The Ballad Exchange

Be warned I'm an absolute novice when it comes to working with fiberglass.

As I believe I've mentioned in another post my boat had the small bulkhead in starboard side glassed in as opposed to bolted on to the hull (like all the other bulkheads). I was able to remove the bulkhead without using force

I would like to replicate the original way of bolting the bulkhead to the hull. My plan is to cover the bulkhead in thick plastic and position it correctly using the old shelves. Apply fiberglass and epoxy. Wait for the epoxy to cure and then drill the holes. As it is getting colder by the day my only option is to use West Systems 205 hardener. But what kind of fiberglass should I use? What weight and what weave?

Mads: what you see there is an example of the poor secondary bonding properties of polyester resin. Polyester sticks to uncured (air-inhibited) polyester resin pretty well, so it's good for laminating new pieces. But it's a lousy adhesive for sticking to wood, epoxy, vinylester, or even fully-cured polyester resin. Looks like the tabbing was added well after the hull layup had cured. That's why it came off in your hands.

Now epoxy is an excellent adhesive. Sticks to nearly everything; stays flexible, up to 5000psi bond strength. It does need proper surface preparation to work, tho. First, you'll want to grind the hull back to bare glassfibre. You can do this with a disc sander, an angle grinder, or (my favorite) a diamond grinding cup. You don't want to get too crazy, tho, because that coarse-weave fabric on the inside of your hull -- called woven roving -- is pretty important for hull strength. So I'd actually recommend skipping sanders or grinders for this task & use a stiff wire wheel in a grinder or drill. All you need or want to remove is the paint on the roving, for about 10cm either side of your bulkhead.

Two hints, here: first, mark an offset line (say) 20cm from one edge of the bulkhead before you start grinding and erase all sign of where it goes. When you have bare glassfibre, you can re-mark your guideline from your offsets. Second, wear heavy gloves when using a wire wheel. Hard on bare flesh.

Once you are down to gold-colored resin and roving, and the surface is decently scuffed, you'll want to de-wax the whole area using xylene (or equivalent de-waxer) and a clean cloth. Polyester resin has wax added to make it cure, and this can interfere with a good secondary bond.

You'll also need to grind the plywood down to a bare surface & feel comfortable with its integrity. We plan to both bolt and epoxy all our bulkheads into place. this particular one transfers the force of your aft shroud to the hull, so a firm attachment is more important than easy removal.

Lots of fabrics can be used, from 6 to 18oz. Thinner fabrics are easier to wet out and conform to bends better; thick ones are stronger and reduce the number of layers needed. Glassfiber tape (6" or 8" width) is nice because the edges don't ravel. My preferred material for this job is biaxial tape: this is a heavy (very!), non-woven material consisting of two layers of flat glassfiber set (usually) at opposing 45 degree bias, (usually) thru-stitched to a light epoxy-compatible mat.



If you can find it, this stuff has lots of advantages. The fibers have no crimp, unlike woven fabric, so they go immediately into tension. Very strong & stiff. It conforms surprisingly well to curves, as the fibers can slide past each other. It builds quickly -- at 17-18oz total 'weight', only one or two layers should be needed. And the diagonal path of the fibers distributes loads extremely well. A 90 degree biaxial tape would also work here, but I bet the bias tape is stronger in practice. Our plan is to tape one face of the bulkhead, let cure, then tape the other face, then drill, seal the hole, and bolt the entire assembly into one big tabbing sandwich. That way, you aren't relying wholly on the glue integrity of the plywood's face veneer to hold the panel captive.

BTW, one trick for wetting out biaxial tapes or cloths is to lay a couple strips of the right length on cardboard, wet out the mat side with a foam roller, flip over the strips, then vigorously roller epoxy into the fiber side until the fibers go almost transparent. It can be hard to wet it all the way thru in situ. Then, squeegee out excess epoxy with a plastic spreader -- you want as little resin-to-glass as possible for maximum strength. Full wet-out, but no more. You can use the squeegeed resin and a chip brush to pre-wet the hull and plywood before taping. With the bulkhead in place, tuck the tape into the corner and work it gently into place. Two plastic spreaders are helpful, here: one holds the tape into the corner, while the second smooths it down. There will be mess. Best to lay up all layers on one tab on a single day; as that way they bind chemically instead of just physically. Should be able to lay down 2 layers of biax or up to 4 layers of 10oz fabric/tape at one time, without cooking the lamination. If you can drive the temperature inside the boat for 24 hours or so after the epoxy sets, that will increase it's ultimate strength. Anything from 40-50*C will be great, if you can do it. If not, it's still pretty strong. You'll need to wait a bit before painting if using a urethane paint. Also, rinse the cured epoxy with water and a scrubby pad (Scotchbrite or similar) to remove the amine blush that tend to form on many epoxies, incl. WEST brand.

Best of luck!

Good advice from Bob, AND ... maybe bolt the chainplate to the bulkhead with a couple of bolts to make certian everything lines up when the epoxy cures.
When I'm using epoxy I wear a couple of pairs of vinyl gloves so that when a hand gets too goopy i can peel off a layer and keep working with a fresh glove.

Thanks to both of you Sounds like great advice. Looking forward to working with fiberglass and epoxy for the first time I want the bulkheads in place first so that I can use the old shelves (and the chainplate) to hold the bulkhead in place. Sadly I'm still waiting on the vinyl welting to arrive - should get here sometime next week.

Christmas came early this year

Looks like you are well prepared. You may need more resin and hardener than shown in the photo. Epoxy is neat stuff to work with: no smell or fumes and great results, but try to avoid skin contact as one can become sensitized to it over time, causing skin rashes. I hope the welting arrives soon. It looks like you are serious about getting the boat back out on the water!

Oh good -- you bought some Six10! It is amazing stuff, tho expensive by the gram. My Christmas arrived a couple days ago -- 10 liters epoxy, a big bucket of silica, and enough cloth & biax to fabricate a water tank and a rudder. Our rudder is past rescuing.

Glass work is fun if you don't mind the mess. I'm still learning by trial-and-error, but like most mechanical tasks it becomes routine after a few attempts. We had a good time building new cockpit hatches last month from epoxy, cloth, and foam core material (which we poured from liquids -- lots of fun). The large ones weigh 2.5kg less than the wood originals. We got to try out System3's primer and WB polyurethane paint, too. But you can see from the photo why bright white is a bad color for deserts!



ETA: one further tip on the Fast Epoxy. After mixing (and I like a solid minute or two with a drill, to ensure perfect stirring) a large batch such as you would use for laminating, it's not a bad idea to pour it into a shallow tray, such as frozen dinners come in. In a round can or jar, it can kick very quickly and harden before you get it applied. It can even catch on fire! Spreading it out thin helps slow initial kick. This is especially important when using thickeners, as they prevent convective cooling. Thick epoxy or polyester resins will go off in minutes, and a fast hardener even more so.