When to Sandblast Bottom

C

C-SIDE

Member
Sep 6, 2009
313
Michigan City, IN
Boat Info
2001 340 Sundancer
Engines
6.2L w/ genny
I went up to my boat this weekend and the bottom of my boat looks awful - paint is not even, exposed areas of the hull, i.e. no paint, some areas are smooth as a baby's ass while other areas are rough.

My questions are:
  • How do you know if its time to sandblast the bottom and start over or just repaint it?
  • Let's say I just repaint it and not sandblast it, even though it should be sandlasted, is that such a big deal?
  • Can I do any harm to the boat if I choose to sand the rough areas and paint the bottom?
Any help would be much appreciated

Thanks,
Chris
 
You should be able to sand the bottom and save the cost of sandblasting. Most people don't get serious about sanding, but if you will get after the paint and feather out the thick/thin using a rotary sander with about 80 grit paper and end up with 70% or so of the bottom white, before you repaint, you'll have good results.

Sandblasting is a last resort and normally only used where there is a paint chemistry incompatablilty between the old paint and what you want to use. Honestly, we only sand blast here when we don't know what is on a boat and don't want to take chances. Sandblasting is very aggressive and should only be done by someone with experience. SOmeone who doesn't know what they are doing, can do a lot of damage. As an intermediate step, some people soda blast a boat bottom, but it is an expensive way to remove paint when careful sanding can give you the result you need.
 
Chris,

I would reiterate what Frank said as well as offer this cautionary advice. Bottom paint dust is very unhealthy - after all it works by killing marine life. If you take this job on yourself, be sure to use a good safety mask, not just a dust face cover. Also if you can use a sander that has a vacuum dust pickup you will find there will be less mess.

Henry
 
Henry - sound advice, thank you.

I will be doing the work outside so hopefully that will mitigate some of the danger - I better pick a windy day!
 
Don't skimp on the respirator. They're only about $30 - $40 at Home Depot. A full face shield is less than $10. You can even get full-body, white, Tyvek-type jump-suits for under $10.
 
Chris,

I did the power hand sanding thing for the same conditions you described two years ago. I would also suggest you go to HD and get one of those cheap tyvek overall painter's suit. I didn't do it when I did ours, but probably should have. You may also want to re-think the windy day plan if there are other boats nearby, as the dust makes a real mess.

Henry
 
hey C-Side,

I am currently re-doing the bottom of my boat.

http://clubsearay.com/forum/showthread.php?t=24963

The sanding is taking a long time, but I want to do a complete inspection of the bottom, paiint a barrier coat on it, then bottom paint.

I am using Interlux products.

Their website is very informative:

http://www.yachtpaint.com/usa/default.asp

West Marine also has a basic video too:

http://www.westmarine.com/webapp/wcs/stores/servlet/westadvisor/10001/-1/10001/Bottom-Paint.htm

It is a lot of work, buy at least I will know the condition of my boat hull......
 
Here's the thing...
The paint is "uneven" on the bottom because, over the years, areas have de-bonded and flaked off.
Then the bottom gets sanded and re-painted.
More areas de-bond and flake off. And the bottom gets repainted again.
What you end up with over time is a mess. Some spots have 5 layers of paint, some have 3, some have eight...

Well, your boat's only ten years old so it shouldn't be that bad. Mine was- and two years ago it all "let go" and sheets of paint came off the bottom when it was put on the hard overnight.

Eventually, it'll have to go if you continue to use modified epoxy instead of an ablative antifouling. If you're gonna patch it up, be sure to scrape all the rough edges back to be sure there's no loose paint that you're going to paint over.
 
You guys are amazingly helpful - thank you

I think what I'll do is spot sand the rough areas, paint the whole bottom and hope for the best. I don't have the time to strip all the paint off, although that's what I'd really like to do. I'm training to do a triathlon, have 3 kids and to quote Four Suns an angry wife - how come they never understand?

Worse comes to worse, in 2011 I'll strip all the paint off and start from scratch.

I got a rough quote from my marina and its about $1,500 to sandblast and paint - I can think of a few better ways spend $1,500

Chris
 
Chris,

Don't paint the bottom until the boat is ready to back in the water next spring. Some bottom paints can be finicky and don't take to well with long term exposure to air. Do your prep work now if you want and plan to do a quick scuff up and paint in the spring if you want to get a jump on the spring commissioning.

Henry
 
I had one SR blasted with walnut shells and the last one done with soda. The results were the same as was cost. Voids were fared and barrier coat installed. Went with a teflon offshore top coat with copper that worked well for Lake Michigan. We currently use Awlgrip ablative paint that has been trouble free. It gets recoated every three years and power washed each fall. We do touch up the smile and bootstripe. IMO, ablative paint pretty much eliminates the need for blasting. We paint right over a dry powerwashed bottom with no other prep and this has worked fine.
 
Sandblasting is more abrasive than sodium bicarbonate (soda). Sand will not desolve as soda will in the rain. Make sure that what ever work is done complies with your state and local rules as bottom paint is a hazardeous material. You son't want it blowing off and into the water. Remember to protect yourself if it is a DIY project as the paint can harm humans was well as sea growth.
 
Here's a little tip for the shrinkwrapped boats. If you're planning on sanding in the spring, use the wrap as a dust barrier. Try and cut it down the middle and weigh the halves down over the sides. So when someone rants about a little dust they can't blame you.
 
Looks like a good sanding job would be all you require.
 
Take it from somebody who knows, where that boat is located at Oselka they aren't going to be too happy about somebody sanding their bottom there. I walk by your boat almost every day lol.
 
C-SIDE said:
Yes, that thought has crossed my mind Carver370 - thoughts?

Thanks
Click to expand...

I shouldn't be saying this since I work right there (not at Oselka) but if you go there on a Sunday in the off season most likely nobody will even batt an eye. I have had to do this for about 15 years! My boat is there as well and I do all my own sanding and everything but I pick my times and make sure I clean up afterwards.

Non windy, maybe even a day when it had rained in the past few hours or a day or so would be best so everything isn't blowing around. After looking closely though it seems like a lot of what you think might be paint coming off could just be a less than enthusiastic power washing job...

I personally take my random orbital sander with a vacuum attached to it and lightly sand the areas that need it and repaint the waterline and bow area..
 
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