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Bottom Paint Sanding

Jun 25, 2004
246
Hunter 306 Pasadena MD
I'm going to be sanding and applying bottom paint this weekend for the first time and one of the requirements at my yard is dustless sanding equipment. They don't have any specifics listed, just dustless. As such I have two options for dust extraction that I'd like to see if anyone has thoughts on:

Both options will involve me using my dewalt 20v max random orbital sander as its the only sander I have with a dust collection port. I'll use this with an 80 grit abranet pad. I of course will use a respirator with appropriate cartridges, eye protection, and will likely wear a tyvek suit for both sanding and painting.

Option 1: hook the sander up to my 2.5 gallon shop vac that I dont care about and throw away the filter bag when I'm done

Option 2: I'm a project manager at a general contractor and just todaypurchased some new festool ct26 extractors for my finish guys. I could take one of these down to the yard and connect it to my sander, however I'm somewhat apprehensive about filling a brand new dust extractor for my carpenters with blue bottom paint. Does anyone have experience with how bad this will clog up the filters and how easily it'll come out of the extractor?

Thanks in advance for the advice
One problem: good luck finding the respirator cartridges in the time of COVID19. I haven't seen any available anywhere: not sure what I'm going to do this year.

After one disastrous experience with bottom paint not adhering correctly, which required 100% removal, I always scuff sand with course sandpaper. Just enough to put some scratches for the new paint to adhere to. I usually use a small hand sander along the waterline, followed by a quick sanding of the remaining 95% with a pole sander. Last time, I used water-based ablative (Petit eco-hydrocoat) on top of non-water-based (Interlux Micron CSC), and had no problem.
 
Jan 11, 2014
7,159
Sabre 362 113 Fair Haven, NY
Check out this article from Practical Sailor on a DIY dustless system - I think it was written by Drew Frye who is on this forum:
That's Drew in the photo and he's always tinkering and inventing, usually with good results. I did try the sump pump hose on my DeWalt RO sander and the Dust Deputy, but had difficulties getting it to seal to the DD and the sander.

Which ever method one chooses, direct to the vac, home brew dust collector, or Dust Deputy, a long hose is important. The short hoses that come with Shop Vacs is just too short and too much time and effort is spent dragging the vacuum around.
 
Jun 25, 2004
1,105
Corsair F24 Mk1 003 San Francisco Bay, CA
The drawback to wet sanding is that the water drips down the hull and onto the ground. The boat yard needs a catchment system with a separator to catch the toxins. Ive worked in boatyards with a catchment system. You have to wash down the ground at frequent intervals to prevent drying and dust blowing around.
In other DIY yards with pollution abatement measures, they supply Hepa filter vacuum/sander combo for rent at nominal daily rates.

We do the bottom paint job in a barn on a farm (the animals don’t live in the barn). We attach vacuums with hepa filters to an orbital sander. We dispose of the toxic dust in a double bag in the landfill. I’m not sure that’s the best way, but it’s the best we can come up with.
 
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Jul 19, 2013
202
Pearson 31-2 Boston
Several years ago I wanted to sand a poorly washed bottom properly and so I went to Home Depot and bought a new Ryobi random orbital sander and Rigid wet/dry vacuum. I returned several times trying to find a fitting to connect the two. Rigid even sells a connection pack, but none worked with the 1 1/4" OD Ryobi dust port. I enlisted several Home Deport staff on this quest and finally a grizzled grey-beard came back with a reducing coupler from Plumbing, one end is male to the Rigid hose, the other is female to the dust port. This setup has worked well, be sure to get a 10' or longer flexible hose as the standard 7' hose is too short to be useful.

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Also as has been mentioned, an ablative bottom in good condition only needs a very light pass unless you are taking down excessive paint buildup which is chipping. The basic single speed orbital sander is it is very hard to properly modulate, tending to leave swirls in the paint, so if possible use a variable speed sander with a low setting.
 
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Nov 26, 2012
1,429
Hunter 34 Berkeley
The first thing to determine as you prepare to apply bottom paint, is the existing paint hard or ablative.

Hard need sanding. Ablative does not require sanding as it wastes both paint and money.
Do NOT paint the bottom without sanding it first. It will come off by noon the next day.
 

Bob S

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Sep 27, 2007
1,633
Beneteau 393 New Bedford, MA
The drawback to wet sanding is that the water drips down the hull and onto the ground.
I agree. It does also when power washing if you use ablative paints. I like Dave's comments on a DIY system.
 
Feb 18, 2021
2
Catalina 34 Florida
From what I understand you want to sand an object without making dust. Anyway no matter how hard you try not to make dust, a small amount of dust will be anyway. I used a makita orbital sander BO5041 5-Inch in a small apartment to fix a small defect on the table and in about 20 minutes in the room it was like a fog, it didn't occur to me to open the windows, but I was learning from my mistakes. This model did quite a well job, and came with several accessories, but if you already have a sander you can look here(The Best Orbital Sander Review - Updated for 2021 ) to find accessories for it.
I hope I helped you!
 
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Oct 22, 2014
14,543
CAL 35 Cruiser moored EVERETT WA
Welcome to the forum @Goddard

You are right about dust and sanding. The yards require no that you mitigate the production of dust, paint chips etc. you need a vacuum attached to the sander and a filter to stop the fine dust from blowing out of the vacuum.

Post something about you and your boat in the Sailors Lounge. We like to see pictures of your boat.
 

dmax

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Jul 29, 2018
345
O'Day 35 Buzzards Bay
I'm surprised there are yards that still let you sand the bottom, around here (Massachusetts), very few yards let you paint the bottom yourselves and I don't know of any that would allow you to sand it beyond a light sanding for adhesion.
 
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Jul 19, 2013
202
Pearson 31-2 Boston
I'm surprised there are yards that still let you sand the bottom, around here (Massachusetts), very few yards let you paint the bottom yourselves and I don't know of any that would allow you to sand it beyond a light sanding for adhesion.
For the past six years I've been in Liberty Marina in Danvers which allows bottom sanding but naturally requires the use of a vacuum system. Previously Hewitts Cove in Hingham actually rented out the bottom sanding equipment. I would be surprised if most DIY yards dont permit bottom sandng, but that could be, I would understand why. YouTube is full of DIY videos of people sanding bottoms without vacuum systems...
 
May 17, 2004
3,105
Beneteau Oceanis 37 LE Havre de Grace
Our marina provides the sander and vacuum to borrow for free; just requiring that you pay them for the vacuum bag. I don’t know if they would have words with anyone who tried to use their own without a vacuum, but I wouldn’t blame them. I’m happy to use their equipment and not cover my own in bottom paint dust.
 
Jan 24, 2017
526
Hunter 34 Red Bank NJ
thirty years ago I used graphite sanding blocks with a bucket of water. These blocks worked amazing well due to the fact that they slowly erode away as they are used and never clog due to this feature. They unfortunately smell like rotten eggs as they ware away however they worked fantastic. The great advantage is that using them is unlike 80 grit paper which clogs after about five minutes. these blocks strip off the paint very easy as they melt away without cloging. They can be used dry or with water. Very messy but bottom sanding is a messy job anyway that you do it . The original company I believe stopped selling them however a similar product is sold on Amazon for about $35 for a pack of eighteen. It's called mirical eraser strip & sand.

Good luck
 
Jun 8, 2004
8,588
-na -NA Anywhere USA
@Bob S
@rgranger started to hit on why yards are strict on sanding. First the dust can and will fly on boats even 200-300 feet away. New boats required a full exterior cleaning. As for used boats, the dust would get into the pores of the gel coat ending with the yard having to redo the entire surface of that boat. All that costs the yard and time with owners screaming. Then there are state agencies as well as EPA who periodically inspect depending on locality who will demand the yard to halt operations and clean up no matter what it takes but the fines were generally very high. In some cases, insurance carriers would drop coverage on a yard. That said, marinas and yards have become more strict over the years.
 
Mar 26, 2011
2,784
Corsair F-24 MK I Deale, MD
a. There are HEPA bags for practically every vacuum.
b. If you use a dust collection bucket or dust deputy, you can use any vacuum, not just a shop vac. I use an ordinary vacuum with a bag, because it is quieter.

The other trick is to get a long, cheap hose to go between the sander and the vacuum. That way you don't have to keep moving the vac. HD sells some cheap sump pump hose that is very light. It might be this:cheap hose

Even if it were not a rule, vacuum sanding is far neater and more pleasant. It's just the right way to do it.
 
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