gelcoat spraying tips and observations from first, somewhat successful time

ianmoore

Petty Officer 2nd Class
Joined
Jun 5, 2014
Messages
169
Hello,
Restoring my 1959 Glasspar, and just sprayed the hull with Gelcoat/. I initially had tried rolling on the transom, but it made for a lot of extra sanding.
I bought the cheap HVLP gun from Harbor Freight and decided to give it a go. I had a couple of semi-comedic mis-steps, but ended up with a pretty smooth coating, which i am now sanding down.
I was using the US composites standard white non-waxed gelcoat. I came up with a system that worked pretty well for me. I found that if i tried 16oz, the gel would start kicking before i was finished with it. I ended up going 12 oz at a time. I thinned it about 10% with stryene, and was able to get a pretty consistent stream that gave good coverage. I could typically get one hull side(down to the spline) with one run through. I did 5 coats, with the 5th being a waxed gel. I actually used some gelcoat i had that was already waxed. That was a bit thicker, so i had to thin almost 15%

On the Harbor Freight gun, it is good to clean it a bit before you use it. I found that even thinned, the inline strainer created too much drag in the gun. I didn't use it.
I had to be pretty vigilant about actually cleaning the gun, not just running acetone through it. I would take the cleaner, and even a small screwdriver and get out any gel that was in there. With that done every couple of coats, and a good deal of acetone through the gun after each coat, i was able to get pretty good results.

Now if someone could come up with a robot sander!
Ian
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,581
Hello,
Restoring my 1959 Glasspar, and just sprayed the hull with Gelcoat/. I initially had tried rolling on the transom, but it made for a lot of extra sanding.
I bought the cheap HVLP gun from Harbor Freight and decided to give it a go. I had a couple of semi-comedic mis-steps, but ended up with a pretty smooth coating, which i am now sanding down.
I was using the US composites standard white non-waxed gelcoat. I came up with a system that worked pretty well for me. I found that if i tried 16oz, the gel would start kicking before i was finished with it. I ended up going 12 oz at a time. I thinned it about 10% with stryene, and was able to get a pretty consistent stream that gave good coverage. I could typically get one hull side(down to the spline) with one run through. I did 5 coats, with the 5th being a waxed gel. I actually used some gelcoat i had that was already waxed. That was a bit thicker, so i had to thin almost 15%

On the Harbor Freight gun, it is good to clean it a bit before you use it. I found that even thinned, the inline strainer created too much drag in the gun. I didn't use it.
I had to be pretty vigilant about actually cleaning the gun, not just running acetone through it. I would take the cleaner, and even a small screwdriver and get out any gel that was in there. With that done every couple of coats, and a good deal of acetone through the gun after each coat, i was able to get pretty good results.

Now if someone could come up with a robot sander!
Ian

Been looking into doing some spraying of gelcoat in the future. Have not picked up a HVLP gun yet but have been looking into it. Appreciate your post and insight to the application process
 

gm280

Supreme Mariner
Joined
Jun 26, 2011
Messages
14,585
A very interesting thread. Can you post some pictures of your project? I'd like to see it and your efforts as well. What tip size is the HF HVLP spray gun? I know when I spray PPG primer coat(s) of various types, I have to use a 1.7mm or larger like 1.8mm, or even 2.0mm tip size. Because the viscosity of the primer. I would think gel coat would be pretty thick as well. But never using any, I honestly don't know. And what air pressure did you spray at? I use a regulator at the gun set to 30psi to get the 10psi internal tip pressure, like the gun manufactured stated. I need more info....
 

ianmoore

Petty Officer 2nd Class
Joined
Jun 5, 2014
Messages
169
No Title

This gun has a 1.4mm tip. You can order bigger tips from Harbor Freight if you call customer service. I think they have a 1.7mm and a 2.2mm as well. I sprayed at 40psi as well(should have mentioned that).
The gun is definitely not perfect for the job, but it's also quite a bit cheaper then some of the other options, and when you don't plan on doing it again, becomes more of a solution. The thinning with Styrene was necessary to get it to flow smoothly. I had a friend come over and check my work. He had a job gel-coating speedboats a few years back, and said that my cured surface looked good in terms of what to expect with orange peel after spraying. I did a couple of hours hand-sanding at 220 yesterday and was able to get much of the orange peel off.
I apologize for the pics. Really hard to see what the surface looks like, but only have the iphone camera:
 

Attachments

  • photo220022.jpg
    photo220022.jpg
    126.6 KB · Views: 2
  • photo220023.jpg
    photo220023.jpg
    114.5 KB · Views: 2

Woodonglass

Supreme Mariner
Joined
Dec 29, 2009
Messages
25,924
Did you do any calculations to try and determine how thick the gel coat was when you finished. They recommend 20 mils (penney) cuz with the sanding you'll prolly end up about 1/2 that. From what I can see, Looks to me like you did a darn good job with the equipment and methods you used.:encouragement:
 

gm280

Supreme Mariner
Joined
Jun 26, 2011
Messages
14,585
ianmoore what is your next step? Are you going to drop down to 400, 600, 800, 1000, 2000 grit and then polish, or what?
 

ianmoore

Petty Officer 2nd Class
Joined
Jun 5, 2014
Messages
169
Woodonglass . I didn't have a good way to measure the thickness, though i practiced on the transom first, both with application and sanding depth.
I went a bit heavy on coats since i was unsure of my actual depth. My thinking was that most people shoot 3 coats, and with my gun and thinned gelcoat would probably need a couple more.
gm280 I plan on switching to 400 on once i get all of the orangepeel off. Getting close, but still have quite a bit of work to do
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,297
looking good.......may have to hit HF for a HVLP gun
 

52FordF2

Petty Officer 1st Class
Joined
May 31, 2013
Messages
372
How was the removal of the Blue tape. Right after spraying but still tacky or did you let harden?
 

ianmoore

Petty Officer 2nd Class
Joined
Jun 5, 2014
Messages
169
Removal of the blue tape was mostly uneventful. Couple of small sticks, but was able to get them off.
I did let it cure before i removed it
 

ondarvr

Supreme Mariner
Joined
Apr 6, 2005
Messages
11,527
Just keep in mind that adding styrene will reduce the weathering, water resistance and crack resistance of the gel coat. And the more you add the greater the affect. Yellowing in the sun is normally the first thing you will see. Some colors are more affected than others, but since the entire surface will yellow at about the same rate it may not be noticed at first.
 

ianmoore

Petty Officer 2nd Class
Joined
Jun 5, 2014
Messages
169
Thanks for the tip on that. I read about that as a possibility. The rest of the hull, below the spline, does have a bit of that
 
Top