Barrier Coat Longevity

[Keegan]

My boat came new with a thin barrier coat on the bottom of the solid FRP hulls. To effectively shield against osmosis, how often should one replace the barrier coat? Every two years? longer?

What is the best way to re-apply the barrier coat for the best result? Is there a preferred brand of barrier coating that is considered the "gold standard"

Thanks
Keegan

[edboat]

A good barrier coat should last a long time provided the bottom isn't damaged. I have seen barrier coats that have lasted 10 years with no issues. To determine how good a barrier coat is ask to see the perm rate of the coating. The lower the moisture perm rate the better the coating. Most boat yards will put on a coating that will have you coming back in 2-3, or 4 years to replace.
The best way to reapply a barrier coat is to take the coating off if it is not adhering to the hull. If it is adhering sand or blast off the old anti-fouling and reapply to the old but abrated barrier coat. When you get the correct amount of barrier coating on you can then apply a first coat of anti-fouling to get a chemical bond.
When applying coating make sure that you get the correct amount of milage on the hull. A lot of the yards will tell you there are putting on 2 coats of paint, which is OK as long as they get on the manufactureres specified milage per coat. Most don't. Milage is the amount of paint applied measured in MIL's a mil is a thousandth of an inch in the states and micron's in most of the rest of the world. If you aren't getting the correct amount of coating on the hull your paint job will not last as long. There is a lot involved in getting a good barrier coat as well as good anti-fouling over it and the important thing is the prep for the coating. Without good prep no matter what type of coating you are getting it will not preform as well as it should. Prep is everything.

[GordMay]

The best manual on Barrier Coating comes from Gougeon Bros:
Gelcoat Blisters: Diagnosis, Repair & Prevention ~ West System (002-650)
Gelcoat Blisters: Diagnosis, Repair & Prevention

See also:
Repairing individual and early stage gelcoat blisters ~ by Tom Pawlak
http://www.westsystem.com/ewmag/17/p...inggelcoat.pdf

Excerpted from the West System “User Manual” < WEST SYSTEM Epoxy >

EPOXY BARRIER COATING:
The object of barrier coating is to build up an epoxy coating that provides an effective moisture barrier and a smooth base for final finishing.

Apply a minimum of two coats of WEST SYSTEM epoxy for an effective moisture barrier. Apply three coats if sanding is to be done. Moisture protection will increase with additional coats, up to six coats or about a 20-mil thickness. Additives or pigments should not be added to the first coat. Mixing thinners with WEST SYSTEM epoxy is not recommended.

Disposable, thin urethane foam rollers, such as WEST SYSTEM 800 Roller Covers, allow you greater control over film thickness, are less likely to cause the epoxy to exotherm and leave less stipple than thicker roller covers. Cut the covers into narrower widths to reach difficult areas or for long narrow surfaces like stringers.

Complete all fairing and cloth application before beginning the final coating. Allow the temperature of porous surfaces to stabilize before coating. Otherwise, as the material warms up, air within the porous material may expand and pass from the material (out-gassing) through the coating and leave bubbles in the cured coating.

1. Prepare the surface for.
2. Mix only as much resin/hardener as you can apply during the open time of the mixture. Pour the mixture into a roller pan as soon as it is mixed thoroughly.
3. Load the roller with a moderate amount of the epoxy mixture. Roll the excess out on the ramp part of the roller pan to get a uniform coating on the roller.
4. Roll lightly and randomly over an area approximately 2 ft x 2 ft to transfer the epoxy evenly over the area (Figure 30).
5. As the roller dries out, increase pressure enough to spread the epoxy into a thin even film. Increase the coverage area if necessary to spread the film more thinly and evenly. The thinner the film, the easier it is to keep it even and avoid runs or sags in each coat.
6. Finish the area with long, light, even strokes to reduce roller marks. Overlap the previously coated area to blend both areas together.
7. Coat as many of these small working areas as you can with each batch. If a batch begins to thicken before it can be applied, discard it and mix a fresh, smaller batch.

8. Tip off the coating by dragging a foam roller brush lightly over the fresh epoxy in long, even, overlapping strokes after each batch is applied. Use enough pressure to smooth the stipple, but not enough to remove any of the coating (Figure 31). Alternate the direction in which each coat is tipped off, 1st coat vertical, 2nd coat horizontal, 3rd coat vertical, etc. A WEST SYSTEM 800 Roller Cover can be cut into segments to make a tipping brush.

Recoating

Apply second and subsequent coats of epoxy following the same procedures. Make sure the previous coat has cured firmly enough to support the weight of the next coat. To avoid sanding between coats, apply all of the coats in the same day. See Special preparation-Cured epoxy. After the final coat has cured overnight, wash and sand it to prepare for the final finish.

[GordMay]

Does anyone have any experience with “ CeRam-Kote Coating Products”?
CeRam-Kote Industrial Coatings

[edboat]

I have a lot of experience with CeRam-Kote. 4 of my boats have CK on the bottom as the barrier coat. It is extremly tough and has a very low moisture perm rate. I will also admit that I am a rep for the products. CeRam-Kote came out of the oil and gas industry, compared to that industry the salt water environment isn't to bad. I don't want to use this forum to push the coating, but if anyone has questions I will try to answer them either here or through PM.

[Boracay]

Does anyone have any experience of using powdered copper in epoxy as a barrier coat on fibreglass?

Looks great in theory...

[edboat]

Powdered copper has been mixed with epoxy to be used as an anti-fouling paint. There have been mixed reviews on these products. I have never seen it used as a barrier coat.

[GordMay]

Epoxy Barrier-Coat additives are usually mostly Auminum powder.

[cooties]

What sort of things could cause damage to the barrier coat other than impacts? Do barnacles cause damage?

[slug]

Moisture enters the laminate from both sides

How long an exterior barrier coat lasts is unknown

Best advice is to keep an eye on it and measure moisture content when the boat has been hauled out for an appropriate time