to consider in choosing a Polyurethane paint or gelcoat'
I have discussed the pros
and cons of paint and/or gelcoat in another page.
What really needs to be
explained is whether or not you can even use gelcoat to begin with. If the
boat has a paint finish already on it, you cannot put gelcoat over it. It
all needs to come off right back down to the original gelcoat and maybe
As far as preparation goes,
you will be facing pretty much the same amount of work ether way. Only
difference with gelcoat is that much of that labor comes after the
application of the gelcoat.
If there are repairs to be
made you must do them in polyester resins. Gelcoat will not stick to epoxy.
Now we need to determine if
the boat needs to be faired. Fairing is a long and laborious job that is
meant to fill-in larger areas so that when you view the finish at an angle,
you don't see wavy spots or "oil can" dents in the hull. Fairing is done
exclusively on vintage cars. Look at a door on a nicely restored car and you
won't see any waves or dimples anywhere. If you are needing to fair the
surface, you need to decide to what extent you want the surface to look
like. Certainly on a boat we don't need to reach the standards of Concourse
Cars. But in my case with Flying Cloud I knew that I would never have the
opportunity to fair her in the future. She was in bad shape and of course I
went much farther than was really needed on a cruising boat.
But I think the photos show the proof of my labor. UNTIL I hit the first
if you want to more
about fairing, click on this link
The main difference between
gelcoat and paint is that for paint, the primer is sanded and double checked
for mars, sags or other problems and then the topcoat is applied by spray or
roll/tip. Once cured, you are finished.
So its about the same amount of work either way. Its just the sequence of
events that are reversed.
gelcoat will need to be heavier in thickness for a couple reasons. Gelcoat
does not level out like paint. Even with special additives to thin the
viscosity, a certain degree of texture or "orange peel", will be present
after cure and will need to be sanded, sealed and polished.
Gelcoat is normally sprayed on in multiple coats to achieve enough thickness
to allow for the initial sanding and polishing.
The cured thickness you
want prior to initial sanding is a minimum of 30 mils and max 35 mils. This
will allow for a final thickness around 20 mils. Any heavier than 25 mils
and you run the risk of spider cracks in a few years.
Normal maintenance can
reduce the thickness by 2 to 3 mils a year. If you compound and polish it
You should be able to spray
10 mils per application. Allowing for shrinkage in the initial cure, this
would be about 4 coats, or;
1. 10 mils
gelcoat with little or no additives and no surfacing wax
2. 10 mils gelcoat, same as above.
3. same as above but with a small amount of surfacing wax.
4. 10 mils with additives and surfacing wax.
Allow the coats to harden
for several hours between coats. Coats 1 - 3 will feel tacky after hardening
to a point that you can't leave an impression with your finger nail.
Coat 4 should have no tacky
feeling at all because the surfacing wax will migrate to the surface as the
cure cycle takes place. This is important because you can't sand it until it
Gelcoat is very thick and
in order to spray it must be thinned. The less you thin it the better. But I
use a 2.2 millimeter tip on my HVLP gravity feed gun.
NEVER thin gelcoat with
acetone, MEK or lacquer thinner. The best product seems to be a product
called "patch booster" and is available from a number of companies that
manufacture resins. 10% to 15% is all you need.
On the third coat add about
10% surfacing wax and let it cure for about 24 hours. Now it can be sanded
with 180 grit to remove all orange peel. This is also the point at which you
would start fairing and making the surface smooth and straight.
The final coat will be done
with a 1mm tip adding between 30% to 40% patch booster and 10% surfacing
This application will be more like spraying paint. because this is thinner,
watch out for sags and runs. Allow a couple minutes between coats to get
about 10mils. Spray the about 5mils with the first coat and wait and recoat
in 2 to 3 minutes.
Let this cure about 24 to
48 hours. Wash the surface with naptha and a concentrated liquid
Now start sanding with 320
grit paper. I prefer wet or dray paper because the water keeps the
gelcoat from clogging the sandpaper. If you don't feel you are making
headway, switch to a slightly heavier paper like 220 or so.
Once the entire surface is
sanded to the point that you can't see any shiny spots (when looking at it
dry) you are ready to start working down to the final finish. Go from 320 to
400, on down to 800 grit and finally finish up with 1000 grit wet.
This is about the same
amount of labor as sanding all that primer when preparing for paint.
The main point here is to
look at the dried surface and be sure that all the previous sanding marks
from the heavier sand paper, are gone. If everything has the same look that
the 1000 grit does, you are now ready to polish.
there are a number of polishing/buffing compound available. But we prefer a
product called Aqua Buff. It comes in two different grits and is available
Start polishing with the coarse grit and once the entire boat is polished
follow up with the fine grit.
Buffing and polishing is
generally interrupted as polishing on an d wiping it off. NO! Wax on, wax
off was only in a movie.
Polis is small areas and
keep the pad moving around slowly so as not to burn the surface. No need to
keep adding compound when you see it starting to shine. Basically buff until
you see the gelcoat starting to shine. Keep buffing more without adding more
Once you see that your efforts are not making in difference, move to another
area and repeat until the entire boat is free of the sandpaper marks.
On gelcoat we like to use
Mequires products. Keeping the gelcoat waxed is very important.