Friday, 25 April 2014

Glass Tape Fillets

Today I taped & filleted the port side of the cabin/deck joint, all the way back to the transom along the cockpit coaming as well, with one length of 2” tape. Also, the port dagger board opening on the deck got tape around its edges.

Using the WEST system pumps sure makes it easy! I started out by brushing resin on the whole length of the corner, then mixed up a batch of thickened resin using wood flour and pushed it into the corner with the round end of a stir stick. I’m using “craft sticks” from the dollar store, which are like tongue depressors and come in a pack of 30 or so.

An important thing about epoxy is that it needs to be well stirred. It’s not like polyester resin, which you can apply hardener to afterwards and it will kick off—or even put it in the sun and it will kick! No: epoxy needs the actual molecules of the resin and the hardener to be together or it won’t get hard. So you need to stir it well. And part of stirring it well is making sure the sides and bottom of the container you’re stirring it in get scraped regularly. To this end, I shaped the stir sticks to conform to the cups I’m using, which are 10 ounce paper hot drink cups that I bought in a package of 50 from the Wholesale Club. I found the angle of the bottom and side by laying one stick across the top of a cup and resting another stick on the bottom of the cup and against the side of the cup, and striking a line on the standing stick:

Then I transferred that angle to near the end of another stick, and used that as my pattern to mark other sticks with. The ends were cut off with garden shears, giving me sticks that connect with the sides and bottoms of the cups perfectly, so the resin is constantly scraped off and mixed in.

(I don’t work on top of the stove; it just happens to be the best spot to set up on around here.)

I used the round end of a stir stick to make the fillet curve, not pushing the curve of the stick right into the corner, but just loosely passing it over the thickened epoxy to make a fairly robust fillet. One pump of resin and hardener made enough thickened epoxy to do about 18" of fillet. Then in another cup, another pump of resin and hardener (well stirred!), which was flooded onto the fillet by brush with a light touch. The tape was laid over and more resin brushed onto it.

One needs a light enough touch with the brush that the curve of the fillet remains, but firm enough to straighten out the cloth tape. Once the tape is wetted out, you can push it around with the brush by poking it with the end of the bristles, as if you were stippling. Little pushes move the tape well. I’m talking about sideways, across the width of the tape here, so that it comes out more or less straight in its length. The length doesn’t get moved, except that it gets pulled constantly towards the yet-to-be-done end as it gets stroked with the brush.

By the time I was done I was feeling like I had too much sun, and didn’t think to take more photos. Maybe the starboard side will be good for that; that’s the sunny afternoon side anyway. I’m finding it interesting that I’m even taking photos; this blog is good for that. Usually I just forge ahead and take pics later, sometimes wishing I’d documented my build. And most often I’m feeling like I’m rushing to get the thing done before the resin goes hard. I did go through two brushes, as the first one started to get hard about half-way along.

But I think this is the only way to do a long continuous piece: by mixing up small quantities as you go, and doing the whole thing with little batches, rather than making one long fillet and coming back to the beginning to lay the tape down, only to find that it's started to kick already.

I didn't think to mention this until now, but this method of putting the tape right on the freshly made fillet is so much easier and faster than making a fillet, trying to sand it smooth, and then applying glass to it. Very little sanding is needed now; mostly just taking off the tape edges.

No comments:

Post a Comment