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The Epoxy Panel after 1 year

  So, it has been an eventful year for the epoxy panel. It has endured everything the New England weather managed to throw at it :)  In the summer, it was blasted by pure southern sun for days on end (90º +), it was soaked by acid rain, whipped by dust laden winds and in the winter, it had been encased in solid ice for many days as well as buried under as much as 18" of snow at which time it received no light but was truly tested by freeze and thaw cycles.

  This is what the panel looked like when it was new and what it looks like now.

Unvarnished exposed epoxy - Click for enlargement (large files)


 Observations & Conclusions  


Fabric 'whitening' - It seemed from the 6 month sampling that the whitening of the fibers had stabilized. It seems now that this condition has worsened somewhat on all the patches but I would say that the change is the worst on the less viscous epoxies, namely MAS and Raka as well as WS207. It is clear that the epoxy shrinkage caused the fibers near the surface (covered by thinner layer of epoxy than the surrounding) to telegraph through and those fibers were affected the most.

To me, it is still a puzzling phenomenon and the only explanation I can think of is that somehow, moisture has penetrated to the fibers through microscopic fissures opened up by UV degradation and perhaps oxidation being the aggravating factor. The 'crackling' of the surface is very much similar in appearance to old oil paintings with chipping paint. The logical progression may be that the long polymer chains in the epoxy break, the epoxy shrinks away and the fissures open up more and more until capillary action introduces some H2O into the fiberglass - and local delamination follows. It is interesting, however, that the unvarnished patches blocked from light also show some whitening, indicating that UV is not solely responsible for this type of damage.

I would also like to mention that I have paid less attention to surface quality as far as the uniformity and thickness of epoxy coating is concerned than I would on a kayak hull. In a strictly controlled scientific test, this shortcoming would be attended to, however, I believe my sloppiness has inadvertently shed more light on the 'fiber whitening' causes than perfectly uniform coatings.

One very important fact (and a conclusion) has emerged from this. The fibers buried the deepest in the epoxy filler coats, show no or less damage and whitening than fibers covered under thin coating. This seems to be universally true for almost all the epoxies. In order to eliminate this unsightly phenomenon on a clear coated fiberglassed surface, the fabric must be buried under more filler coats of epoxy than it seems to need at the moment. "At the moment", means when you think you are done glassing and the boat looks like it is ready for varnish. If you want to keep your wooden boat looking like a glossy gem for many years, put on two or three more filler coats of epoxy for insurance. If you see any fiberglass weave on the surface or fibers sanded through prior to varnishing you are guaranteed to get a fabric print through at best and 'fiber whitening' at worst. The insidious nature of this comes to light only months later and there is no cure, short of sanding everything off. There is no reason to worry though since this condition can be 'nipped in the bud' as you epoxy and with minimal weight increase.

Click on the images to get a real close-up view. The effect is hardly noticeable from the small images.
The picture on the left is a perfect illustration of the damage caused by thin filler layer over the fiberglass. The image on the right shows a 'blob' of thicker coating (perfect clarity of coating) surrounded by damaged fibers due to thin epoxy coat. (Raka)

So how did the epoxies do relative to each other in this respect?

Fabric Whitening
(no varnish, exposed epoxy)
System Three lowest % of white fibers
East Sys  
MAS worst

Now, the fabric whitening of the varnished, exposed patches (one goal of this test) rank as follows:

Fabric Whitening
(varnished, exposed epoxy)
Raka best - not a single strand
MAS excellent too
System Three imperceptible but very good
West207 light but visible - poor wet out*
West206 fabric weave visible
East System fabric weave visible
* My fault when epoxying - the fabric showed from the start so it gets an unfairly low score here

It is quite clear from the test that varnish reduces 'whitening' significantly but it doesn't prevent it in all cases. It is also reasonable to assume that varnish effectiveness is not only confined to UV blocking but to its moisture and chemical resistance as well.

Erosion of WS206 at 6 months (left) and at 12 months (right):
West System 206 epoxy (5:1 mix) is very water resistant and generally, the lower the ratio of hardener to resin in the formula the more water resistant the epoxy is. Of course, that is true only to the extent that the epoxy can tolerate long term UV degradation and oxidation - meaning, if the surface stays intact no water can get through.
I believe the degree of damage on the WS206 epoxy is also partially due to application of fresh epoxy on previously cured (and blushed!) substrate. I did attempt to clean the blushing but the washing and sanding was not sufficient for a durable mechanical bond. So, here is a case in point and a lesson in (im)proper surface preparation. Take a real care when working with blushing epoxies.


Color (hue) changes -
Another unexpected surprise was the effect of light on the color change of the wood. It's beyond a doubt that the light-shielded portion of the panel stayed generally lighter than the exposed areas but the striking contrast between the colors actually came from the epoxy itself. Some epoxies went on as very clear coatings (SYSTEM THREE, RAKA) but darkened beyond all expectations in relation to others. WEST207, on the other hand, has a strong yellow-green coloration to start with but it turned out to show the least amount of discoloration. It seems that the hue change is entirely due to the particular epoxy chemistry and less to the effect of light. The epoxy darkened consistently even under the light exclusion band.
So, my conclusion here is that the changes in the color of the wood are largely due to epoxy chemistry and that the color of the raw epoxy mixture has almost no bearing on what your wooden hull will look like later on. Do not assume that a dark colored epoxy will become darker on the hull in the long run than a completely clear brand of epoxy (clear, meaning no hue or coloration). The opposite may indeed be true.

Check out the 'new' panel at the top of the page and compare the colors of the WS207, MAS and System Three. At the beginning, they show minimal differences. Notice the change after one year.

Color Change
varnished and unvarnished, epoxy)
  East Sys least color change
  System Three largest color change


Gloss and Oxidation (microscopic chemical erosion of the surface layer)- These two go hand in hand. The more a surface is oxidized the less glossy it is. Resistance to oxidation was one of the objectives of the test and the table below ranks the epoxy brands by "glossiness".

(no varnish, exposed epoxy)
West207 absolutely top
Raka very good
System Three no loss of gloss*
East System not much better than WS206
West206 no gloss
* System Three had a mate non glossy appearance from the beginning of the test and there has been no further deterioration - it basically stayed the same. It is slightly glossier than MAS at this point.

West System unconditionally wins the "no varnish - gloss" test closely followed by Raka. WS207 shows no oxidation at all. West System claims their 207 formulation contains UV blockers and it shows.
As a note of interest, when I cleaned the remnants of the duct tape with lacquer thinner, the varnish stayed completely inert, however, the oxidized epoxy surfaces dissolved into sticky sludge. It would appear that once that epoxy degrades to some degree, its chemical resistance to organic solvents (like lacquer thinner) declines rapidly.

All varnished portions of the panel maintained the same degree of gloss.

  Clarity and overall condition of varnished epoxy - The holly grail of the test. Just to refresh the mind after so much verbiage, the objective was: Which epoxy will discolor the least and maintain the best clarity.

(varnished, exposed epoxy)
Raka best
MAS virtual tie with Raka
System Three very good
West207 good
East System fabric weave visible but OK
West206 fabric weave visible - opaque
  Protecting your wooden boat - Despite the good results from the "Clarity test", I say it is still a good idea to cover your hull with some light proof material. Make absolutely sure to allow the epoxy and varnish (or any coating) to cure to perfection before you slap a sheet of suffocating plastic over it. Give your new coatings at least a month to dry and harden. Protecting the hull in such a manner that permits some air circulation is very beneficial. If you have done your epoxy work properly (especially the wetout and thick filler coats) there is little to worry about.

Temperature changes have little effect but light degradation is a fact of life with epoxies and UV resistant coating is indispensable. The choices for clear coat are few; there is varnish, polyurethane, sprayed automotive clearcoat and the newer two part polyurethanes. The polyurethane builds up faster, has a superb gloss and abrasion resistance but at this point you might as well adorn your boat with gold leaf - it's that expensive! ($50-60 per 1.33quart). It gets worse still, once you mix up your two part batch, you either use it or lose it - there is no pouring it back into the can like paint or varnish. So, is it all worth it? Check out the gloss and some of my findings with the two part polyurethane.

And the test goes on!  Now, that the degradation of the epoxy has set in, it will accelerate and the differences between the brands will only accentuate. More stuff to follow...keep tuned :)

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Vaclav Stejskal
10 Colonial Court apt. 73
Stoneham, MA. 02180
Tel:  781-481-9261


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Last page update: 11 January 2020

Epoxy test panel after 2 months