Bottom paint

Hi Trawler Friends i an getting the bottom of my Trawler ready for new Pettit Hydrocoat Bottom paint . my ??? is i have removed all old bottom paint to the glecoat . Will this paint stick to it well i know they put it on the new boats . I have the old gelcoat sanded to a 80 grit finish. it looks like the old bottom paint was on the white gelcoat before. i just don't want this pricey paint to fall off. what do you think. thanks Captain Bill

Barrier cost is necessary. I don’t believe the hydro cost will adhere to gelcoat.

It is always best to refer the manufacturers application instructions:

http://www.pettitpaint.com/media/4010/pettit-hydrocoat-antifouling-bottom-paint-pds-17.pdf

Bare Fiberglass:
All bare fiberglass, regardless of age, should be thoroughly cleaned with Pettit 92 Bio-Blue Hull Surface Prep or de-waxed several times with Pettit D95 Dewaxer. Proceed with either Sanding Method or one of the Non-Sanding Methods below.

Sanding Method - After the surface has been de-waxed, sand thoroughly with 80-grit production paper to a dull, frosty finish and rewash the
sanded surface with Pettit 120 or 120VOC Thinner to remove sanding residue. Then apply two thin coats of this product, following application
instructions. Careful observation of application instructions will help ensure long-term adhesion of this and subsequent years’ antifouling paint.

Non-Sanding Method - To eliminate the sanding method, three alternative methods are
available:

1) Thoroughly clean, de-wax, and etch the surface with Pettit 92 Bio-Blue Hull Surface Prep
using a medium Scotch-Brite® pad in a swirling motion or wash the fiberglass at least three
times using Pettit D95 Dewaxer. Then apply one thin coat of Pettit 6998 Skip-Sand Primer.
Use a 3/16” or less nap when applying by roller. Consult the primer label for complete
application and antifouling top-coating instructions. Apply two thin coats of Hydrocoat.

2) Thoroughly clean, de-wax, and etch the surface with Pettit 92 Bio-Blue Hull Surface Prep
using a medium Scotch-Brite® pad in a swirling motion. Thoroughly rinse all residue from the
surface and let dry. Then apply one coat of Pettit 4740/4741 H2-Prime Epoxy Primer or Pettit
Protect High Build Epoxy Primer (4700/4701 or 4100/4101). Consult the primer label for
complete application and antifouling top-coating instructions. Apply two thin coats of
Hydrocoat. See Pettit Protect User Manual for complete detailed instructions.

3) Easy 2-Step Sandless Method - Thoroughly clean, de-wax, and etch the surface with Pettit
92 Bio-Blue Hull Surface Prep using a medium Scotch-Brite® pad in a swirling motion.
Thoroughly rinse all residue from surface and let dry. Make sure that the entire surface has a dull, frosty finish. Wipe surface to remove any excess moisture and apply two thin coats of Hydrocoat.

Barrier Coat:
Fiberglass bottoms potentially can form osmotic blisters within the gelcoat and into the
laminate. To render the bottom as water impermeable as possible, prepare the fiberglass
surface as mentioned above (sanding method) then apply two or three coats of Pettit Protect
High Build Epoxy Primer (4700/4701 or 4100/4101), per label directions. Apply two thin coats
of Hydrocoat. See Pettit Protect User Manual for complete detailed instructions.

A Barrier coat is advisable, but not required. Barrier coat isn't a primer to enhance adhesion, it is a barrier to prevent water intrusion and blistering.

Thank you I did call Pettit and they said it's okay to put that right on the gel coat

Did you dewax the hull before sanding? If not the sanding can heat up the wax and drive it into the gel coat and then the bottom paint may not adhere well.

I have been using Pettit Hydrocoat for the last several years. It has adhered well to whatever was left of the conventional Antifouling that preceded it. Where the bare FG has been exposed by the flaking off of very old paint, PH has also adhered well.
Its only downside is that it is not cheap. My prep is simple. A very aggressive power washer that removes all the slime and a scraper if there are barnacles, mussels or oysters.
I have hard growth if the lift guys put me on the beds in the same spots for a couple of years, then leave them exposed. I have had oysters in the shaft tubes.
Last year, after the barnacles on the running gear getting too much, I tried Pettit cold Galvanizing spray on all of the running gear and on the old CQR. I have high hopes for fewer barnacles. I have not had any hard growth where I have used Hydrocoat.

Thank you all for the good advice

There was no wax on it just a lot of old paint and I had it water and glass bead blasted off right to the gel coat. I'm starting fresh and clean

If I had a hull cleaned of all prior bottom paint I would not pass up the opportunity to do barrier coating. Having done it once myself it's just Too much work or too expensive prep to ever do it again.
Some mfg voided their hull warranty if hulls were sanded to deploy bottom paint.

Absolutely if you are down to bare gel coat, take the time and relatively small dollar outlay to do a barrier coat of epoxy. If you are DIY it is easy to do just some crawling around. The paint is about $80 per gallon and for my previous 32’ I used maybe 6 gallons or so.