Best time to apply anti-fouling paint after applying epoxy barrier primer?

[Easterly-30]

Someone told me that I should apply my anti-fouling paint as soon as the minimum re-coat time has elapsed after applying the epoxy barrier coat. Does that matter? Will it affect the adhesion of the anti-fouling paint? The Pettit SR-60 instructions don't say anything about this. I'm using Pettit Protect epoxy primer. Thanks.

[barnakiel]

I know the following applies to International paints:

- thumb tack test the epoxy primer,
- apply first coat of antifouling.

The idea is to bind the two paints.

In a word, do NOT exceed the overcoat time as specified by the maker of the epoxy primer.

I have seen boatyard people applying the same technique - painting first AF coat over still sticky/tacky epoxy primers.

b.

[wingless]

According to the Pettit Protect Technical Bulletin the time between epoxy coats and the time to top coat are specified versus temperature in the application data section.

Follow the manufacturer's instructions.

[zboss]

The difference is in forming a chemical vs. a physical bond.

You can apply anti-fouling at any time (pretty much) after the application of the epoxy... this is why you can apply anti-fouling over the years after the barrier coat has been applied.

This will give you a physical bond, since the paint is able to bind to the surface through the ridges and valleys you create when sanding... what you lose is the chemical bond that can be created between the epoxy and the hard anti-fouling.

I just went through this with Pettit. I applied four coats of high build epoxy and two coats of the Pettit Trinidad SR. I called Pettit and talked to them directly... you can apply their Trinidad hard anti-fouling NO SOONER than the prescribed time but up to 14 days after the application of the epoxy, in order to achieve a chemical bond. The sooner the better.

I was advised by Pettit that I should be good for a number of years with this application but then after that only apply their ablative paints once the second coats of the hard paint starts to show through. This preserves the hard paint while avoiding long term paint build up and the need to soda blast at some time in the future.

[Easterly-30]

Thanks all! Those were all great comments. So, I have gleaned from the above that it is not absolutely necessary to paint the ablative on the same day as the epoxy in order to achieve a chemical bond, but that the next day would be good too. However, according to the Pettit technical bulletin the time from epoxy to bottom paint at 90 degrees is 3 to 6 hours; therefore, it ought to be put on the same day.

[zboss]

3-6 hours is the MINIMUM time needed before beginning the next coat. This is to allow time for the paint or epoxy to off-gas the volatiles. If you paint over sooner, you risk enclosing the volatiles and preventing the epoxy from ever curing properly.

A couple of more details that will help you plan your painting days:

It is the start of fall here in DC. We are by the water. In the morning, there is still dew on pretty much everything and it takes several hours for that dew to burn off. You can't paint or apply epoxy over a dew or wet surface. So, the sun comes up at around 7 AM right now and it takes about an hour to burn the dew off.

So, the earliest you can begin painting is about 8 or 8:30 AM. Assuming you are outside.

Then, it takes about an hour to paint one coat on each side of the boat, lets assume you are working in tandem with a partner so it only takes an hour to do the whole bottom... you are finished applying the first epoxy at 9 or 9:30 AM. Then you have to wait about 3.5 or 4 hours for before applying the next coat. So, you can begin painting the next coat at about 1 PM. Then, 1 hour.

Second coat... starts at 2 and takes an hour... third coat starts at 7 PM and takes an hour.

You can't paint after 7 or so according to Pettit. Dew problems as the paint/epoxy puts off heat when curing. What are you to do? Not paint late in the fall is what you do.. because you need to apply when the temp is higher, or you spread out your painting over a number of days.

Remember you need AT LEAST 3 coats of Pettit protect. So, the more the better and that is assuming you are actually painting the correct thickness on the hull, which you don't know unless you use a mils tool.

The reality is that working in those monkey suits is REALLY HOT and uncomfortable. Also, be sure to wear good chemical respirators when painting the epoxy and the Trinidad SR. Both chemicals have warnings that say "KNOWN to cause cancer" not "MAY cause cancer". Also, the Trinidad SR smells like BLOOD. Its nasty!

[wingless]

Originally Posted by zboss

Both chemicals have warnings that say "KNOWN to cause cancer" not "MAY cause cancer".

The MSDS sheets have the standard: "Warning: This product contains chemicals known to the State of California to cause cancer."

So, if the product is applied elsewhere, normal precautions, as-defined in the MSDS, are appropriate.

It may just be that living in California causes cancer...

[Capt Hugh Wilde]

Put on the epoxy and when it has dried enough to leave a fingerprint in it without getting any on you finger, it is ready to overcoat.

[Krogensailor]

I think we're getting epoxy paint/primer and epoxy mixed together here. Chemically bondeing epoxy primer to top coat makes good sense. But epoxy barrior coat, as in west epoxy rolled onto the bare hull, needs to kick off completly before any painting is done. And the thought that there is a , " risk enclosing the volatiles and preventing the epoxy from ever curing properly", wouldn't be the issue. Epoxy, as such does not cure by off gassing of volatiles. It is a chemical linking reaction, not an evaporation one. So I'd say you apply your epoxy barrior coat's. "Put on the epoxy and when it has dried enough to leave a fingerprint in it without getting any on you finger, it is ready to overcoat". Yes, overcoat with more epoxy, not paint. It has to cure completly before priming with any paint. Let it kick some number of days. Sand with, say 120. Apply primer and then do the fingerprint, or what have you test, apply bottom paint. I'm thinking that would be the correct sequence. I could be wrong.

[Capt Hugh Wilde]

Originally Posted by Krogensailor

I think we're getting epoxy paint/primer and epoxy mixed together here. Chemically bondeing epoxy primer to top coat makes good sense. But epoxy barrior coat, as in west epoxy rolled onto the bare hull, needs to kick off completly before any painting is done. And the thought that there is a , " risk enclosing the volatiles and preventing the epoxy from ever curing properly", wouldn't be the issue. Epoxy, as such does not cure by off gassing of volatiles. It is a chemical linking reaction, not an evaporation one. So I'd say you apply your epoxy barrior coat's. "Put on the epoxy and when it has dried enough to leave a fingerprint in it without getting any on you finger, it is ready to overcoat". Yes, overcoat with more epoxy, not paint. It has to cure completly before priming with any paint. Let it kick some number of days. Sand with, say 120. Apply primer and then do the fingerprint, or what have you test, apply bottom paint. I'm thinking that would be the correct sequence. I could be wrong.

I was speaking of epoxy barriercoat, not epoxy. Most barriercoat can be overcaoted with barriercoat for anywhere from a week to a month without sanding.
But the last coat before bopttom paint should be allowed to dry till you can leave a finger print in it with out getting any wet paint on your finger

[Krogensailor]

"epoxy barriercoat" ? Are you talking about a paint product? In my neighborhood barrier coat is straight epoxy applied in a number of coat's, allowed to harden and then painted over.

[Capt Hugh Wilde]

Originally Posted by Krogensailor

"epoxy barriercoat" ? Are you talking about a paint product? In my neighborhood barrier coat is straight epoxy applied in a number of coat's, allowed to harden and then painted over.

Yes, a high solids epoxy paint, such as Devoe 235, International Interprotect,
or Awl-Grip Hull Guard and Pettit also has one.

In the mid 90's I did several blister jobs using a process where after blasting and drying, the large defects were repaired thickened epoxy and sanded.
Then a coat of barriercoat was sprayed on the bottom.
Then a mixture of the barriercoat mixed with cab-o-sil was troweled over the first coat to fill any small defects.
This allowed to dry until hard enough to sand.
When all defects were corrected, sprayed 2 to 3 coats of barrier over a course of 2 to 3 days.
On the last barrier spray, it was allowed to dry until you can leave a fingerprint in it without getting any on your skin.
Then spray a light coat of bottom paint. Allow to dry a couple of days,, then spray the rest of the bottom paint on her.
Then let her set for 3 to 5 days to let the whole job cure together.

I liked that most of the work can be done with an airless sprayer, and most of the barriers have a 2 to 4 week overcoat window without sanding when you apply another coat of barrier.

However, do not do this with any vinyl paint system, as the bottom paint will spider web.

Last winter I saw a Hatteras 45 that I used this process on in 1994, and she had been stripped back to the barrier, it was in perfect condition, they cleaned it up, put a light coat of barrier on her, then shot the bottom paint over the soft barrier.
Good for another 20 years.

[barnakiel]

Painter beware some epoxies blush and if this is your case, you must remove the blush prior to painting over or else the AF paint will simply slime down.

On some products they actually say to wash down plenty of times, dry out for weeks then sand lightly, only then paint over.

So I think the on-tack method saves plenty of time and effort, huh?

b.

[Capt Hugh Wilde]

Originally Posted by barnakiel

Painter beware some epoxies blush and if this is your case, you must remove the blush prior to painting over or else the AF paint will simply slime down.

On some products they actually say to wash down plenty of times, dry out for weeks then sand lightly, only then paint over.

So I think the on-tack method saves plenty of time and effort, huh?

b.

Using straight epoxy resin, you are spot on. That is why I prefer to uses a epoxy paint based barrier coat system after the gross repairs are made with epoxy resin products.

[Ryban]

Reviving an old thread for my sake here, but, what exactly is the different between epoxy barrier coats, epoxy primers, and straight-up epoxy? The internet seems mostly devoid of technical information, and mostly full of opinions.

As I understand it, epoxy barrier coats are two-part epoxy resins with high solids content (often proprietary) to improve moisture resistance. This also gives them their opaqueness.

Epoxy primers -- I really can only seem to find what they're for, but not what they are.

Why would the thumb-tack overcoat rule for antifouling apply to an epoxy barrier coat or an epoxy primer, but not to a straight-up epoxy?

I'm creating my own epoxy "barrier coat" with an epoxy resin, pigment, and graphite powder, and am in doubt about when to apply my anti-fouling after the final coat of epoxy.