Bottom Refinish

[wufibugs]

There have been quite a few threads of late dealing with keel issues and bottom paints. I am a bit confused by the many products that can be layered onto the bottom. At this point I have settled on only 2 things: I will soda blast both the keel and the bottom, and I want to finish with Copper Pro SCX hard.
1. What I have learned is that once the keel is blasted bare it is essential to follow immediately with either por-15 or a barrier coat of some kind before any new rust can get a foothold. If not por 15, then what?

2. Once I have all the paint off the bottom, what is my first step? One or more barrier coats or a primer or both?

3. How many finish coats should I aim for? I suppose more is always better up to a certain point of diminishing returns.

 

[TLW]

You are asking for a lot of information, and I will let others address much of it. I will, however, address barrier coats because it is a real pet peeve of mine. I don't know how ,any times I've seen an add for a used sailboat with the the owner bragging: "I've got two coats of Inter-protect 2000." I just shake my head and think - 'man, you don't have a barrier coat and you wasted every penny you paid for this.'

The product is excellent, but it requires a certain thickness to be effective. Four or five coats is needed to reach the required depth of product. Additionally, you need to plan the application procedure. It is best for the coats to have a chemical bond. That means there is a window of time between coats when the next coat should be applied. A mechanical bond is possible if you miss this window for some reason, but requires sanding before next coat.

You also have to plan how you are going to coat under the straps, if in a hoist, or lower pads in a cradle, and still maintain the application window for the chemical bond. The process is easy enough to apply with a roller, but four or five coats with a roller starts to take on a slight orange-peel appearance and may not suit the hardcore racer. So, sanding after four coats and a fifth coat with mechanical bond is possible. A sprayed barrier coat eliminates the orange-peel, but you need the equipment and still have to deal with straps/pads. We always dedicated a new (cheap) spray gun to each boat, and threw it away after the final coat. We cleaned it after each coat, but not thoroughly as we were using it again in a few hours (chemical bonding window) and it was pretty gummy after the fifth use.

Unused product (small amount) from one coat could be kept (refrigerated) and mixed with fresh product from the next coat. I didn't mention, I guess, that this is a two-part epoxy product and must be mixed prior to use. It then has a short time it should sit prior to application. All this has to figure into the application window, so there is really no sitting around time. Mix - wait - apply - save extra product - clean sprayer (or discard roller) - Repeat four more times, moving straps or lowering pads.

Again, EXCELLENT PRODUCT, and not as complicated as it seems, but you do need to plan ahead, budget time, and have enough product.

Wow - that was lengthy. Aren't you glad I'm not addressing your other questions?

 

[wufibugs]

That is precisely the kind of information I need, and I thank you for it. Just to make sure I am clear on this. Do you feel that Interprotect is the best of he barrier coatings? A I also correct in thinking this product is designed for the bottom, not the keel?

 

[fstbttms]

3. How many finish coats should I aim for? I suppose more is always better up to a certain point of diminishing returns.

Two coats of anti fouling paint on the hull, three at the waterline and leading/trailing edges of the appendages.

 

[Chris Patterson]

Ok, I've got a question then. And trying to stay within the spirit of the post, but why only two full coats? If a person is trying to maximize times between hauls, is more not gooder?

 

[shemandr]

About the keel: You only have to be certain to coat it immediately after prep if its an iron keel. Lead and steel are much more forgiving. Iron begins to oxidize almost before you stop sanding. You do not need barrier coat on the metal. Barrier coats were made to prevent water intrusion into the fiberglass laminate, thru osmosis, which cause blisters. Keels can be coated with epoxy (As opposed to barrier coat which is epoxy with micro plates of impermeable material).
FWIW: If an ad for a boat for sale says "(Whatever # of) barrier coats...." it means the boat could have had blisters.

 

[rgranger]

... We always dedicated a new (cheap) spray gun to each boat, and threw it away after the final coat. We cleaned it after each coat, but not thoroughly as we were using it again in a few hours (chemical bonding window) and it was pretty gummy after the fifth use.

And spraying epoxy is very dangerous to your health. You need to have specialized respirator equipment.... with an external air supply, don a tyvec suit and full face protection.

 

[fstbttms]

Ok, I've got a question then. And trying to stay within the spirit of the post, but why only two full coats? If a person is trying to maximize times between hauls, is more not gooder?

There is a point of diminishing returns. You can put more than two coats on, but after a certain point, you are wasting paint. The 2/3 scheme has been found to be optimum from a cost & performance standpoint.

 

[TLW]

Regarding your question of "best product" - I have been away from the business for a while, so I'm sure new and/or improved products have come along. I believe Inter-Protect to be a great product. On my own racing boat, I used VC-Tar, sprayed, because it was absolutely smooth - slicker than gel-coat, but messier to apply. I imagine all current products are good and whatever fits your DIY scheme is acceptable.

As far as number of coats of anti-fouling, as discussed above - Some "paints" such as VC-17 will thin and dissolve the previous coat with each new application. So, two coats just assures good coverage, more coats just evaporate or run on the ground (or more likely, down your arm.) When VC17 was new (early 80's, I think) it was demonstrated with a coating on a pice of aluminum foil, showing how thin the coating was. It can't be "built up" to any appreciable thickness.

Other paints, different story, of course. Need to just read up on any that interest you.

 

[gpd955]

Ok, I've got a question then. And trying to stay within the spirit of the post, but why only two full coats? If a person is trying to maximize times between hauls, is more not gooder?

Application as fstbttms describes and having your boat routinely checked by a diver is probably the best way to maximize time between haulouts. Having a "built in" reason to haul the boat (like needing to repaint) will force you to maintain the boat better below the waterline. Paint isn't the only reason to get the boat hauled. You'll be able to catch any potential problems before they become emergencies. While you may want to maximize the time between paint jobs, you definitely should have a routine haulout to inspect the boat. Just my opinion.

I have a good friend who hasn't pulled his boat in 7 years. I'm waiting for that call to come get him!!

 

[wufibugs]

Doing a little research uncovered this quote from another forum of 2 years ago:

"Bluewater Marine Paint technical dept. They are recommending their new formulation of coal tar epoxy, Marine AC 70 (although they said their traditional coal tar epoxy works fine). Apparenlty the newer stuff contains a different by-product (tar) that is less noxious and easier to work with...may be what you were refering to as "new generation". The sequence is 1) sandblast 2) AC70, let dry overnight 3) fair w/ epoxy putty, let cure overnight 4) 2nd coat AC70, let dry overnight 5) 3rd coat AC70, let dry."

Since I will be using their finish paint, this seems like appropriate, if not intensive, regimen for the keel. I will have to ask them if the finish SCX hard goes on the keel as well after the AC70 dries.

Andrew, just to be safe, would I be advised to use a barrier coat first? What about a primer on top of that before applying the SCX?

 

[Joetech]

Iron Keel?

As was mentioned before, you don't NEED a barrier coat over a lead keel. I have a Cat 22 with an Iron keel and I used POR 15 which is great stuff. It comes out a little slick. The first year I did just POR 15 and bottom ablative and it rusted through in places. The next season I ground out the rust and put a couple of coats of barrier over the POR. I had 2 coats of barrier on the fiberglass the year before. The combination fo POR and Barrier work very well, at least in fresh water. That was 5 years ago and overall the Iron keel looks good every fall at haul out. I only need to torch up the very bottom of the keel where sometmes it gets into the muck as the water drop in the fall. Last fall I had to crank up the keel to back out of the slip in September. The rest of the keel looks fine, no rust spots.

 

[shemandr]

Andrew, just to be safe, would I be advised to use a barrier coat first? What about a primer on top of that before applying the SCX?

I'm not familiar with those products. So, I don't know. I can't imagine that using a barrier coat would be harmful to the keel. I just meant to convey that barrier coats were developed to protect fiberglass bottoms from osmosis specifically in regard to blisters.

 

[Rich (P303)]

Soda blast... wash with water... scrub with vinegar and water to neutralize... wash with water... fair bottom... 4 coats of Interlux epoxy (change colors)... 3 coats of bottom paint (first coat is a flag coat... let say red... then 2 coats of blue)... go sailing. Your all set till you see the flag coat again. Make sure the flag coat goes on hot over the last of the Interlux (epoxy will not transfer to your finger... but you can leave a thumb print). Good luck!