Cheesy Epoxy

[Boracay]

It would appear that in order for antifouling to bond to epoxy it needs to be applied as the epoxy is setting, as it becomes "cheesy".
As I need to recoat and antifoul the bottom of my "new" boat I am about to try this.
Has anyone had any experience in this area?

[irwinsailor]

I did a West system barrier coat a few years ago and painted after the epoxy cured and have been having the paint peal off. A couple of months ago I heard for the first time that paint can be applied before the cure. I wish I had done it.

[delmarrey]

and my bottom paint is doing just fine. Just give it a good sanding with 80 grit.

West System Epoxy.........................

Final surface preparation

Proper finishing techniques will not only add beauty to your efforts, but will also protect your work from ultraviolet light, which will break down epoxy over time. The most common methods of finishing are painting or varnishing. These coating systems protect the epoxy from ultraviolet light and require proper preparation of the surface before application.
Preparation for the final finish is just as important as it is for recoating with epoxy. The surface must first be clean, dry and sanded.

1. Allow the final epoxy coat to cure thoroughly.
2. Wash the surface with a Scotch-brite(TM) pad and water to remove amine blush. Dry with paper towels.
3. Sand to a smooth finish (Figure 32). If there are runs or sags, begin sanding with 80-grit paper to remove the highest areas. Sand until the surface feels and looks fair. Complete sanding with the appropriate grit for the type of coating to be applied-check coating instructions. Paint adhesion relies on the mechanical grip of the paint keying into the sanding scratches in the epoxy's surface. If a high-build or filling primer is to be applied, 80-100 grit is usually sufficient. 120-180 grit may be adequate for primers and high-solids coatings. Finishing with 220-400 grit paper will result in a high-gloss finish for most paints or varnishes. Grits finer than this may not provide enough tooth for good adhesion. Many people prefer wet sanding because it reduces sanding dust and it will allow you to skip Step 2.
4. 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.
Proceed with your final coating after the surface has dried thoroughly. To reduce the possibility of contamination, it is a good idea to begin coating within 24 hours of the final sanding. Follow all of the instructions from the coating system's manufacturer. A good trick used by professionals, is to make a test panel to evaluate the degree of surface preparation required and the compatibility of the finish system.

Finish coatings

The function of a finish coating like paint or varnish over an epoxy barrier coat, is to decorate the surface and protect the epoxy from sunlight. In doing so, the finish coating extends the life of the epoxy moisture barrier, which, in turn provides a stable base that extends the life of the finish coating. Together the two form a protective system far more durable than either coating by itself.
Protection from sunlight is a primary consideration in the selection of a finish coating. Long term UV (ultraviolet) protection of the barrier coat depends on how well the finish coating itself resists UV and keeps its pigments, or its shield of UV filters on the surface of the epoxy barrier coat. A high gloss finish reflects a higher proportion of the light hitting the surface than a dull surface. All other thing being equal, a white (especially a glossy white) coating will last the longest.
Most types of coatings are compatible with epoxy. Thoroughly cured epoxy is an almost completely inert hard plastic. This means most paint solvents will not soften, swell or react with it. However, it is still a good idea to build a test panel to assure coating compatibility.

Coating types
Latex paints are compatible with epoxy and they do an adequate job of protecting the epoxy barrier from UV radiation. In many architectural applications latex paint may be the most suitable coating to use. Their durability is limited.
Alkyd finishes-enamel, alkyd enamel, marine enamel, acrylic enamel, alkyd modified epoxy, traditional varnish and spar varnish-offer ease of application, low cost, low toxicity, and easy availability. Their disadvantages are low UV resistance and low abrasion resistance.
One-part polyurethanes offer easy application, cleanup and better properties than alkyds. They are also more expensive and some may be incompatible with amine cure epoxy systems such as WEST SYSTEM epoxy, although 207 Hardener may offer better compatibility. Test first.
Epoxy paints are available in one-part and two-part versions. Two-part epoxies offer many characteristics similar to the higher performance polyurethanes. They are durable and chemical resistant, but offer limited UV protection compared to the linear polyurethanes.
Two-part linear polyurethane (LP) paints offer the most durable protection available. LP's are available as pigmented or clear coatings and offer excellent UV protection, gloss retention, abrasion resistance, plus compatibility with epoxy. However, compared to other types of coatings, they are expensive, require more skill to apply and present a greater health hazard, especially when sprayed.
Bottom paints are available in a variety of formulations. Most bottom paint systems are compatible with epoxy and can be applied directly over a prepared epoxy barrier coat. If you are unsure of compatibility or have curing or adhesion problems with a specific bottom paint, use only a primer recommended for that bottom paint over the barrier coat. Follow the recommendations given for preparation of fiberglass surfaces. Other paints, including marine LP's and primers, are not recommended for use below the waterline.
Primers are usually not needed to help a paint film bond to epoxy, although interfacing primers may be required with some specialized bottom paints and high-build primers are useful for hiding scratches or flaws in the substrate. If the instructions on your paint or varnish recommend a specially primed surface, follow the recommendations given for fiberglass preparation. Self-etching primers do not work well on an epoxy coating because of epoxy's chemical resistance.
Polyester gelcoat is a pigmented version of the resin used to build fiberglass boats and other products. Gelcoat is sprayed into a mold before the glass fabric and resin are applied to provide a smooth pre-finished surface when the part is removed from the mold. It is not often used as a post-production finish coating, but it can be applied over epoxy and is useful in some repair situations. Refer to 002-550 Fiberglass Boat Repair and Maintenance, published by Gougeon Brothers, for detailed information on patching gelcoat over an epoxy repair.
Follow all instructions from the coating systems manufacturer. It is a good idea to make a test panel to evaluate the degree of surface preparation required, and the compatibility and handling characteristics of the finish system.

For detailed instruction on the application of these techniques in repair and construction, refer to specific WEST SYSTEM instructional publications and videos. For complete descriptions of all WEST SYSTEM products, including selection and coverage guides, go to the Product Guide.

To help you identify and prevent potential problems associated with using epoxy, go to the Problem Solver.

For complete information on the hazards associated with epoxy and the precautions you can take to avoid them, go to Health & Safety.

To see how these techniques have been put to use in a wide range of repair and construction applications go to the Projects pages.

[hellosailor]

I'd suspect the paint peelingand the "cheesy" problem are both from amine blush as mentioned in the Problem Solver pages. Once cured AND PREPPED the epoxy should take a wide range of coatings without problem, but you'd need to check with the paint maker for compatibility.

I've put bottom paint (offhand, I think it was Micron66, a hard paint) over cured epoxy (Copperpoxy, a full season old and aged) without any problems.

[Alan Wheeler]

NEVER paint over uncured Epoxy unless it is another Epoxy. And even then you have to be careful you don't have a Solvent base in your Epoxy paint. Certainly don't put Anti-foul over Epoxy when wet. It does not make the two surfaces "bond". The only way to Anti-foul is to ensure the Epoxy has cured. Ther Manufacturer will state min and max repaint times and you need to know these for both Epoxy and for the next coating system to go over. Some paints MUST have a Primer, some don't, so always follow the instructions.
For Epoxies that have well cured, YOU MUST abrade and use a Primer.

[Steve Kidson]

My ply decks were sheathed and coated with an Epoxy resin. It was well sanded with an 80 grit paper and thoroughly cleaned down prior to 2 coats of primer/undercoat (Pre-kote by International) and 2 coats of International Interdeck.

This was done some 18 months ago and shows no signs of peeling/lifting etc.

Deck is now as tight as a drum, not a drop of water gets in (under normal circumstances).

Fair winds

Steve

[irwinsailor]

It is true that I misunderstood the instructions and did NOT apply a primer to the bottom before applying the bottom paint. I did however sand the epoxy.
The peeling that we have had in not all that much but I would like it better if it did not peel.

[seaclusion]

I have put epoxy barrier coat on three different boats over the past 20 years (WEST system on two and Interlux on one) and put the first coat of bottom paint on as the epoxy is just curing. Not wet but still tacky to the touch. I use a cheap modified epoxy bottom paint of a contrasting color to the final coats of bottom paint as the tie coat. Then I paint several coats of ablative over this.

In twenty years I have not had a failure of any type. When the color of the cheap modified epoxy bottom paint starts to show through I know it is time to haul and put on a few more coats of ablative. I no longer have to scrape fifteen coats of old bottom paint off before applying anti-fouling and the ablatives seem to work great at keeping off growth here in the sub-tropics.

Having said all that, you should always follow the manufacturers directions on application techniques in case your particular brand may be incompatible with this technique.

Richard

[Alan Wheeler]

It is important to understand that there are many wide and varying conditions and reasons why one person may have good results and another bad. It is important to follow the manufacturers recomendations, as this narrows done the possibilities of failure occuring.
One of the many reasons why you should not paint over a still curing Epoxy is the epoxy actually will not adhere to the wet paint very well. BUT!!! it does depend on the paint AND most importantly, what solvent base the paint is using. Think of it this way, would you apply oil to the surface of a coat of cured Epoxy and then apply a paint coat? Well some paints use a mineral based solvent, some don't. When a paint using a mineral based solvent is wet, the tacky Epoxy surface actually creates a barrier by trying to stick to the solvent, NOT the paint. Then the solvent eventually dries away and leaves a poor bond. It is much like painting on a damp surface too early in the morning.
Cured Epoxy has a very hard and VERY smooth non-porouse surface. Once cured, it is very hard for anything to stick to it.
Most Solvent based paints adhere to the under paint in two ways. The solvent attacks the surface of the paint underneath and the two layers bind and the other is a mechanical key due to the porouse nature of paint. Cured Epoxy will not bind in any other way than mechanical bond. So it MUST be "Keyed" by ruff sanding first.
The reason why Epoxy can be placed over itself when new and still adhere, is that the crosslinking chains are still occuring for many days after the epoxy is hard. Epoxy will adhere to itself by chemicaly bonding to the layer beneath.

He is a little more info that maybe of interest. The raw Material of Epoxy is made by just a handful of companies worldwide. It is NOT sold to the end consumer by these companies. The epoxy companies that WE know, buy the raw material ion huge quantities and then slightly modify it to suit their needs and on sell it to the consumer. So all in all, the basic make up of Epoxy today is pretty much the same, no matter what brand name you choose. Hardeners actually have the greatest influence on performance of Epoxy than the Epoxy itself by the way. Modern Epoxies are what are considered as "high solids" Epoxies. They cure by the creation of a complex molicule chain creating via an exothrmic reaction. While the Epoxy is liquid, these chains can readily come together. As the Epoxy hardens, the chains coming together become harder and slower till finaly the chains can no longer be made. But trapped in the cured Epoxy is still uncured epoxy. The curing proccess can go on for months and eventually will never fully cure. By allowing the epoxy to go through an initial cure process of ruffly 24hrs, you can then make a much stronger and harder Epoxy by heating it. The heat softens the Epoxy and allows the exothermic reaction to continue. Those chains that have not come together during the initial cure process are now allowed to move more freely and will come together more redily. A temperature of about 50 C is applied to continue the cure, for another 24 to 48hrs.

[seaclusion]

It is indeed important to follow manufacturers directions. Interlux recommends recoating it's barrier coat before the epoxy has had a chance to fully cure and recommends that the first coat of bottom paint be applied before the barrier coat has fully cured (usually less than 12 hrs depending upon ambient temp and humid).

The Gudgeon brothers, probably the foremost experts on working with WEST brand epoxy, recommend the same proceedure when using WEST epoxy.

So I reiterate, always follow manufacturers directions and in this case recoat within the specified time frame.

Richard

[Alan Wheeler]

Yes follow the instructions, because both those groups note a minimum and maximum time. Which tends to be the trend for ALL coatings.