Days, not hours.

You want a 100% cure otherwise reaction products could interfere with the paint /varnish. High quality blushless epoxies mean that you don't have to wait weeks, as in the past, but trying to move too fast will slow you down.

Best bet is to check the manufacturers' instructions for both the epoxy and varnish. If you can, use a coating system from the epoxy manufacturer. Compatibility is better that way. If you can't do that, wait the extra time.

If you're worried about losing momentum, work on the sails, rigging or trailer while th epoxy cures.

Have fun,

Laszlo

Hi Laszlo,

 I should have advised that I'm using all CLC recommended products, MAS epoxy, Interlux Primer Pre-Kote, and Interlux Brightsides paint.  I did check the cans and they dont indicate how long to wait after epoxy application for primer or varnish.

   Here's MAS's FAQ: http://www.masepoxies.com/faq

If you scroll down to number 5, you'll see a chart that lists cure times for their slow, medium and fast hardeners adjusted for temperature.

   Wow...that MAS FAQ shows that at normal room temperature their epoxy cures on 7.5 days.  Is that how long everyone waits to apply primer or varnish?

I followed their guidelines. I fiberglassed my kayak last summer, but not when it was really hot, and I think my wait time was about seven days.

Keep in mind that this is not the interval between resin coats. I laid down my cloth, put the first coat of resin and then, when the resin got sticky and a cotton ball stuck to it, I laid down another resin coat. Then the next morning I did a light sand and laid down the third coat. Then I waited a couple of days and sanded the resin in preparation for varnish, but then waited five more days before varnishing. In doing this, I was following the instructions in Nick's book, "Building Strip-Planked Boats," starting at page 151 and running through the next chapter. But he doesn't address the wait time between resin and varnish, so I checked the MAS FAQ and followed that.

Nick discusses varnish and paint wait times on page 165 in his book, and it varies by product. The way I think it through, it took me about eight months to get to the finishing stage, so I didn't want to rush and mess up at the end.

Cheers.

An answer and another question:

After building one CLC boat using MAS epoxy, slow hardener and Interlux Schooner Varnish, I vowed to wait 3 days between epoxy and varnish in the future. Otherwise, the build up of epoxy dust on the sandpaper was driving me crazy. I was building in the winter but I did manage to maintain the minimum reccomended temperatures in my shop.

Now I am having trouble with this year's project. I used West System 105 resin and 206 slow hardener on a plywood surface and it sat around a few weeks before I sanded it. This epoxy is advertised by CLC as a "Laminating Resin". I am sure the resin / hardener ratio was correct. It sanded well, but I then varnished the piece with Cabot Marine Varnish. It has been four days now and the varnish has not dried at all. This same can of varnish has behaved properly on all the other pieces, which were bare wood. 

Could it be that this brand of varnish is just not suitable for West Silver Tip Epoxies?

Or, maybe I should I not use the 105 / 206 epoxy on an exposed surface to be finished with varnish, and only use it to laminate / glue pieces together? I am planning to coat a very large surface with the 105 / 206 and then paint it.

And how should I repair the mess I have made? Will I have to dissolve the goo and  scrape down to bare wood before re-doing this surface?

Thanks to all,

John Doyle

John,

You talking about West or System 3? System 3 makes SilverTip laminating resin, not West.

Laszlo

Laslo,

Thanks, I was getting my products confused. I am using West System 105/206, not Silver Tip laminating resin. So I spoze it is OK for prepping a surface for varnish. Still wondering about this sticky situation with the varnish not drying. I am keeping a portable electric heater focused on it but no progress yet.

Does anyone have experience with this problem?

Many thanks,

JohnD

John,

You've just found out why people end up almost religiously devoted to a set of products that they know work.

MAS and Silvertip are no-blush epoxies, Schooner  is a very epoxy-compatible varnish. West is known to blush. I know nothing about Cabot, but from what you describe it's not one of the varnishes that plays well with epoxy.

Some varnishes can't tolerate any blush at all, some can't handle any epoxy reaction products, some are incompatible with the thinners in lower-solids epoxies, some varnishes have thinners that epoxy is incompatible with.

Best bet is to check with the Cabot people and see if their varnish is supposed to work on epoxied surfaces and what kind of surface prep they want. Worst case, you may have to scrape it all off, thoroughly clean the surface and re-apply a different brand of varnish or topcoat. Hope nit.

Good luck,

Laszlo

   Any cured epoxy is a suitable substrate for varnish or primer or paint. Treat all epoxies as though they blush (they all do to some extent, under certain circumstances of temp and humidity), and the underlying epoxy becomes just an inert plastic. For me, that means a scotch-brite and water scrub (or wetsand), thorough sanding, an alcohol wipe, and finally a clean solvent wipe. Every time.

My last boat was built with 6 different epoxy formulations (not counting slow/fast hardeners) from 4 different companies with probably 4 different types of coating, and no problems.

prep the surface, measure and mix the resin before adding filler, let it fully cure, and properly prep the resulting surface and it won't be the epoxy that is causing the paint problems.

 I just want to add that beside the blush issue, that there are some temperature and humidity issues this time of year. If your shop is cold, that's another variable...and don't forget that the average temp of your shop includes the early morning hours.   

Check out this temp chart for West hardeners...

http://www.westsystem.com/ss/hardener-selection-guide/

This seems to indicated that if your shop is colder that 60 F, your resin may not be curing...

After a fairly quick search, I can't find any tech bulletins on Cabot varnish, but other manufacturers (Pettit) recommend temps above 50F. Most varnish specs recommend not varnishing when it's raining or extreemly humid...I think it inhibits drying and induces blush.

BTW I think the reason the 206 hardener is listed as a laminating resin is that it's not as clear as their 207 Special Clear Hardener (which in my opinion is not as clear as MAS.) 

Cheers

Thanks for all the comments!!

I got input from CLC too, basically on most of their boats they sand when the epoxy is ready to be sanded, then prime and varnish immediately after sanding.

I will concede that I have made mistakes at each point which have added time and steps to rectify (first boat), but I found this discussion of wait times to be largley academic. If you havent spent a few days properly sanding the final epoxy coat to prep it for the first varnish coat, then you havent sanded enough. Simple as that.

I am now on my second weekend of sanding to take the next step to varnish. getting all those little shiny depresions out from every surface is an exercise in patience and dogged determnation. I may not be done sanding even after this coming weekend. the last of my worries will be whether the epoxy has firmed up during those weeks of sanding.

David

>>If you havent spent a few days properly sanding the final epoxy coat to prep it for the first varnish coat, then you havent sanded enough.

Respectfully partially disagree. Experience counts a lot. My first epoxy-covered boat took weeks to get ready for varnish. My latest took a day and the varnish job was better. The boat was also bigger.

The main difference was practice in applying epoxy so that it would be a thin even coat - no sags, drips and high/low spots, and practice sanding so that the time was used effectively.

All the more reason to build lots of boats.

Laszlo

Laszlo---

Does it matter if I have a few shiny specs on the epoxy before I varnish?

Thanks!

Larry

Larry,

My personal opinion? No, it doesn't matter as long as they are really small (pinhole sized or so)  and there are isolated, not occurring in clusters. Now some of the "Best in Show" winners may disagree with that, but it won't make any difference as to how your boat behaves and most people will not notice the difference in finish quality. It's only an issue if you're trying to win a prize.

Have fun,

Laszlo