Which Sander To Prep Bottom?

[Lepke]

I have an air driven Mirka. It has built in vacuum pickup and long hose. Big shop vac also has a long hose so I can get the noise away from where I'm working. There are many cheaper brands, some are very noisy.
I have a wood boat and use the sander topside and have never had an issue with pollution. Also nice inside. Usually just a tack rag to clean up.
Amazon or Ebay is where I get my disks. Sometimes less that 50% of local prices.

[Ex-Calif]

Originally Posted by Sid at SailAway

So it looks like an orbital sander is the ticket. Ex-Calif mentioned a Bosch, what model?

A doodle bug sander is also called a palm sander or finishing sander. They are smaller than the orbitals.

I used this model but can't recommend it. Although we worked it hard we eventually killed it. Burned up the motor.

Amazon.com: Makita BO4556K 2.0 Amp 4-1/2-Inch Finishing Sander with Case: Home Improvement

For the Bosch I think we have two GSS230 orbital sanders. It seems popular to have the dust extractor on new models. I would vote against for a couple of reasons.

- Holding the sander upside down against the hull is hard enough - lighter is better
- The dust extracting ones often use proprietary paper with "holes" in them to let the dust out through the pad - I prefer to be able to cut whole sheets into thirds and not be captive to their stuff.
- I like the mechanical connection - not sticky paper...

Recommend getting good quality 3M paper.

[ztsf]

Absolutely, you need a dust catcher. Use a random orbital sander. Use 80 grit on final prep for most bottom paints. Wear the best dust mask you can.

Check and see if you can rent a larger vacuum model - maybe an 8". They collect more dust and work way faster than than a smaller 5" model.

[thinwater]

While a dust mask is a good idea (I prefer the 1/2 face rubber sort with HEPA cartridges), if you are getting signifigant dust--enough to worry about Tyvecs--there is something wrong with the dust collection.

Working without dust collection is irresponsible for common sense reasons:

• You are messing up another persons yard.
• People may be painting topsides nearby. Or they just finished painting before you got there and you are going to ruin their hard work.
• They may simply not want your bottom paint on their deck.
• The dust isn't good for you.

This goes for any sanding operation.


----


My tip is to buy a long, lightweight extension tube for the vacuum. I like some of the very light, cheap sump pump hose they sell at HD. Makes it much easier.


Don't forget to check the vacuum frequently; if the bag fills/clogs vacuum will drop and you will make a mess.

[Sid at SailAway]

Originally Posted by misfits

If all you want to do is "prep" the bottom for paint, I'd recommend a drywall screen attached to a broom handle. If you're looking to do a complete bottom job, orbital sander attached to a vac.

When we bought her we had her stripped back to gel coat and started from there. So, fortunately, the bottom has only two coats of bottom paint build up plus, of course, the barrier coat. All I really need to do is rough up the bottom for new paint as she's pretty smooth down there.

I think what I need based on info here, is something between the drywall screen and an orbital. Therefore, this suggestion from Ex-Calif makes sense. Amazon.com: Makita BO4556K 2.0 Amp 4-1/2-Inch Finishing Sander with Case: Home Improvement

It's cheap enough risk burning it up and not worry about it. This is actually the easy part, hard part is deciding how to protect the saildrives....

[Greggegner]

Unless you are in great shape, weight of the sander is very important. I suggest a nematic sander with Velcro attachment. A good mask is required and a paint suit is recommended. The drywall sander looks good, but a bottom requires more pressure to sand than drywall. Another option is sand blasting with a soft medium. If you are going to coat the bottom that is what I would use. You can rent them.


Greg S/V Sweet Dreams
Pearson P385 out of Racine Wisconsin

[boden36]

Have not sanded the bottom paint in 25 yrs and have no problems with adhesion.
I guess for a racing boat is is necessary, but for a cruising yacht with ablative antifoul I reckon it may be more trouble than it's worth.

Regards,
Richard.

[Reefmagnet]

Originally Posted by boden36

Have not sanded the bottom paint in 25 yrs and have no problems with adhesion.
I guess for a racing boat is is necessary, but for a cruising yacht with ablative antifoul I reckon it may be more trouble than it's worth.

Regards,
Richard.

Same here. I use an industrial scotch bright that is normally used for scuffing car paint for touch up work (and use it wet). Our latest boat had thick paint that needed sanding along the waterline where extra coats had been added over the years to the point of flaking, so I had to power sand this. I personally prefer 40 grit for this job because it's quick and I reckon the courser the sanding disk, the less fine dust and the less dust problem.

With random orbital sanders, the wattage and no load rpm are good indications of suitability for task. For wood and paint prep, the higher cost, lower powered units with 10000 rpm no load speeds are best. For jobs like a/f and sanding fibreglass or fairing materials the high power units with no load speeds of 12000 rpm or greater work the best. I prefer 5" versus the 6"models for the lighter weight and better performance on curved surfaces.