How to Repair Cedar Siding: Splits, Rot and Woodpecker Holes

Cedar siding repair depends on how deep the damage goes: cracks and small holes get filled, soft wood gets hardened or cut out, and rot gets a new board. Repairs usually fail on small details, like bare steel nails that leave black streaks or pure silicone caulk that the Western Red Cedar Lumber Association says does not work well on cedar. This guide covers each damage type, plus the right nails, caulk and finish.

Match The Repair To The Damage

Decide what you are dealing with before you buy anything. The same grey board can be harmless weathering or hidden decay, and the repair for each is different.

What you see	What it means	Repair	Common mistake
Grey, rough, firm wood	Weathering only	Clean, let dry, refinish	Treating it as rot and cutting out good boards
Hairline split or crack, wood firm	Surface damage	Clean, fill, sand, prime, paint	Caulking a crack instead of filling it
Soft but not crumbly spot	Early decay	Harden or consolidate, then fill	Filling straight over soft wood
Spongy or crumbling all the way through	Rot	Cut out and replace the board	Patching over it and trapping moisture
Round holes in spring	Woodpecker, possibly hunting insects	Cover with metal, add a deterrent, check for insects	Filling holes while the bird keeps drilling
Black or reddish streaks at nail heads	Iron stain from the fasteners	Replace the nails, then clean the stain	Scrubbing with steel wool

The awl test settles most arguments. Push an awl or screwdriver into the board: sound cedar resists the point even when it looks tired, while decayed wood lets it sink in. Check the places where water collects, such as butt joints, bottom courses, and boards that meet trim, roofs, decks or grade. The cedar association recommends at least 2 inches of clearance between siding and a roof or deck, and at least 6 inches above grade, so a board closer than that is a repeat-damage risk even after you fix it.

Before You Sand Or Scrape: Lead Paint In Pre-1978 Homes

If the house was built before 1978, old paint on the siding may contain lead. The EPA says to assume lead is present when the age of the home is unknown, and it recommends hiring a certified lead inspector or risk assessor rather than relying on home test kits, which are not always accurate. Its DIY lead-safe guidance also covers containment, HEPA cleanup, and protective gear.

• Wet scrape painted areas instead of dry scraping, and avoid sanding painted surfaces where you can. If you must sand, use a sander with a vacuum attachment connected to a HEPA vacuum, or a wet-sanding sponge.
• Do not use open-flame torches, and do not run a heat gun hotter than 1100 degrees F, because lead paint can give off toxic fumes above that.
• Paid contractors working on pre-1978 homes must be lead-safe certified under the EPA rule. The rule does not cover homeowners working on their own homes, which makes your own care more important, not less.

Most of this page is about bare cedar, but if the boards are painted and the house is old, settle the lead question first. If you decide to hire out the work, the section on when to call a pro further down covers what to look for.

Clean The Area First, And Keep Steel Wool Away

Dirt and mildew hide damage and stop fillers and finishes from bonding. The cedar association says a periodic wash with a mild non-phosphate detergent usually restores the surface, and that mildew can be confirmed with a household bleach test: mildew discoloration disappears within 15 to 30 seconds. Remove it with oxygen bleach or a commercial mildew remover, and rinse well. Our guide to the best way to clean cedar siding walks through the full wash.

Two cleaning habits cause repairs to fail. First, never use steel wool or wire brushes on cedar, because metal deposits react with chemicals in the wood and leave dark blue-black stains, the same chemistry as nail stains. Second, do not cover dirt with fresh finish: the association warns that sealed-in dirt and mildew keep growing under the coating. Let the wood dry completely before you fill or finish. Its finishing guidance puts the limit at 20 percent moisture content or lower before applying a finish.

Fix Splits, Cracks And Small Holes

A split that has not gone soft is a filler job. Filler restores the surface and sheds water; it does not add strength, so it belongs only on boards that pass the awl test.

1. Remove loose splinters and old flaking paint, then clean the crack with a damp cloth. PC Products, which makes an epoxy filler, suggests wiping the surface with denatured alcohol or acetone to remove contamination before filling.
2. Mix the two-part filler in small batches. The listed sanding time for our pick is as little as 15 minutes, which also tells you how little working time you have.
3. Press the filler into the crack with a putty knife, slightly proud of the surface, so there is something to sand back.
4. Sand flush once cured, working with the grain, then prime and paint. PC Products warns that semi-transparent and transparent stains rarely match the surrounding wood on its epoxy filler, so plan on a solid finish over a filled repair.
5. Check the temperature range on your product. PC Products says its epoxy needs extra time below 50 degrees F and is not recommended at or below freezing, so repair in mild weather.

For soft but not crumbly wood, a hardener or consolidant goes in first, then the filler. Our guides to repairing wood rot with epoxy and replacing rotted exterior wood cover the products and the soak-in step in more detail, and our exterior wood filler comparison compares fillers by type.

Woodpecker And Insect Holes

Round holes that appear in spring are usually a bird, not a rot problem. Colorado State University Extension says woodpeckers drill cedar and other siding to excavate nests, to hunt insects, and to drum for mating and territory, that damage peaks in spring and typically ends by July 1, and that cedar siding is particularly vulnerable. Because they sometimes drill after insects, look inside a hole before closing it. If you suspect carpenter bees, see our guide on keeping carpenter bees out of wood.

• Cover holes with aluminum flashing, tin can tops or metal sheathing, painted to match the siding, as the extension service suggests.
• Add a deterrent while the bird is active. The extension lists 7.5-inch mirrors placed flat against the damaged area, hawk silhouette mobiles, reflective pinwheels and black plastic strips.
• Do not trap or harm the bird. Woodpeckers are protected under federal law and lethal control requires a federal permit from the U.S. Fish and Wildlife Service.

Filling a hole with filler is fine once the bird has stopped, but a patch alone will be drilled again if the cause remains.

Replace A Rotted Board

A board that crumbles or lets an awl sink in deeply cannot be saved with filler. Cutting it out is more work, but it removes the problem instead of hiding it.

1. Pry the damaged board free carefully, starting near a joint, so neighboring boards do not crack. Remove leftover nails.
2. Look at what is behind it. If the housewrap or the sheathing is wet or soft, fix that first, because a new board over wet backing rots again.
3. Cut a replacement from matching cedar in the same profile and thickness. Pre-prime the back, the face edges and every cut end. The cedar association says to always prime or stain end cuts, and recommends an alkyd oil primer on end grain exposed by cuts.
4. Fasten with the right nail, described below, and nail each board on its own so it can move.
5. Leave the joint gap the manufacturer specifies, then seal joints with a suitable exterior caulk, covered in the next section.

Hot-dip galvanized (ASTM A153), aluminum or stainless steel nails are all corrosion-resistant on cedar, with stainless No. 304 for general use and No. 316 near the coast. Source: Western Red Cedar Lumber Association

The association also recommends splitless siding nails with blunt points and ring or spiral shanks for holding power, with at least 1-1/4 inches of penetration through sheathing and insulation. It does not recommend electroplated or mechanically galvanized fasteners, and it says to avoid copper nails, which react with cedar.

Siding type	Thickness	Nail size per the cedar association
Bevel	1/2 inch or less	2 inch (6d)
Bevel	7/8 inch and up	3 inch (10d)
Board and tongue-and-groove	5/8 to 3/4 inch	2 inch (6d)
Battens	3/4 inch	3 inch (10d)

Space nails according to the siding pattern and do not nail overlapping boards together, since that restricts movement and encourages splitting. This guide covers lap and board siding. For shingles and shakes, our pages on fixing cedar shake siding and replacing a single cedar shingle are the better match.

Caulk: What Goes Where

Caulk seals joints and gaps, not damaged wood. Use it where boards meet trim, windows and doors, and use filler for damage inside a board. The cedar association lists high-performance acrylic-latex, acrylic, acrylic-silicone, polyurethane, polysulfide and terpolymer rubber sealants as suitable, and says pure silicone and clear caulks do not work well on cedar.

Material	Use it for	Do not use it for
Two-part filler or epoxy	Cracks, holes and chips inside a board	Gaps between boards that move
Paintable exterior caulk	Joints at trim, corners and board ends	Filling holes in damaged wood
Pure silicone	Nothing on cedar siding	Any joint you plan to paint
Metal flashing	Woodpecker holes	Structural rot

The association also points out that caulk is not a permanent fix and needs regular maintenance, and it should not seal places where moisture has to escape, such as under windows. Inspect caulked joints every year and renew them as they crack.

Refinish So The Repair Lasts

A repair that is left bare or finished with the wrong product shows up and fails early. The cedar association says solid stains and paint give the best service life over stain-blocking primers, semi-transparent stains typically last 2 to 4 years with wide overhangs, and transparent stains have the shortest life, around a year. It also advises two coats of penetrating oil-based stain on textured cedar and says one coat of solid stain is only marginally adequate, so use primer plus topcoat. Our pages on sealing cedar siding, stain colors and long-term maintenance go deeper on finishing.

• Match the existing finish type: latex over latex, oil over oil. The association says never put an oil-based product over latex.
• Make sure the wood is dry to the touch before applying anything.
• Expect some brown bleed from the wood. The association says extractive bleeding is caused by moisture, mild staining washes away over weeks, and persistent stains may respond to oxalic acid solutions or commercial cleaners that are handled carefully.
• If you are restoring a whole wall of weathered boards instead of repairing a few, see our guide to restoring weathered cedar siding.

When To Call A Pro

• The rot reaches the sheathing or framing behind the siding, not just the boards.
• Several boards across a wall are affected, which usually points to a water source you have not found.
• The house is a pre-1978 home with painted siding and you would rather not manage lead-safe containment yourself.
• The work is high enough that you would be on a ladder above one story. Ladder safety is your call to make carefully, and hiring out is a reasonable answer.

Frequently Asked Questions

What Do You Use To Patch Cedar Siding?

For cracks and small holes in sound boards, use an exterior-rated two-part filler or epoxy, sand it flush, then prime and paint. For gaps where boards meet trim or each other, use a flexible exterior caulk instead. Soft or crumbling wood should be hardened first or, if it is crumbly all the way through, cut out and replaced.

Can You Use Silicone Caulk On Cedar Siding?

Pure silicone is a poor choice. The Western Red Cedar Lumber Association says pure silicone and clear caulks do not work well on cedar and are not recommended. It lists acrylic-latex, acrylic-silicone, polyurethane, polysulfide and similar paintable sealants instead.

Why Are There Black Streaks Around The Nails In My Cedar Siding?

Iron from the nails reacts with natural extractives in the cedar and leaves blue-black stains. The cedar association recommends only hot-dip galvanized, aluminum or stainless steel fasteners. Replacing the offending nails is the fix, because cleaning the stain without removing the iron source lets it come back.

How Do You Tell Weathering From Rot On Cedar Siding?

Press an awl or screwdriver into the board. Grey, rough cedar that resists the point is only weathered and needs cleaning and refinishing. Wood that feels spongy, crumbles, or lets the tool sink in easily has decay and needs hardening or replacement, whatever its color.

How Do You Fix Woodpecker Holes In Cedar Siding?

Cover the holes with aluminum flashing or similar metal sheathing painted to match the siding, as Colorado State University Extension suggests, and add a deterrent such as mirrors or hawk silhouettes. Woodpeckers are federally protected, so lethal control needs a federal permit.

Conclusion

Good cedar siding repair starts with sorting weathering from rot, then matching the repair to the damage: fill what is firm, harden what is borderline, replace what is gone. Use hot-dip galvanized or stainless nails, avoid pure silicone, prime every cut end, and finish with a product that matches what is already on the wall.