A quarter inch gap at a trim joint is all a winter storm needs. In a season that could bring up to three quarters more rain than usual (see Part 1), those small gaps can turn into real repair bills.
It helps to think of exterior paint as protection, not decoration. Its main job is keeping water out of the wood. Caulk does the same job at the seams. When either one fails, rain goes straight into the wood underneath.
Signs your paint has stopped protecting you
- Peeling or flaking, especially along the bottom edges of boards and on sills. This often means moisture is already behind the paint.
- Chalky paint. Run a fingertip across it. If color comes off, the paint is breaking down.
- Cracking in a scaly pattern, common on older homes with many layers of oil paint.
- Bare gray wood, even in small patches. Unprotected wood soaks up water quickly.
- Cracked or shrunken caulk around trim, windows, doors, vents and hose spigots.
What to fix first
If a full repaint isn’t in the budget before winter, start with the walls that take the most weather. On the Bay Area Peninsula, that’s usually the south and west sides.
- Seams and openings. Pull out failed caulk and reseal with a quality exterior sealant. It’s one of the best value repairs you can make.
- Bare and peeling wood. Scrape and sand to a solid edge, then prime the same day if the weather allows.
- Flat surfaces. Sills, trim tops and railing caps hold standing water, so they fail first.
- A full repaint of the worst sides during a dry week. The rest can wait until spring.
Why a dry week matters
Every paint and caulk manufacturer sets limits on moisture and temperature for good reason. Paint over damp wood and you trap the water underneath, which causes the very peeling you were trying to prevent.
We test the wood for moisture before we start, and we watch for a clear day or two afterward so everything can cure. That’s why fall is the sweet spot. Once winter settles in, good painting days are hard to find.
Which sealant, and which primer
You can spot a cheap caulk job from the sidewalk a year later. The beads have pulled away from one side of the joint, split down the middle, or gone hard and gray. Why? Usually it’s a painter’s acrylic caulk on a joint that moves. Wood trim swells in wet weather and shrinks in the sun, and an acrylic latex bead isn’t made to stretch that far, winter after winter.
On a trim joint that moves, the sealants worth paying for are polyurethane and the hybrid polymer sealants (sold as “hybrid” or “MS polymer”). They stretch, they grip wood, and they take paint. Pure silicone stretches and lasts too, but paint won’t stick to it, so it belongs where the joint stays unpainted. Siliconized acrylic is fine on joints that barely move. It’s the wrong tube for a long trim board on a south wall.
How the bead goes in matters as much as what’s in the tube. All of the old caulk comes out first. New sealant laid over cracked old caulk sticks to the old caulk and fails with it. A deep gap gets a foam backer rod pushed in before the sealant, which keeps the bead thin enough to stretch and stops it sticking to the back of the joint, where it would tear.
Bare redwood and cedar want an oil-based (alkyd) stain-blocking primer. The tannins in those woods bleed brown through many water-based primers, and the stain comes up through the topcoat once the wood gets wet. Any other bare wood gets a good exterior primer the same day it’s scraped, before dew and weather get to it.
Where caulk does harm
Some gaps on a house are there on purpose. The bottom edge of each lap siding board stays open, so water that gets behind the board can drain out. Caulk that line and the water stays in the wall. The same goes for the joint where a metal drip cap over a window or door meets the trim under it, and for the small weep holes along the bottom of many window frames. A crew that caulks every seam it can reach seals them all shut.
Caulk can’t fix everything
Caulk closes a gap. It can’t repair rotten wood behind it or make up for missing flashing. If the wood under a failed seam feels soft, it needs repair first. Part 3 shows you how to check. Caulking over rot hides the problem until it gets bigger.
Before the next storm
- From the ground, look at the caulk on the south and west walls first. A bead that has pulled away from one side, split down the middle or cracked into pieces has failed, and that joint is letting water in now.
- Press a fingernail into the beads you can reach. Good sealant gives and springs back. If it feels like hard plastic, it has stopped stretching and will crack the next time the weather swings.
- Look at the bottom edges of the lap siding, the drip caps over windows and the weep holes in the window frames. If someone caulked them shut, don’t add more. That caulk needs to come out.
- Note every joint that sits over soft wood. Those get carpentry first (Part 3), and the sealant goes on after.
Recaulking a few ground floor joints with a polyurethane or hybrid sealant is a fair homeowner job on a dry day. Anything you’d need a ladder for, a whole side of the house, and any joint over bare or soft wood is crew work. The cost of waiting is the wood behind the joint. A seam that needs a tube of sealant this fall can need a new piece of trim by spring.
How long does a fall touch up take?
On a typical Peninsula home, caulking and spot priming usually takes a few days, depending on the weather. A full exterior repaint takes longer. We’ll look at your home and give you a written estimate.
Will fresh paint stop every leak?
No, and we’d be wary of anyone who promises that. Paint and caulk cut down how much water reaches the wood. Leaks from flashing, roofing or windows have to be fixed where they start.
Learn more about our exterior painting, or request an estimate for a touch up before winter.