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Old 09-11-2011, 13:02   #1
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Bottom Paint Question

so i want to do a bottom repaint. What is the fastest/not going to break the bank way to get off the old paint down to the gelcoat. I was thinking possibly electric die grinder with scotch pad type pads. Honestly though im looking for a faster approach. In the past my research kept leading me to soda blasting but thats not really attainable for me. So im thinking sand blasting. I would rather spend 600 on a used compressor/equipment to sand blast then pay that much or more to have my boat soda blasted. I know sand blasting isnt near as good as soda blasting but it sure will get the job done right?
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Old 09-11-2011, 13:39   #2
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Re: bottom paint question.

Would it not be cheaper to rent a compressor and blaster for a day than to buy the rig and have lying around after the job is done?
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Old 09-11-2011, 13:47   #3
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Re: Bottom Paint Question

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Originally Posted by albergsailor View Post
so i want to do a bottom repaint. What is the fastest/not going to break the bank way to get off the old paint down to the gelcoat. I was thinking possibly electric die grinder with scotch pad type pads. Honestly though im looking for a faster approach. In the past my research kept leading me to soda blasting but thats not really attainable for me. So im thinking sand blasting. I would rather spend 600 on a used compressor/equipment to sand blast then pay that much or more to have my boat soda blasted. I know sand blasting isnt near as good as soda blasting but it sure will get the job done right?
The problem is that sand blasting can be too aggressive, damaging the gelcoat. Then it becomes porous and you get blisters. The popularity of soda blasting is because it is much harder to damage the gelcoat.

So my suggestion would be, if the current paint is sound, wet sand it and re-coat.
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Old 09-11-2011, 16:55   #4
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Re: Bottom Paint Question

, the current paint is not sound. Thats what i thought i was going to here about the sand. Well i figured that i could just blast alot (not all) of the paint away and then hit the rest with the die grinder. I would use the hell out of a compressor as long as it could blast. Im sure that with the right attachments/compressor a soda blasting setup can be built quite inexpensively. the (every thing you need) soda blasting kits are like 10000 dollars plus if i remember right. Maybe i should go to blasting school and figure it all out. i guess it all comes down to funds
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Old 09-11-2011, 17:05   #5
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Re: Bottom Paint Question

Chemical strippers work very well
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Old 09-11-2011, 17:23   #6
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Re: Bottom Paint Question

I also used a chemical paint stripper. I crane the boat into my back yard and secured it on stands and up on 8" blocks. Laid down a bed of wood chips and then used the stipper with a paint scraper. It took off the gelcoat also, that was fine with me. Used a epoxy barrier x 3 to 4 coat and have not had a problem and that was 7 years ago.
Oh, by the way when all done I raked up the wood chips with all of that paint, bagged it up and put it into the garbage..... real clean way of doing it!
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Old 09-11-2011, 17:31   #7
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Re: Bottom Paint Question

I hate to burst your bubble but you cannot legally sand blast in the USA anymore. I was shocked a couple of months ago when after a decade in the Caribbean I returned to Florida to do a refit of my boat.
- - I got out my sand blasting equipment and proceeded to use up the old sand removing crusty sealife and stuff from my boat's bottom side.
- - Then I went to my traditional supplier of sand for sand blasting to buy some more sand. No go - I was told they do not sell it anymore as it is banned and/or carries too much legal liability for them to deal with it - silicosis hazard.
- - So I asked what is being used, and they said "Black Beauty" a sintered coke product. It is a black sharp granular material. It didn't work in my "sand" blasting equipment until I purchases a new gun. Black Beauty sells for $12.05/60 lbs here in Florida.
- - So you might have to check and see what "soda" blasting costs compared to the new "abrasive blasting" materials.
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Old 09-11-2011, 17:42   #8
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Re: Bottom Paint Question

After doing this myself you need a really big volume compresor better to go to a pro in my opinion.
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Old 09-11-2011, 18:52   #9
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Re: Bottom Paint Question

A 7" softpad on a milwaukee 6088 with 36 grit imperial purple or green discs. I can do a 50' sailboat bottom by myself in 1 day if it's already tented. I have done 100's of bottoms. There is certainly a learning curve, and you can gouge up a bottom if you haven't learned to feather the trigger, but it's not that hard a technique to develop. Turn of the bilge and waterline are the only tricky points, and a little practice makes perfect. A box of visqueen, a 6088 (about 130 bux new, unless you get the variable speed), a box of grit (another +/_ 100), some preservation seal and duct tape for tenting, a few 1x pokes, a good vacuum, a tyvek and full face(200$), and off you go. Just don't try to use chems or a DA, anything but the softpad is a waste of time. Don't use anything finer than 36 either, I see people sanding bottoms with 80 all the time, it's silly. The barrier coat will fill the 36 profile just fine, even just bottom paint will if you do at least 2 coats, you wont be able to see the 36 profile at all. I can sand much quicker than most sand blasters with way less setup and cleanup. Just go for it...
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Old 09-11-2011, 20:39   #10
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Re: Bottom Paint Question

thank you thank you thank you, thats exactly what i needed to know. when i first got the boat i used a belt sander on the bottom because i could not find a soft pad that fit my angle grinder, i remember trying to make a softpad out of the buffer that came with a sander/polisher, boy did that piece of sandpaper go flying even after using glue. I was really pissed that i could not find a "soft pad" in any of the stores. Untill now i did not know that such an attachment existed. I just googed soft pad and found them online. Anyone know if any local stores carry these? I also cant wait to do some experimenting with my harber freight diegrinder using fiberdisc. I just got a voltage limiter for it so maybe it will come in handy. thanks again for all the advice i should have consulted the experts here about this long ago.
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Old 10-11-2011, 00:24   #11
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Re: Bottom Paint Question

Don't know where you are but you can get everything you need here.

Fisheries Supply


I suggest either the 36 grit 3M Green Corps, or the Imperial (the purple stuff). Sometimes I go back to 40 grit with Imperial because it's so aggressive when fresh, depends on the bottom. It does stay sharp longer, but I use more Green Corps than anything. I like the Stikit better than Hook-and-loop. I never use the spray adhesive, it just screws up your nice $40 softpad. Just keep it clean. If you start to throw discs just wash it with soap and water and spin it dry, spray adhesive buildup will cause failure every time. The secret is to feather the trigger just like the operator of a spray gun does when painting. If you just lock it on you will get little half moon gouges at each end of each stroke. This will cause your trigger finger to cramp up, but such is life. Don't hang up your pad in a jackstand trying to get too close, don't get ambitious and try to get too close to the waterline with the pad, and dont kick back off a block under the keel into your face. 36 grit hurts. Make sure you get and wear a good full face. You can go with the $80 2 strap if you will only be doing this once, but I recommend the $200 nicer model, your body will thank you. Clean up well, and remember if you do it on a weekend when no ones around you'll get less bitching. Finish the waterline by hand with 60 to get the last bit of paint off, and 80 to sand up to the tape line. Usually the waterline takes me almost as long as the rest of the bottom. Of course you'll have to move blocks and jackstands to get those spots, just roll your tent up for them to move the blocks and then drop it back down. Hard work but simple. I find it really helps to have 2 guys do a bottom, one on either side, so you can get a little competition going. Keeps morale up...
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Old 10-11-2011, 00:48   #12
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Re: Bottom Paint Question

OP, here is some first hand recent experience:

Just had this done in Marmaris, Turkey. Two men each with a paint scraper scraped off 8 coats of Micron66 and the barrier coat in 2 days. Each swipe of the scrapper took most everything off down to the gel coat. Then 1 1/2 day using an electric sander and the job was complete to come back with new barrier coat then Micron77.

Our boat is a 16m (53') ketch with a mod wing keel and skegged rudder. This should help you in determining how long it will take. Be sure that who ever does this work wear protective clothing and a good respirator.

If you have any blistering in the gel coat, this process will make the blisters obvious. Be sure to repair the blistering and also be sure to buy a good barrier coat...really stupid to pinch a penny on barrier coat, but I know some who have done this...freakiing nuts!

You will get lots of opinions on brands and types of antifouling. You generally will get what you pay for, and I have found most complaints about antifouling come from people who take shortcuts in preparation, etc.

Bill
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Old 10-11-2011, 06:20   #13
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Re: Bottom Paint Question

IHMO, the least violent method of removing bottom paint is the chemical stripper, although the material and fumes and cost are a major factor.

- - Then you have the "sanding" methods which involve aggressive attacking of the bottom so the more "technique" you employ the least damage you do to the boat's underlying hull. The idea is to remove the paint but not the gelcoat or any of the laminate that comprises the hull.

- - I find the 6 inch random orbital sander a good "in the middle" tool to remove the paint with minimal "dishing" or digging into the underlying hull material. But it does take longer. (first photo below)

- - The large angle grinders like the Milwaukee 6088 are aggressive and get the job done much quicker. (second photo below) But along with the speed comes the danger of dishing or digging into the hull.

- - The various sizes of sander/grinders all require proper attention to "technique" to avoid damaging the hull while rapidly doing the job.
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Old 10-11-2011, 07:11   #14
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Re: Bottom Paint Question

Wet blast it. Just make sure the hand is not a moron that will blast the gelcoat away.

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Old 10-11-2011, 07:19   #15
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Re: Bottom Paint Question

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I also used a chemical paint stripper. I crane the boat into my back yard and secured it on stands and up on 8" blocks. Laid down a bed of wood chips and then used the stipper with a paint scraper. It took off the gelcoat also, that was fine with me. Used a epoxy barrier x 3 to 4 coat and have not had a problem and that was 7 years ago.
Oh, by the way when all done I raked up the wood chips with all of that paint, bagged it up and put it into the garbage..... real clean way of doing it!

I have been involved with most methods out there to strip bottom paints and have some practical opinions on options for removing your old anti fouling. I list them here from best/ easiest to most difficult:

1.) Easiest way: Hire a professional to bead blast the bottom, the last project we did was a Cape Dory 27, contractor came with a specialized box truck with all equipment in the vehicle. They completely tented off the boat and ran high volume vacing equipment hoses under the tent to suck up the old bottom paint as they blast. Equipment shoots plastic beads, gets most of the paint off, does no damage to the hull. In the end we still spent a good deal of time sanding. Somewhat environmentally friendly if high volume vacing equipment is utilized. Expensive, the Dory was over $800.00.

2.) Soda blasting: Basically same as the above except contractor shoots baking soda in a high pressure water stream as the cutting medium. On the hull I witnessed soda blasting being performed on there was some damage to the gel coat; contractor claimed he was just opening up blisters. Soda blasting equipment usually allows the operator fine adjustment of the amount of blast medium allowed into the water stream as well as the water pressure level. This allows the operator to fine tune the gear and if experienced he should only use the amount of soda and water pressure required to remove the paint and not damage the surface being prepped. The soda blast left a much cleaner final surface than the bead blast process but in the NY metro area was much more expensive. Environmentally the process is not as clean as the bead blast method as the paint and soda runs all over the ground making cleanup more difficult in a marina environment.

3.) Chemical Stripping: For the do it yourself guy/ gal without very deep pockets I feel this represents one of the best methodologies. I have personally used a product called “Peel Away” http://www.dumondchemicals.com/html/peelaway.htm on many occasions and can attest that the products work as advertised. Basically the stripper is painted on the hull and covered with a wax paper. After the proper dwell time a scraper is used to lift the old paint from the hull. Depending on the thickness of the old bottom paint you may have to do a couple of applications to remove as much paint as possible. You will still have to spend a fair amount of time sanding if you want a perfectly clean bottom prior to recoat, however if done correctly you can remove 80% of the old paint prior to the final sanding. This method is much cheaper than any blast process. I have even used “"Peel Away's” home version paint strippers sold in bulk at Home Depot with no discernable difference over their "Marine" more costly products. Environmentally it can be very clean allowing the stripped paint to drop onto plastic tarps then wrapped up for disposal. From an efficiency standpoint this is a much faster and cleaner method than sanding and scraping alone.

4.) Sanding alone to remove bottom paint represents the stone ages in the hierarchy of bottom paint removal methods. It probably represents one of the least desirable projects you can do on your boat. It doesn’t matter what machinery is used, a belt sander, palm sander, DA sander, random orbit sander or whether it’s connected to a vacuum or not or whether your completely encapsulated in a nuclear/ biological suit with a filtered air supply and little gnomes handing you filtered spring water, sanding is painfully slow, very physically demanding and extremely dirty. The high powered larger pad sanders can cause damage to gel coat if not utilized properly. In the end this is probably the most cost effective method of paint removal. If you choose this process wear a full Tyvec suit and good quality resperator, (Not a dusk mask) goggles and gloves. Environmentally this is the dirtiest process of all and will send old dry bottom paint everywhere. If you value your relationship with your neighbors the boat should be as far away from them as possible. There is reasonable priced sanding equipment like the “Rigid” brand random orbit sanders that can be attached to a shop vac for dust control, while not perfect they go a long way to minimizing sending toxic paint into the atmosphere. Good luck with your project
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