Fiberglassing Tools and Tricks

If you need to do some fiberglassing with cloth and epoxy resin, this Instructable can save you some mess and grief. Manufacturers of fiberglassing and epoxy materials offer booklets that can provide you with instructions for success. However, through my own experience I have developed helpful tools and tricks you won't find in the books. Intro photo is of solid 14-foot boat hull on the right and its twin on the left that I fiberglassed and painted, one my several projects that taught me these lessons.

The yellow plastic spreaders are recommended for pushing the epoxy into the glass cloth, however they are hard to grip when your gloved hands are wet with epoxy. I used two screws and nuts to attach the plastic handle of a defunct disposable foam paintbrush to each spreader. I prefer the rubber spreader for big jobs and added a handle made from a length of broomhandle that I slotted, and two strips of sheetmetal to add side-to-side stiffness. Both kinds of spreaders are available where epoxy products are sold and by mail order.
The shape of the scissors enable them to easily cut fabric that is flat on a table, and they have a palm bar rather than the usual cumbersome thumbhole. The scissors have a spring-open feature, are Fiskars item 9911, Wal-Mart, $14.
I use waterless handcleaner, such as Goop brand, and a stiff brush to clean these tools before the epoxy can set, and after many uses those in the photo are still clean and not sticky.

I found a way to mix small batches of epoxy resin and its hardener, in proper proportions, even if the liquids are in large containers. A little effort in advance will make the job easier. Mixing epoxy in graduated containers is costly, and measuring the liquids in a graduated container then pouring together into a small mixing cup can lead to inexact proportions. First, get sleeves of a few sizes of clear or translucent plastic or paper cups (not waxed!) that will hold the different amounts of mixed material you think you might need, with enough room free at the top of the cup to allow for stirring. Using the following notes, make a reusable "calibration half-cup" for each size cup and for each size batch within that cup size.
Note the half-cup has its upper rim cut off so it will nest perfectly onto the side of a new cup. It is marked "2R:1H," to denote that this half-cup is to be used with epoxies that call for a ratio of "2 parts Resin to 1 part Hardener."

Photo shows how "calibrated half-cup" is put onto the side of a cup that will be used for mixing a small batch, and the calibration marks transferred to the new cup.
For each cup size, take a new cup and put WATER into it that is about one-third the amount of the final batch of mixed epoxy, and make a mark at that level on the outside of the cup. Pour all that water into a clean cup and mark its level on the outside and label that mark as "H" for hardener. Put water into the first cup again, to its marked level, pour that water into the second cup on top of the water already in it, then repeat. Mark the top of the water level on the outside of the second cup and label it "R+H" for resin plus hardener.
Repeat the procedure if you want to calibrate the second cup for a larger epoxy batch in that same cup size, putting the level marks on the opposite size of the cup. Cut the calibration cup in half vertically, and keep it with your stash of that size cup.

Small mix cup has calibration marks (fattened to aid in photography) transferred to it from the calibration half-cup, and the marks will be visible through the translucent sides of the cup. Viewing into the cup, carefully pour hardener into the cup to the first line, then carefully pour resin up to the top mark, and you will have exact mix ratio. Mix and use from that one cup, then discard it.

Vaccuum bagging is great for clamping fiberglass tightly over a shape and removing air bubbles, but it is too complicated and costly a procedure for occasional use. For smashing wetted cloth tight to the sharp bow of a hull, I made clamps by backing up foot-square blocks of 4-inch thick foam rubber with squares of 3/8-inch thick plywood and wooden sticks. Before use, I wrap plastic wrap around each foam clamp and tape it to the wood backside. Two slide clamps squeeze the cloth and conform it to the hull mold's shape. Rubber foam can be cleanly cut using straight edge guides and a hotwire cutter. Click on link to see album "Cutting Rigid Plastic Foam," click on "READ FIRST" instructions for reading and printing fine text. http://www.flickr.com/photos/sm_vermn/tags/foamcutter

Wet fiberglass cloth can be made to wrap over a sharp edge, but it will lift up off the edge before the epoxy sets unless it is clamped in place. Here is the full-body version of the foam block clamp. I used a sheet of white upholstery foam, 1-inch thick, to press the wet cloth around the bottom of the hull (facing up in this photo). I pre-cut strips of a stretchy 5-inch wide colored foam, sold in rolls at home centers as a barrier between the top of a house's foundation and the house itself, marked each strip in sequence. Once the fiberglass was wetted out, I smoothed a precut strip of thin clear plastic tarp over the wet fabric as a mold release, placed the white foam sheet over that, then stretched each strip of the colored foam and taped its ends together with duct tape.

The hull after the foam has been unwrapped. The fiberglass conforms so well to the shape, even where it is folded double across the front edge of the bow, that it is virtually invisible.

Once cloth is wetted onto the deck and the edges trimmed, thin plastic sheet is smoothed over it, pulled down and taped to keep the cloth wrapped over the sharp edge of the deck until the epoxy sets.
These hints come from an article I had published in the 01 Aug 1998 issue of MESSING ABOUT IN BOATS magazine. It contains other information that does not fit the step-by-step format of Instructables. Click link to an album that contains the article, click "READ FIRST" instructions for reading and printing fine text. http://www.flickr.com/photos/sm_vermn/tags/toolsntricks
To see my related projects, enter unclesam into the home page search box, scroll and advance pages to view them all.
U.S