Prep Requirments for Barrier Coat??

[tboylan]

I am purchasing a pre owned Gulfstream that has never been bottom painted. I would like to know what is required to prep the gel coat for barrier coat. I prefer not to get the dust flying and so am thinking about wet sanding by hand with 80 grit. Do I just need to make sure the surface is dulled to the point where it no longer shines? Or is there more to it than this? Also, what techniques do you use to mark off the water line so the paint stripe on the sides will look nice and straight?

Thanks in advance for your feedback!

 

[Shutterbug]

Pretty sure Interlux site has more than enough info. on hull prep for painting or barrier coat, so not sure about the proper grit other than I'd make sure the bottom was good and dull and then clean.

Sure others can chime in but the simplest method for me on striking a waterline was to put boat in water for several days, haul boat, make a pencil mark an 1,2 or 3 inches above the waterline in several places, run painters tape.

 

[tboylan]

Thanks for the feedback. I went to the Pettit site. Lots of good info there.

 

[seasick]

Thanks for the feedback. I went to the Pettit site. Lots of good info there.

AS you will probably read on the site, the key point is not so much the sanding but being sure that any wax or mold release products are removed. Each manufacturer has the appropriate solvent for the job. For barrier coats, application is critical, read and follow the instructions. Also note that some barrier coat applications require the first coat of bottom paint to be applied withing a certain time span. If you wait too long, the bottom paint may not adhere correctly.

 

[onoahimahi]

I went through this last year with my 1994 Sailfish which came up from NC and had never been bottom painted. The thing had sat on a lift for all its life and the gel coat was already dull and chalking so I wasn't too worried about wax or mold release chemicals. Nevertheless, you should follow the direction about stripping wax because if it is there, you may be just pusing it around with the sand paper

I got good advice on this over at Hull truth - here is one of the threads:

http://www.thehulltruth.com/boating-for ... tions.html

I'm into woodworking and used my Dewalt 5" random orbital sander connected to a shopvac for dust collection - it worked fine. I used 80 grit paper and no wet sanding. After one year, there was absolutely pealing of the barrier coat anywhere on the boat.

Figuring out where the waterline should be for me was a challenge because I had to do it without launching the boat. Here is one post on it:

viewtopic.php?f=2&t=19718

Once I settled on some reference points, I "calibrated" a level by removing the pitch of the boat as it sat in my driveway with a block of wood. Then I moved the calibrated level around the boat making a bunch of marks. Then I ran the masking tape between the marks and painted like normal. Photos of my calibrated 2X4 level are below

-Scott

 

[onoahimahi]

A few more photos:

[Edit: 2 of 3 photos deleted due to quota]