Do I need to strip my bottom?

[barnakiel]

I think the range of 3 to 8 coats depends on dry thickness perhaps. Not all products contain the same amt of solids nor do they dry to the same thickness of a single coat. Add the application method (brush, roll-on, spray, airless, etc.)

And so 3 or 8 may each be correct, depending on which product you use.

Back to OP: my take is that if all the doubt comes from visual differences (rather than surface bumps or other surface challenges), I would just paint it over. Not a recommendation, only my own attitude on my own boat.

b.

[Alita49DS]

A cautionary tale: at the suggestion of the yard, I let them sand blast the bottom of my boat this year.

They did a good job of removing the old paint and not damaging the gel coat.

However, and this is a huge however, they failed to protect the openings to the stern tube through the sea cock that keeps it cool and/or the exit point. The result was that fine sand entered and the fibreglass stern tube rotated and was destroyed. Within moments of the boat being splashed and drive engaged. The sand had set like concrete.

I ended up spending a huge amount of money to have the boat repaired and usable.

[a64pilot]

Be sure the glass is dry before you barrier coat it.
My boat had little "pox" blisters on it when I bought it. Little .25" blisters that were in the gel coat. They were in clusters, only a couple of cluster on the whole hull, maybe 10% coverage?
One year later at first bottom job, most were gone, last years bottom job, they were all gone.
PO paid to have the boat stripped and barrier coated. I feel certain there was moisture still in the glass when it was barrier coated and this trapped moisture led to the "Pox". Moisture eventually dissipated, I assume to the interior of the hull over a three year period.
I can't figure out any other reason for the "Pox" disappearing and not growing in size.

In my case, I'm not so sure barrier coating a then 27 yr old boat made sense, maybe should have just had a bottom job done.

[stnick]

I would find a yard to water sand blast the bottom. Does not remove it all but sure does 80% . Than rough up do 2 barrier coats and 3 coats of Tropic Sea Hawk made in Largo Fl for the gulf. I painted first coat RED next two coats Dark blue. In fla I have to ge the bottom scrapped every 30 days in Summer. So when the diver sees red i have another year. I'm running 3.5 years between haul outs now. Im in the river so 50/ 50 salt and fresh water
I could go 4 years in all salt water. !

[skipgundlach]

I did a massive bottom job. You can see our bottom job work here: Pictures: Flying Pig Refit 2011-2012/Bottom Job

At the risk of thread drift, drying out blisters is not a matter of exposure or heat or barns or the usual. Blisters are a product of uncatalyzed water soluble material (UWSM). Add water and they expand slightly. Any boat built of polyester resin (most until relatively recently) will have some, if not a lot.

Until that's gone (not merely dried out), you'll have the risk of repetition, even under barrier coats, as ours were after a PO had peeled and barrier coated.

The solution (pardon the expression) is to wash it out - water, under pressure, preferably, rinse, repeat, grinding all non-laminated areas away as you go, until you get no more weepage. THEN you can repair and fair. We saturated the hull with a hose one day, and pressure washed it the next. Any time we saw tell-tale weeps, we ground the underlying lamination voids out. After we'd had several repetitions of no-weep, we brought in a steam pressure washer; that showed two TINY places, after chasing which, we considered ourselves finished.

Following our repair, we used an epoxy-based fairing compound capable of going to a full inch without sagging; we didn't ever allow more than a maximum of about 1/4 inch. The rest we built up with new glass and West System epoxy.

This is the fairing compound we used. It comes in one and two gallon pails (mix batches, total 2/4 gallons): http://www.axson-technologies.com/si...0UltraFair.pdf

An example at retail: https://www.merrittsupply.com/produc...ltra-fair-kit/

We used cheap thin plastic cutting sheets (like a cutting board but very thin) to mix on, and then washed them with acetone, ditto application tools. Several hours to green, but a full day made it like concrete, despite the expected full cure being several days. Best to do your rough sanding when it's firm enough that you can't ding it with your fingernail but not any more than a full day out unless you want a great deal more work than you could have had earlier.

I learned about Sherwin Williams marine coatings from a paint pro (boat and airplane paints) in the same yard; he used them on his boat. They make a great tropical-waters ablative (tested in Key Biscayne), in two mixes, as well as barrier coat, to milspec levels. Talking with their head tech told me that there is such a thing as too much barrier coat; I no longer recall the number, but there is a specific mil thickness they recommend not exceeding - get a mil gauge to see how deep any coat is as it's applied. I think we used 4 or 5 coats, in differing colors, to alert us to any damage as well as when we ran out of bottom paint. First several BCs were red, and final gray; first AF black, top red...

You put on the first coat of AF as the BC topcoat gets 'tacky' - a very limited window. That's why you'll see pix of black over gray nearly simultaneously:

You can see the paint (barrier coat and bottom paint) portion of our work here: Pictures: Flying Pig Refit 2011-2012/Bottom Job/4 - Barrier and Bottom Coats

We launched in late January 2013, and the boat has never been further north than the fecund waters of the Charleston City Marina, mostly being in the tremendously foul ICW at Vero Beach FL or in the Bahamas.

In that 4.7 or so years, it's been scraped irregularly, and, when I'm in the Bahamas, scrubbed (ground on a falling tide, put on lots of weights and use a hookah to breath while I take a deck brush to the hull) occasionally.

This last trip back - after being in the Bahamas for over 2 months without ever scrubbing - from Green Turtle Cay to Vero - took ALL the growth off.

We are starting to show the next color down in many places; we used 2 coats everywhere and 3 or more coats at the waterline and hard points, including the entirety of the bow-to-tip-of-rudder bottom-most line.

Based on our usage, we probably will have to pull the boat sometime before it actually needs it, to attend to something else important, but our FIRST coat isn't gone at close to 5 years. However, a suggestion my buddy made, while wonderful initially, has not held up well at all: Do the reveal stripe in brilliant white Pettit Vivid. Indeed, it cleaned readily - but most of it in many areas is now gone, leaving our fairing compound exposed where it happened to be, or gelcoat, where there hadn't been damages needing attention. I think I'd do it again, but with massive numbers of layers, as it ablates TOO easily. Back to Sherwin-Williams...

They make two types of ablative paint. My buddy, because they didn't have my type in stock, used the harder (presumed - designed for boats over 10 knots rarely at rest) ablative; it still gives great service. We use the softer ablative, designed for our type of use - under 10 knots, and frequently at rest.

Here are the relevant links for both types of bottom paint. Spec is 2-3 years, and easily-brushed slime is typical after 18 months per their info, but we’ve gotten much longer from ours.

Copper Bottom Anti-Fouling Paint #45 - Protective & Marine – what we have, available in 4 colors - I don’t recall now whether I had to go to FTL for it, but I THINK they inter-office shipped it to the local S-W shop, as it wasn't in stock in the FTL store, and was ordered for us.

Seaguard Ablative Anti-Fouling Coating - Protective & Marine – what my buddy I told you about has, and he’s happy; it’s more likely to be in stock, though you might have to go to some major marine area to get it.

In either event, of course, you'll more likely find it in marine areas, but it could be shipped anywhere. Ours was $85/gallon in 5-gallon buckets in late 2012. I have no idea how much it will be today, but we were on the order of a third to a quarter of "marine" products that most folks use. The only improvement I could think of would be tin

https://www.paintdocs.com/docs/webPD...&prodno=N51B45 – ours

https://www.paintdocs.com/docs/webPD...prodno=P30BQ12 – buddy’s

They also made our barrier coat; https://protective.sherwin-williams....3Aproduct-6939

Our prior bottom paint had been the very best West had to offer; we got much less time from it, at massively more cost.

According to my paint pro, the US Navy and Coast Guard use it; I certainly have been pleased.

YMMV, but at that price, and if you haul regularly, it's worth a shot.

FWIW, in the godawful areas of St. Marys GA, cleaning was a matter of using a wide drywall taping knife (very wide spatula) and running stripes down the hull at next to no effort. If we'd been sailing, they might have even just ablated off, but we spent an entire summer at a dock there (those docks are now gone courtesy of Irma). We have found no circumstances of hard growth that would not flake right off...

L8R

Skip

[Suijin]

Originally Posted by Jim Cate

I'm not a pro, but to me 8 coats of barrier seems a bit over the top (!) to me. Most of the pro folks seem to apply 2 or 3 coats. I doubt that the next 5 coats bring much advantage to the system.

Jim

Most of the pro folks want to get it done quickly and at a price that the customer will accept. And they use the "retail" product which is thicker and rolls out to a greater mil thickness per coat.

In addition, if you're sanding it smooth after application (which you really should do, or live with the orange peel forevermore), you're taking off a good amount of material.

And epoxy is not fully waterproof. The thicker the better.

[stnick]

Wow I had no idea you had that many blisters, Yes NO WATER BLASTING
Any sand blaster would never blast around a stern tube and ruin a cuttless, And I have seen that done by a know it all yard manager sand blasting for the first time ! After the bottom job on that 40 is main ship it did not make it away from the yard 1/2 mile
Bothe props wer repulled and neww cutless bearings replaced all on the yards dime. ! Your doing all the right things with all those blisters
I did have a few blisters 10 on my Sabre after grinding i used a heat gun to speed the dry time. in a circle and watched the water boil off. Than west system epoxy seal the hole.
Glass and marine fairing compound followed.
Keep up the hard work.

[ramblinrod]

My company consults on and performs bottom work for a lot of boaters.

First some definitions:

Adhesion Failure: Large chunks of anti-fouling paint have flaked off, and it is difficult to roll on more paint without it pulling off in chunks and redistributing with the new paint. Solution, get it all off down to the gelcoat or barrier coat and stop using cheap anti-fouling paint.

Chemical Incompatibility: New paint wrinkles the old, or makes it look like alligator skin. Solution, get it all off down to the gelcoat or barrier coat and use barrier primer and quality anti-fouling from the same maker.

Primer: A paint with excellent adhesion characteristics. Never apply anti-fouling to gelcoat without at least one primer coat in between.

Orange Peel: Peaks and valleys (looks like roller stipple) in the surface that increases with each coat, common to most barrier coats. Solution: Spray, or
apply specified build coats, allow to fullly cure, sand smooth, and then apply thin film as tie coat.

Barrier Coat: A two part epoxy paint with excellent adhesion and water impermeabilty characteristics. Usually requires 4 coats for max effectiveness. One coat may be used as a primer coat. When multiple coats are applied while green to achieve chemical bond and avoid sanding, orange peel will increase with each coat rollled. Solutions are to spray, or apply 4 coats, allow to fully cure, sand to smooth surface then apply a final thin film coat of barrier and then antifouling while last barrier coat is still green.

Cheap anti-fouling paint never pays off. It builds over the years, and then adhesion starts to fail requiring complete stripping at an expense that moe than negates any saving in paint purchase price. For power boats, the poor fuel
Economy associated with a rough patchy bottom, more than negates the paint purchase price savings. On sailboat bottoms, clean and smooth vs clean and right can make the difference of a half knot, which may seem like nothing, but at 5 knots vs 4.5k knots, one will sail 120 instead of 108 miles per day. If two boats leave an anchorage at 10 in the morning and first arrives at the next at 5 pm, the first can enjoy a swim 45 minutes sooner than the latter.

A good bottom adds value to a boat, for anyone who knows about such things.

[flyingfin]

Its the bottom of your boat, not the hood of a classic Corvette!
The bottom paint is simply to prevent growth. As long as you have faired and primed any glass, your structural integrity if fine. I have seen people go way overboard on stripping bottoms, or spend weeks on end chasing osmotic blisters. Blisters can stay for 10 years and never grow larger, then when you finally punch them open they are still full of un-cured resin and not allowed any water to penetrate the hull. Aesthetic concerns are all on deck!

[UNCIVILIZED]

Originally Posted by skipgundlach

I did a massive bottom job. You can see our bottom job work here: Pictures: Flying Pig Refit 2011-2012/Bottom Job

At the risk of thread drift, drying out blisters is not a matter of exposure or heat or barns or the usual. Blisters are a product of uncatalyzed water soluble material (UWSM). Add water and they expand slightly. Any boat built of polyester resin (most until relatively recently) will have some, if not a lot.

Until that's gone (not merely dried out), you'll have the risk of repetition, even under barrier coats, as ours were after a PO had peeled and barrier coated.

The solution (pardon the expression) is to wash it out - water, under pressure, preferably, rinse, repeat, grinding all non-laminated areas away as you go, until you get no more weepage. THEN you can repair and fair. We saturated the hull with a hose one day, and pressure washed it the next. Any time we saw tell-tale weeps, we ground the underlying lamination voids out. After we'd had several repetitions of no-weep, we brought in a steam pressure washer; that showed two TINY places, after chasing which, we considered ourselves finished.

Following our repair, we used an epoxy-based fairing compound capable of going to a full inch without sagging; we didn't ever allow more than a maximum of about 1/4 inch. The rest we built up with new glass and West System epoxy.

This is the fairing compound we used. It comes in one and two gallon pails (mix batches, total 2/4 gallons): http://www.axson-technologies.com/si...0UltraFair.pdf

An example at retail: https://www.merrittsupply.com/produc...ltra-fair-kit/

We used cheap thin plastic cutting sheets (like a cutting board but very thin) to mix on, and then washed them with acetone, ditto application tools. Several hours to green, but a full day made it like concrete, despite the expected full cure being several days. Best to do your rough sanding when it's firm enough that you can't ding it with your fingernail but not any more than a full day out unless you want a great deal more work than you could have had earlier.

I learned about Sherwin Williams marine coatings from a paint pro (boat and airplane paints) in the same yard; he used them on his boat. They make a great tropical-waters ablative (tested in Key Biscayne), in two mixes, as well as barrier coat, to milspec levels. Talking with their head tech told me that there is such a thing as too much barrier coat; I no longer recall the number, but there is a specific mil thickness they recommend not exceeding - get a mil gauge to see how deep any coat is as it's applied. I think we used 4 or 5 coats, in differing colors, to alert us to any damage as well as when we ran out of bottom paint. First several BCs were red, and final gray; first AF black, top red...

You put on the first coat of AF as the BC topcoat gets 'tacky' - a very limited window. That's why you'll see pix of black over gray nearly simultaneously:

You can see the paint (barrier coat and bottom paint) portion of our work here: Pictures: Flying Pig Refit 2011-2012/Bottom Job/4 - Barrier and Bottom Coats

We launched in late January 2013, and the boat has never been further north than the fecund waters of the Charleston City Marina, mostly being in the tremendously foul ICW at Vero Beach FL or in the Bahamas.

In that 4.7 or so years, it's been scraped irregularly, and, when I'm in the Bahamas, scrubbed (ground on a falling tide, put on lots of weights and use a hookah to breath while I take a deck brush to the hull) occasionally.

This last trip back - after being in the Bahamas for over 2 months without ever scrubbing - from Green Turtle Cay to Vero - took ALL the growth off.

We are starting to show the next color down in many places; we used 2 coats everywhere and 3 or more coats at the waterline and hard points, including the entirety of the bow-to-tip-of-rudder bottom-most line.

Based on our usage, we probably will have to pull the boat sometime before it actually needs it, to attend to something else important, but our FIRST coat isn't gone at close to 5 years. However, a suggestion my buddy made, while wonderful initially, has not held up well at all: Do the reveal stripe in brilliant white Pettit Vivid. Indeed, it cleaned readily - but most of it in many areas is now gone, leaving our fairing compound exposed where it happened to be, or gelcoat, where there hadn't been damages needing attention. I think I'd do it again, but with massive numbers of layers, as it ablates TOO easily. Back to Sherwin-Williams...

They make two types of ablative paint. My buddy, because they didn't have my type in stock, used the harder (presumed - designed for boats over 10 knots rarely at rest) ablative; it still gives great service. We use the softer ablative, designed for our type of use - under 10 knots, and frequently at rest.

Here are the relevant links for both types of bottom paint. Spec is 2-3 years, and easily-brushed slime is typical after 18 months per their info, but we’ve gotten much longer from ours.

Copper Bottom Anti-Fouling Paint #45 - Protective & Marine – what we have, available in 4 colors - I don’t recall now whether I had to go to FTL for it, but I THINK they inter-office shipped it to the local S-W shop, as it wasn't in stock in the FTL store, and was ordered for us.

Seaguard Ablative Anti-Fouling Coating - Protective & Marine – what my buddy I told you about has, and he’s happy; it’s more likely to be in stock, though you might have to go to some major marine area to get it.

In either event, of course, you'll more likely find it in marine areas, but it could be shipped anywhere. Ours was $85/gallon in 5-gallon buckets in late 2012. I have no idea how much it will be today, but we were on the order of a third to a quarter of "marine" products that most folks use. The only improvement I could think of would be tin

https://www.paintdocs.com/docs/webPD...&prodno=N51B45 – ours

https://www.paintdocs.com/docs/webPD...prodno=P30BQ12 – buddy’s

They also made our barrier coat; https://protective.sherwin-williams....3Aproduct-6939

Our prior bottom paint had been the very best West had to offer; we got much less time from it, at massively more cost.

According to my paint pro, the US Navy and Coast Guard use it; I certainly have been pleased.

YMMV, but at that price, and if you haul regularly, it's worth a shot.

FWIW, in the godawful areas of St. Marys GA, cleaning was a matter of using a wide drywall taping knife (very wide spatula) and running stripes down the hull at next to no effort. If we'd been sailing, they might have even just ablated off, but we spent an entire summer at a dock there (those docks are now gone courtesy of Irma). We have found no circumstances of hard growth that would not flake right off...

L8R

Skip

Thanks for sharing this!!!

[skipgundlach]

Originally Posted by UNCIVILIZED

Thanks for sharing this!!!

My pleasure.

We were astounded at the difference in speed with a faired bottom. At least a knot...

We kept getting "put some paint on that and go sailing!" from watchers. We're glad we did the anal finishing job we did; we're assuming it will also pay off when it's time to peel off the remainder...

L8R

Skip

[CanoeBuilder]

I would completly strip the bottom before repainting, it may seem hard work but with the new finish it will be worth it.

[Ryban]

I'm going to go to the ACE on the island tomorrow and get some 40 grit to play with. I think I'll hit the questionable spots with 40, and leave the rest with 60.

Here are a few photos that show the bad spots, the good spots, and one of the photos shows the difference between before and after sanding -- black regions haven't been sanded, red have been. I'm not sure if the red is from paint beneath the black paint, or just a result of sanding the black paint somehow.

https://photos.app.goo.gl/5XaAg0jTv8GFUx4g1

[ramblinrod]

Originally Posted by flyingfin

Its the bottom of your boat, not the hood of a classic Corvette!
The bottom paint is simply to prevent growth. As long as you have faired and primed any glass, your structural integrity if fine. I have seen people go way overboard on stripping bottoms, or spend weeks on end chasing osmotic blisters. Blisters can stay for 10 years and never grow larger, then when you finally punch them open they are still full of un-cured resin and not allowed any water to penetrate the hull. Aesthetic concerns are all on deck!

"Cosmetic" bottom blisters, even fairly minor, can devalue a boat by 15%.

A major osmosis issue requiring a gelcoat peel and hotvac can cost 10s of 1000s, and make the boat very undesirable compared to one that doesn't have it.

For anyone concerned with performance, it may be wise to spend a little time, effort, and money on the bottom, before considering new sails.

[UNCIVILIZED]

Originally Posted by skipgundlach

My pleasure.

We were astounded at the difference in speed with a faired bottom. At least a knot...

We kept getting "put some paint on that and go sailing!" from watchers. We're glad we did the anal finishing job we did; we're assuming it will also pay off when it's time to peel off the remainder...

L8R

Skip

Yep, it surely makes a difference, especially when the wind is light. Here's a good article on bottom jobs Small Things Big Wins

And for the newbies, there's naught which says that you can't use a grinder to remove old bottom paint. Sometimes it's the best tool there is, especially with coarse abrasives if you have a lot of paint to remove. Yes, you need a bit of technique, but it's just sanding. And often times the majority of a boat's bottom can (& should) be done this way, unless she's already got a smooth, racing type finish on her underside.

Another tool is to affix a square, rectangular, or octagonal piece of plywood or plexiglass to a sander or grinder's pad. And then attach sheets of sandpaper to that. It prevents gouging, while allowing the removal of larger quantities of material with a fair degree of precision.