I know I mentioned that I had a lot going on during this rebuild period. With other demands (who doesn't have those?), I had plenty of down-time when I couldn't get to my shop so I would read and research the uses of both Polyester and Epoxy Resins. My personal experiences with both showed amazingly different results when the two were used. Here are the lessons I learned during my research and build project -
Polyester Resin (PR for short) - is not a great glue/adhesive. It will not "grab and hold" two objects together.
PR is great for laminating fiberglass fabrics together when "wet" layers of fabrics are laminated together and allowed to cure "as one". PR structures become a super-strong and durable panel/part when they cure "as one". PR is not great at putting already cured panels or pieces together or in-place. Epoxy is much, much better at doing that.
PR is much easier to "wet" fabric for laminating with regard to absorption and spreading - however, work time is much shorter. I found that 12~16 ounces of Polyester Resin was the most I could handle/manage at a time. I would measure out multiple cups of resin in the usable increments to best match the needs of that time, but would not add the hardener/activator until I had fabric, new roller, brush and plan ready. Work time could be 2 minutes to 5 minutes depending on the weather. Mixed PR will harden/flash much quicker in the container than it will rolled out on your panels. I lost a couple of "cups" of mixed PR because I took too long to get it rolled out. Count on using a roller or brush "1-time" and only 1 batch when using PR. It starts hardening that fast.
PR good points - panels and pieces can be worked and sanded in hours - not days like Epoxy Resin.
Most important - Only PR will dissolve the bonding of normal fiberglass "mat". Epoxy Resin will NOT dissolve the bonding chemicals used in making mat. The 1708 biaxial fabric is stitched together and not bonded so the Epoxy Resin was OK to use.
PR does not like bonding to Epoxy Resin. You can go the other way and bond Epoxy Resin to PR, but not PR to Epoxy Resin - Be sure you remember this important characteristic.
Epoxy Resin (ER for short) - is a fantastic glue/adhesive when putting fiberglass panels, wood, or materials together. The best demonstration I can give is the "roller bond". At the end of each segment of lamination, I would take the brush and roller off the handle. I'd lay both on the plywood top that I used as a mixing station. A 4" roller was the tool I'd use more than any other tool - no matter what the resin - Polyester or Epoxy. Once cured, the PR saturated roller could be removed with the tap of a hammer to it's side or end. The ER saturated roller was permanent. When you hit it hard enough to move it - you pulled the plywood fiber and core material from the plywood. The bond was that magical and that much stronger - it transformed that cardboard and fabric roller into a solid, strong object capable of pulling/ripping the very fiber out of left-over 3/4 Marine Plywood - Amazing stuff!
ER, even the thinner "laminating epoxy" I used from US Composites was more difficult to "wet" the 1708 fabric with. The good news here is that ER gives you a lot more time. I could easily go 10 ~15 minutes working time with the ER before the roller would start getting sticky. Cured Epoxy must be cleaned and prepped before additional layering/applications can be done. The ER develops a waxy film during the cure. Soap and water are needed to get rid of that film. Then sanding, prepping, and wipeing down with isopropyl for the next application was followed over and over during the many lamination cycles.
All of the panels - floor, transom boxes, backwash tray, deck, and inside walls were all made using Polyester Resin and 1708 fabric (17 ounce bi-axial fabric). I used luan to make the panel patterns. I pre-cut the fabric layers and number of plies to be used to include the 2 square footprints for each of the seats pedestals . Once test-fitted, I would spread plastic on my worktable and move the luan plywood onto it. Two coats of Mold Release was applied and allowed to dry (about 30 minutes). I then poured the PR onto the flat surface and layer the number of fiberglass fabric I wanted for the panels. My floors would be 3 layers thick + 2 layers where the seat pedestals would be - a total of 5 in those high-stress areas. After about 3 hours, the wooden pattern could be pulled away and the fiber panel left to cure.
I would use ER to join every piece of lumber into the hull, transom, and deck. Stainless and Brass screws were combined with ER to form those tenacious bonds described earlier. All of the PR Fiberglass panels were bonded to the boat using the Epoxy. All tabs (small layers of fabric strengthening a joint) where the transom, stringers, keel, transom knee braces, interior sides, and seat pedestals joined the hull or deck were done with ER and 1708. I used 11 gallons of Polyester Resin and 10 gallons of Epoxy Resin on this project.
Next time, I'll talk about the pour foam experience. Not at all what I thought it would be - excitement was missing for sure........
First photo is the center floor panel ready for PR/Fabric
Second photo is the two interior side panels - the same luan pattern was used, just flipped and the other side coated with two layers of Mold Release.
Third photo is the rear floor panel with it's 3 layers of 1708 and the 2 layers for the seat pedestal. Because I wanted these to be "as one" - I laid these layers out all at one time. The flooring panels were too big for me to handle all at once and I would have needed 3 people helping, so I did the floor in 3 sections (rear, middle, bow).
Fourth photo shows how those luan panels were used as patterns to make the 3 flooring panels. The bow form was more complex, so I used the frame you see here to get the exact fit I wanted before transferring that to a solid panel I would then use as the pattern base during laminating.
Regards, Gordon
