Bottom Blasting

[tsl]

Minaret,
Thanks for the help. The boat is outside a stainless fabricating shop and 80 feet from the blast room. We though we would just blast (using crushed glass)the keel since it has many layers of flaking paint on it and the ospho would not see all the metal.

As for barrier coating. I was planning on doing it but if the original gelcoat is in tact. I'm thinking of skipping it. I intend to use this boat very sparingly sailing it a month or two a year starting in Milwaukee and heading for the Bahamas. Placing it on the hard when I am way. It's been sitting in the water in the Caribbean and DC area for years. Apparently with no barrier coating and no blisters. I'm open to be screamed at for this line of thought. Comment/screams welcome.

One other point : The boat has been on the hard for at lease three years. Might not be a better time to put barrier coating on.

[Cheechako]

are you sure the bronze layer isnt epoxy resin? Is it more amber or bronze? It would make sense that the paint might not stick to it if they let it fully harden and didnt sand before painting...? If it's epoxy... leave it there!

[minaret]

Originally Posted by tsl

Minaret,
Thanks for the help. The boat is outside a stainless fabricating shop and 80 feet from the blast room. We though we would just blast (using crushed glass)the keel since it has many layers of flaking paint on it and the ospho would not see all the metal.

As for barrier coating. I was planning on doing it but if the original gelcoat is in tact. I'm thinking of skipping it. I intend to use this boat very sparingly sailing it a month or two a year starting in Milwaukee and heading for the Bahamas. Placing it on the hard when I am way. It's been sitting in the water in the Caribbean and DC area for years. Apparently with no barrier coating and no blisters. I'm open to be screamed at for this line of thought. Comment/screams welcome.

One other point : The boat has been on the hard for at lease three years. Might not be a better time to put barrier coating on.

As long as it reads dry on a moisture meter as well as having no blisters after years of immersion it should be fine without a barrier coat. It was probably built with a vinylester skin coat or better if that is the case. Just make sure you get a dry reading first, you can have osmosis and saturation without having blisters. If you go that route make absolutely certain you don't blow through the original gelcoat, it may be a high quality vinylester that is helping to keep things as they are. You might price out the required amount of 2000e and see if you are interested in doing it as insurance for your own peace of mind, but I wouldn't call it necessary. It's actually pretty cheap if you do it yourself and don't count the lay days as an expense because you are already in the yard. It will also gaurantee that your bottom paint gets a much better bond and will never flake, because you can get a chemical bond to the epoxy primer with the bottom paint. A primary bond is always much better than a secondary. Always happy to help!

[tsl]

Great help ALL!!

You won't believe this. My best guess is the the bronze like coating (more black than bronze in better daylight) is coal tar epoxy (as Cheechako predicted). I think the entire bottom was coated from day one. 20 years later is still there. The many layers of bottom paint do not stick well to this coating (I could likely hand scrape the layers of antifouling off in one agonizing day). The epoxy is very rough. Super size orange peel
Saturday we will blast with the soda (won't take more than an hour or two) Blast the keel with crushed glass and report back here with the results. I was very fortunate to have someone well before me make a smart decision and have the bottom coated. I believe the boat was in the Caribbean as a charter boat. Someone was ahead of his time!!!
I also noticed that the last layer of gelcoat was blue. Last applied so it was the layer closest to the glass. It's very thin but easy to see at different spots around the boat where the gelcoat had been chipped. Is that typical?

[tsl]

Yes , of course we will not remove the epoxy and likely take Minarets advise and find something to act as a transition coating 2000e is a good starting point.

[tsl]

Bottom blasting over. Soda was very slow. Tried Glass beads next (it was handy) still went very slow and neither soda of glass beads did anything the the black base coat.
Purchased black cinder product from Menards. I was told that this is about as aggressive as it gets.
The ate right through the bottom paint but did little to the black base layer. Held the nozzle in place to eat through the black (taking 10 to 15 seconds) and it immediately ate into the gel coat. We saw no way of removing the black without tearing up the gelcoat so we left the black on. We think it is Coal tar epoxy.
Found three blisters in the rudder. Nothing on the hull. I feel very lucky someone got this hull protected very early.
I'm now testing a few paints to see if I can get anything to stick to the black paint. Coal Tar epoxies are known not to allow much to stick to them. The profile left by the blasting should help things. Anyone have a suggestion as to a paint that will stick to the coal tar epoxy?

[minaret]

Originally Posted by tsl

Bottom blasting over. Soda was very slow. Tried Glass beads next (it was handy) still went very slow and neither soda of glass beads did anything the the black base coat.
Purchased black cinder product from Menards. I was told that this is about as aggressive as it gets.
The ate right through the bottom paint but did little to the black base layer. Held the nozzle in place to eat through the black (taking 10 to 15 seconds) and it immediately ate into the gel coat. We saw no way of removing the black without tearing up the gelcoat so we left the black on. We think it is Coal tar epoxy.
Found three blisters in the rudder. Nothing on the hull. I feel very lucky someone got this hull protected very early.
I'm now testing a few paints to see if I can get anything to stick to the black paint. Coal Tar epoxies are known not to allow much to stick to them. The profile left by the blasting should help things. Anyone have a suggestion as to a paint that will stick to the coal tar epoxy?

More coal tar epoxy. This is one reason why I always advocate grinding instead of blasting. Even when grinding coal tar sucks, it gums up your paper bad. But I can grind to the original gel nice and fair without blowing through. I don't like blasting because I feel like I have less control and it exacerbates the mess. Grinding is also often much faster with less setup time and less clean up. JMHO.

[Cheechako]

I'd say you're lucky to get a boat that was done new. How about more coal tar epoxy with copper dust mixed in?

[bobconnie]

As Cheechako said more coal tar epoxy and lots of copper dust, you already have a good base and nothing else will stick anyway!! and remember the Ospho on the keel!! best thing I ever found for steel I used it a bunch on our colvin,also cole tar epoxy for bottom paint for over 10 yrs ! worked so much better the other types of bottom paint we tryed before that !~! just our 2 cents

[Celestialsailor]

Originally Posted by minaret

More coal tar epoxy. This is one reason why I always advocate grinding instead of blasting. Even when grinding coal tar sucks, it gums up your paper bad. But I can grind to the original gel nice and fair without blowing through. I don't like blasting because I feel like I have less control and it exacerbates the mess. Grinding is also often much faster with less setup time and less clean up. JMHO.

What do you think of chemical strip? Is it any faster?

[Celestialsailor]

Originally Posted by minaret

More coal tar epoxy. This is one reason why I always advocate grinding instead of blasting. Even when grinding coal tar sucks, it gums up your paper bad. But I can grind to the original gel nice and fair without blowing through. I don't like blasting because I feel like I have less control and it exacerbates the mess. Grinding is also often much faster with less setup time and less clean up. JMHO.

What do you think of chemical strip? Is it any faster?

[lancelot9898]

I too have a boat that has spent its entire life on the water with a week or so evey several years hauled out for repainting with an ablative paint. Even in spite of the ablative paint there is 25 years of build up and I need to soda blast to remove. Also on day one when the boat was new, I had black tar epoxy put on prior to any bottom paint, but now I'm concerned after reading this post that soda blasting will not remove that layer. I need to remove that layer since small blisters are evident, but I would like to determine a better and cheaper way other than a peeling operation. Someone mentioned grinding and I'm wondering about the pros and cons of doing it that way.

[tsl]

I think focusing on getting something to stick to the Black Paint (thinking it's coal tar epoxy) is my the easiest way to go. I intend to add a few more layers of barrier coating once I test adhesion.

We spent only 4 hours blasting the many many layers of bottom paint of 40 ft hull. I can't imagine grinding or chemically stripping.

Lancelot; It's unlikely your coat tar epoxy will act exactly like my layer of unknown black stuff. I suggest you blast down as far as you can go (likely to the black)then grinding or chemical stripping might be the way to go.
My rudder had three blisters on it and they were easily seen with the black on top of them. Grinding them will be easy.
Most importantly, don't buy a bunch a soda media. It is expensive and takes a long time to get the bottom paint off (way tooo long). Menards (a Midwest building supply store ) has the black stuff for a fraction of the soda. Sand is even cheaper and would work fine as long as you did not blast through the Coal tar epoxy. One thing sounds like a given: you won't be able to remove the coal tar epoxy by blasting without endangering your gelcoat. The coal tar Epoxy is rubbery and with stands the blast but the gelcoat is easily attacked.

[minaret]

Originally Posted by lancelot9898

I too have a boat that has spent its entire life on the water with a week or so evey several years hauled out for repainting with an ablative paint. Even in spite of the ablative paint there is 25 years of build up and I need to soda blast to remove. Also on day one when the boat was new, I had black tar epoxy put on prior to any bottom paint, but now I'm concerned after reading this post that soda blasting will not remove that layer. I need to remove that layer since small blisters are evident, but I would like to determine a better and cheaper way other than a peeling operation. Someone mentioned grinding and I'm wondering about the pros and cons of doing it that way.

Maybe start here for some idea of pros and cons-

http://www.cruisersforum.com/forums/...ion-71361.html

[minaret]

Originally Posted by Celestialsailor

What do you think of chemical strip? Is it any faster?

I hate it. It's slow and incredibly messy. Scraping many garbage bags full of toxic goo from overhead is a nightmare. It gets tracked everywhere and stains everything it touches (god forbid you get some on a deck). It was banned from our yard after people kept tracking it everywhere and getting it all over the bathrooms in attempts to wash up. Never again.