How to Fix Rotted Wood Siding | Tips to Save Time & Money

When you're painting the exterior of your home there is a good chance you could encounter rotted or damaged wood on your siding, window sills, trim, or shutters.  

Many folks are tempted to just paint over top of it to try and cover up the unsightly spots, but this is only putting a bandaid on the situation.  The best thing to do is to repair or replace the affected areas to restore your home to its former glory.

For a lot of people this sounds like more work than they want to attempt, but it's not as difficult as it may seem.  This week's post will give you some rotted wood repair tips to help you tackle it on your own.

Wood Replacement Patch

Depending on the extent and the size of the rot or damage to the wood, there are times when it's best to replace the damaged section with new wood.  When it comes to siding, it is generally pretty easy to find and buy a clapboard section that will match the profile of the existing clapboards of your house.

Remove The Damaged Section

My favorite power tool for cutting out and removing the affected spots is an oscillating saw.  These saws use a blade in an oscillating action to make plunge cuts into small areas, making them the perfect tool for this type of project.  A simple homeowner model can be purchased for under $50. 

Cut out a section of your siding where the patch needs to be made, being careful to only cut through the siding and not into the plywood sheeting underneath.  

Gently slide a small prybar or 5-in1 tool behind the piece to be removed from the bottom side and pry out to loosen the nails holding it in place.  

Once the siding and nails have been removed, take it into your local lumber store to match up the profile so you can purchase a section of clapboard long enough for your patch.  While you're there you can also have a custom paint match done so you can touch-up your patch.

Prepare Your Patch

Measure and cut your patch to fit.  If you don't have power tools you can purchase a plastic miter box and hand saw to do the job.  

Before you nail-in the patch, apply a coat of a good bare wood primer to all six sides -- front, back, top, bottom, and each end.  Also prime the ends of the siding you just cut on the house.

Once the primer has dried, you can even apply a couple of coats of paint on the siding before you install it.  

When it's ready to be installed, take a high quality acrylic latex caulking and apply a bead to the back of the siding patch near the edge that will be butting-up to the existing siding.  Also apply a bead to the back edge of the siding on the house where the patch will be butting-up to.  This is called "back-caulking" and will help to prevent any water from making it's way behind the wood.

Install The Patch

Slide the clapboard piece into place and nail it into the plywood sheeting with some 7d or 8d ring-shank nails.  Also nail down the loose edges of the existing siding that you cut.  Use a nailset to set the heads of the nails just below the surface of the wood.  

Fill your joints and nail holes with some wood filler, and apply your touch-up paint once the filler has dried.  If your touch-up painting spot is too obvious, you can try painting the entire length of the clapboard where you did your replacement.  As long as your color match is not too far off of the original you should be able to get by with not having to repaint a wall from corner to corner.

If you're replacing a section of trim the process is nearly identical to patching siding.  Just make sure that when you nail-in your new patch that it is being fastened into some solid wood framing.

Epoxy Wood Repair Patch

Some areas of trim and window sills are either too difficult to remove, or too difficult to find a replacement piece that will match your existing profile.  In this case your best option is an epoxy wood filler.  

Epoxy wood repair products are generally a two-component (part A & part B) that must be mixed together in order to harden.  Once they are mixed together you typically have a few minutes to mold and shape your compound before it dries and becomes unworkable.  Once it has set-up, epoxy dries harder than the wood -- yet remains flexible enough to expand and contract with it.  It can be nailed or screwed-into, can also be painted and sometimes even stained to match the surrounding color.

Prep The Area To Be Filled

Grind out the rotted wood with a trim router, die grinder, or rotary tool using a v-shaped grinding bit to get down to solid wood, because the epoxy will not stick to rotted wood.

Scrape off the paint down to the bare wood in the immediate surrounding area where your patch will be applied because the epoxy needs to bond to bare wood.

Tape off the surrounding areas (siding, trim, etc.) to keep from getting the epoxy on an area where you don't want it.

The wood must be dry before you can apply the epoxy.

Preserve & Prime

Drilling some holes in the wood surrounding the patch and injecting a borate wood preservative will help to prevent any further decay.

Brush on an epoxy primer to the exposed wood where the patch will be applied to help the epoxy adhere better.

Apply Your Filler

To form the epoxy compound to the profile of the surrounding wood you can make a "molding knife" using a plastic putty knife by transferring the profile onto the knife with a pencil then cutting it out using some tin snips or heavy-duty scissors.

Epoxy won't stick to most hard plastic, so using a piece of plexiglass as your mixing board and a plastic putty knife as your mixing tool, mix as much of the part A together with the part B that you can easily work with before it begins to set-up.

Using a putty knife, fill the entire cavity with the mixed compound.  You can use a scrap piece of wood as a straight edge where you need to make a flat surface, and your molding knife that you cut to form your profile to match the existing trim.

Once you're done applying the filler, allow it to dry per the manufacturer's instructions.  Then take some course-grit sandpaper to sand off any large edges, and smooth out the remaining patch with some med-fine grit sandpaper to get it ready for paint.

Now you can apply an acrylic primer to the epoxy and the bare wood; caulk all of your cracks, gaps, and joints; and put two coats of your paint match on the area.

If you want your patch to last, make sure you use a high-quality epoxy filler system.  I like the ones from Advanced Repair Technologies, System Three, or Abatron.  They are more expensive than the brands you can pick up at the local hardware store but they will hold up much better.

If you're located in the Greater Pittsburgh or Western Pennsylvania areas and would like some assistance with your wood repair or house painting project please give us a call at 724-898-2446, visit our 'Contact Us' page, or click on the button below to have us contact you.

photo by:  Random McRandomhead / CC BY 4.0