Fiberglass Blister Repair
The first photo shows one of the blistered areas as I am starting to grind away the blistered gel coat. Both the port and starboard sides at the stern had patches about 6" x 18" that had blistered apparently due to (winter) shrink wrap that had trapped rain/moisture. I used some 3M grinding discs to remove the blistered gel coat but any sander or grinder would do. I have also used a Dremel.
You can see I am working in the dark, my usual mode no matter the time of day!
Photo 2 shows the ground port stern area with epoxy resin applied. This was recommended to seal the areas that were ground out so they could be smooth. Most of the epoxy was subsequently sanded away. Realize that the polyester gel coat does not chemically bond to the epoxy so the sanding helps with the mechanical bond. I used 150 grit and 320 grit for this.
Photo 3 shows one of a few failed attempts at applying gel coat. The gel coat used here was from the Evercoat gel repair kit. Available at West Marine or Jamestown Distributors. With enough sanding the brush technique might have worked. But the gel coat was not hiding the black underlayment in the spots that had been ground out, so as the video says, if you don't like it, grind it out and do it again! And again!
Finally I decided to buy gel coat in a bottle (Jamestown Distributors) and spray it. The experience with Evercoat had convinced me that straight white gel coat matched very well so I bought a quart of white. Jamestown has gel coat with wax, which means when you are done spraying you do not have to spray a top coat to seal or add anything to the gel coat. You do need to thin with acetone to spray. To about the consistency of whole cream from what I read. And do not try to use preval sprayers (another failed attempt). I used my compressor and spray gun set to 40psi (recommended 35-50psi). The recommended approach is to sand out with 320 grit an area twice as large as the repair and mask off. Adjust the gel coat to air ratio on a scrap surface to get a smooth spray.
You can see I am working in the dark, my usual mode no matter the time of day!
Photo 2 shows the ground port stern area with epoxy resin applied. This was recommended to seal the areas that were ground out so they could be smooth. Most of the epoxy was subsequently sanded away. Realize that the polyester gel coat does not chemically bond to the epoxy so the sanding helps with the mechanical bond. I used 150 grit and 320 grit for this.
Photo 3 shows one of a few failed attempts at applying gel coat. The gel coat used here was from the Evercoat gel repair kit. Available at West Marine or Jamestown Distributors. With enough sanding the brush technique might have worked. But the gel coat was not hiding the black underlayment in the spots that had been ground out, so as the video says, if you don't like it, grind it out and do it again! And again!
Finally I decided to buy gel coat in a bottle (Jamestown Distributors) and spray it. The experience with Evercoat had convinced me that straight white gel coat matched very well so I bought a quart of white. Jamestown has gel coat with wax, which means when you are done spraying you do not have to spray a top coat to seal or add anything to the gel coat. You do need to thin with acetone to spray. To about the consistency of whole cream from what I read. And do not try to use preval sprayers (another failed attempt). I used my compressor and spray gun set to 40psi (recommended 35-50psi). The recommended approach is to sand out with 320 grit an area twice as large as the repair and mask off. Adjust the gel coat to air ratio on a scrap surface to get a smooth spray.
The spray goes farther than you think, as my white motor mount can attest to. The spraying worked very well as shown in the above left photo. The black dots are bugs. I tried to get them out carefully but not all could be rescued. I had mixed up about 1cup of gel coat which required 4cc's of hardener for the 60 degree weather that day. I used a horse medicine syringe from Tractor Supply Co. to measure the catalyst in cc (1cc = 1ml).
I put on about 10 coats, waiting a couple minutes between coats for the solvent to flash off. Have lots of acetone on hand to clean up the sprayer with and do not take so long that the gel coat in the gun kicks off. I emptied the jar and spayed acetone through about three or four times, then soaked the parts in a small tub of acetone.
The finish had a slight orange peel that was to be expected from what I read. After letting it cure I started sanding with 320, 400, 600 grit then rubbing compound. The result is shown in final photo. If you stare hard you can see the line separating the original and new gel coat. I did not try and feather the new gel coat and I could have done without the drop of brown color but it really turned out well! My advice would be if you have a very small repair to do stick with the Evercoat. But do not be afraid to leave the gel coat proud and sand it smooth! A large repair (there were two large areas and a 6" x 12" on the stern plus others) is probably easiest to spray. But could be brushed in a pinch if you put on a lot of coats and sand, sand, sand.
Final disclaimer is that I do not have experience spraying paint. This is the first time I used the spray gun that I had bought at Home Depot a couple years ago. So if I can do it, anyone can!
I put on about 10 coats, waiting a couple minutes between coats for the solvent to flash off. Have lots of acetone on hand to clean up the sprayer with and do not take so long that the gel coat in the gun kicks off. I emptied the jar and spayed acetone through about three or four times, then soaked the parts in a small tub of acetone.
The finish had a slight orange peel that was to be expected from what I read. After letting it cure I started sanding with 320, 400, 600 grit then rubbing compound. The result is shown in final photo. If you stare hard you can see the line separating the original and new gel coat. I did not try and feather the new gel coat and I could have done without the drop of brown color but it really turned out well! My advice would be if you have a very small repair to do stick with the Evercoat. But do not be afraid to leave the gel coat proud and sand it smooth! A large repair (there were two large areas and a 6" x 12" on the stern plus others) is probably easiest to spray. But could be brushed in a pinch if you put on a lot of coats and sand, sand, sand.
Final disclaimer is that I do not have experience spraying paint. This is the first time I used the spray gun that I had bought at Home Depot a couple years ago. So if I can do it, anyone can!
Photo and Story By Robbin Roddewig
Temp Catalyst to gel coat
55-60 17-21cc hardner/quart
61-65 13-16cc hardner/quart
66-70 9-12cc hardner/quart
55-60 17-21cc hardner/quart
61-65 13-16cc hardner/quart
66-70 9-12cc hardner/quart
The repair, modification and/or maintenance projects on this page are provided to show how one person accomplished a given task. Some projects are hazardous, dangerous and expensive and should be attempted only by professionals.. No warranty of success is included nor implied with any of these projects. The Webmaster, contributors and authors, will not accept, nor be held responsible as a result of any use of the material presented.
Click on photo to enlarge
Home
