View Full Version : Timing: Varnish over CPES

09-21-2007, 10:32 PM
The varnish over CPES topic has been covered here, but I am looking for the latest information......we are ready to start finishing spars, hatches, etc., which have been sealed with CPES. The CPES now on these items is well cured.

The Smith & Company website recommends applying varnish on CPES before it cures, but after the solvents have evaporated. Specifically, Smith says:

"When it shows a glossy film everywhere, meaning it is no longer soaking in upon application, the surface is sealed. Now allow enough drying time that film shrinkage from final solvent evaporation does not telegraph the grain pattern to the surface......The final coat of CPES is the adhesion-promoting primer, and the first coat of varnish must be applied after the solvents have evaporated, but before the CPES resins have fully cured. If you apply that last coat of CPES in the afternoon, then apply the first coat of varnish the next day. The reason CPES works this way as an adhesion-promoting primer is that it is designed to be VERY slow-curing. It actually takes several days, so it finishes curing after the first varnish coat has cured, and thus glues down the varnish with a flexible epoxy glue."

My question is how critical do you think this timing is between the final CPES coat and the first coat of varnish? The bold text above seems to indicate about 18 hours between, but this is all so dependent on temperature. I'm working in a shop which is currently 65 degrees F around the clock.

What time between CPES and varnish works for you? I want to put on the final coat of CPES and then varnish with the right time between the two.

09-22-2007, 12:20 AM
The Smith CPES comes in two flavors, Warm and Cold weather, and that as well as the temperature/humidity probably impacts the cure times.


Other brands will cure at different rates also.

Best bet would be to try some test pieces of wood, assuming your weather stays the same during the tests as the actual application.

09-22-2007, 12:44 AM
Thanks to the ever vigilant Thorne.

We are using the standard or Warm Weather version.

Yes, I have read the table and see the numbers for pot life and cure time, but the time between the CPES coat and the varnish coat is not shown and is ambiguous in the literature.

I am into this, and down this CPES road now and more or less have to play along. I must say though that if I had known what this stuff is like to work with I would have never allowed it into my life. It is horrible to apply, horrible to sand........it is just plain horrible. I just touched a bit to see how it was curing, after having applied it 24 hours ago, and almost immediately felt something happening in my hand. But, I've dug my grave and now will lay in it.

So, 18 to 24 hours between CPES and varnish with standard/warm weather formula? Somebody give me a number so I can sleep.....

09-22-2007, 11:12 AM
Don't think the timing is quite **that**critical, but if you want a number for a shop at 65 degrees, I'd say 24 hours.

Sorry that you've had a bad experience with the stuff. Sure hope that the improved sealing and thus improved life of the varnish provides payback. I've used it on some spars and found the finish to be very nice, better than my varnish over 50/50 BLO/Turps, but that's on a small boat with everything stored indoors.

Wild Wassa
09-22-2007, 02:05 PM
I think painting at 65F or slightly below that is about the best temperature for brush painting with modern varnish.

I'm presuming the varnish that you are using is a modern poly/oil blend varnish and not a traditional oil based varnish so at 65F or slightly below that temperature the paint will go on reasonably well. But don't overstroke the varnish in an attempt to level it.

Following Smith and Co's advice for getting a chemical key between the CPES and the varnish, 16 hours appears best for applying the varnish with a latitude of up to 20-24hrs at 65F after the final and uniform coat of CPES has been applied.

I'm not big on using Multiprime as a primer to give a chemical key to the next film following it. I'm a big fan of CPES but not as a primer for paint. I like physical keying because at some stage there will be a need to remove the varnish and I'd prefer not to remove the CPES while removing the varnish. I'm not disputing Smith's advice, I just prefer a more upmarket quality over the life of the boat ... because plan for the varnish removal now. "Glueing the varnish to the epoxy," Smith say. I remove lots of varnish, I prefer it to come off readily.

If I was painting the spars. I would let the CPES cure fully, then uniformly sand the CPES with #280 add a boundry layer of normal epoxy and key it uniformly to #320 and to the varnish, I would add Penetrol, to aid the physical keying and also to improve the levelling of a poly/oil blend ... if you don't mind me saying because after CPESing the surface just isn't adequate for painting, I find.


09-22-2007, 04:58 PM
Thanks, Warren (and Thorne) for the detailed information and for sharing your experience.

I totally agree that I'd rather the varnish come off alone in the future, and the CPES stay entombed where it is. I've noticed that one of the benefits of CPES (or similar put on by previous owner) under varnish is that a good water-based stripper (citris strip) will easily remove many coats of varnish and not touch the epoxy/cpes, and therefore the stripping process does not impact the wood. I don't know if this old epoxy/cpes was allowed to cure totally before varnishing......I suspect it did cure and that is why the stripping took all the varnish and left the epoxy.

If you've had good luck with letting the CPES cure first, then sand, then varnish, I think I'll go with that. Sanding and varnishing is enjoyable compared to the tedium of thinking about what is happening at the molecular level. Bloody chemists.

We'll be CPESing in a half hour. If the stuff works into our brains we may waver and varnish in 16 hours. Hopefully, though, we'll keep our heads and let it cure first.

09-22-2007, 05:18 PM
I was planning on using Epifane's Wood Finnish with a top coat of their regular Gloss (highest UV protection). I also see that Smith is recommending and selling it now on their website. The Wood Finish is decribed as "...based on phenolic modified resins and tung oil...". How close that is to polyurethane I don't know. For some reason though, hopefully not just for money, Smith & Co. recommends it now.

Wild Wassa
09-23-2007, 10:03 PM
"based on phenolic modified resins and tung oil."

Take away "based on" and what is left is 'varnish'.

"based on" ... means not a traditional varnish, but your average modern day poly/oil blend varnish. Just as good but with faster drying times, more UV stabilizers and retardants in the emulsion ... but once the can is openned use it.


09-26-2007, 08:13 AM
.....Sorry that you've had a bad experience with the stuff. Sure hope that the improved sealing and thus improved life of the varnish provides payback......

I think it will pay off in some of my applications.....I just seemed to use CPES in more places than I originally imagined. It's nasty stuff to work with......I expect that in a few months when we are sailing instead of restoring, I'll get over it. I just abhore plastic. I'd simply hate it except that I find it so useful (zip lock bags, bic pens, and so much else). I hate it, but I use it, so I abhore it.:)

09-26-2007, 08:29 AM
I'll play the voice of dissent.

I think you REALLY need to let the CPES come to a full and complete cure before applying any subsequent coating. The only times I've ever seen problems with anything over CPES were applications that closely followed the published cure time of the epoxy. I've made it my personal guideline to let any CPES cure for at least two days beyond the published time, and I do everything within reason to keep the piece consistently warm throughout that cure time.

09-26-2007, 09:44 AM
Thanks, Figment.

I am thinking I'd rather avoid the high-tech 'chemical key' of CPES by letting it cure and become a stone, then finish. It is an option that appeals in many ways, one of which Warren pointed out above. Besides the chemistry, I like the option of letting it cure because then it is inert and not conceptually part of my finish. When I look at my tiller I don't want to see or think 'epoxy'. Besides that mumbo jumbo, I want a good looking, long lasting finish.

09-26-2007, 10:54 AM
Personally I leave chemistry to the chemists. If Steve Smith says to recoat when partially cured, that's how I'll do it.

After all, you don't let varnish fully cure between multiple coats, right? Same with paint in most cases. As far as I'm concerned, CPES falls into the same category.

Wild Wassa
09-26-2007, 01:39 PM
"After all, you don't let varnish fully cure between multiple coats, right?"

I'm a professional boat painter and that is exactly what I do.

I explain to the owners that I want their boat for a minimum of 3 months (and often longer if the owner can afford to be without the boat) if I'm going to paint her. I like each coat to start to polimerize and be well on the way to hardening before moving on to the next coat.

I find that the longevity of the paint is greatly enhanced if I allow each coat to harden up.

That doesn't mean that I don't do quick jobs but a quick varnish job is about 4 weeks minimum for 4 coats of poly/oil blend. I like a coat of varnish to be well set before moving on to the next coat. Varnish will not actually harden for about 3 months at 20C.

With polyurethane, there are times when I've done 10-12 coats in a day, sanded between coats ... but I only look at that as one thin coat.

If I'm polishing the paint I wait at least 4 weeks at about 20C before cutting and polishing.

Don't ever view paint as having set hard in under 30 days at 20C, no matter what type of medium you are using.

The boat below was painted in an afternoon at the insistance of the owner, about 8 coats of oil based. We booked a heat booth and had the booth for the day, and a drying space next to the booth was booked for a week. I told the owner that the boat shouldn't be turned over for a particular amount of time which was about 5 days even if the paint felt dry. He didn't listen and he and his mate trailered the boat later in the afternoon of the painting because the guys who rented the drying space, wanted the owner to come and pick the boat up at 7am one week from the painting. ... and as he said to me over the phone about 4 hours after the painting of the hull, "It felt dry so I trailered the boat home. I didn't want to go back there at 7 in the morning." My guarantee doesn't cover this type of paint failure.

The boat when it came for painting.


The boat after the painting.


Not much had changed in surface quality.


09-27-2007, 04:03 PM
Personally I leave chemistry to the chemists. If Steve Smith says to recoat when partially cured, that's how I'll do it.

Hey Thorne, I agree, mostly, but here's what's behind my questions:

I realize that finishes prematurely fail when manufacturer directions are not followed. However, it is unclear whether when a chemist is recommending a method, is he relying on laboratory results, or real world (empirical) results.

Every application of any material (especially chemicals) is done in unique conditions, so no blanket statements can be totally accurate. Therefore, I like to wade through as much literature and different perspectives as I can before deciding what to do.

So, I believe in questioning authorities....even chemists, and in those cases when I am an authority (I am a geographer), I question myself. Usually not out loud though, so few people know how nuts I am.;)

Wild Wassa
09-27-2007, 04:56 PM
Manufacturers cater to the safest denominator, that gives a guaranteed usable result across the board to the average user. Whereas the professional practitioners and the heavy users of products raise the bar to new levels, while still remaining consistent with using good techniques.

After detailing my use of BoatCraft Pacific's Aquacote several years ago to Auscraft Marine a SE Oz distributor of BoatCraft Pacific's materials and to the manufacturer in Queensland (many times) and having Auscraft Marine come and look at my results using Aquacote 2 pack water based polyurethane, and heard from BC P that the problem with their paint was actually me, BC P finally changed their application instructions of Aquacote to a more usable level. Their instructions for use then were not giving good results with Aquacote for many people. It is a difficult product to use for part-time painters. Using the product took me along time to understand and even longer for the manufacturer. In the last data sheets BC P have increased the dilution rate and cross linking rate by 50% with their poly clear coat. I can remember a chemist fighting me over that one at least 4 years ago ... but still up the dilution by another 5% above the manufacture's data. The manufacturer is still getting there slowly.

Don't think that we as users of products can't draw any manufacturer's attention to improving their products and have the manufacturers respond favourably to our suggestions. When I was first experimenting with Flood's Floetrol it was not recommended for use by Flood with a water based two pack polyurethane. BoatCraft Pacific basically read me the riot act when I told them what I was doing to their paint with Floetrol. No data existed then with Floetrol added to a 2 pack water based poly. I told Flood about what I found with its use and how I thought it was best used ... the last time I talked to Flood and asked them about their findings with Floetrol added to a 2 pack water based poly ... a chemist at Flood told me that is what Floetrol is for.

It is through feedback to manufacturers that changes for the better happen with many lines. Each time I talk to Steve Goodman at Auscraft Marine, I still tell him what I have found with BC P's products since last seeing him.

It has taken me years to understand some of these products and to discover how to improve their usage. I don't stop exploring with any product ... there are always some improvements that we can find and make with a product to make our use of them, work better for us.

I don't change products that work for me ... but it can take a while before the changes that I made to them, do work well. I can only imagine now how difficult some of these paints, resins and glues are to use for part time users when only following manufacturer's instructions.

Do you find that just as you are coming to the end of using or doing a new process with paint, that that is when you discover how best to do it and you have deviated from the manufacturer's recommendations? ... and sometimes more than just slightly.