: I did not varnish the inside of my first couple of kayaks and after
: a few years the glass inside the cockpit broke down, even though
: the boat was kept indoors, out of the sun, when not in use. I
: now varnish the inside, but only use a couple of coats.

: John

Any area regularly exposed to sunlight like an open canoe or the cockpit of a kayak should be varnished to protect the epoxy.

What you could be seeing is water intrusion through a layer of fiberglass/epoxy that is not waterproof.

I have seen on old stripper interiors where the surface has dirt imbedded in the cloth with whitist cloth,
and in worst cases, areas of de-lamination.

This is caused by not sealing the cloth (after wet-out) with an additional coat of epoxy.

On the hull or deck interior, a seal coat is not normally applied. When dry wood and fiberglass cloth are wet-out
at the same time they battle to absorb resin. Wood does so more slowly, so after squeegeeing off excess resin from
the fiberglass (as you should to remove excess resin to prevent wrinkles of cloth floating on pools of resin), the wood may still absorb more, leaving the fiberglass drier than expected and NOT WATERPROOF.

Another single coat of resin will ensure a water proof surface.

If interior surfaces are coated with temperatures rising you will have some bubbles in the epoxy as wood off gasses.
These pinholes cannot be sealed later (see Nonlinear Dynamics of Surface-Tension-Driven Instabilities) trust me,
and these holes will admit water vapor.

SO, coat with dropping temperatures.

Sounds like it's not worth it? Wait ten years, you'll see.

Rob

I hear, I forget, I see, I remember, I do, I understand.

Confusius