Although I agree with some of what Active Captain says, I don't agree with other parts. I believer would take far more than 3-5 Preval sprayer propulsion cartreges to completely re-gelcoat a C Dory. (16 oz max liquid sprayed with one propellant cartrege, but with viscous gel coat the amount that can be sprayed is less) One of the problems with using the Peval for people who are not used to using it, is that the gel coat has to be thinned to spray with these sprayers, and thus is difficult to get good finish and thinning with styrene will give a softer finish. Also as you mix the different containers, there is some risk of defects at overlap spray patterns. (each glass container contains only about 5 to 6 oz). Also after spraying gel coat, it must be covered from the air to cure--and this involves spraying Poly vinly alcholol--a mold release wax. I agree that for small dings, there is no question that re-applying gel coat is the way to go. It can be applied with a sprayer, or with a brush or small pallet knife. Many times it is not necessary to use a sprayer--just manual direct application and cover with an occlusive surface--like mylar film works very well. When I redid the 18 foot CC I purchased at hurricane salvage auction, the majority of the gel coat repair of scratches was done with a artist's pallet knife, just wipe on, cover and then wetsand to smooth. A few larger places required a Preval sprayer. But I would have to have a significant structural repair before I used the sprayer (and I have been using them for over 35 years)
However, gel coat does not adhere well to epoxy repaired surfaces. Someone posted that they had success with some primer. I have not used this primer. The generally accepted method is to use polyester materials to repair dings which will be gel coated.
Awlgrip or other two part urethanes are best used (much better than gel coat in my opinion) for a boat where the gel coat is gone--and boats in the tropics will eventually get to the point where the gelcoat is not repairable. Then any dings have to be filled, (in this case best with epoxy for better adherance), at least two coats of epoxy primer applied, with sanding and fairing between coats, and finally several coats of the two part polyurethane (like Awlgrip). I agree that it is hard to spray and different than other paints, but those who are good at it, make a mirror like finish, which is superb. The Awlgrip is harder than Gel coat (Hatteras finished all of their boats with Awlgrip for many years--not sure about current production). Although people do roll and tip, I have never seen a job as good as a good spray job. (I have only sprayed masts, and other relitatively small areas with Awlgrip--I don't have the experience to do boats with Awlgrip--so I hire a very good painter at $50 an hour to do the job--for me this is a better solution. I have also rolled a number of decks with non skid, which works much better than gel coat for non skid, and painted deck houses, trim etc with roller and tip brush using Sterling)
I have never seen any of the craftsmen I work with redo an entire large boat with gel coat--although it is occasionally done. (the initial build has gelcoat sprayed into the highly polished, waxed mold) We get 10 years out of a good Alwgrip job. Touch up is rare, because of the hardness of the paint--and generally the owners are careful, using fenders etc. Also I have sprayed clear coat over the pigmented base, and then if a ding recurs, you can easily respray the clear. Also one can use true metalics and cover with the clear for a classic gold cove stripe.
But, differences in techniques are what make the boating world interesting. Each technique can be used and it depends on what the craftsperson is most comfortable with.
However, gel coat does not adhere well to epoxy repaired surfaces. Someone posted that they had success with some primer. I have not used this primer. The generally accepted method is to use polyester materials to repair dings which will be gel coated.
Awlgrip or other two part urethanes are best used (much better than gel coat in my opinion) for a boat where the gel coat is gone--and boats in the tropics will eventually get to the point where the gelcoat is not repairable. Then any dings have to be filled, (in this case best with epoxy for better adherance), at least two coats of epoxy primer applied, with sanding and fairing between coats, and finally several coats of the two part polyurethane (like Awlgrip). I agree that it is hard to spray and different than other paints, but those who are good at it, make a mirror like finish, which is superb. The Awlgrip is harder than Gel coat (Hatteras finished all of their boats with Awlgrip for many years--not sure about current production). Although people do roll and tip, I have never seen a job as good as a good spray job. (I have only sprayed masts, and other relitatively small areas with Awlgrip--I don't have the experience to do boats with Awlgrip--so I hire a very good painter at $50 an hour to do the job--for me this is a better solution. I have also rolled a number of decks with non skid, which works much better than gel coat for non skid, and painted deck houses, trim etc with roller and tip brush using Sterling)
I have never seen any of the craftsmen I work with redo an entire large boat with gel coat--although it is occasionally done. (the initial build has gelcoat sprayed into the highly polished, waxed mold) We get 10 years out of a good Alwgrip job. Touch up is rare, because of the hardness of the paint--and generally the owners are careful, using fenders etc. Also I have sprayed clear coat over the pigmented base, and then if a ding recurs, you can easily respray the clear. Also one can use true metalics and cover with the clear for a classic gold cove stripe.
But, differences in techniques are what make the boating world interesting. Each technique can be used and it depends on what the craftsperson is most comfortable with.