections of a fishing weir stake (carbon dated 5,000-7,000 years old) believed to be hemlock. The photos are courtesy of the conservation lab at Bates College in Lewiston, Maine.
The benefits of using SP-11 Waterlogged Wood Treatment:
- Is safe to use in large quantities and does not need to be heated or diluted.
- SP-11 has small molecular weight polymers which allow for easy penetration.
- It is highly soluble in water which aides in deep and fast penetration.
- It does not break down in acidic conditions.
- Artifacts that may need to be re-glued can be done so once the wood has dried.
- Treated and dried wood is not sensitive to humidity or temperature changes.
- SP-11 will not darken the wood leaving it looking more natural.
- Does not add significant weight to the wood.
This oak post was recovered from the site of the Popham Colony in Maine, and treated with SP-11 to prevent it from cracking and deteriorating after it was unearthed. The founders of the colony, which was established in 1607, buried these posts in the ground as foundations for barns and other structures.