Replacing a Single Broken Picket Without Damaging the Rest
Match the board before pulling anything
Cedar fence boards come in more variations than people expect. Widths run at five and a half or seven and a quarter inches, thicknesses at five eighths or three quarters, and tops are cut square, dog eared or pointed. Measure the damaged board in place, photograph the top cut, and buy its replacement first, unless you have somewhere to hold the old one up for comparison.
Getting the old one out
Each board is fixed to two or three horizontal rails. Work a flat bar behind it at every rail and lever slowly against a block of scrap so the bar never crushes the boards either side. Rushing this splits the neighbours, and a one board job becomes a four board job. Where nail heads have already pulled through the face, cut the shanks behind the board with a reciprocating blade rather than fighting them.
Fasteners
Ring shank stainless or hot dipped galvanised nails grip cedar and leave it clean. Electroplated fasteners streak the face black within a season here, and those streaks never come off. Two fixings per rail, set in three quarters of an inch from the edge, is plenty. Driving them right at the edge guarantees a split on the first hot dry week.
Leave a gap
Cedar arrives wetter than it will stay. A board butted tight against its neighbours in spring will cup or push once summer dries it out. An eighth of an inch of space either side is the normal allowance and it costs nothing to leave. Hold a scrap of ply or a couple of stacked washers against the last board as a spacer while you nail, and the spacing stays honest along the whole run.
Colour
Fresh timber beside fifteen year old grey cedar looks precisely like what it is, and nothing hides that immediately. Left alone it weathers close over one or two seasons. Where the mismatch cannot be lived with, a solid colour product applied across the entire run is the only fix that works, since treating one board on its own makes it stand out more.
Check the rail behind the gap
A board that cracked without hail or an impact usually had help. Push on the rail behind the opening while it is exposed. If the rail flexes, or if a fixing came out with wet fibres stuck to it, the rail is the real fault and the next board along will go the same way shortly. A rail that has softened where it meets the post can often be scabbed with a short length of treated timber bolted through, which buys several years without touching the rest of the run.