Bottom Paint Sanding

[P12nash]

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

 

[capta]

Sorry, I can't answer your question, but it does make me long for the good old days when I'd just take a sander to the hull, no respirator, dust collector, fancy suit or eye protection. That was my first job in a boat yard, sanding, prepping and painting boat bottoms. That metallic taste, especially when I broke for a smoke, is as fresh in my memory as if it was an hour ago. lol
How did I ever make it to 73?

 

[markwbird]

I am sure they mean sanders with the built in vacuum. Most yards require them.

 

[Ralph Johnstone]

I'm going to be sanding and applying bottom paint this weekend for the first time

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.

 

[P12nash]

I am sure they mean sanders with the built in vacuum. Most yards require them.

I guess my real question is whether that typically means I need a legitimate HEPA dust extractor to be "dustless" or if any shop vac is sufficient

 

[P12nash]

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.

Ablative. I was under the impression from reading online that I should hit it with a quick round of 80 grit to knock off anything especially loose. Another question I have is if I can put any ablative on top of my existing? I'll be selecting a bottom paint based on recommendations for my region - New England.

 

[Rich Stidger]

Ask if your yard has a sanding setup that you can use or rent. If you do use your own vacuum, Rigid makes a fine dust bag for the inside of their shop vacs that is intended for drywall sanding. I would think that would be perfect for bottom paint as well.

 

[P12nash]

Ask if your yard has a sanding setup that you can use or rent. If you do use your own vacuum, Rigid makes a fine dust bag for the inside of their shop vacs that is intended for drywall sanding. I would think that would be perfect for bottom paint as well.

My yard actually subs out this work and doesn't have any equipment that they'd use for it. The Rigid dust bag is exactly what I'd be using if I use my shop vac

 

[rgranger]

The only thing to sand on ablative is places where any buildup has occurred or to sand of barnacles.... and maybe smooth out a rough spot. If you need to fair a gouge you should clean that out also before you start fairing.

 

[PaulK]

I use duct tape to attach my shop vac to my DeWalt hand sander. The bayonet-mount of the dustbag on the sander is the same size as the hose, so two or three layers of tape over the butted pieces and it holds for an hour or two. Getting a new filter and throwing out the old one after antifouling is probably a good idea. Messing up new equipment for your business is probably not.

 

[shemandr]

Considering realities I would go with the shop vac. Well, I already have. I used a shop vac with my orbital sander. I worked pretty well. I think your yard will probably want ground covering or maybe even a tent. If anyone is painting while you're sanding expect some complaining.

 

[Ralph Johnstone]

I was under the impression from reading online that I should hit it with a quick round of 80 grit to knock off anything especially loose.

Don't know what service your yard offers but we always start with their pressure washing the boat while it's still in the slings. And this beast could blow a hole through the hull if held close enough.

After the boat is in the stands, go after the areas that were under the straps with heavy 3M Scotch-Brite scouring pads or equivalent, just make sure they're heavy. Use these open pads and not sandpaper as sandpaper clogs with the organic material. Also use loads of water which avoids dust and keeps the pad clean but only if your yard approves. Our effluent is filtered before discharge to the ocean so no worries.

I don't bother scuffing the pressure washed areas unless I can see loose paint. Most ablative bottom paints contain volatile solvents which dissolve the previous ablative and ensure a good bond. If your's is water based, all bets are off.

I always like to leave the boat for a day before painting to ensure most of the water is out of the paint. Maybe this is what avoids loose paint. See that the paint will be much harder the next day.

As far as ablative over ablative goes, no problem assuming they are main stream ablative paints. Hard over ablative is not recommended (no solid base).

 

[capta]

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.

I'm sorry, but I really disagree with this. A good sanding gets the old ablative paint back to something the new paint can adhere to.Sanding isn't about cleaning off barnacles and grass, the pressure washing should have done that well enough.

 

[Davidasailor26]

My yard rents dustless sanding kits for just the cost of the vacuum bags you use. As far as I can tell they’re just regular shop vac bags, but I haven’t looked too close.

Most paint manufacturers list paint compatibility charts for going between the same and different types of paint. Pettit’s, for example, is at https://www.pettitpaint.com/media/4361/pettit-paint-compatibility-chart-2019.pdf. I follow the manufacturer’s recommendation to light sand between seasonal applications of matching ablative.

 

[Ralph Johnstone]

I'm sorry, but I really disagree with this.

.

And well you should. After all, this is a forum and there is little I am willing to accept without some sort of proof.

My first clue comes in part from the West Marine product description:

I see the paint dries, it does not set by cross linking with oxygen (as do most paints) so its solvents are likely able to re-dissolve the paint after it dries. This is the case with this paint. Take some new paint and rub it onto some previous ablative paint. The surface of the old paint stays sticky until it dries. Take an organic solvent like acetone, benzene, or lacquer thinner to old ablative paint and watch it dissolve onto a solvent soaked rag. Does a good job of dissolving the old ablative.

Given that the old paint dissolves nicely in its own solvents, you are going to set up as good a bond as possible under the circumstances, sanded or not.

 

[Bob S]

Not sure if the yard would allow wet sanding. It keeps the dust down. I read years ago on this site about using drywall wet sanding screens with a pole. Use a bucket of water and it gives you a good reach.

https://www.lowes.com/pd/Marshalltown-3-25-in-x-9-25-in-Pole-Sander/1000204345?cm_mmc=shp-_-c-_-prd-_-tol-_-google-_-lia-_-217-_-hardsurfacetools-_-1000204345-_-0&store_code=1758&placeholder=null&gclid=CjwKCAjwkun1BRAIEiwA2mJRWeAkvJWqOvYZ54WqnDtD0pLyKGowv9HO5MXAkRmVb4y5hdYrPzxGYBoCJC4QAvD_BwE&gclsrc=aw.ds

 

[Ralph Johnstone]

I read years ago on this site about using drywall wet sanding screens with a pole.

Could work as long as you get the dirty parts under the straps and only use the water in the bucket. Don't worry about the rest of the hull.

 

[dlochner]

Check with the manufacturer's website for prep before painting. Ablative paint often needs a quick sanding to remove any loose paint and give some tooth for the new paint.

The best DIY dust collection I have seen and used is a Dust Deputy. I have one and used it when I removed the bottom paint from my boat. Connect a long hose to the Dust Deputy, connect the Dust Deputy to a good shop vac, the small ones aren't strong enough, and 99+% of the dust will be collected. I put a filter bag in the shop vac to collect anything that gets that far. When I did the bottom of my boat I collected 5 gallons of paint dust in the DD and the filter bag in the vac was empty.

 

[rgranger]

Not sure if the yard would allow wet sanding. It keeps the dust down. I read years ago on this site about using drywall wet sanding screens with a pole. Use a bucket of water and it gives you a good reach.

https://www.lowes.com/pd/Marshalltown-3-25-in-x-9-25-in-Pole-Sander/1000204345?cm_mmc=shp-_-c-_-prd-_-tol-_-google-_-lia-_-217-_-hardsurfacetools-_-1000204345-_-0&store_code=1758&placeholder=null&gclid=CjwKCAjwkun1BRAIEiwA2mJRWeAkvJWqOvYZ54WqnDtD0pLyKGowv9HO5MXAkRmVb4y5hdYrPzxGYBoCJC4QAvD_BwE&gclsrc=aw.ds

I like this idea.... and will probably borrow it the next time I bottom paint. Seems to me that if the goal is to keep toxic dust from flying around the yard, the best way is to not produce any in the first place. The final issue will be... what to do with the bucket of slurry you end up with. You can't just pour it down a drain. I guess you could let the water evaporate over time and then collect the solids and dispose of them properly.

 

[dmax]

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:

Dustless Sanding - Practical Sailor

Since 1974, Practical Sailor’s independent testing has taken the guesswork out of boat and gear buying.

www.practical-sailor.com