Boatbuilding Blog

September 16, 2007

Notes About Epoxying, Priming, and Painting

Filed under: Building - Before Flipping, Building - Painting — tomlarkin @ 11:04 am

(From spending way too much time searching on the internets 🙂 Your mileage may vary.)


  • You don’t need to prime epoxy, but it helps make a really smooth surface.
  • You really, really need to wash the surface – even if your epoxy says it’s no-blush.
  • Adding pigment to the epoxy makes it easier to see how fair the surface is.
  • Alternating epoxy pigments and primer colors makes it easier to see if you’ve sanded through a layer.
  • Wash each layer well, and give the epoxy lots of curing time before topcoating.
  • Learn how to roll & tip paint for a great-looking finish.
  • EasyPoxy, Awlgrip, and Interlux are the most popular paint brands, and all seem to work well.


Barrier Coating, Finishing and Tips

Apply a minimum of two coats of WEST SYSTEM epoxy for an effective moisture barrier. Apply three coats if sanding is to be done. Moisture protection will increase with additional coats, up to six coats or about a 20-mil thickness. Complete all fairing and cloth application before beginning the final coating.

Wash the surface with a Scotch-Brite pad and water to remove amine blush. Dry with paper towels.

Let the epoxy cure very, very well, wash the surfaces with a 10% solution of ammonia and water, then get it very clean with plain warm water…then sand it…and if the epoxy is completely should have no paint adherence problems without a primer. Without a good cleaning with water/scotchbright scrubbing or ammonia/water then water scrubbing…you just sand in any blush that might be around on the surface.

If a high-build or filling primer is to be applied, 80-100 grit is usually sufficient.

After you are satisfied with the texture and fairness of the surface, rinse the surface with fresh water. Rinse water should sheet evenly without beading or fisheyeing. If rinse water beads up (a sign of contamination), wipe the area with solvent and dry with a paper towel, then wet sand again until beading is eliminated.

Then shell coat the part with pure epoxy and allowed to dry for 3 days. Don’t skip the 3 day part or you will be sorry.

The pigment makes getting a good finish on the epoxy much easier. Tiny bubbles and slight irregularities show far better when there’s some color in the epoxy. And white will show this best.

Too much epoxy is not really any better than not enough. With 6oz cloth I have usually found that the second or sometimes third coat rolled on is enough.

For the first two coats I used FLAG Resin and slow hardener, then after getting a little smarter, I switched to MAS Low Viscosity Resin and slow hardener for its better self leveling characteristics (all things being relative, the latter was a breeze compared to the FLAG resin applications –don’t do that for barrier coating unless you have a lot of patience and flat surfaces only). After each barrier coat application I sanded by hand, my best sander, with 3M 220 Imperial (stikit – the newer purple stuff).


Process for Applying High Build Primer –

There is nothing in most primers that sticks any better to properly sanded epoxy resin than there is in the paint itself.

There is a difference between sanding raw laminating epoxy, which doesn’t cut well at all, and sanding primer, particularly a high-build primer which cuts like silk. Drudgery is in the gland of the laborer.

Primer doesn’t add anything unless your filling/sanding job isn’t very good and you have a lot of small irregularities to hide. The paint goes on and sticks just as well to properly sanded epoxy as it will to primed epoxy. If you did properly fill and sand the surface, it should be just as smooth in the epoxy state as it would be with multiple coats of sanded primer. You can prime if you really enjoy more sanding and like to watch your sandpaper fill up, but is isn’t going to do anything to improve the paint jobs texture or adhesion.

WEST 105/205/barrier coat additive, topcoated with plain 105/205 then sanded to 120 on a random orbit with no primer and Brightside rolled and tipped over it. Work done outside in the summer, no thinner added. I have had good luck with Brightside in years past. I used a foam roller and a very good badger hair brush on fancy jobs. Need to move fast and keep the wet edge. Experiment with thinner to help it flow and keep wet edge. I rolled vertical and brushed horizontal and except for one spot where I lost the wet edge, people thought it was a spray job.

Sandable primers, as what was told to me were only to be used for minor surface imperfections and microfairing and were thus sanded semi transparent as to not shrink and move at different rates than their compatible top coats and was in no way to make up for fairing work of the substrate.


Pettit’s Easypoxy Primer covered the epoxy very nicely, and sanded out easily.

I used to use Interlux, but I now use Petit EasyPoxy. The EasyPoxy is really tough.


Two coats of Awlgrip 545, which stinks like hell and probably gave me cancer, but is the best paint I’ve ever worked with. mixes easily, rolls on evenly with great coverage and sands like a dream, especially when compared to sanding epoxy.

The industry standard these days is Awlgrip 545 primer. This stuff is works really well, but it ain’t cheap. I used some System 3 epoxy primer on a multihull last year, and I was not happy with the application or the result. The advantage of that epoxy primer is that it has low VOC’s, which is great….but the performance was really lacking, so back to the respirator and the 545…or this new stuff.

Interlux 404/414

I have been using Interlux Epoxy Prime Kote 404/414. It is a multi-purpose two-part epoxy primer for use above and below the waterline and it makes a great sanding surfacer. Sprays and brushes very well. Alternate color of primer surfacer to help pick up low spots/scratches. Epoxy primer can be easily tinted with resin colorant.

I’ve been using the Interlux 401/404 epoxy primer with good results. It’s a bright white color with a flat-ish finish, so you can use it as a finish coat for some interior applications–lockers, bilge, etc. It’s a lot less expensive than the Awlgrip product. The 404/414 is a good surfacing primer. It sands well. It’s a bit porous, so it takes stains easily.

I’ve applied gallons of the stuff with the small foam rollers from home Depot: “rollerfoam “” ultra fine foam for the smoothest finish ” “all paints and coatings “. I’ve always added the maximum thinner recommended; 25% of the 2333N Brushing reducer .This has lain out smoothly for me ,though I carry a foam brush to tip if needed. Answer – Used the “Rollerfoam” that Bill Perkins recommended–worked like a charm. Used one roller cover for the whole bottom and topsides of this 18′ ft. boat. Coat tended to stipple, especially as the 404/414 began to cure–so used a foam brush to tip it off.

Answer – don’t roll and tip the primer! Just roll it on with a tight foam roller cover, let it cure, then sand it smooth before topcoat. Sand it down to 220 or 360 grit


Roll & tip instructions:

I think the key is not loading too much paint on the roller pad… apply an even thin coat of paint but not any more than necessary on the roller. This fairly thin layer of paint… when tipped just layes down very smooth and uniform. I found that the badger brush works better because I think the tips of the brush seem to stay more wet than the foam. Brightsides is good too. I prefer Easypoxy and am used to it.

Don’t Use Copper Powder in your Epoxy

Filed under: Building - Painting — tomlarkin @ 10:51 am

I was going to mix copper flakes into my underwater epoxy as a built-in anti-fouling paint. Sam mentions it in his book. I asked him about it:

—–Original Message—–
From: Tom Larkin
Sent: Monday, June 25, 2007 6:01 PM
Subject: Copper bottom paint

Hi Joel,

Sam’s book talks about coating the bottom with copper powder mixed into epoxy to keep from having to bottom paint every year. Do you carry anything like that?  If not, do you know of a supplier for that kind of coating? There’s a supplier for copper flakes ( for a do-it-yourself solution. Would you recommend that?


      — Tom Larkin


Sam’s answer:

From: Joel Mill
Sent: Thursday, July 05, 2007 7:17 AM
To: Tom Larkin
Subject: RE: Copper bottom paint

Tom:  After trying that product out for several boats and seeing thru the years how it performed I regret putting it in the book.  It still required annual haulouts and exasperating hand sanding to renew the copper exposure to the exterior and the anti-fouling qualities weren’t really very good.  Best thing is use an ablative bottom paint like Micron CSC by International and just roll a new coat on every year.  Regards Sam

So, I’m going to use Interlux 404/414 primer and Interlux Micron CSC bottom paint. I’m going to try to stick to a single paint supplier on the theory that the paints will be formulated to work together.  I’ll probably use Interlux Brightsides for the topsides (if they make it in black).

Epoxy Bond Failure

Filed under: Building - Before Flipping — tomlarkin @ 10:33 am

When I put the 6 oz glass layer on the boat I followed the standard advice to fill the weave of the cloth the same day. The rule is to add a few more coats of resin on the same day, adding each coat when the previous one was tacky. This is supposed to create a great bond between the layers, without the need to sand or to wash off any amine blush. I did exactly that, rolling on two layers the same day I added the glass. The final coat was complete at about 9 PM that night – a long, difficult day. The boat looked great! The weave was filled. I had dreams of turning the boat over in Mid-July.

A few day later I washed the hull and sanded the whole thing with a longboard and a random-orbital sander. While I did that I noticed a few areas with a strange feathered-looking edge where I had sanded the top layer pretty thin. One day I took a putty knife to one of the areas. To my horror, the putty knife slid under the layer and peeled off a long strip of epoxy!

Putty knife scraping off epoxy and fairing compound

I was shocked, but hoped it was just in the one place. It wasn’t. Everywhere I tried, I could do the same. Some places adhered better than others, but most could be peeled off the same way. Some areas had two distinct layers. It took a lot of time to do even one square foot, and I occasionally gouged through the glass layer into the wood. The good news is the glass layer itself seems to be attached well.

This was the largest piece I scraped off I spent weeks scraping the hull, from mid-July to early September. It was incredibly depressing, moving backwards instead of turning the hull upright and starting the interior. By September first I was done, and the hull was stripped down to the glass, sanded, and ready to move forward again. 

I still don’t know what the problem was. When I was adding the fill coats I reused the mixing buckets and the foam roller. Maybe the partially-catalyzed resin contaminated the mix. Maybe I didn’t mix the epoxy enough (although the layers cured fine). Maybe the humidity changed and dampened the hull between coats. I have no idea. I don’t think it was a bad batch of epoxy. I tried some tests with the same 4-gallon container and didn’t see the same problem.