For those not familiar with powerrodsmike, he is now the owner of a hot rod fabricating shop, and previously worked for many years laminating fiberglass bodies at one of the most well-established firms that make and sell fiberglass bodies. Mikey posted the following very good comments on the bulletin board, and I've copied them into my project journal (with his permission) in hopes that they may prove helpful to others in the future.
To put this advice in context, take a look at these two photos. The first one shows a myriad of detail lines, which can be prone to formation of voids if Mikeys advice is not followed, as the glass can sometimes spring back away from the corner before the resin gells, even if it was once wet-out. The second photo shows a really nasty void at the corner of a door flange...a spot where I will be certain to use the technique that Mikey describes the next time I do any lamination. Thanks again to Mikey for the good advice!
Powerrodsmike posted "If you need to build a sharp outside corner in a part you are making in a mold, such as a door jamb edge or detail line, just mix up a batch of goop using 1 part tooling resin, 1 part tooling gelcoat, 1 part milled fibers, 1 part microballoons and 2 parts cabosil. Measure by volume.
The resultant paste should be able to spread smoothly, maintain a peak of at least 1" and when you pull a putty knife through it it will leave a trough that the sides will not fall in ...to the full depth of a 3" knife. The proper amount of resin to fillers shoud be such that it will be a satin or flat color...not glossy and wet looking. Adjust your materials accordingly to get the right mix.
Mix well, then catalyze at about 2% by weight.
Pack and spread this into the corner after gelcoating ,(gelcoat should be cured enough to not leave a fingerprint when you touch it) using a tongue depressor or similar radius tool. The radius should be about 1/4"...That is about the minimum that chopped strand mat will bend.
Let the material get hard, the lay up over it.
The glass won't spring back, and you will be rewarded with a hard, durable outside corner, with minimal chance of transfer.
You can also pack your seam lines and any sharp detail lines in the body you may have prior to doing your layup.
The stuff will last several days to a week in a cool climate before it starts to pull on the gelcoat.
The stuff also makes a good fiberglass to fiberglass adhesive and bedding compound, but don't use it to glue flat panels together...it will transfer right through 1/4" thick panels..strong and hard stuff.
Using roving and resin is a frustrating way to do outside corners, and it winds up being really resin rich anyway...not good for an outside corner.
I would also consider using some kind of core material in your roof panel. The large semi flat panels have a tendancy to move around in the sun without it. Be careful if you are going to glue anything to the underside of your roof...it will telegraph through in time."
Here is the body shell after being removed from the mold. Now it's time for the least pleasant part of the whole process, in my opinion. I think the itching from fiberglass that I got while making the parts was insignificant, compared to the dust generated when trimming the excess off the edges of the parts! I guess like they say, no pain, no gain????
Of course, after that, there is still a lot of work ahead: patching defects, filling voids, sanding, priming, sanding, sanding, sanding, painting, sanding, polishing. But, it's still fun, right?
Here is the mold in the process of being dissassembled from the part. A time of mixed emotions...happy to have created the body, but I sure wished that I had fewer defects to fix!!!!! If you look closely, you can see a spot where the gel coat pre-released, and I failed to catch it. (:
But, being the eternal optimist, I hope that next time I can do better, having learned from my mistakes. One might view this entire project as a long series of problem solving steps and trial and error!
I found it a lot easier to laminate some areas of the body with the mold tilted on its side. The areas that I found especially difficult to laminate on this body were the roof just above the door openings, and the area around the windshield and door pillars. Ther must be some tricks to those spots that I havn't figured out yet! Any suggestions, Mikey?
One experiment that I tried that actually worked the first time: I decided to move the firewall back several inches. I cut the front several inches off the part before laminating any firewall, taped a sheet of cardboard tight to it with duct tape, and then laminated flanges up against the cardboard. This gave me a nice flat flange to attach a steel firewall to. (I decided that I wanted the extra engine setback because of a decision to use a 454 instead of the SBC that I bought earlier.)
Here is how the mold looks from the side, fully assembled. (I thought I'd chosen a photo that was taken before making the laminate, but I see now that the part has already been laminated in this photo.) Making the molds on this project seemed to go smoothly enough that I think it lulled me into a false sense of security when it came time to make the finished body.
Lesson #1- Don't push the dry time of PVA. I was anxious to get an early start on the Labor Day weekend that I made the body. I started really early, and there was heavy dew on the grass when I sprayed the PVA. I learned the hard way that PVA dries slowly under high humidity conditions, and in a couple of spots where I sprayed the PVA on too heavy, it must not have been totally dry when I sprayed the gel coat. Moisture inhibits the cure of gel coats, causing me to have some spots of alligatoring.
Lesson #2- Pay really close attention to the gel coat thickness. I had one spot that I obviously sprayed too thin. Oxygen inhibits the cure of gel coat, which also caused alligatoring in another spot. Even worse yet, I got the gel coat on too heavy in a couple of other spots, causing the gel coat to pre-release from the mold before I got them covered with the first layer of laminate. I learned the hard way that the time required to make a laminate is much less than the time required to repair a laminate with a defect like pre-release!
Lesson #3- Inside corners need extra care! An inside corner that one encounters when making a male part is much harder for me to laminate than an outside corner on a female mold. I had several places that I thought the glass was laying down flat, only to discover later that the glass had sprung back, forming a void between the gel coat and the first layer of laminate. Next time, I'll use extra caution in those areas, resorting to applying a putty if needed, or else filling in concave areas with some long strands of roving and resin before I apply the first laminate.