Bottom Coat - It's coming OFF!

Jun 1, 2016
156
Hunter 28.5 Lake City, MN
Last Saturday, my son & I went up to our boat to try a number of things, to get the bottom coat off our 78 Hunter 28.5. For the most part, it only has a black ablative coating on it. I have put several coats of Interlux ACT on the bottom, but I'm not sure what the previous owner(s) put on, though I suspect somewhat the same.

Last year, there were a few spots that had chipped off, so I scraped those areas off and put on one or two coats of Interlux 2000E as a barrier coat, and them another coat of two of ACT. I had decided at that time that this year, I should strip it all off and redo the bottom.

So, Saturday the idea was to try a bunch of things, to see what would work, and what wouldn't.
Tried a sander (50 grit) with a vacuum for the dust
Some citrus stripper (though it was recommended NOT for fiberglass. May try it yet on the keel).
Also tried a sharpened putty knife scraper.
Tried the scraper with a heat gun as well (peels off, rather than scrapes, not nearly as clean!).
Lastly, we tried a Sawzall with a scraper knife.

It was the sharpened putty knife (1.5") that worked the best for us. What we learned was that the scraper had to be VERY sharp. As a matter of fact, we typically sharpening them about every 10 minutes or so, with a flat sharpening stone (and some water). The coating comes off reasonably easy as you scrap, through not all the time. Different areas seem to react a bit differently to the scraping. Sometimes it's a bit harder to get off, and takes a bit more work to chip it off, but for the most part, we found that we could scrape off LOTS of material in long strokes where the coating was thinner. Thicker portions took a bit more work. We scraped for about 3 hours on Saturday and probably completed at least 20% of the bottom. I worked on it again today for another 2 hours but didn't make quite as much progress (I'm 70, not quite as spry as I used to be!).

To keep the boatyard happy, we put tarps down on the ground to collect the scrapings, and use a vacuum for the final cleanup. It's going to be a lot of work yet, but not NEAR as bad as trying to sand it all down. I'm guessing that the bottom will take us about 10 hours. I'm a bit more skeptical about using scrapers on the rudder, but I'm sure that we'll try it. May just use a course grit sander on the keel, and hopefully some 5200 to help the "Hunter Smile".

I did try the Sawzall blade (4", though they do have a 2" that might work too), which I sharpened as best as I could. It worked kind of OK, but you couldn't remove near as much material as with the putty knife blades. I was a bit concerned about it digging into the fiberglass, but with the blade at a steep angle (sawzall close to the hull) it didn't seem to dig in. I seemed to ride up on the top of the coating, rather than take it off.

The few spots where I put on barrier coating last year, comes off quite a bit harder. I may just leave them as is, and put another coat over the top of those few areas.

Plans are for 4 barrier coats of 2000E and 2 coats of Micron CSC.

Hope this helps someone to get the bottom coat off their boat...
I know that every bottom is different, so your mileage may vary!

Sir Michael
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Likes: Ward H

RoyS

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Jun 3, 2012
1,739
Hunter 33 Steamboat Wharf, Hull, MA
I shake my head when I watch boat owners and yard workers applying a new coat of bottom paint every Spring. Eventually they will all be where you are. Most of us have only one bottom scraping job in us, then never again. Suggest you use a multi-season ablative and only re-coat about every four years. Touch up as necessary in between. You will never have to do that job again.
 
Jun 1, 2016
156
Hunter 28.5 Lake City, MN
Roy, that's what I'm hoping for. The Micron CSC is supposed to be multi-seasonal. I strongly suspect that with the barrier coat, I'll never have to remove it again (maybe somebody else in xx years!?).

Sir Michael
 
Jun 1, 2016
156
Hunter 28.5 Lake City, MN
My son and I are very nearly done with the putting a new bottom coat on our '78 Hunter 28.5. Most of the bottom only had some ablative coating, with only a few areas that had any barrier coating.

About 80 to 90% of the bottom, we were able to scrape off with the sharpened 1.5" putty knives. The rest had to be sanded off, this included the rudder and keel and a few other spots around the bottom of the boat. The scraping went really quickly, but the sanding, even with 40 and 50 grit sandpaper went pretty slowly. I even had a guy swing by and asked how I'd gotten the bottom so clean and white. He's a guy that is contracts out to sand the bottoms, which is a LOT of work!!! I felt pretty good about that.

There were a few rust spots on the keel, but I used some "metal prep" to remove the rust. I had learned about this stuff when working on car bodies, when repainting cars years ago. I also put some fast drying 3M 5200 around the seam between the keel and the fiberglass to hopefully seal that up (at least for a while!). I'm sure that the "Hunter Smile" will come back eventually... I used a more aggressive grinder to remove most of the coating from the keel.

I did discover that there was some deformation under the starboard rear cradle rest, this became more apparent when the black coating was removed. I'm going to have a local welder modify the cradle to remove the bars and put on adjustable pads. Apparently, he's done quite a few boat cradles in the marina. I was told that the deformation is not that uncommon and that the barrier coat will fill in the minor cracks.

We put the Interlux 2000E on, 3 good heavy coats and 2 coats of the Micron CSC, and it's done, with the exception of the resting area under the cradle. That will be done this weekend when the boat is hung on the crane.

This is a job that I'm so glad is done, and that I won't do again. I would very much believe that the barrier coat should last a long time. I didn't find any blisters or problems, other than the deformation that I mentioned previously. I figured this was pretty good, considering that the boat is 43 years old!

On the more personal side, I found that I could only put in about 2 hours or less, working on the boat, on any given day. I'm 70 years old and not near as spry as my 38 year old son. It took a bit longer than I had hoped, but we did get the job done in about 6 weeks working 2 to 3 days a week. I made a lot of trips up to the boat (50 minute drive for me, and about 25 minutes for my son). I have a Comma 2 on my '19 Camry (reference "www.comma.ai") which made the drive go quite easily, as it steers the car very nicely. I averaged about 40 mpg on the trips. Not bad!

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Sir Michael