How to Repair and Prevent Wood Rot

Rot occurs whenever water gets into cracks or penetrates a wood finish and can't dry out. Seal these cracks and maintain the finish to protect wood's beauty and integrity. Consult a pro for structural rot repairs, but you can tackle small ones yourself.

Difficulty: Moderately challenging

Instructions

Things You'll Need:

• Liquid Wood Hardener
• Epoxy Or Polyester Wood Filler
• Paint And Paintbrush
• Primer
• Wood Dowels
• Mixing Container
• Awl
• Sandpaper
• Awl
• Drill And Bits
• Putty Knife Or Plastic Spreader
• Rasp Tool
• Rubber Sanding Block Or Power Sander
• Sandpaper
• Wood Chisel Or Electric Drill With Spade Bit

Repair decayed wood

1. Use a wood chisel, an electric drill with a spade bit, or another tool appropriate for the situation to remove all wet, loose and unsound wood.

2. Probe the surrounding area with an awl. If it feels as solid as unaffected areas, drill numerous closely spaced holes of 1/8-inch (3-mm) diameter in the wood and inject a liquid wood hardener as directed by the manufacturer.

3. Mix two-part epoxy or polyester wood filler as directed. Mix only what you can apply and shape in a few minutes. Once the material hardens--and it does so quickly--you must throw it away.

4. 

   Fill the hole or build up the affected area with the wood filler, using a putty knife or flexible plastic spreader (see A). Press hard to work the initial layer into the surface for a good bond.

5. Clean off the applicator and mixing container immediately.

6. 

   Use a rasp tool to roughly shape or level excess filler as soon as the filler sets up, but before it dries completely (see B).

7. Use medium or coarse sandpaper to further shape and blend the patch when the filler is completely dry. On flat surfaces, use a rubber sanding block or power sander. On contoured surfaces, use wood dowels or other appropriate shapes to back the sandpaper.

8. Blow off the dust and apply freshly mixed filler to fill any remaining depressions or pinholes, or to build up more material as needed to attain the desired shape.

9. Use medium, then fine sandpaper to smooth the patch and feather it into the surrounding wood.

10. Touch up the patched area with primer and paint.

Take preventive steps

11. Use naturally decay-resistant or treated lumber for decks and other outdoor structures. Never allow untreated lumber posts or lumber to rest directly on concrete.

12. Clean joints between deck boards or between a deck and a house so debris and dirt won't retain moisture.

13. Inspect for peeling paint or other paint failures, especially near joints, such as mitered trim corners at roof eaves or where window and door casings contact sills.

14. Probe these areas with an awl to search for soft or wet, spongy wood (wood that resists being probed is sound).

15. Seal cracks with caulk. If possible, use screws to close any open miter joints. Bore pilot holes for the screws to avoid splitting the wood, and then inject adhesive caulk into the joint before driving in the screws.

16. Sand any bare wood and apply wood preservative before you apply a primer. Caulk joints after priming and before the top coating. Preservative greatly increases the likelihood of a better, longer-lasting paint bond.

17. Create ventilation through trimmed posts or columns by providing space for air to circulate between the trim and the floor surface and an outlet vent at the top. In some cases, this requires cutting 1/2 inch (12 mm) off the bottom of the trim. Lay a board that's 1/2-inch (12-mm) thick on the floor against the post and rest a handsaw on the board as you make the cut. Use small metal louvers pressed into drilled holes to vent the tops of posts or columns.

18. Avoid positioning outdoor sheds, such as one for trash cans, against wood siding. Elevate sheds above the ground on concrete blocks or short sections of 6-by-6-inch (15-by-15-cm) pressure-treated posts.

19. Make sure crawl-space vents remain open, especially during the summer, or add vents where there are none.

Tips & Warnings

• Epoxy dries very fast and is very hard to remove--good points, except when it comes to you and your tools. Clean up as you go along.
• Build up deep holes in layers about 1/2 inch (12 mm) thick. Slightly overfill a flat surface.
• Shape the filler with whatever tools seem appropriate on contoured surfaces or corners.
• Rasps come in a wide variety of shapes for flat and contoured surfaces.
• Rasping is not required, but sanding off a lot of hard, dried material takes more time and effort.
• Drive nails into large damaged areas and let the heads stick up a little so they will be embedded in the filler but lie below the finished surface.
• You can cut, shape, smooth and drill into cured epoxy just as you can wood.
• Read warning labels and wear goggles, gloves, a dust mask and any other recommended protective equipment while working.

on 11/22/2005 After 20 years as a professional painter and decorator, I have found that using an epoxy based filler has one major flaw - after a period of time, the wood expands and contracts, but the epoxy does not. This leads to the filler being seen. I would recommend an exterior poly filler, which is rubber or nylon based. This filler tends to expand and shrink better than epoxy fillers, and lasts quite a considerable time longer.