The Shop
A Little Ditty About an Air Bubble
"Hey man, you don't have to leave those air bubbles in the deck! The floatation goes in the hull."

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   An old laminators joke about bubbles such as this being left during the laminating of a part. Laminating is the term used to describe building of a fiberglass part. The mold is first sprayed with gelcoat then the fiberglass is put in in layers, (laminated) to the designed thickness or strength. It is the first layer of glass that is important to the cosmetics of the part. If an air bubble is left here it's easy for it to break away as you can see. On this page we will repair the voids. Usually the best way to match the color is to order the gel from the boat manufacturer. You will have to give the hull number and model. If the boat is old or gel unavailable the color can be matched but we will get to that on another page later. Bear in mind that the images below are about three times their original size.

  The following series of pictures is designed to take you right through the procedure. We'll start with this close up. Here the void has been cleaned and scraped out with a knife to remove all loose flakes and stuff. Sometimes when you start a deal like this the bubble may run a little or a lot larger than what actually shows, this is why you should dig at with a knife. Then scuff in and around it with a very coarse sandpaper like 36 grit. The area should be cleaned liberally with acetone. The surrounding trim should be protected from the acetone, gelcoat and any thing else that may give a problem later. Mask off or cover areas that may get spills or overspray on them in order to save time on the cleanup. Always try to look ahead as far as you can see
 

   In this image the gelcoat has been placed. For mixing and blending gelcoats, colors, and small amounts of resin, I keep a supply of waxed paper cups and popsicle sticks from the grocery around, but you can use butter tubs cut off plastic popbottles or other cans except styrofoam. Styrofoam will disintegrate. the amount of gel required for this repair only amounts to about two tablespoons full. The amount of hardener needed is only four drops. If you really want to figure it out the ratio should be between 1.50% and 4.00% . If you go overboard on the hardener the gel will boil, (begin to generate small air bubbles) and will leave pinholes in the repair. So if you slip and overdo it with the hardener, no big deal, chuck it out as you will only have to dig it out later. It is important to work the mixture into all the void a little at a time so as to build it from the bottom up rather than just blob it on top and take a chance at creating small bubbles within the repair. For this you can use a popsicle stick or whatever. I like to use a small artist brush. There are sanding aids that can be added to the gelcoat to help relieve the sticky surface that will be left when the gel is cured, but on small stuff like this it's more a bother than it's worth. I just wipe the area with acetone after the repair is completely cured, and it removes the tackiness so as not to plug up the sandpaper.
 

  Now this next step may seem a little weird, but bear with me and it will become self explanatory. We spray a little lacquer, black or any contrasting color, over the repair. Just a fog, not heavy, as it will take to long to dry. We are using this as a tracer to show up the scratches, low areas, and other imperfections as the area is sanded. I keep spray cans of lacquer in a few colors around just for this, darker for lighter repairs, lighter for darker repairs. Before spraying the tracer (lacquer) wipe the area with acetone to create a clean surface for good adhesion. This is important. You don't want the tracer to just wipe away when you sand. You want it to stay in the scratches until you have sanded them away.
 

    Begin the sanding with a course paper, 36 to 80 grit dry, to get the heavy excess gel off. Use a small wooden block with rounded edges. Rubber blocks tend to follow the surface and therefore can produce a wavy surface when you are actually trying to shape something. They are good for finishwork tough. Then carefully sand it until the surface is smooth an about flush with the surrounding area. Low areas will show up at this point. If there are any, clean the tracer off with acetone and refill low areas and continue until you have a surface like the next picture.
 
 

  This view shows the repair after it has been sanded with 80 grit dry. Care should be taken not to sand any more than is absolutely necessary or you may sand through the surrounding area. Be careful not to dig with the sandpaper. Take nice, easy, even strokes with not so much pressure as to bind or stop the stroke.
 
 
 

  Now go back over the area with the tracer again and use wet-or-dry paper with water starting with about 150 - 180 grit. Use your wood block. Tip; use a spray bottle to deliver the water, and just a little dish or laundry soap in it. (bottle makes it easy to handle the water and keep the area wet, soap makes the paper cut quicker and last longer.)
 
 
 
 

  This view is an excellent example of what the tracer is supposed to do. The scratches that you see were either left by the previous grit (coarser) paper or from a piece of sand, or other foreign particle, scrubbing between the paper and the part which now are full of black lacquer. At this point you must decide if these are to deep to sand away. If so then they must be cleaned and filled.
 
 

  This image is what the repair should look like as you progress with the sanding. Graduate from 180 to 360 to 400 to 600 grit, tracing between each step except the 600 as the paper at that point will be so fine the tracer will plug it up. Be sure to increase the size of the area each time so as to remove the scratches at the edges of the repair.