Fiberglass, upside down

[Interim]

A couple years ago I read a couple methods of fiberglassing the bottom of a surface, but I can't find them.

I have a crevice in the leading edge of a centerboard, which, when trailered, is pointed down. I've ground it out, and put in a coat of resin. But I need to get some cloth in there now. In the first attempt, gravity was irresistible. Has anyone tried taping a bit of plastic wrap on a surface to hold fabric and resin in while it hardens? Are there other methods?

Any tips would be appreciated.

--john

[GreenLake]

Get a stiff bit of plastic foil like the stuff that is used for display "windows" in product cartons or even the material for overhead projector foils (if that hasn't gone the way of the dinosaurs yet).

As long as you don't trap air right at the plastic, you will get a very smooth surface (and it will not require much sanding).

For CB dings, my favorite repair material is 3M High Strength Marine Filler. That has chopped glass strands mixed in. Even though it's a polyester-based product (not epoxy) it's worked well for the purpose. I've used it for repairs where it stood proud up to about 1/2" or so without problems on my CB.

Easy to use, non sagging, but the foil trick makes it even nicer.

[Interim]

so the plastic won't stick to the resin? or do I not care if it sticks?

Thanks for the tip.

--john

[GreenLake]

Plastic foil won't stick.
At least not the kinds I mentioned. (The black or gray stuff they make laptops or printer cases from or use in some consumer items is different. So plastic isn't all the same.)
If you are not a trusting soul, you apply just a bit of wax (e.g. floor wax) on anything you don't want the epoxy to stick to, but then you may need to take that off before sanding/painting, so not ideal for this case. But, again, foil doesn't stick.

[talbot]

I just had to do the same repair on my board. I have found that a viscous putty like Marine-Tex works well on overhead surfaces. The issue when you combine it with cloth is that the putty doesn't wet out the fabric the way regular laminating resin does. You need to really work it into the fibers. But it sticks to the inverted surface.
And to everything else. Expect to go through several pair of nitrile gloves, and whatever you wear while doing the job will be your boat-repair togs ever after.
Also, Marine-Tex sets up very hard, harder than the surrounding polyester. It helps to sand it as soon has it hardens.
Finally, because the stuff is so hard, bottom paint or striping enamel won't stick to it. If you have a painted hull and need to fill a gouge that goes into the underlying glass, you have to reprime the repaired area before painting.

[GreenLake]

Talbot, just use 3M High Strength Marine Filler next time. It is glass reinforced, so no need to wet out anything (unless you really need to apply larger patches - more about those below). It's Polyester (or perhaps PolyVinyl) so there's no big chemical or hardness difference to your gelcoat. I found the sanding behavior reasonable. I've used Marine Tex, but my recollection is that the 3M product was a tad "stiffer" during application.

I usually prefer epoxies for repairs, but this filler is an exception. It's worked really well for me, esp. on CB repairs. It definitely can be used to "build up" an edge, not just to fill an indentation.

For sanding epoxy and epoxy-based products. If you can get to them during the green cure phase, then using a sharp scraper or a blade is your best bet to quickly level drips, sags and similar accidents, so later sanding does not need to remove a lot of material.

If I needed to apply an actual patch, I would laminate it on a level surface on top of a sheet of plastic, and then transfer the final patch like a sticker. If you tape the edges so no air can get in, it won't pull away from the repair (or prop it up with something like a foam pad).

If you use SystemThree GelMagic (their "glue") rather than their laminating epoxy, you get the advantage of a less runny epoxy, but one that is still able to wet out most fabrics. You may be able to do the same with some thickening of West System, but, as you know, I'm partial to the pre-mixed stuff (and it's well-stocked around here).

[tinafred]

Has anyone used a vacuum system to ensure contact/limited air? I use it for inlays/making plywood of exotic wood for my custom furniture business. The polyurethane bag that a center board might be place in comes in up to 8 ft x 8 ft. I plan on some centerboard work on my DS3 this winter. This all said, I work on wood using System epoxy as glue, filler for custom inlays but never any fiberglass work.

[GreenLake]

Some here have worked with that extensively, you may want to go back in history and read the "core project" thread. I just assume that when someone asks a general question about a small repair that they are not already set up for vacuum bagging. In that case, it seems too much overhead, although in other cases, it makes a big difference. However, there are a number of techniques you can use in small repairs that allow you to apply a patch with minimal fuss.