Epoxy Top Coat

Submitted by bug_hunter on Mon, 03/23/2020 - 15:52

Hey Guys,

Hope all are well.  

Finished wet-out and coating the outside of the hull of my cedar strip kayak, and have a little(hopefully) issue.  I used a squeegie to start he initial wet out, and was not happy as it seemed too dry.  Part way thru, I went to a brush application and squeegie off.  I put a total of three coats on.  I used a torch to raise and pop any bubbles.  The final finish was quite clear, but not smooth.  Couple bubbles, and lots of runs.  Started with the long board and some 40-grit to knock them off, but in some locations, I can starting to see some of the weave.  In those areas, I stopped sanding.  Not the end of the world from a cosmetic standpoint as I do not believe they will deter from the look of the boat.  Once I'm done with the entire hull with 40-grit, I'll hit it with some 80-grit and 120-grit.  The question:  Should I put another coat of epoxy over the entire boat, or is what I have sufficient?  Don't mind adding another coat, but then there is more sanding (fairing).  Hate to put it on, and take it all off again.

Thanks again for all the advice, and again, I hope everyone is holding up and healthy.

Greg

When an area of fiberglass is under-saturated, it looks light-colored. Since the coating came out "quite clear" it seem that you got the glass saturated.

Bubbles were either caused by application technique, or rising temperatures. It is very important to do this first coat in a situation where the temperature will FALL, not RISE while it is curing. If the temp rises during cure, air will be released from the wood, causing bubbles. 

The first coat USUALLY comes out lumpy-looking. Most important is that the glass is well saturated and invisible. 

Hitting the weave with sandpaper is not good. Sandpaper is a bunch of tiny rocks that smash their way through the material, creating debris. If you sand into the glass, this dust will get into the fabric, making it visible, no matter how many overcoats of epoxy. Which brings me to discussion of one of my favorite tools: The Cabinet Scraper.  The big difference is that the scraper CUTS material, where sandpaper pulverizes it. If you use one on the areas where the weave was exposed, another coat of epoxy WILL hide the weave, because the fibers have been sliced cleanly. The scraper really "does a number" on bumps and runs, once I started using it, I wondered how I ever got along without it. Here's a link to a YouTube video that I made about it: https://www.youtube.com/watch?v=QtR1etP8CRk 

As far as another coat is concerned, when in doubt, do it. Even though its expensive and tedious, there have been several time where I got to fairing and wished I'd done another coat. 

 

bug_hunter

Tue, 03/24/2020 - 10:48

Thanks a lot for the input.

The issue I have with the use of the scraper is that it is a point of use tool.  As I understand its use, it will address the individual defficiency, but will not fair the boat.  And could "un-fair" the boat.

I do believe I will followup the long board work with another coat of epoxy.  Could I apply is over an 80-grit surface, or would 120-grit be better?  Suggestions on applying the final coat? (squeegie, brush, roller)  I am currently leaning towards brush as that is what I am most comfortable with, but would switch to another process if thee are benefits.

Thanks again,

Greg

JohnAbercrombie

Tue, 03/24/2020 - 13:23

Greg-

Jim's comments are exactly what I would say as well.

When in doubt, add more epoxy.

It's best to avoid runs and drips. On your next boat, it would help to read Ted Moores (Canoecraft or Kayakcraft) books on the right way to remove epoxy when wetting out glass.

I will add: The epoxy and glass layers are thin. If the hull isn't fair before you glass, I'd stop worrying about long board fairing if you plan to add a clear finish.

If you are painting the boat you can use fillers (Microlight or balloons) in the epoxy top coats to make sanding easier, and give thickness for using a long board.

I apply fill coats with a squeegee, generally. It's better to add thin coats with no runs than to try to add fewer thick glossy layers of epoxy.

A carbide scraper is an excellent tool for taking care of runs and drips, though you do have to wait until the epoxy is fairly hard before scraping (or sanding).

I like this scraper:

https://www.leevalley.com/en-ca/shop/tools/hand-tools/scrapers/20095-carbide-scrapers

Buy extra blades.

Another possibility would be a Bahco:

https://www.bahco.com/gb_en/ergotm-heavy-duty-paint-scrapers-with-dual-component-handle-pb_665_.html

A good sharp steel cabinet scraper will also work well, though it's harder on the hands if you are doing much work with it.

 

 

bug_hunter

Fri, 03/27/2020 - 22:58

Hey Guys,

I brushed down another layer of epoxy today (method per KayakCraft), and despite my efforts, still have several runs.  I tried to remove them with a scraper (Hyde 10400 molding scraper), and did not have a lot of luck.  Maybe too early, seemed to gum up.  I didn't want to press too hard as the surface still seems a bit soft.  My next try is going to be the cabinet scraper.  I plan to make one tomorrow out of an old table saw blade.  Could someone give me a detailed description of the process of scraping the runs?  Do I scrape the entire boat, or just selective spots?  At what point do I switch from scraping to sanding?  This is my last epoxy coat, and need to prepare for varnish.

Thanks a lot for helping the rookie.

Greg

JohnAbercrombie

Sat, 03/28/2020 - 02:52

Greg-

If the epoxy is still a bit soft, it won't scrape or sand very well. It's a bit 'rubbery' or as you said, gummy.

I'd just flatten out the worst runs with the scraper then sand, being careful not to sand into the cloth. It's expensive, but you can always add more epoxy and sand most of it off until you get the surface you want.

Using the cabinet scraper takes a bit of practice - both in 'sharpening' and turning the edge and actually scraping.

A decent mill file and a burnisher (hard steel rod, twist drill shaft or even a screwdriver shaft if you don't have anything else)  can do the job to set up the scraper  for boat work

So don't get too impatient. If you want a very glossy 'piano finish' when you varnish, the epoxy needs to be absolutely smooth - Sand with a block (a stiff foam block works for me) until there's a uniform matte finish to the epoxy. The varnish won't hide anything - I learned this sad lesson on my first few boats, laying on thick layers of varnish trying to hide mistakes! :)

JayBabina

Sat, 03/28/2020 - 14:28

"I plan to make one tomorrow out of an old table saw blade. "

I'd love to see a video on that. Sounds like quite a project. Scraping epoxy runs is really easy. You did nothing wrong except not wait until the epoxy was hardened.  I have a lot of scrapers and sometimes I use my super cheap red devil scraper with one of those 4-way cheap blades and it works fine. I have carbide ones and flat cabinet scrapers but to scrape epoxy runs, you could almost use a kitchen knife on edge. You can even use a flat sharp chisel and slowly carve it off. I think Rob Macks has an extensive video on sanding the kayak  www.laughingloon.com  in prep for varnish.

 

When I first started building runs were a problem. I bought a set of differently shaped scrapers (concave, convex, fat, etc.) that worked just fine. I still get the occasional run and a single edge razor blade works just fine.

This is the blade of an small back saw that I never liked anyway. Too lazy to grind off the saw teeth, I put a piece of tape over them.File & burnish the other edge, and voila! Use any non-stainless steel. I recently bought a nice-looking set of scrapers on Amazon, but they were made of stainless steel, and couldn't be filed or burnished properly.scraper

daviddewitt

Sun, 05/10/2020 - 19:25

I actually take a different approach and sand out runs (and those pesky bubbles) with 120 grit sandpaper using a 5” Festool RO sander with an attached vacuum.  It takes longer but, being less aggressive,  gives me much better control than with 60 or 80 grit.