Cedar Shake Siding Problems: Curling, Splitting, Moss and What to Do
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The most common cedar shake siding problems are curling and cupping, splitting, moss and mildew, rusted or popped nails, and rot along the bottom courses. Nearly all of them trace back to moisture. Scattered damage can usually be fixed shake by shake, but widespread rot or brittle, split courses mean that wall is due for new siding.
Cedar shakes show up all over Ladue, Town and Country and Kirkwood, sometimes covering the whole house and sometimes just the gables and dormers. Early September is when a lot of owners finally walk around the place after a sticky summer and notice what changed. That's good timing. You want to find these problems before the first hard freeze, not after it.
Why do cedar shakes curl and cup?
Curling and cupping happen when the two faces of a shake dry at different rates. The sun-baked front dries and shrinks while the back stays damp against the wall, so the shake bends.
You'll see it worst on south and west walls, and on thinner sawn shingles more than thick hand-split shakes. A slight cup that still lies flat at the butt is mostly cosmetic. A shake that has curled enough to lift away from the course below is a different story, because now wind-driven rain gets behind it. Those need replacing.
What causes cedar shakes to split?
Age, weather and nailing. Old cedar loses its natural oils, gets brittle, and opens up along the grain, and Missouri's freeze-thaw cycles widen every check that holds water.
Nailing causes plenty of splits too. Nails driven too close to the edge, overdriven nails and a single nail through a very wide shake all set up cracks as the wood moves. A split by itself isn't a crisis. A split that lines up over the joint in the course below is, since it gives water a straight path to the sheathing.
How do you get rid of moss and mildew on cedar shakes?
Clean it gently with a cleaner made for wood siding, rinse with low pressure, and fix the conditions that let it grow. High pressure tears up cedar fibers and leaves a fuzzy surface that holds even more moisture.
Shade and humidity are the culprits. North walls, sides that face a tree line and any spot that gets hit by a sprinkler every morning will grow green or black film every summer. Trim back branches so sun and air reach the wall. Keep shrubs a couple of feet off the siding. Skip harsh chlorine bleach, which can blotch the wood's color and burn your plants. If moss is actually growing out of the shakes, the wood underneath has probably been wet for a long time, and it's worth probing with a screwdriver.
Why are the nails failing on my cedar siding?
Cedar contains natural extractives that react with plain steel. Uncoated or cheaply galvanized nails corrode, leave dark streaks running down the shakes and eventually lose their grip.
When that happens, shakes start to slip out of line or drop out entirely after a windy night. Black streaks below each nail head are the early warning. Any repair or re-siding should use stainless steel or hot-dipped galvanized fasteners, which is what cedar suppliers generally recommend. Reusing the same type of nail that failed just restarts the clock.
Why is the bottom row of shakes rotting?
The lowest courses take the most water. Rain splashes up off patios and mulch beds, snow piles against the wall, and soil or mulch that's built up over the years can end up touching the wood.
Check where roof lines meet a wall, too. A missing kick-out flashing or an overflowing gutter can dump water down the same few feet of siding during every storm, and the rot there tends to be worse than it looks. Fixing the bottom courses without fixing the water source is wasted money.
Should you repair or replace cedar shake siding?
Repair when the damage is scattered and the wood around it is still solid. Replace when the problems are everywhere on a wall, or when the sheathing behind the shakes has gotten wet and soft.
| What you're seeing | Usually repair | Usually replace |
|---|---|---|
| Curling or cupping | A handful of shakes | Most of a wall, lifting at the butts |
| Splits | Isolated cracks | Brittle shakes cracking as you touch them |
| Moss and mildew | Surface growth that cleans off | Soft, spongy wood under the growth |
| Nail failure | A few slipped shakes | Rust streaks and loose shakes across the house |
| Bottom-course rot | One or two courses near grade | Rot that continues into the sheathing |
Individual shakes can be swapped by cutting the old nails, sliding in a new piece and fastening it properly. If you're handy, This Old House covers the basic technique for replacing wood shingles. New cedar won't match the weathered color at first, which is one reason a lot of owners refinish after a repair round.
What are the finishing options for cedar shake siding?
You can let cedar weather naturally, stain it, paint it, or coat it. Each choice trades the look of the wood against how often you'll be back on a ladder.
- Left natural. Cedar turns silver-gray. It still needs regular cleaning, and bare wood is more exposed to the moisture problems above.
- Semi-transparent stain. Penetrates and keeps the grain visible. It needs recoating more often than any film finish.
- Solid stain. Hides more of the grain and lasts longer than semi-transparent, but it does wear and fade.
- Paint. Cedar tannins bleed through latex paint as brown stains, so a stain-blocking primer is a must. The shakes also have to be dry.
- Ceramic coating. A thick, flexible film over sound, repaired and primed wood. It covers the grain the way paint does, so it's for owners who want a painted look that holds up.
Rhino Shield is that last option. It's a ceramic elastomeric coating installed as a system: cleaning, repairs, caulk and sealing, primer, then multiple coats of ceramic topcoat at 8–10 mils, backed by a 25-year transferable warranty. Our page on coating cedar and wood siding covers how it's done on shakes. If you love the natural grain, a stain is honestly the better fit, and we'll say so.
Shake houses take patience because every course has to be checked and every bad piece dealt with before anything goes on. One customer was happy enough with the result to make an open offer:
"The crew proved to be even better than what I was told to expect. Their attention to detail is superior. I invite anyone to come to my place and look at their work."
— James B.
That kind of detail work is what keeps a coating on cedar for decades. You can browse finished homes in our gallery of applications.
Frequently Asked Questions
Can you paint cedar shake siding?
Yes, as long as the shakes are sound, clean and dry. Cedar needs a stain-blocking primer first, or tannins will bleed through as brown stains. Paint covers the grain, so if you want the wood look, stain is the better choice.
Can you replace individual cedar shakes?
Yes. The damaged shake is split out, the old nails are cut, and a new shake is slid into place and fastened with stainless or hot-dipped galvanized nails. The new piece will look lighter than its weathered neighbors until it ages or the wall is refinished.
Is it better to stain or paint cedar shakes?
Stain if you want to keep the grain and don't mind recoating more often. Paint or a ceramic coating if you'd rather have a solid color and longer intervals between refinishing. Either way, prep and dry wood matter more than the product.
When should cedar shake repairs be done in Missouri?
Fall is a good time, before freeze-thaw cycles get into open splits and loose shakes. Coatings and stains have minimum temperature limits on their labels, so it pays to book exterior work while the weather still cooperates.
Want a second opinion on your cedar shakes?
Rhino Shield of Missouri will walk your elevations, show you which shakes can be saved and which can't, and give you a straight answer on finishing options. Schedule a free estimate or call 314-239-7947.
