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Repairing Exterior Wood Elements on Your Historic Building

Repairing Exterior Wood Elements on Your Historic Building | Wisconsin Historical Society

If the original wood elements on your historic house or building have rotted or are missing wood, you can often repair them with architectural epoxies. By repairing your original wood elements instead of replacing them, you preserve precious old growth wood that is not available except through salvaging. In most cases, repairing original wood is also more cost-effective than replacing it.

Use of Architectural Epoxies on Historic Wood

An architectural epoxy is a specialized two-part epoxy wood conditioner and putty used to repair rotted wood. Architectural epoxies were developed for wood repair in the boat industry. Water caused deterioration and rotting of. Over time, chemists perfected these epoxies so well that they are now used extensively to conserve historic wood.

Laboratory testing, field testing and a track record of over 30 years have proven that, when used sparingly, architectural epoxies are sustainable and comply with the Secretary of the Interior Standards for Rehabilitation.

Best Uses of Architectural Epoxies

Architectural epoxies contract and expand well with the wood. They are best used on rotted wood and wood with missing material or large holes. Architectural epoxies cure from the heat created by the chemical reaction between the wood conditioner and putty. The thicker these epoxies are applied to the area being repaired, the faster and more thoroughly they will cure.

You can purchase an architectural epoxy at a home improvement store. Make certain the epoxy you choose was made for use on wood. The more expensive epoxies are usually the more effective products. Always follow the manufacturer's instructions and safety recommendations. You should oil prime and paint architectural epoxies just like any historic wood.

Guidelines for Using Architectural Epoxies

Before you start using architectural epoxies to make wood repairs, consider the following guidelines:

  • If you can splice a piece of salvaged old growth wood onto an area where the wood has rotted, this approach will always be preferable to using epoxies. This splice repair is called a scarf joint or a Dutchman.
  • If you cannot use a wood splice to fill areas with major rot or large holes, consider mixing sawdust with the two-part epoxy and packing it into the larger voids. Lightly sand and paint over the fill.
  • Never apply epoxy to areas where it is not needed. For example, if your window sill has gaps in the wood where the softer wood grain has eroded — known as grain checks — use epoxy to fill in just the checks. Do not allow the epoxy to spill over onto the rest of the window sill.
  • Never use architectural epoxy to fill nail holes or small cracks or splits in wood siding. You should fill nail holes with glazing compound made of boiled linseed oil. You should use a more appropriate wood filler to repair siding cracks and splits.
  • Never use architectural epoxies as a primer or sealer for end grain. Sealing the end grain can impede the ability of wood to absorb and release moisture. For example, if you repaired bottom rot on a railing baluster (spindle) with epoxy, you'd have to drill multiple 1/8-inch-diameter holes (called weep holes) through the epoxy patch and into the solid wood above it to allow moisture to drain out the bottom. Without these weep holes, the moisture would be trapped in the good wood above the patch and could cause more wood to rot.

Applying a Two-Part Liquid Epoxy

Follow these steps:

Step 1

EnlargeImage of wood repair.

Source: Bob Yapp

Here is the first step to applying a two-part liquid epoxy to the rotted end of a porch baluster.

Step 2

EnlargeImage of wood repair.

Source: Bob Yapp

Here is the second step to applying a two-part liquid epoxy to the rotted end of a porch baluster.


Step 3

EnlargeImage of wood repair.

Source: Bob Yapp

Once you have a completed epoxy patch, drill holes to ensure moisture can drain from above the patch.

Step 4

EnlargeImage of wood repair.

Source: Bob Yapp

Here you can compare a completed epoxy patch with oil primer to a similarly deteriorated baluster.







The information presented here is not intended to provide comprehensive technical advice or instructions on solving historic preservation issues. Any information contained or referenced is meant to provide a basic understanding of historic preservation practices. Read full disclaimer.