How to Re-Caulk Teak Deck Seams (and When the Deck Is Beyond Saving)

Walk the whole deck in good light, then again right after rain or a washdown, when bad seams stay dark longer. Signs of failed seams:

• Caulk pulled away from one or both plank edges, leaving a hairline gap
• Cracks, splits or chunks missing from the caulk
• Caulk that has gone hard, shrunk below the deck surface, or lifted above it
• Black mildew growing in gaps along the seams
• Drips, stains or a musty smell below, under that part of the deck

Mark every bad seam with a bit of tape so you can plan the work.

Two quick checks from Teakdecking Systems (TDS): press a fingernail into the caulk. Healthy caulk is firm but takes a slight mark; if it leaves no mark at all and feels brittle, it has hardened past the point where it can flex with the wood. And if the cabin gets wet after rain or a washdown and you can't blame a fitting or hatch, suspect the seams. TDS says there is no fixed replacement age: condition decides. It gives roughly 10 to 15 years for its own caulk in a temperate climate and less in strong sun or heavy use (a maker's figure, not a rule).

Recaulking only makes sense if there is enough wood left. Each sanding and every harsh cleaning takes a little off the top. Warning signs that the deck may be past saving:

• The wooden plugs (bungs) over the screws are paper-thin, missing, or screw heads show through
• The seams are so shallow there is barely room for a bead of caulk
• Planks are loose, cracked, or lift when you step on them
• The deck underneath is soft, or leaks are coming from many places at once

If you see these, get an opinion from a teak deck specialist or surveyor before buying caulk. Replacement, a partial refit or a synthetic deck may make more sense. If you look at synthetic (PVC) "teak," BoatUS notes the strips are usually built into panels from your templates, warranties run from about five to 20 years depending on brand and installer, and the better materials have the color and the caulk lines running all the way through so scuffs can be sanded out. They're glued down to stay; one maker told BoatUS it's easier to buy a new boat than to remove PVC decking.

Pick a short, out-of-the-way seam and do steps 5 through 12 on it before committing to the whole deck. You will learn how hard the old caulk is to remove, how your caulk handles, and how long it really takes to cure in your weather.

Use a caulk sold specifically for teak deck seams, and use the cleaner, primer and tape that its maker specifies. Practical Sailor's test of teak deck caulks covered polysulfide, polyether, silyl-modified polymer and silicone-based products, and found their prep steps differ:

• Polysulfide such as BoatLIFE Life-Calk: BoatLIFE sells it for teak decks and says it resists teak oils and fuel. Practical Sailor notes it needs a primer on oily woods like teak and takes days to become tack-free. BoatLIFE also makes a teak deck sealant that, per Practical Sailor, skips the primer.
• One-part teak seam caulks such as Teakdecking Systems SIS 440: TDS says it needs no primer on properly prepared seam walls.
• Other systems use a dedicated cleaner and primer with a waiting window before caulking.

Practical Sailor also warns that silicone-based caulks can cause "fisheye" in varnish or paint nearby if surfaces are not cleaned well. Do not mix brands or types in the same seam, and do not put new caulk over old.

Run a sharp utility knife down both sides of the seam, right against the wood, to cut the caulk free from the plank edges. Then pull the strip out with a reefing hook. Work slowly and keep the blade and hook vertical so you do not chip or round over the plank edges or make the seam wider. Some pros use a router with a guide on big jobs, but one slip cuts into the planks; leave power tools to people who have used them on a deck before. Watch for screws and plugs as you go.

New caulk sticks to clean wood, not to leftover caulk. Scrape and sand both side walls of the seam until there is no old caulk or gray, dead wood left; TDS uses a seam sander and then a solvent wipe. A strip of sandpaper wrapped around a thin stick works for a few seams. Vacuum out all the dust and debris, including from the bottom of the seam. Look at the depth: you need room for a proper bead of caulk.

Bond breaker tape goes on the bottom of the seam so the caulk sticks only to the two side walls. TDS explains why: if caulk bonds to the bottom too, it is pulled three ways every time the planks shrink, and it tears or rips away from the wood. Press the tape flat to the bottom. TDS warns not to use it in shallow seams, where the caulk nozzle tends to lift the tape and push it against the walls, which ruins the bond. Use the tape your caulk maker recommends.

Teak is oily, and that oil keeps caulk from sticking. Right before you caulk each section, wipe the seam walls with acetone or the cleaner your caulk maker names, using clean rags and changing them often (TDS recommends acetone on a fresh cloth). If your caulk requires primer on teak, brush it on the seam walls only and caulk within the time window on the label. If you miss the window, check the label for what to do next.

Cut the nozzle to match the seam width. Push the tip down into the seam and lay the caulk from the bottom up, pulling the gun along in one steady motion so the bead rises slightly above the deck. Stopping and starting or changing direction traps air bubbles. Overfill a little: TDS suggests buying 20 to 25 percent more caulk than the seam volume because you leave a small crown and lose some when tooling.

Right after filling a section, drag a flexible putty knife along the seam at a low angle, pressing the caulk down into the seam to push out air and make it bond to both walls. Leave it slightly proud of the wood; it will be sanded flush later. Scrape most of the smears off the planks now, while the caulk is soft. On a small repair next to varnish or gelcoat, painter's tape along both edges keeps the mess off; pull it before the caulk skins over.

Cure times vary a lot: Practical Sailor's test found products that were tack-free in minutes and others that took days, with full cure taking a week or more. Keep foot traffic and washdowns off the new seams for the time on your label, and protect them from rain if the label says to. Sanding too early tears soft caulk out of the seam.

When the label says the caulk can be sanded, take the crown down level with the planks using a sanding block or a sander with a dust bag, working along the grain. Sand only until the caulk is flush. Every pass also removes teak, and the planks never grow back. Vacuum and rinse with fresh water.

TDS lists the habits that shorten deck and seam life: acid-based two-part cleaners, bleach, harsh scrub pads and high-pressure washing. They say pressure washing opens the grain and weakens the bond between caulk and teak. Rinse with fresh water often and use a gentle teak cleaner (see the teak care guide).

TDS recommends looking over the seams once or twice a year. Look for the same signs as in step 1 and fix small failures right away, before water gets under the planks. Record which caulk you used, the date and which seams you redid in BoatMend, so the next repair uses a compatible product.