How many skim coats?

Okay, so my Shearwater Sport is pretty much built.  Time for the final coat(s) of epoxy.  The manual says "Skim coats", but doesn't say how many.  And the skim coat(s) are for the inside as well as the outside?  If more than one, a 220 scuff sand in between?




4 replies:

« Previous Post       List of Posts       Next Post »

RE: How many skim coats?

   Probably at least 2 skim coats to fill the weave, then at least one more coat.  That will probably be a minimum if you did a good job with glassing. Keep the coats thin: runs, drips and excess build up actually create more sanding work.  You can search the forum or watch the build videos on this site to understand the topic "fill the weave."  Scotchbright pad or very light scuff sanding between coats until the weave is filled - don't sand into the cloth fiber. Damage the glass absolutely as little as possible - add coats until you can sand without hitting any glass fiber. Or maybe I should say don't sand into the cloth unless there is a big lump/bad area at a curve or joint or overlap somewhere that needs to be removed/made flat, so that area can then get its cover-coats along with the rest of the boat. Once the weave is filled (is no longer detectable when sanding), add probably one more coat, then do final sanding - the goal being to get so you can achieve a flat-sanded surface, at about 180-220 grit, that becomes a uniform dull grey, no localized shiny spots on the surface when sanded with a flat pad. (Go to 220 or better if you're going to varnish, otherwise sanding swirls might potentially show when you do your first coat of varnish.) If you actually achieve this uniform dull/grey finish you're well on your way to being able to do a furniture-grade-level paint or varnish finish.  If you get close, just so long as there is no raw glass fiber sticking out from the surface of the epoxy, you'll still have a watertight, durable, serviceable and nice boat from a 10 feet away viewpoint.

RE: How many skim coats?

   I forgot to add, how well you finish the inside is up to you. I never go for a full "fill the weave" finish inside anywhere. Typically just one light sanding of the original glassing coat, and one overcoat, with light finish sanding in areas that won't be be visible. Don't sand over the final epoxy coat in any area that won't be getting paint or varnish - you want to leave that last coat shiny.

In visible areas of the cockpit (those that need to be varnished or painted for U/V protection) maybe I go for a bit better finish - not so much as to fully fill or smooth out the weave, but to ensure the general smoothness of the wiping, waxing and bailing surface so it doesn't have nooks and crannies, making it harder to keep boat clean and dry.

RE: How many skim coats?

Bubblehead - Thanks for your reply, however, per the manual, I filled the weave as I went.  So I've sanded to boat to smooth out at least some of the imperfections in that job and these are the final coats before varnish.  The first one is on.  Took about 1 1/2 cups.  Just wondering whether to spend cup or so of epoxy or declare victory.


RE: How many skim coats?

   If you are able to sand to a smooth, flat surface with no (or few) low (shiny) spots without cutting into any glass fibers, there's very little to be gained from additional epoxy coats.  And where there are minor shiny spots, hit them lightly with the scotchbrite pad before varnishing or painting.  Give a good, lint free alcohol wipedown just prior to applying the first coat of varnish or paint.  Use the time saved from not doing the extra coat of epoxy to add an extra coat or two of varnish.  Getting the extra varnish on will never be easier than now, and having 5 (or more!) coats allows the top couple of coats to be "sacrificial." Extra varnish coats (for me) aren't about looks, they are about longevity of the finish, and saving work maintaining the finish over the life of the boat.  Depending upon how you use, store, U/V, salt exposure, etc. 3 to 8 years from now the surface of the varnish will start to age - become more brittle, yellow, have micro-cracks, be prone to mildew growth that won't want to wipe off, etc..  When you've got a good deep varnish finish, all you need to do is lightly sand through the first couple of weathered coats, and then add back some new coats to refresh your finish. Having 3 or fewer coats on as an initial finish means that ALL of your varnish is aging (impacted by oxygen and U/V), and as soon as that first coat near the wood "ages-out" you are into a much more involved strip and re-varnish project.  If kept protected by top coats, those undercoats might go for 20 years or more without ever failing. 

And contrary to some others' opinions, I'm a firm believer in waxing over paint and varnish a couple of times/year. (Don't wax for at least 2 months after applying varnish, let the varnish get good and hard.) I believe the wax layer protects the top varnish layers from the elements, and for the same reasons as above, adds to THEIR longevity. On a kayak a wax job is over and done with almost before you start - and if waxing a couple of times per year adds an EXTRA 2-3 years before ever needing any varnish refresh, that's a great thing.

« Previous Post     List of Posts     Next Post »

Please login or register to post a reply.