My Petrel strip-built kayak requires a strip of bias-cut fiberglass to join the exterior seam between the deck and the hull, as well as an additional layer of fiberglass on the hull. In some spots, I can see the second layer of fiberglass; it other areas, it’s not visible. Why is this? Obviously, I’d like invisible, just like the single layer on the deck, hatches, coaming rim, etc.
What can I do to keep this from happening?
this has happened to me when not using enough epoxy. You really have to make sure you have enough, and squeegee it into the fiberglass.
you’re the builder, so you will always see it, but i noticed that nobody else saw my boat’s imperfections until I pointed them out. 
It would be great to add another picture or two to ensure we understand what we are looking at. but in general, the key element for making glass disappear is 1) ensure the glass is fully wetted out and filled and sanded smooth and 2) avoid/take care to eliminate outgassing or any other contamination that prevents the glass fibers from being invisible.
i can’t tell from the pictures if we are seeing reflections or dust patterns from glass that is not filled/sanded or if, for some reason, the glass itself is not transparent. a wipe with denatured alcohol with tell you where you stand.
assuming you don’t have a defect in the glass itself, then this is all going to be about care in sanding and blending glass edges in…and that can sometimes just take time and care to get there. i find that it can be accelerated and made easier by painting the glass edges with raw epoxy to make it easier to blend. also using a lighter weave (2 oz glass) can also make it easier to blend and make second layers disappear.
i would also highlight that dark stained hulls tend to show imperfections more than light colored hulls. most glassing imperfections are going to tend to take on a white-ish color so it contrasts more with dark stained wood behind it. but as Matt mentioned above, this will typically be much more noticable to you then the average observer.
below is my petrel play - warts and all. the warts are visible if you are way up close and looking at the hull very carefully. they practically disapear and are harder to find in the white stained deck. but from a couple steps back…its all good
h
Well, that’s plenty of good advice from some experienced kayak builders! Thanks for the help. Your kayaks look beautiful, by the way.
-d
How old was the glass cloth and where did you buy it?
Good quality fiberglass cloth is coated with chemicals that help it wet out. These chemicals are water soluble so over time they are lost to humidity in the air. Also, some cheap cloth may not have these chemicals.
I once made the mistake of using old cloth and learned this the hard way.
