Rot-damaged porch support post. The Joy Of Old Houses:

Repairing Rotted Exterior Wood

In This Article:

We dig out the old rotten wood, apply a liquid wood hardening agent, then fill in the voids with epoxy wood filler.

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Skill Level: 2 (Basic) Time Taken: 2 Hours

By , Editor


Wood damage caused by rot is a common problem with old houses. There are 3 requirements for wood decay fungi to flourish: 

  1. The moisture content of the wood needs to be above 29%, 
  2. The wood needs to be exposed to oxygen, 
  3. The temperature needs to be above 40 degrees Fahrenheit. 

The fungi that cause wood to rot are everywhere, and all they need are a moist warm place to do their dirty work. If wood gets wet but dries quickly, the fungi will not have a chance to grow and feed on the wood fibers. Thus, any design that prevents water from puddling on wood, or allows for maximum air flow around the wood, will last longer.

This century-old porch post had some minor rot damage, mostly around the nail holes First we sanded the area, then we used a flat screwdriver to pick out the soft and wet chunks of wood.


We applied an epoxy product called LiquidWood from Abatron. LiquidWood is a thin, runny material that goes on with a paint brush and soaks into the damaged wood fibers. The wood needs to be dry and free of flaking and crumbling loose rot, but less severely rotted wood can remain. The epoxy will saturate the softer areas and harden them Applying epoxy resin to old rotted wood to preserve the architectural details.


LiquidWood is a two-part epoxy resin. Equal volumes are mixed together and applied like paint.

One drawback to LiquidWood is it's long curing time. Abatron's instruction say that LiquidWood will harden overnight, but our experience is that it takes much longer to fully cure. We let this post sit for a week, in summer weather with temperatures in the 70's every day, before it was fully dry to the touch. Granted, it felt only slightly tacky during that time. I believe LiquidWood can be covered over before it is fully cured, because I have made many repairs that way.

Heat expedites the curing process, and on other jobs I have used a heat gun or a hair dryer to help LiquidWood harden faster.

When the LiquidWood was dry, we applied a layer of Abatron's WoodEpox, which is an epoxy dough-like filler material. One way to apply WoodEpox is with a putty knife. Applying epoxy wood filler to fill holes in old exterior wood.


Another way to apply WoodEpox is by hand. Rubber gloves should be worn when handling this product.

At 70 degrees or higher, WoodEpox seems to take several hours to fully harden. At cooler temperatures the material may take a few days to harden. One way to check for adequate hardness is to scratch the epoxy with a fingernail. If the scratch shows up as a lighter color, the epoxy has hardened.

After the WoodEpox was hard we used a rasp (such as Stanley's Surform tool) to shave down the excess material. Sometimes there are still voids after shaving down the excess, so more WoodEpox may need to be applied. We often fill small voids with caulk.

When the surface was satisfactory we applied a coat of oil-based primer, followed by a coat of exterior latex satin-gloss paint.

Update - 5 Years Later:

This repair is still holding up perfectly. I have seen other patching materials (like Bondo) separate from the wood, but Abatron's wood filler has stayed put.




Tools Used:

  • Basic Carpentry Tools
  • Putty Knife
  • Sanding Tools


Materials Used:

  • 2-Part Epoxy Wood Hardener
  • 2-Part Epoxy Wood Filler


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Copyright 2001, 2005

Written March 26, 2001
Revised January 5, 2005