By Andina Foster,

Based on 12 years experience maintaining a 71 foot by 20 foot beam classic BoatPict.jpg - 12711 Bytesyacht with teak decks, built in 1966. This is empirical advise which should be modified where circumstances dictate and the author accepts no responsibility for nuthin.

The techniques for caulking teak decks are entirely different for new construction as opposed to maintaining a teak deck. This article refers to the latter.

Background & Theory
No Nos Things you never do to a teak deck.
Do Doos Things you should always do to a teak deck.
Tools List of tools & equipment you will need.
Supplies List of supplies and materials you will need.
Stage 1 Removing the old caulking.
Stage 2 Applying the masking tape.
Stage 3 Mixing the caulking compound.
Stage 4 Applying the caulking.
Stage 5 Removing the masking tape.


There are two basic types of teak decks. Modern ones are decorative teak laid over a sub deck of fiberglass or other construction which forms the structural support. The traditional decks are planks of teak laid over a frame where the teak itself forms the structure of the deck. Re-caulking of a decorative teak deck is only necessary when there is physical deterioration of the caulking to restore appearance and to stop water damage due to trapped moisture under the wood. Re-caulking of structural teak decks is a continuous process which commences about 10 minutes after the deck was first laid and continues until the boat is abandoned. Teak should never be laid over steel plate decks. Inevitably the teak seams will leak and the trapped water will rust the steel causing it to swell and lift the teak off. On steel boats where deck webbing creates some areas where teak has to be laid over flat steel, the webbing should have as many holes cut in it as possible to allow water to escape and air to dry any cavities.

Traditional teak planks have cotton pounded into the seams when they are laid. This is quite an art and there are very few artisans left who can do it properly. The cotton serves a number of purposes. First it tightens the crack to minimize movement, and make the deck more contiguous. It seals the bottom of the crack so polysulfide (caulking) will not run through later. It is under high compression so it expands and moves with the teak when it moves. It absorbs water from a leak and swells to stop the leak. With modern polysulfide caulking compound I have found that pounding cotton into a seam while making repairs makes little difference and is not worth the trouble. If you have a crack that goes right through from a seam, by all means pound some in to stop the polysulfide running through (or tape it underneath with duct tape if there is access).

A groove is cut out of the top of each of the cracks between the planks to provide a cavity for the caulking compound. There are many schools of thought on the best shape of the groove cross section (width, depth, round, Vee, or rectangular) but here is my analysis. Teak deck caulking fails nearly always due to the caulking pulling away from the sides of the groove when the teak shrinks (dries out) and/or moves while underway. This would suggest a number of basic requirements:-

OK what are the practical limits?

Next a list of No Nos - absolutely forbidden things you should not even consider doing (and why).

List of Doos, things you should do to help maintain your deck (and why).

OK the deck leaks and you need to re-caulk, here we go.

List of tools you will need:-

Supplies you will need.

Supplies and tools you DON'T need.

STAGE 1, Removing the old caulking.

Timing the job with the weather is important. Caulking can only be done when the deck is thoroughly dry and has been thoroughly dry for at least a week, because that is how long it takes for the wood to shrink. If you calk when the deck is at maximum shrink, then all it can do is expand and press on the caulking. If there is any moisture and the teak is not at maximum shrink when you caulk, then when it eventually dries out, and it will, the caulking will be in tension and you risk it pulling off the sides of the groove. Ideal conditions are not always possible but at least you know what is ideal.

Go to stage 3 and read the first paragraph then come back here - there is something you need to have prepared 6 hours in advance.

Keep in mind as you establish the area you are going to re-caulk that you have to be able to reach every part of the work area from outside the perimeter later on when you are placing and smoothing the polysulfide. Don't "paint yourself into a corner". If the deck has some slope in the direction of the seams, you need to do shorter runs so that the polysulfide does not run down to the lowest spot and cause a problem (or use the thicker grade of polysulfide but it is much harder to work). You might need to do every alternate 1 or 2 foot strip, then come back next time and do the pieces in between, using some of the old caulking to make a dam. Identify the areas you intend to caulk and mark with a piece of chalk, or masking tape.

Don't tackle too large an area. Each quart does an area about 2 feet by 10 feet (2" planks) but this varies considerably with groove width and depth. There are various formulas around for calculating total running feet but they are only a very rough guide due to all the variables. If you choose too small an area, you will have caulking compound left over at $25 qt. If you choose too large an area, even though you plan to mix up multiple quarts, you may not be able to do it all in one session. Leaving the masking tape on deck overnight usually results in some of it lifting off due to moisture. Murphy's law dictates that no matter what area you do, it will require just a little bit more caulking compound than you mixed up. So leave the remainder for the next sesstion or touch up later with some 3M 101.

Use the scraping tool to dig into a good section and draw towards the loose (leaking) caulk to be removed. Separate each side then pull it out. Don't throw it overboard - it will never degrade - drop it in one of those pails. Needless to say, be very careful not to slip out of the groove and scrape a nasty scratch in the teak. Don't panic if you do - just don't look at it. After about 3 months it will go away with swelling from moisture, fading from sunlight and erosion of the scratch edges.

Use the scraping tool to clean any loose stuff from the groove edges and bottom. Use the vacuum frequently to clean it out. If there are any soft spots in the teak, they have to come out. Use the Dremel tool if necessary. The groove will no longer be straight edged but the caulk will fill in the void. Don't be tempted because of cosmetics, to leave a piece of spongy teak. It will only collect water and get worse. Yes teak does rot, believe it or not. I think some sections of the wood are more prone to rot than others depending on where they were in the tree.

If the groove runs up to, or under a deck fixture, use the Dremel tool to dig out right up to the fixture and under-cut the fixture as far as possible.

Inspect the groove. If the width is too narrow, or the depth too shallow, or the sides soft and fragile - then you need to re-groove (see the earlier discussion on optimum width and depth). This is where you use the mini skill saw. Do it by eye. Set the depth to the desired groove depth. Run down one side, then turn around and go back up the other side, removing a little teak from the sides to provide a good foundation for the new caulking. If you are making it deeper you may need to do some runs in the center to remove the remaining material. Where you can't get in because of deck fixtures and for those seams on the end grain, use the Dremel tool.

In particularly bad spots, where you really should replace a piece of plank but don't want to tackle it, I have used an epoxy paste to repair the wood. It will only be partially successful because the epoxy will eventually crack off the teak as it moves, the epoxy deteriorates in sunlight, and the rot will continue despite all attempts at repair. I have had best luck with the West System epoxy thickened with teak sanding dust or #405 filleting blend.

Stage 2, Masking.

This is pretty straightforward. You need to be fairly precise but not too finicky. If a little polysulfide ends up on the top of the teak, it will be so thin that after it sets it can be rolled off. If the tape sticks over the groove in a spot, the polysulfide will run under it. Use a razor blade to trim around the detail spots. Roll or rub the edges down to make sure they are stuck well. Avoid pieces of tape turning the corner over the edge and projecting down into the groove.

There must be at least 2 inches of masked area each side of any place to be filled. If the planks are 2" wide and you have adjacent grooves to be caulked that works out fine, if not you need to put an extra piece of tape to make up the width. Don't forget to tape the edges of deck fixtures.

When masking is completed, take some more masking tape and tape it around outside the perimeter. Later on, after you pull up the tape but the caulking is still wet, it will be very difficult to know what is wet and what is not so the perimeter outlines will help you avoid stepping on them until they set.

Stage 3, Preparing the Polysulfide.

The manufacturer(s) claim a 3 hour work period once the polysulfide is mixed. Don't believe them. The trick is to put the (unopened) polysulfide cans with their hardener in the refrigerator at least 6 hours before use so they are at about 40 degrees when you go to mix them. Even then, you will only get about an hour of good working time. One good reason for doing a quart at a time instead of struggling to use up a gallon mix before it sets up. Return to stage 1

Do this work on the dock if you can, it is very dangerous as any spill will be a total catastrophe and a dock disaster is better than a boat disaster. Take that cardboard box and cut an opening in it to make a work area. Leave about a 12 inch wall on the front and angle up 45 degrees on both sides to the top. Do all the mixing in the box.

Put on rubber gloves right now. Don't be tempted to do any of this without them, the moment that black stuff sees any exposed skin it will jump up to 3 feet and get on you before you even see it. As soon as a glove gets icky, peel it off, drop it in a pail and put on a fresh one.

Have tongue depressors handy for scraping. Have lots of paper towels ready. Turn the can of polysulfide upside down and remove the bottom with the can opener. Trying to work through the paint can type lid and to pour from it is impossible. They leave about 3 inches of space in the can to let you mix without spilling. Open the hardner can. Lately they have been a plastic screw-off lid which is easy. Some may still come in a mini paint can so again, open the bottom with the can opener, there is no way you can scrape the contents out from under the lip if you remove the normal lid.

Scrape out all the hardener into the can of polysulfide. Never try to do a partial mix, always mix the whole quart with all the hardener, even if you only have a small job to do. It would help if they made the hardener a white color so you could see how well the mixing is going but with the colors nearly identical you have to judge when mixing is done. Use a paint stirrer stick (never a power tool) and stir it in. Use plenty of up/down motion to work it through and repeatedly scrape the bottom corners. Avoid trapping air bubbles in the mix. We need to get the hardener dispersed so throughly that every molecule of polysulfide is in contact with a molecule of hardener so there are no soft gooey spots which don't set up. It takes at least 5 minutes of dedicated stirring - you can't over do it but you sure can have a mess later if you didn't stir enough.

Squeeze the can opening at one side to make a pour spout. Pour the mix down the center of the cartridges so it builds up from the bottom without trapping any air. You still have the gloves on don't you? And work in the box where the drips won't do any damage. Wiggle the plunger in until all air has been allowed to escape. Air bubbles and pockets cause two problems, one is voids in the caulk seam which either stay there of have to be filled if they rise and pop, the other is they compress under pressure in the caulking gun and expand every time you try to stop caulking forcing liquid to continue to come out when you least expect it.

Put one of the cartridges in the freezer to help stop it setting up while you use the other. Keep them out of the sun and as cool as possible.

Stage 4, Caulking (finally)

If you haven't already read section 5, read it before you start caulking so you are familiar with timing.

Fresh pair of gloves on. Have a stack of plastic spreaders handy. Lots of paper towels handy. Extra gloves handy. Pail for dirty towels, etc. Lock the cat below deck. Unplug the telephone. Hat and sunglasses on before the gloves get dirty.

Place cartridge in the gun. BEFORE trimming the end and piercing the foil seal, pump the trigger on the gun and pressurize the plunger quite hard. This will force out any air bubbles trapped between the plunger and the liquid. Air bubbles are a nuisance because they continue to expand after you release the pressure and cause the cartridge to dribble all over the place.

RELEASE the pressure and trim off the end of the nozzle to leave a 45 degree hole about 3/16 inch diameter. Use a long nail or awl to prick the foil seal inside. Squeeze the stuff into the grooves. Work about 2 or 3 feet at a time, then squeegee the surface flush as necessary with the spreaders. As they get icky, discard them in an appropriate container for recovery later and take a fresh one. It is OK to scrape up the excess from one area and trowel it into an area that didn't fill. Check back as you go, for bubbles that need pricking and perhaps re-filling. If an area has a slope and it is tending to run down leaving one area low as it runs out the other end, come back to it later as it starts to thicken. If necessary, just let it set partially full, you can repair it during a subsequent caulking session or even use some of the 3M 101 to patch it.

Stage 5, Removing the masking tape.

Removing the tape is much more critical than it would first appear. If you remove it too early, it will pull stringy bits off the groove which will fall onto the deck, and mess up the teak and nice caulk surface. If you remove it too late, the tape will be embedded in the caulk and become a mess to be trimmed with a razor later when it is fully set.

Have the pail(s) ready to catch the icky tape which will be flapping in the breeze and threatening to get over the white salon top.

Under normal circumstances you need to remove the tape one hour after you did the caulking. Normal circumstances mean a mild temperature (70 degrees F) with no sun on it. It will then take about another two or three hours before the surface is no longer tacky and about 24 hours before it is safe to walk on.

BUT every 10 degrees hotter, halves the time frame and every 10 degrees colder doubles it. So if you are in the noonday sun with no shade, and the deck is running 120 degrees, that is 50 degrees hotter so you halve the 60 minutes 5 times. So one hour to removing the tape becomes 30, 15, 7.5, 3.75, 1.875 or 1 minute and 52 seconds. This is an extreme case but I have done caulking under these conditions and about the time you squeegee one section flat, it is time to pull up the tape. It is fully set and ready to walk on in an hour. The opposite is the case if it is colder. You should not try caulking below 50 degrees and the time to removing the tape would be 4 hours with maybe 2 days before it is safe to walk on. In all cases, a little testing is a good idea to time tape removal.


Please send me your comments, criticism, encouragements and particularly any ticks you learn that I should include in this guide for others. When I do my next job I will remember to take pictures and add them to this work.

Andina Foster,