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Starting with bare wood, assuming you have removed any old finish and sanded your teak down to a uniform color, you must first clean the surface by wiping it with a rag saturated in denatured alcohol. Then go over the surface with a tack cloth to remove anything the alcohol rag may have missed. This will remove any residual sanding dust and surface oils.
Mask the surrounding Gelcoat or painted areas by carefully applying masking tape. The only masking tape acceptable for use on a boat is the high-quality, more expensive blue variety sold at painting supply stores and better home-improvement stores or at the marine store. Don’t even think about using the cheap brown kind. The blue tape will come off clean even after days of baking in the sun or intermittent rain showers.
The first coat of varnish must be thinned fifty percent with mineral spirits or whatever the varnish manufacturer recommends. This makes a sealer coat that will penetrate deeply into the teak wood and combine with the natural oils already present. Apply this and all subsequent coats with a fine natural bristle brush that's been prepared by flexing several times to remove any loose bristles (I've had good luck with those foam brushes). Make sure the weather is forecast to stay dry and the humidity is low before beginning. This first coat will dry quickly, and most of it will penetrate into the wood and not leave any gloss on the surface.
The second coat can be applied on the same day as the first coat. It is also thinned, but only twenty-five percent. This is the second sealer coat and will prepare your teak for all subsequent coats of straight, un-thinned varnish. You can get away with good quality badger hair brushes for a few dollars and throw them away after each use.
Wait at least 24 hours and then sand all the pre-coated teak with 220-grit sandpaper to smooth the surface again and dull any gloss that might have resulted from the first two coats. After sanding wipe the surfaces down with a clean alcohol soaked cloth, followed by a tack cloth. Now you are ready to start building up coats of clear varnish. Never work directly from the can, as exposure to air will ruin the varnish. Pour just what you need in a smaller container and seal the can.
Beginning with the third coat, it is important to apply the varnish carefully so that no spots are missed and no sloppy runs are evident. This coat will be the first full gloss coat, and mistakes made from this point on will show in the final finish. Try to work on a calm day so that windblown trash won’t stick to the slow-drying varnish. Use a clean brush and watch for shedding bristles that can sometimes come out of the brush and stick to the finish.
After the third coat has dried overnight, you will need to once again sand all the surfaces lightly with 220-grit paper; then wipe them down with a clean cloth for the fourth coat. It takes a minimum of five coats to get a decent finish, and about nine coats for a gleaming yacht finish that will turn the heads of everyone walking down the dock past your boat. Varnish must be maintained by applying two new coats every three or four months. These coats are also applied by lightly sanding with 220 grit paper between coats. If this schedule is maintained, your teak will always look great and you’ll never again face the difficult task of removing a peeling finish and sanding down to the bare wood.
Be scrupulous about cleanliness. Sweat can ruin a whole mornings application as can rain, dust, or bugs. It can be very helpful to have someone follow you, pointing out holidays, bristles that have come out of the brush, or sags where you've applied too much varnish. Wear gloves. Avoid applying varnish to hot teak.
Be sensitive about the application. When the varnish's fresh, it goes on so smoothly that you'll be convinced you're putting it on too thin. Later in the application, the brush will start to "drag". That's the time to dump the rest of the varnish, brush and mix up a fresh batch. You should probably never have more than a few ounces in the cup at any one time.
Once the can's been opened, don't shake it. Pour the varnish from the can to the container through a filter being careful not to introduce air bubbles. If you need to mix the varnish use a clean (alcohol and tack cloth) stirrer and stir slowly so you don't introduce bubbles into the varnish. Throw the stirrer away after each use.
95% of the results come from the prep work. Get that done right and the varnish'll bring smiles and comments.
Capt. Douglas Abbott
USCG/MCA IV/C.I./M.I. 500-ton Oceans
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Last edited by oceanscapt; 06-08-2010 at 04:38 PM.