Glass wetout problem

Submitted byRonPW onWed, 05/01/2019 - 21:05

I am in the process of building a cedar-strip canoe. I am using Raka Epoxy. I have a little experience using epoxy. I built 2 strip kayaks 18 years ago (Mas epoxy) and a SUP last year (raka). The kayaks wet out very nice, did a sealer coat, everything went well, very clear, no glass seen under two fill coats, lots of varnish, still very nice after all these years. The Sup (raka) last year seemed to show a little of the cloth under certain light and angles. I chalked it up to maybe using glass I purchased from a internet company, thought maybe wasn't compatible. After researching, could not find any issues with Raka wetting out, Everybody seems very pleased with their product, so I went with them and this time I used their glass. I checked the calibration of the pumps they sent me, all looks accurate. My shop is in my basement, average 68 degrees, 35 percent humidity. Raka recommends a sealer coat so I did that, on the morning of application I warmed up epoxy and hardener in warm water bath (Trying to get best wet out possibility.) After wetting out glass i noticed the cloth looked like it did not wet out good, thought maybe will be better after 1st filler coat, still looked the same. I sent pictures to raka,,(they are very helpful), but were puzzled after quizzing about application process they stated all process seemed correct. I made a tough decision and spent many hours and a lot of sandpaper to sand it all off. They did send me new epoxy & glass. I have done 3 test panels and keep coming up with glass being visible (it is a little better than what I sanded off the canoe, but still there) My shop does have very bright LED shop lights right above canoe,,, but test panels show even in normal or outdoor light. I am attaching some pix. Any thoughts would be appreciated.

visable glass visable glass

I have had similar problems and believe they were all due to old fiberglass.  Fiberglass has a coating called sizing that helps the epoxy wet it out or something and when it gets old it doesn't function as well.

Sizing (from Wikipedia)

A coating or primer is applied to the roving to:

  • help protect the glass filaments for processing and manipulation.
  • ensure proper bonding to the resin matrix, thus allowing for transfer of shear loads from the glass fibers to the thermoset plastic. Without this bonding, the fibers can 'slip' in the matrix, causing localized failure.


Kyle T





Thu, 05/02/2019 - 12:54

First, your pictures don't look bad, really - but I know how every small flaw jumps out at one as the builder.

I haven't used any of the products you are using but I have noticed differences between fiberglass materials.

I've painted my kayak projects for the past few years, so the only areas where wet-out problems would 'show' is on the hull interior.

Most of the 6 oz cloth I've used has a very soft feel and it wets out well, but some of the lighter 3-4 oz fabrics feel quite 'stiff', and they have been much more difficult to wet out, and to get good adhesion to wood, especially if it had a seal coat.

Water can certainly ruin glass cloth, and I suspect that very high humidity isn't good either, but I have no proof of this. I generally buy larger quantities of glass and the rolls are hung (for years) in my basement, but it never gets extremely damp here on the BC coast - about 50% RH year round.

With fresh cloth from a company with rapid product turnover, storage and 'old' cloth shouldn't be an issue.

BTW, getting the boat warm as well as warming the epoxy both help with wetout in my experience.

John VanBuren

Fri, 05/03/2019 - 06:37

In reply to by JohnAbercrombie

I have had my best wet out success with System Three SilverTip Epoxy. Yes, I know it is a premium product and costly, but does wet out very well. If I were you I would purchase a small quantity of the Silver Tip and experiment with it. By the way, I have found Jamestown Distributors to have the best price for Silver Tip.

I hope this is useful,

John VB

I've used RAKA a lot with never a wet-out problem other than one time I tried some glass that was a bit stiffer than my usual glass (like John described)  Can't remember where I got it from. I had the same problem you describe. It wet out but not to the extent I was used to. I lucked out and pulled it off before hardening. I wiped it down with alcohol and later a light sanding before my next try.

I learned to buy my glass from places that do clear layups (build kayaks / boats etc) Their glass always wets out perfectly. I may pay a few more dollars but the security is far worth it. If you have some leftover glass from your previous builds, give it a try. Its the only way of finding out. I don't think its the age of glass. I have some very old glass around and it still wets out perfectly. Maybe some glass is better with polyester? 

Thanks everyone for the insight, after much thought & more research including some test panels ( using the two different rolls raka sent me). It makes me think maybe the glass has been compromised by either high humidity (Co. is in Florida) or maybe a bad production batch. Like I stated earlier Raka has been very helpful. I think I will try glass from another source. Like Jay stated maybe getting from glass from actual kayak or canoe site. (the 2 times I used Raka, one glass purchase came from a surfboard supply Co. and the other from the epoxy supply Co.) both came up with same results.


Mr. John Abercrombie,

I just used paint for the first time on the hull and coaming of a kayak using a designated boat paint called "Total Boat JD Select" from Jamestown Dist. No idea how it will hold up but it did apply very nicely and looks good. Haven't gotten it wet yet as it was just completed yesterday. I wouild like to know what brand paint you use and any other pertienent thoughts concerning painted and painting kayaks.

Thank you,


I suppose this should be a new thread ? If you prefer to reply direct echtinaw(at)iCloud(dot)com

fwiw, i agree with your thought that it looks like the glass itself.

i would test with 4 oz e-glass from a reputable supplier like CLC or other supplier that knows its product is going to be used on clear/bright finished cedar strip boats.

i am wondering if they accidently sent you a batch of s-glass (not e-glass).  it has very much this look even if perfectly wet out.


Rob Macks Laug…

Wed, 05/08/2019 - 11:46

EVERY epoxy is different. I've been working on strippers for more than thirty years and unless you've worked with different epoxies you'll never know that.

System Three epoxies have a much longer set up time than MAS. I'm not familiar with RAKA but I'm sure there are differences.

I've noticed a tendency for MAS to create more bubbles during mixing.

Epoxy manufacturers each have different ideas about what they want from their product. Epoxy is designed foremost for strength

and most boat builders paint over epoxy.

Epoxy is a syrup, thicker when cold. Add a hardener and it starts to thicken more EVERY SECOND.

Take a piece of fiberglass cloth. Pull out a thread. Pull the tread apart to get an individual fiber.

IF you want a transparent lay-up you must be able to totally wet the surface of that fiber and all the other fibers in the cloth.

To do that with consistency see -

Live Long and Paddle

Rob Macks

Laughing Loon Custom Canoes & Kayaks



“All things are difficult before they are easy.” - Thomas Fuller