Final Fairing Compound

[CaptPatrick]

Most of you who've worked with epoxies and making highly visible modifications to your boats know first hand the work that goes into fairing things up.

In the beginning, the job is pretty simple, but as you get closer to "paint ready" that devil in the details takes over and you're chasing pin holes, scratches, and very minor dips. And to make life even harder, so many different colors, (green glass, white gel coat, red fairing compound, tan epoxy), are making the surface look like a spotted pup. This resulting camo can make it real hard to see those tiny details. Nobody's going to see the several thousand flaws you corrected, it's the two or three that slipped by that will stand out like a turd in a punch bowl, screaming "Look at me!", that get seen.

OK, time to prime with 545 and turn it all white. It'll take more than one coat of primer to cover all those different colors, especially the darker ones.

So, now you've got it all pretty and white and start discovering all those devils that have to get further filled and faired. It's sure nice to get rid of the spotted pup, but do you go back to Awlfair or mix your own epoxy fairing compound? The Awlfair brings back the pup, the epoxy takes forever to harden before you can sand again.

Maybe you've done some paintable woodwork and know the joy of using acrylic spackling compound. Easy to apply, fills every pin hole and minor grain ridge, super easy to sand and can be easily hidden by any color or type of paint.

Of course you'd never use spackling compound for your boat fairing project. And even though some marine painters will use 3M acrylic putty to chase pinholes, I don't.

So what's the solution?

Mix up a small quantity of 545 primer, which is a true 1:1 epoxy but sets up much faster than standard epoxies, and mix in your microbaloons & cabosil to the desired consistency. This mix will be the same color as your primed surface, will adhere completely, and sand just like the straight primer. Un-like normal epoxies, the Awlgrip primers have a fairly long pot life when left in bulk, but cure rather quickly when laid down in a thin coating. So don't spread your mix out like you would with standard epoxy compounds. Leave it in the mixing cup...

After sanding, a final light coat of 545 primer can be applied if necessary, but there will be no dark colors to hide, and it may be possible to proceed with your top coat or color base without further priming.

The really nice thing about this mix is that it really does work just like acrylic spackling compound. You can skim it on with a blade or spreader, paint it on, (I save a bit that is still fairly liquid when thickening the rest), smear it on with a finger, or whatever works in a particular spot. And, when hardened, it literally melts away under 220 grit sandpaper without clogging, bringing you that elusive "paint ready surface".

Br,

Patrick

[bob lico]

brother talk about timing that right wear i am at on the composite window project.do you still wait the nomal 15 minutes after putting the 545 and the activator together?? i would like to use microlight (410) and colloidal silica(406) together with the 545 primer is this ok?

[CaptPatrick]

Bob,

Yup, the recommended induction time is 15 minutes and should proceed mixing in of the thickners. However, I have often skipped this proceedure, either from impatience or lack of attention, without any difference in the results.

I'm not a user of Microlite, or just about any Guegeon product for that matter. Too many other choices... 410 Microlite is a phenolic microbaloon material and as such will leave you with a deep tan color. To acheive a thick consistancy & convert the 545 into a fairing compound, you'll need a lot of the microbaloons and a bit of cabosil. Cabosil is the same stuff as the West 406, just different brand names...

I have used a blend of 410 Microlite and 405 Fillet Blend in order to color match the epoxy for use with teak, acheiving an almost invisable joint while still not over squeezing the epoxy. As opposed to wood glues, epoxied joints require a bit of thickness to have proper strength.

I've gone back to using the 404 High Density filler since moving to TX, but only because my main supplier doesn't stock milled fiberglass.

[Bill Cuthbertson]

Capt Pat,

What is your choice of fairing compound for the first few rounds. Do you like the awlfair or regular epoxy with the low or high density filler. I have sanded the gel coat down to a solid surface. I think I read in a previous post about sanding it down to an almost paper thin coating, is this just for the severly crazed surfaces or the whole boat. Is there any benefit to priming the boat with 545 before starting the initial fairing, it seems like I read in the awlgrip application guide that if you are using awlfair you should prime it first. Thanks in advance.

Bill

[CMP]

Great topic, Capt. Pat. I never really "got" the fairing game well...

CMP

[CaptPatrick]

Capt Pat,

What is your choice of fairing compound for the first few rounds. Do you like the awlfair or regular epoxy with the low or high density filler. I have sanded the gel coat down to a solid surface. I think I read in a previous post about sanding it down to an almost paper thin coating, is this just for the severly crazed surfaces or the whole boat. Is there any benefit to priming the boat with 545 before starting the initial fairing, it seems like I read in the awlgrip application guide that if you are using awlfair you should prime it first.

Bill,

For real heavy and quick build up, you want a light weight very open epoxy material. My mainstay is using vermiculite as my main filler with the addition of enough Cabosil to prevent sagging. A dash of microbaloons helps the consistancy too. Great for quick bulk filling.

Always prime first with a thin coat of straight mixed epoxy.

From there, and in thicknesses up to 1/4", Awlfair is my principle choice. Priming under the Awlfair is necessary, but can also be done with a thin coat of straight mixed epoxy. Best adhesion will be achieved when the Awlfair is applied over a slightly tacky primer coat. Both cured epoxy primer and 545 should be sanded before the first batch of Awlfair is applied.

The cause of gelcoat cracking can be traced back to either stress cracks that occur from flexing at points that stop the transmission of the natural flex such as corners where two or more flat surfaces meet, blunt force impacts, and age cracking, also called spider cracking.

Stress cracking usually requires some re-designing of the intersection that both reinforces and further spreads the loading by use of larger fillets.

Impact cracks are usually just patch work fixes.

Age cracking occurs when the gelcoat has continued to cure for years, & shrinks to the point that the gelcoat can no longer hold the surface tension. This is most common on surfaces that were too heavily gelcoated. Any gelcoat, or even paint, will age crack if applied too thick.

All gelcoat cracks must be sanded out before re-gelcoating. Age cracking may only be evident in some areas and not in others of the same vintage. But even those areas not showing cracking are shrinking at the same rate as the others. Sooner or later, those areas are likely to age crack too. Best to sand down, at least to the point of transparency, all old gelcoat prior to painting or re-gelcoating.

Br,

Patrick