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#1 2004-10-20 23:41:05

foroadmin
Administrator

Bottom blasting

Hey Jim,
I noticed your comment about bottom blasting under the fuel tank string.  I had the misfortune (or good fortune) to spot a few blisters on the underside this fall <IMG src="http://www.cc27association.com/f3/toast/emoticons/icon_redface.gif" border=0> and am now in the position of having to deal with it.  Was it the same in your case?  Any learnings you can share?
Rob
Rob Nicholson
Tenacious (1979 MkIII #773)  Post moved from original thread to begin new thread. -Admin

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#2 2004-10-21 01:44:04

davidww1
Member

Re: Bottom blasting

I had Towser's bottom sand-blasted in the fall of '98, removing 20 years of dead and flaking paint plus epoxy/tar barrier in one fell swoop. The blaster was experienced with boats and left a relatively smooth surface from which minimal gelcoat had been removed (I know this because, understandably, this fellow won't touch the pads - you have to clear off under them yourself - and the difference between areas he'd worked on and those sanded by me was probably measureable in microns).

Rick Bott at ABYC organized about 20 boats at the club that needed better bottoms, so it ended up being dirt cheap - $300, which is less than the cost of Peel & Strip, the alternative I was contemplating. This looks even better when compared with a quote of $7000 given by a thieving Georgian Bay marina to a friend who wanted the bottom of his 40-footer cleaned (needless to say, he did the job himself). Rick does this sort of thing as a business, so you could contact him and see if he would set it up at MCC, this fall or next.

I recoated the bottom in spring with six coats of Interlux Interprotect, each coat rolled and tipped on a hard but uncured prior coat, so no sanding was required except on the last coat for better adhesion of the VC-17. Rolling and tipping gives you a very slick finish with none of the orange-peel effect that rolling alone leaves.

There's little more to say about it - adhesion is still perfect over the whole bottom and the bottom is a smooth as any 27 I've seen.

David Weatherston
Towser, Toronto
C&C 27 Mk IV


David Weatherston
Towser, Toronto
C&C 27 Mk IV

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#3 2004-10-21 07:21:05

Guest

Re: Bottom blasting

Hi Dave,
Thanks for this - very informative.  I understand the rolling but what do you mean by 'tipping'?  Had your boat had any signs of de-lamination prior to - mine does and I'd assumed that the gelcoat would have to go?  Also - did you blast above the waterline (as I've seen recommended elsewhere)?
Rob.

#4 2004-10-21 07:49:52

davidww1
Member

Re: Bottom blasting

"Rolling and tipping" means rolling the paint/gorp/whatever on in the normal way - good coverage, even thickness, etc. over a small area, then before the coating has an opportunity to dry or set, running a dry brush lightly over the surface to smoothe it out. It's easy to learn and it makes a quantum leap in the quality of your finish, especially with a relatively viscous coating like Interprotect that does not self-level readily.

I had the boat sand-blasted to the top of the boot-top because when unloaded, the boat was sitting at the bottom of that line. In use, half the boot-top was immersed and that tended to leave the boat looking grubby all the time.

There was nothing wrong with my hull when I did this. According to Rick Bott, blistering is rare on 27's. I wouldn't get too drastic with your repairs - as in removing all gelcoat - if you're seeing only local blistering. Fix the blistered area, lay on some Interprotect, cross your fingers once, then forget about it.

David Weatherston
Towser, Toronto
C&C 27 Mk IV


David Weatherston
Towser, Toronto
C&C 27 Mk IV

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#5 2004-10-24 08:52:14

robbienick
Member

Re: Bottom blasting

hey Dave,

Thanks again.  I guess I'm one of the 'lucky' ones with a C&C27 blister ;-).  That said - after closer inspection by those in the know the problem does appear to be localized so we're gonna go with a plan much as you recommend.  I may cross my fingers twice though.
You mentioned Interlux - I've also heard the name 'VC Watertight' - floowed by VC tar (my anti fouling is VC17).  Any experience (direct or indirect) with these products?
Rob.
Rob Nicholson
Tenacious (1979 MkIII #773)  <IMG src="http://www.cc27association.com/f3/toast/emoticons/icon_lol.gif" border=0>


Rob Nicholson
1979 MkIII <img src="emoticons/icon_lol.gif" border="0" alt="" />

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#6 2004-10-24 11:19:52

davidww1
Member

Re: Bottom blasting

I don't know 'VC Watertight' personally; their web site describes it as a filling compound. 'VC Tar' is what I took off my boat. I'm sure it's effective at preventing osmosis, but it always looks as if it had been put on with a shovel.

David Weatherston
Towser, Toronto
C&C 27 Mk IV

Last edited by (2004-10-25 02:19:36)


David Weatherston
Towser, Toronto
C&C 27 Mk IV

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#7 2004-11-18 22:40:37

Guest

Re: Bottom blasting

Hi Dave;
I probably won't blast, because I suspect around here I'm going to get the "Marina Treatment" you described earlier.  However, I probably should get the bottom painted.  It sounds like you have done this yourself - is that the case, and is it any more difficult than regular painting (house)?  Thanks.
<A href="mailto:heh@numeric.com">heh@numeric.com</A>
Horace Henderson
76 MKIII - Newport RI

Last edited by (2004-11-18 22:44:14)

#8 2004-11-19 00:39:04

davidww1
Member

Re: Bottom blasting

If you want to clean your bottom to bare gelcoat but sandblasting is too pricey or unavailable, there's a product called "Peel Away" that is well regarded (West sells a variation). You brush it on, put a special absorbent sheet over it and leave it for an hour. You then pull the paper off and it brings the paint away with it. Because all the toxic stuff is now on the paper and can be stuffed in a bag, it's easier to comply with the environmental issues raised by paint removal. (I nearly did my boat this way, but the blasting option came up and I jumped for it.) That, however, is not the question you asked, and as this sounds like your first year with the boat, I'd leave this for another year.

If you've never painted your bottom before, it's not a big deal. The core issues are the same as painting your porch railings: remove dead or flaking paint, sand all surfaces to get good adhesion to the bare gelcoat or to existing paint, tape the waterline and roll the paint on in as even a layer as you can achieve. If you want a slick finish, roll-and-tip as described above.

A few caveats:
- When sanding, wear coveralls, goggles and a good-quality face-mask. Bottom paint is toxic (not kill-you toxic, but it's foul). Don't eat, drink or smoke until you've finished and washed up.
- Don't skimp on tools ($30 Black-&-Decker orbital sanders are a false economy). I have a Bosch random-orbit sander with a dust-collection hose connected to a shop vac. This rig probably cost $200, but the first time I used it was a revelation &#150; not only does it do the job in half the time, it's so clean I barely have to wash my hands when finished, so I can sand in coveralls and a paper 3M mask.
- Find out what's on the bottom now if you're painting over something else. Some bottom paints will not adhere to other bottom paint, which is one reason I stripped my boat. If you can't get this information or an educated guess, buy a litre of your preferred paint and do a test patch.

Can't think of anything else. If this is your first time doing this, go down to the yard a couple of weekends before you plan to do your boat, watch people and ask questions. Admittedly this is tricky: the people who are working hard probably have the best information, but one is reluctant to interrupt them, whereas the people who are standing around pretending to work and available to answer questions are close to useless. If you can negotiate this little conundrum, it probably will resolve any remaining issues.

David Weatherston
Towser, Toronto
C&C 27 Mk IV


David Weatherston
Towser, Toronto
C&C 27 Mk IV

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#9 2004-11-19 01:17:23

Guest

Re: Bottom blasting

I'm assuming I won't get through all the layers of paint to the gelcoat unless I use the coarsest grit.  Can you make a recmonedation on how course the grit should be?

#10 2004-11-19 01:19:23

Guest

Re: Bottom blasting

The above is still me - must have got bumped out.Horace Henderson
76 MKIII - Newport RI

#11 2004-11-19 07:28:25

foroadmin
Administrator

Re: Bottom blasting

Can you make a reccomendation on how course the grit should be?
Obviously the coarser the grit, the quicker the job will go.  Warning:  this is the dangerous way to approach the issue.  If you use coarse grit paper/disks, say 40 grit, it will cut through the paint quite quickly, but also into the gelcoat.  This produces an effect called 'profiling'.  This essentially produces flat areas or, even worse, scalloped grooves where impatience leads you to give in to temptation and use the edge of the sander to speed things up.  Bad, bad, bad, but almost everybody does it (and later wishes they hadn't).  If you are going to do the job ,it is worth doing properly and this takes time and patience.  Having done it about 20 times before on a wide variety of boats, here's the basic rules:
Start with 80 grit disks with a random orbital sander, 6" or 8".  Place the sander flat on the hull BEFORE you start it up (every time).  This will help prevent accidental gouging that can occur bringing a full speed disk into contact with the hull at an angle.  It can happen VERY quickly. As soon as you see the gelcoat through the paint, move to a different area.  Don't try to clear all the paint off at ths time.  Once you've gone over the entire hull with the 80 grit, do it again with 120, working right down to the gelcoat this time.  This will give you a quite acceptable surface and you'll probably never want to see a sander again in your life.  Some people continue this to 400 grit, so when you want to kill yourself after the first two hours of sanding just imagine how it could be worse.
This will likely take you a at least a few days to do properly, so be ready to invest time.  And, you will almost certainly want a full face 3-M mask and painters coveralls.  It is well worth the investment.  It's a VERY messy job.  Protect your eyes and lungs. 
Now you can put on the new paints.  If you use VC-TAR, note that it is difficult to get a smooth finish with it.  Some people lay down an epoxy barrier coat, but I don't know how well it goes on over Gelcoat.  As for the VC-17, yes, you can pretty much just roll it on like house painting.  It has the interesting property that it will re-liquify any previous layers which helps with smoothness.  It will not add to or subtract from the level of smoothness the hull had before it goes on.  The first season, you should apply 2 coat of VC-17.  One coat a year after that should suffice.
If you decide to try it, Good Luck.  Remember, the key is patience.
Gord.

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#12 2004-11-19 09:07:04

davidww1
Member

Re: Bottom blasting

>And, you will almost certainly want a full face 3-M mask and painters coveralls.  It is well worth the investment.  It's a VERY messy job.  Protect your eyes and lungs.

That's why I recommended using a rig like mine, with a dust extraction setup. It is astonishing how much it improves life if you're not fighting your way through a cloud of paint dust.

Personally, I'd be reluctant to use an 8" sander. They are so heavy that they're awkward to handle (we're not all as strong as you, Gord) and that leads to mistakes.

I used an epoxy barrier coat (see above) and you can get a very good finish with it. I wouldn't go any finer than 120 paper if using this, because epoxy bonds mechanically and it needs some "tooth" or roughness to get the best grip.

David Weatherston
Towser, Toronto
C&C 27 Mk IV

Last edited by (2004-11-20 01:28:43)


David Weatherston
Towser, Toronto
C&C 27 Mk IV

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#13 2004-11-20 02:12:39

Guest

Re: Bottom blasting

In Florida we have a different set of problems due to salt water and the ugly creatures that like to make a home on your hull.  However, I do have a surefire way to meet this challenge:
1) After the boat is securely hauled and blocked, I make a cursory "walk around" to check out the efectiveness of the two coats of Tinidad that I put on around the turn of the century.
2)  I then gather all the tools and equipment that my wife will need.  The biggest sander/grinder she can handle is a variable speed Makita with a 8" soft pad.  I hate to spend the extra money for the adhesive back disks but I do.
3) I would prefer variable grits starting with 80---then to 120---but she starts complaing that the sander gets too heavy.  So I compromise and start with 100 and finish with 100---making sure that she uses a scraper on any loose flaky stuff and also giving special attention to those pesky barnacle rings.
4)  I closely monitor her progress till I see her using the "edge" of the sander at max RPM's.  I gently remove my dusk mask and remind her to "keep it flat" while kindly offering to bring her back some lunch.  By the time I get back she is usually ready for a break.  After lunch, I point out the spots she's missed and once again remind her to "keep it flat"--suggesting that if the Makita is too heavy she might want to switch to the Rockwell random orbitor--but that it will be much slower.
5) She can generally paint our 27' in about an hour---after I mix the paint for her on our "shaker". She likes the heavy nap 9" rollers for putting on the whole gallon in one coat--but after, once again, explaining to her that two coats are better than one she will usually agree that a short nap roll/tip could provide possibly a 0.05 kt increase in speed.
6) Prior to the actual laying on of paint we do another walk around and mark those nasty little gouges.  She knows these are not good---and goes right for the bondo can or the tube of glazing putty.  I usually suggest another "break" while I mix up a bit of West System with a touch of big bucks filler---with a little accelerator she can get right back to work.
7) I always remind her to save a cup or two of paint for the "pad marks"--it was her idea to tape a 99 cent brush to the can.  Soon as the lift picks up the boat--boom---those pad marks are painted.  The time interval between painting the pad marks and splashing the boat is measured in milli seconds--notwithstanding my wife muttering "dry time" "dry time"---try and find those pad marks next time you haul.
<img src="emoticons/icon_cool.gif">  My wife is always worried about whether or not the paint will "stick"&gt;  (Actually, she is a store mgr at West Marine---and those paint reps spend most of their time hoodwinking store employees).  I always tell her----if you dont know what you're painting over---use a mineral spirits solvent base paint--you might not get the mega chemical bond that the $250/gal fancy paints give you---but then again it won't "melt" off the previous coats.
9)  One other small point.  There are "30 day" masking tapes----and "30 second" masking tapes-----neither of which is true.  Its 8 bucks a roll vs. 89 cents a roll.  Go figure.
Gotta run---my wife has a few non boat related chores for me.
Dave in Ft Myers

Dave Tinder
DAWN BREAKER  Mk3
Ft Myers

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