Repairing Wood Siding Before Paint
By Lemoon's Painting
Wood siding is repaired before it is painted, board by board. Split and soft boards are replaced, popped nails reset and rusted heads treated, failing paint scraped and feathered, and plywood edges sealed. Lap siding needs the right joints caulked and the drainage edges left open. New wood is primed on every face before it goes up, so the paint on top has sound wood under it.
On a stucco house the walls are one surface. On a wood-sided house they are hundreds of separate boards, each with its own nails, its own ends and its own history of sun and water. That is why wood siding takes more preparation than stucco, and why most of the time on a wood-sided repaint goes into the repairs before any paint is opened.
San Diego has more wood siding than people expect: older homes in National City and the city’s Craftsman neighborhoods, beach cottages near the water, ranch houses with wood on the gables, and plenty of stucco homes with a band of siding on one wall.
What kinds of wood siding are common here?
Most of what you see in San Diego County falls into four kinds. Each fails in its own way, so knowing which one is on your house tells you where to look before a repaint.
- Lap siding, horizontal boards that each overlap the one below. Clapboard, bevel and drop siding are all versions of it.
- Board and batten, wide vertical boards with narrow strips covering the joints.
- Plywood panel siding, often grooved vertically, common on homes and additions from the 1970s and 1980s.
- Shingles, on gables, bays and some coastal cottages.
What goes wrong with it?
At the bottom
The bottom boards on a wall take sprinkler spray, rain splash and soil contact. If the siding runs down close to the ground or into a planter, the bottom course is often soft. On plywood panel siding, the bottom edge of each sheet is end grain and tends to swell and delaminate, separating into layers.
At the ends and joints
Butt joints, where two lap boards meet end to end, and corners where siding meets trim are where water gets in. The caulk there may have cracked years ago.
At the nails
Nails back out as boards shrink and swell, leaving heads proud of the surface. Where paint has worn off them, steel nails rust and streak down the wall. Near the coast, in places like Imperial Beach, salt air makes that worse.
Across the face
Sun-facing walls get cracked, alligatored or peeling paint, and boards that cup, split or check along the grain. Shaded walls stay damp and grow mildew.
The repair, in order
Ebenezer’s exterior process starts with a power wash, then a full check of the stucco and wood before anything is masked or painted. On a wood-sided house the second step is the longest, and this is roughly how it goes.
- Wash gently. Wood siding is washed at pressures and distances that clean without raising the grain or driving water up behind the laps. It then has to dry through before repairs continue.
- Probe and mark. Every wall is walked and the boards are checked for soft spots, splits, loose ends and popped nails, with the problems marked.
- Replace what cannot be saved. Rotted, split or badly cupped boards are cut out and replaced with matching profiles. Delaminated plywood sections are cut back or replaced.
- Reset the fasteners. Popped nails are driven back or replaced with new fasteners into solid wood. Rusted heads are cleaned, and near the coast replaced with corrosion-resistant ones where needed.
- Scrape and feather. Loose and failing paint is removed, and the edges of the remaining paint are sanded smooth so they do not show through the new finish as ridges.
- Fill. Nail holes, small cracks and minor dents are filled with an exterior filler and sanded flush.
- Prime. Bare wood, new boards, filled spots and any rust-treated nail heads are primed. New boards are primed on all faces and ends before they go up, a step called back-priming.
- Caulk the right joints. Then the house is masked and painted.
Which joints should be caulked?
This is where well-meaning repairs go wrong. Siding is designed to shed water, and some gaps are there on purpose.
| Joint | Caulk it? | Why |
|---|---|---|
| Vertical butt joints between lap boards | Yes | Water enters through end grain |
| Where siding meets window and door trim | Yes | A common leak path |
| Corner boards and vertical trim | Yes | Same reason |
| The bottom edge of each lap board | No | It lets water behind the siding drain out |
| The bottom edge of plywood sheets | Seal the edge, do not bridge to the sill | The edge needs protection; the gap needs to drain |
| Under the bottom course, above the foundation | No | It is a drainage and ventilation gap |
A paintable exterior caulk is used, applied to clean, primed joints, and tooled so it bonds to both sides.
A word on older homes
Many wood-sided homes in National City and parts of San Diego were built before 1978, and the older layers of paint on them may contain lead. That affects how the old surface may be scraped and sanded. Ebenezer is EPA lead-safe (RRP) certified, so if your home is that age, raise it at the estimate and you will get a straight answer about what the preparation involves and how the old paint is contained.
Where the line is
Replacing siding boards, resetting fasteners and repairing the surface are part of preparing a house for paint. If the damage goes behind the siding, into the sheathing or the framing, that is structural work and belongs to a framing contractor. Ebenezer will tell you plainly when what he finds belongs to another trade. For rot on the windows and doors in particular, see rot in window sills and door jambs.
Ebenezer repairs the siding and then paints it. The repair work is part of his stucco, drywall and wood repair service.
A wood-sided house rewards the time spent on it. When the boards are sound and the joints are right, the paint lies flat and the house looks the way it was meant to. If yours is due, ask for a free estimate and Ebenezer will walk each wall with you and show you, board by board, what it needs.
Common questions
Should the gaps under each row of lap siding be caulked?
No. The bottom edge of each lap board is meant to let water that gets behind the siding drain out. Caulking it shut traps moisture and leads to rot and peeling. The joints that are sealed are vertical butt joints between boards and the joints where siding meets trim, windows and doors.
Can a split siding board be repaired, or does it need replacing?
A clean split in an otherwise sound board can often be glued and fastened closed, then filled and painted. A board that is split along its length, soft, cupped badly or rotted at the end is usually better replaced. Ebenezer looks at each board during the repair check and tells you which he recommends.
Why are there rust stains running down my siding?
Usually from nail heads. Ordinary steel nails rust where paint has worn off them, and near the coast salt air speeds that up. The fix is to clean the head back, reset or replace the nail with a corrosion-resistant one where needed, spot-prime the head with a primer suited to metal and wood, and fill before painting.
My house is old. Does that change how the siding is prepared?
It can. Homes built before 1978 may have lead in the older layers of paint, and that changes how the old surface may be scraped and sanded. Ebenezer is EPA lead-safe (RRP) certified, so ask about it at the estimate and you will get a straight answer about what preparation your siding needs.