Glycol Treatment for Wood

Written by keith allen
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There are different types of glycol; ethylene glycol and propylene glycol, both primarily used for deicing solutions and antifreeze. To prevent cracking, shrinking and warping, green wood is treated with the chemical polythene glycol or PEG, according to the Lee Valley & Veritas website.

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Definition

Polythene glycol (PEG) is soluble in water, non-flammable and non-toxic and is a waxy white substance that is solid at room temperature. PEG comes in either flake form or solid blocks and two molecular weights: 1450 and 1000. PEG 1450 melts at 1100F to 1150F and absorbs into wood more slowly due to the higher molecular weight. PEG 1000 melts at lower temperatures, 980F to 1030F, and may bleed from the wood in hot, humid conditions.

Wood Types

PEG works most effectively on high-moisture content green wood with low oil or resin content. Walnut, poplar, elm, pine, beech, redwood, spruce, aspen, willow and hickory are woods that can be treated with PEG. Some woods to avoid are tropical hardwoods, white oak, cherry and hard maple.

Treating Wood

The green wood workpiece needs to be treated as soon as possible after cutting to retain as much moisture as possible. Wood needs to be immersed in a 30 to 50 per cent water and PEG solution. For a 30 per cent solution use 7 parts water to 3 parts PEG; obviously, equal parts PEG and water will give you a 50 per cent solution. Heating the solutions will enhance absorption of the PEG solution by the green wood, but does not heat above 1400F. The green wood workpiece thickness and species plus the solution strength determine the length of time for immersion.

Drying

Remove the wood from the PEG solution after soaking for the appropriate amount of time. Make sure the workpiece is completely dry before reworking it. You can use a regular kitchen stove to force-dry small pieces, keeping temperatures at 2000F or lower as some wood will discolour under higher temperatures. If the wood develops cracks, that is an indication it was not soaked long enough in the water PEG solution. Properly treated PEG wood will not warp or crack and usually dries very quickly.

Other Uses

PEG has been used to preserve artefacts that have been salvaged from underwater. PEG makes wood dimensionally stable as it replaces the water in the wood and prevents shrinking and warping as it dries. Because of this aspect, it is great for restoring waterlogged items.

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