Well Chris, I have just completed grinding all of the bad paint and gel-coat off of a 42 Tayana. I used Makita products. I used the mid sized makita grinder, It had plenty of power, and wasn't such a brute as a full size large grinder. For the sanding I use either a 5" random orbit variable speed for finishing, or the 5" regular random orbit for the bulk or coarser grits. The real magic is in the abrasives you will use. Regular sandpaper loads up, and doesn't cut very well, however some very ingenious individual came up with a sanding disk that is called a flap wheel. Mounted to your angle grinder, it is capable of removing anything, and I mean ANYTHING, with EASE! they are available in grits from 36, up to 120. These discs, even at 120 grit, could go through the most tenacious material, and show little signs of wear. They cost about $10 each, but the beauty is that you will probably only need 1. I used 2, I stripped off a total deck of cracked and crazed gelcoat, and the entire topsides of 2 part polyurethane, and primer. They are by far the best thing I have used on my rebuild. I will get you the MFG. name tomorrow. I have seen a similar product by WALTER ABRASIVES, but have not yet used one of theirs, because the ones I have won't wear out! One thing to keep in mind, is if you decide to grind the old away, do it with HORIZONTAL STROKES. that way when you go to trowel on your epoxy, you will have an easier time re-fairing it. Don't do it haphazardly.
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Grinder / sander recommendation?
Well, I just finished watching my first haul out. The boat is on the cradle, and I had my first look at her hull. Yep, she's got blisters. With my month-early haul-out I have a perfect opportunity to get the blisters ground out and drying. Only problem is, what to use?
I have a nice (Porter Cable) random orbit sander, and a traditional (Makita) square plate palm sander. I even have a Dremel... However, I'm thinking that working a 27' hull-o-blisters probably warrants something that will work faster, right?
Can anyone recommend criteria / features to look for (rpm speeds? sizes? amps? Something else?). I can go down to Lowe's and roll the dice, but I'm hoping someone can give me something to go on. If you have one that you really like, and you think it was reasonably priced, please let me know
I was looking at a "PORTER-CABLE 4-1/2" 7.5-Amp Angle Grinder", but it looks like these have stone wheels... Don't I want to be using sandpaper discs? Do I have the totally wrong tool here?
Thanks,
Chris
I have a nice (Porter Cable) random orbit sander, and a traditional (Makita) square plate palm sander. I even have a Dremel... However, I'm thinking that working a 27' hull-o-blisters probably warrants something that will work faster, right?
Can anyone recommend criteria / features to look for (rpm speeds? sizes? amps? Something else?). I can go down to Lowe's and roll the dice, but I'm hoping someone can give me something to go on. If you have one that you really like, and you think it was reasonably priced, please let me know
I was looking at a "PORTER-CABLE 4-1/2" 7.5-Amp Angle Grinder", but it looks like these have stone wheels... Don't I want to be using sandpaper discs? Do I have the totally wrong tool here?
Thanks,
Chris
1 - 19 of 19 Posts
Chris,
I like Milwaukee tools myself, but they're really all about the same. Any 4 1/2 inch grinder with those flap discs capnblu mentioned is a pretty good weapon of choice. The bigger the grit the better, I'd start with 36. You may want to check with where you're hauled out, some places require you to attach a vacuum to any sander or grinder to prevent any antifouling on the bottom from getting into the environment (that's how it is where I'm hauled out in CA). I bought a Festool sander for this purpose and attached it to my shopvac with a length of bilge hose. The sander was pricey but one of the best tools I've owned. Have fun!
I like Milwaukee tools myself, but they're really all about the same. Any 4 1/2 inch grinder with those flap discs capnblu mentioned is a pretty good weapon of choice. The bigger the grit the better, I'd start with 36. You may want to check with where you're hauled out, some places require you to attach a vacuum to any sander or grinder to prevent any antifouling on the bottom from getting into the environment (that's how it is where I'm hauled out in CA). I bought a Festool sander for this purpose and attached it to my shopvac with a length of bilge hose. The sander was pricey but one of the best tools I've owned. Have fun!
Yes, we need to put a tarp on the ground when we sand, and I think use of a vacuum is a good idea regardless of the rules, so I'd planned on it. That was one of the criteria I'm interested in - how well does the dust port on various models really collect dirt. Being a woodworker I've seen all kinds of variety in how well they work on other tools.
I use a 4" right angle grinder for jobs like that, really good at taking material off quickly.
2
We are in a "Certified Clean Marina", I rented this from the marina when I did my bottom sanding job.
Combined with their vacuum attachment for fine particles, I found it ideal and not too heavy. After many many hours of sanding my arms still felt like there were going to fall off
Random Orbital Sanders - Festool
and 
Combined with their vacuum attachment for fine particles, I found it ideal and not too heavy. After many many hours of sanding my arms still felt like there were going to fall off
Random Orbital Sanders - Festool
and 
As a follow up question, is an angle grinder interchangeable with a random orbit sander for blister removal? Or do I really want to use the angle grinder for initial blister removal, then the random orbit for when I'm fairing the repaired hull?
I see the use of "sander" and "grinder" mixed somewhat inconsistently in how-to articles, so it's hard to tell just what I need...
Thanks,
Chris
I see the use of "sander" and "grinder" mixed somewhat inconsistently in how-to articles, so it's hard to tell just what I need...
Thanks,
Chris
the angle grinder is the tool of choice, the random orbit is good for paint and fairing but way too slow for real removal of material.
another option for blister opening is a sand blaster in very talented hands, or even a soda blaster but its slower.
another option for blister opening is a sand blaster in very talented hands, or even a soda blaster but its slower.
I do a lot of sanding every year- Love my Festool.We are in a "Certified Clean Marina", I rented this from the marina when I did my bottom sanding job.
Combined with their vacuum attachment for fine particles, I found it ideal and not too heavy. After many many hours of sanding my arms still felt like there were going to fall off
Random Orbital Sanders - Festool
It won't be as aggressive as aright angle grinder if you're grinding out blisters. But my 150 with a heavy grit takes down epoxy REALLY fast.
I just finished the job using a 6" random orbit Rigid sander. Worked great and was aggressive enough to get the job done without going through the hull. On our last boat, I used an angle grinder and will never do it again. The high RPM (22,000) is too much for fiberglass, IMHO. On the other hand, the 6" random orbit sander is quite aggressive, much more than a 5" grinder. The increase of only 1" diameter yields 44% more grinding area.
The Rigid had a silly dust bag that I took off. The good news is that it easily accepts the hose of a Shop Vac. I did the entire hull with the Rigid/ShopVac setup and had great results using 40/60/120 grit. You don't need to press hard.
To get all the paint off, you may not want to grind. We used 1" wood chisels to scrape it off, sharpening frequently. We also used carbide-tipped paint scrapers. When the paint was removed, I used the sander to smooth everything out. MUCH faster than sanding through many layers of paint. Also, the chisels/scraper gave us paint chips vs. paint dust. MUCH easier to collect!
Once I got to bare glass, I used an ice pick to gouge out the few blisters that I had. I would not grind since you will end up going too deep. I also recommend popping the blisters in the fall and filling them with epoxy in the spring. You'll need the winter for them to dry out.
Good luck.
The Rigid had a silly dust bag that I took off. The good news is that it easily accepts the hose of a Shop Vac. I did the entire hull with the Rigid/ShopVac setup and had great results using 40/60/120 grit. You don't need to press hard.
To get all the paint off, you may not want to grind. We used 1" wood chisels to scrape it off, sharpening frequently. We also used carbide-tipped paint scrapers. When the paint was removed, I used the sander to smooth everything out. MUCH faster than sanding through many layers of paint. Also, the chisels/scraper gave us paint chips vs. paint dust. MUCH easier to collect!
Once I got to bare glass, I used an ice pick to gouge out the few blisters that I had. I would not grind since you will end up going too deep. I also recommend popping the blisters in the fall and filling them with epoxy in the spring. You'll need the winter for them to dry out.
Good luck.
Hmm - that's great to hear. I like the idea of the RO sander much more than the grinder. I had been thinking that the grinder seemed like it would be easy to slip with. I had just assumed that I'd be spending WAY too much time going with anything else.I just finished the job using a 6" random orbit Rigid sander. Worked great and was aggressive enough to get the job done without going through the hull. On our last boat, I used an angle grinder and will never do it again. The high RPM (22,000) is too much for fiberglass, IMHO. On the other hand, the 6" random orbit sander is quite aggressive, much more than a 5" grinder. The increase of only 1" diameter yields 44% more grinding area.
The Rigid had a silly dust bag that I took off. The good news is that it easily accepts the hose of a Shop Vac. I did the entire hull with the Rigid/ShopVac setup and had great results using 40/60/120 grit. You don't need to press hard.
To get all the paint off, you may not want to grind. We used 1" wood chisels to scrape it off, sharpening frequently. We also used carbide-tipped paint scrapers. When the paint was removed, I used the sander to smooth everything out. MUCH faster than sanding through many layers of paint. Also, the chisels/scraper gave us paint chips vs. paint dust. MUCH easier to collect!
Once I got to bare glass, I used an ice pick to gouge out the few blisters that I had. I would not grind since you will end up going too deep. I also recommend popping the blisters in the fall and filling them with epoxy in the spring. You'll need the winter for them to dry out.
Good luck.
At this point I'm still hoping I can do a (massive) bunch of spot repairs vs stripping the whole hull, but I need to get back to the boat and do a more thorough survey. I was trying to make an assessment within the attention span of my 4 year old son, so it was a pretty quick one.
I've also heard about using a Dremel tool on the small blisters (mine are smaller than a dime in most cases). That seems like it might be pushing it a bit, but something else to consider.
Arguments in favor of doing the entire hull vs. spot repair are:
1. If there are a lot of blisters, you'll spend nearly as much time feathering each blister as doing the whole thing the right way the first time.
2. If there are a lot of coats of paint, you really need to take it down to bare glass to improve performance.
3. The whole job really isn't that bad. With two of us working, we took Victoria to bare glass in 8 hours (16 manhours). I spent another 6 hours by myself sanding, filling the blisters, and fairing the keel. Then another 6 with final sanding. That's only 18 manhours. Round to 20 manhours for a smooth bottom. Not bad. Assume $80/hr yard rate and that's about $1600 savings. An that's for a 38' hull. 27' will be maybe 75% of that.
4. Once down to bare glass, you have the option of barrier coating which is an enormous time saver in the long run since you will be virtually guaranteed to be blister free after that. I didn't barrier coat since I had only about a dozen blisters that I filled w/epoxy.
It's a really dirty job (hear that Mike Rowe and Dirty Jobs?), but the satisfaction that I gained was well worth it.
1. If there are a lot of blisters, you'll spend nearly as much time feathering each blister as doing the whole thing the right way the first time.
2. If there are a lot of coats of paint, you really need to take it down to bare glass to improve performance.
3. The whole job really isn't that bad. With two of us working, we took Victoria to bare glass in 8 hours (16 manhours). I spent another 6 hours by myself sanding, filling the blisters, and fairing the keel. Then another 6 with final sanding. That's only 18 manhours. Round to 20 manhours for a smooth bottom. Not bad. Assume $80/hr yard rate and that's about $1600 savings. An that's for a 38' hull. 27' will be maybe 75% of that.
4. Once down to bare glass, you have the option of barrier coating which is an enormous time saver in the long run since you will be virtually guaranteed to be blister free after that. I didn't barrier coat since I had only about a dozen blisters that I filled w/epoxy.
It's a really dirty job (hear that Mike Rowe and Dirty Jobs?), but the satisfaction that I gained was well worth it.
Agree, only do the blisters if there only a few of them. If there's a lot, you may never see afew of them and have to do it again soon.
A 4" grinder is fast, and can be fitted with a flap-wheel that is a bit more forgiving. It's great for repairs and cutting.
My favorite sander is a porter cable 7335, it's aggressive enough to do the work fast, and managable enough that it works for delicate things with ease. They aren't really cheap, but mine is over ten years old and I've been using it at work since I got it.
Ken.
A 4" grinder is fast, and can be fitted with a flap-wheel that is a bit more forgiving. It's great for repairs and cutting.
My favorite sander is a porter cable 7335, it's aggressive enough to do the work fast, and managable enough that it works for delicate things with ease. They aren't really cheap, but mine is over ten years old and I've been using it at work since I got it.
Ken.
I have paint scraper that I patented for removing bottom paint. US Patent # 5,951,781 in case you are interested. You can't buy one, I lost my job, then couldn't afford to renew the patent, and it is now in the public domain. However it does work, and I'd lend you one of my test ones if you are interested.
Bottom painted shatters when enough pressure is applied. So this scraper takes off 20 years worth of paint in one pass, in big chunks, not dust. I once wanted to demonstrate it and forgot to bring the carbide blade. No big deal, the aluminum head stripped the paint just as fast, but wore quickly. About 3 hours to strip a 22 foot Catalina down to bare glass. It has a long handle for leverage, supported by a telescopic leg. You lean your weight on the handle and it presses up against the hull. A universal joint allows it to stay on the surface without gouging, and you pull it towards you.
Gary H. Lucas
Bottom painted shatters when enough pressure is applied. So this scraper takes off 20 years worth of paint in one pass, in big chunks, not dust. I once wanted to demonstrate it and forgot to bring the carbide blade. No big deal, the aluminum head stripped the paint just as fast, but wore quickly. About 3 hours to strip a 22 foot Catalina down to bare glass. It has a long handle for leverage, supported by a telescopic leg. You lean your weight on the handle and it presses up against the hull. A universal joint allows it to stay on the surface without gouging, and you pull it towards you.
Gary H. Lucas
Nice device Gary. I have a cabinet scraper that my grandfather designed and I improved. I'd like to patent it to honor him, but the process is daunting even if you're an engineer (I am) with a technical writing and drafting background (I do).
Flexible sanding discs on a 4-1/2" grinder of various grit sizes will be much faster then a Dremel or ANY random orbital sander for removing any sized blisters. You have to bevel the areas out anyway for repair and drainage before repairing so do it fast with a grinder with a flexible piece of circular sandpaper that fits your grinder.
Use the RO sanders for fairing the area smooth.
Get a grinder/angle grinder or whatever you want to call it. I have a Black & Decker which works like a charm with the sandpaper circular attachments.
Use the RO sanders for fairing the area smooth.
Get a grinder/angle grinder or whatever you want to call it. I have a Black & Decker which works like a charm with the sandpaper circular attachments.
RO 150 FEQ Rotex Sander - SANDERS - Festool
I use one of these and, although not cheap, it's amazing. Very powerful. They offer many accesories too including sanding disks for various materials.
Bill
I use one of these and, although not cheap, it's amazing. Very powerful. They offer many accesories too including sanding disks for various materials.
Bill
I currently have 4 patents, the other three are for automation devices in the commercial greenhouse industry. Two were licensed and I got royalties for about 12 years, while they were in force. People frequently ask me about getting a patent. The best advice I can give is to find a copy of a book called Patent It Yourself, which is now out of print but can still be found. I read it after my first patent, and it convinced me to use a patent attorney again, even though the first one was a genuine crook!Nice device Gary. I have a cabinet scraper that my grandfather designed and I improved. I'd like to patent it to honor him, but the process is daunting even if you're an engineer (I am) with a technical writing and drafting background (I do).
A change in the patent law about ten years ago essentially wiped out most small inventors. Patents now have 'renewal' fees due every five years or so. They go up in cost almost exponentially. If you aren't actaully making a profit from your patents you can't afford to have too many, and like mine they wind up in the public domain where the big companies can use them for free. My two licenesed patents had the fees paid by the licensees.
Gary H. Lucas
I thought as much. Sigh. Reading your patent, I went from understanding what it was and how it worked (from the drawings) to totally confused. I know that I can write confusing sentences, but these guys are in another league!find a copy of a book called Patent It Yourself, which .... convinced me to use a patent attorney
I really want to write an article for Fine Woodworking because it's such a great scraper, but am afraid that someone will grab it and make money from my dead Italian grandfather.
Sorry all for hijacking the thread.
1 - 19 of 19 Posts
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