Canoe (fiberglass) major repair

Advice
#1

I inherited a cheap chopper gun Sears 17 footer.

It has multiple (amateurish) patches that need to be redone, along with a pretty major hole (~6") flanked by two linear cracks (2-3’ on each side towards the bow and stern) along the curve where the side meets the bottom. The multiple patches are scattered all over the canoe, including the bow and stern. The gel coat is scratched and gauged all over and one of the gunwales (aluminum) is slightly bent in at the center of the canoe.

I know, I know…I should trash the boat…but that would be too easy.

Planned process, would love comments from those of you with more experience in this area:

  1. Sand the entire canoe down until I reach the stranded fiberglass.
  2. Cut out all the minor repairs & sand inside around repairs
  3. Put some sort of backing on the outside of the minor repairs and lay them up with (6 oz E-Glass? Something heavier to make up the wall thickness more quickly?) from the inside
  4. On the outside, cover the large area of the major hole and the linear cracks with some sort of release agent, maybe just plastic sheeting.
  5. Create a mold by laying up a single layer of 6 oz E-Glass on top of the plastic. (I’m worried about retaining the curvature of the hull bc this repair is on the curve)
  6. Remove mold and plastic/release agent and cut out the major damage hole and the the linear cracks (I am imagining the hole will be shaped something like an airplane prop :smiley: )
  7. Attach the mold created in Step #5 to the outside of the canoe with clamps, ect to provide backing
  8. Lay up the major repair from the inside (using the mold as a backing) with (6 oz E-Glass? 24 oz. Woven roving? Biaxial Mat 1708?)
  9. Cover the entire boat with one layer of 6 oz E-Glass (Not sure about this step - is this done is strips or something?)
  10. Sand, roll and tip finish.
#2

I would have to see the boat to know exactly how I would approach this repair but here are a few thoughts.

I don’t think it would be necessary to completely sand all the existing gel coat off the boat. You could certainly do so, but it would be time consuming. You should certainly plan to sand off all gel coat down to fibers on any area you plan to repair, however. You did not say whether you plan to finish the boat with paint when you are done. Forget about trying to re gel coat it. If you use epoxy, polyester resins like gel coat may not cure reliably over even cured epoxy. If you plan to paint, I certainly would not plan to sand off all the gel coat. Just get it as smooth as you can.

I doubt that you will be able to completely straighten the bent aluminum gunwale. I have been able to partially straighten them using pipe clamps and sometimes a shaped wooden jig applied to the outwale side of the gunwale.

If the patches are easy to remove, go ahead and pull them off. If not, do not cut them out. Just sand them down fair and flush and apply new patches over them as need be.

A complete blanket of 6 ounce/square yard fiberglass would add a lot of weight. This should not be necessary unless the boat is horribly damaged. If it is that bad, through it away.

Although you could use roving or mat, for the type of repair you seem to be talking about, I would simply use 6 oz. plain weave E fiberglass and use as many layers as you need to to achieve sufficient strength and thickness (for stiffness). For through and through cracks, I would plan to use a minimum of 3 layers of 6 oz. cloth. When you cut out your patches, orient them so the fibers of each patch run at different angles to those of the others for maximum strength.

If you can lay your hands on some of the thin, flexible, transparent plastic material of the type that used to be used for overhead projectors, you can probably use that as a backing agent on the outside of the hull to cover a 6" diameter hole. Tape it on securely with clear plastic packing tape. Start your repair with a single layer of fiberglass cloth on the interior. When the epoxy has partially cured to a solid green state, remove the plastic sheet. The first layer of repair might not exactly match the curvature of the hull, but you can address that later by sanding down any high areas and filling in any low areas with additional patches. Complete the interior repairs with at least 2 more layers of "glass, then address the exterior as need be.

If you want to try to get the hull as smooth as possible before painting, you can use a fairing filler mixed into your epoxy such as West System 410 Microlight:

http://www.westsystem.com/410-microlight/

You can apply mixed epoxy and fairing filler to any external areas of repair that are irregular and sand fair and smooth when cured. You can repeat this process to your heart’s content to try to achieve a maximal amount of smoothness, but you might be trying to make a silk purse out of a sow’s ear.

Spray paint the internal areas of repair for UV protection when you are done.

If you plan to paint the whole exterior of the boat, I have been very pleased with the results I have gotten using Petitt EZ-Poxy paint. It gives a gel coat like sheen, although like any paint, it will scratch. Apply it with a foam roller and tip it out with a disposable foam brush:

http://www.jamestowndistributors.com/userportal/product.do?part=106891&engine=adwords&gclid=EAIaIQobChMIwq-IkPam3AIVj8DACh1wiAwMEAQYAiABEgLRGfD_BwE

#3

Thanks pblanc - appreciate the detailed response.

“silk purse out of a sow’s ear.” I think this is the best description of this project!

I will definitely have to cut out/completely remove material. Once I’ve cut out the material, what is the proper way to shape the material/edges around the void? I drew up a few options, and was thinking Option B in this drawing: https://drive.google.com/file/d/1PNjyW5CDW0JKYi1yVyIJy9iZq5RomOZF/view?usp=sharing

I plan on using some leftover (gal each) of West System 105 resin and 205 (or maybe 206 I can’t recall) hardener. It’s old, but from what I have read, there isn’t a defined shelf life on this stuff. This stuff was inherited from my Dad, who also gave me a number of different fillers, though I don’t have the numbers handy. I suspect most any of them would be suitable to fill non-structural defects, then sand out.

The plan was to paint it with some sort of marine grade paint - so thanks for mentioning it is not necessary to remove the gel coat completely - just smooth it out.

The overhead projector material would definitely work - I’ll rethink my backing method once I have a better idea of the size of the holes.

Regarding a complete blanket of 6 fiberglass - I was thinking I could apply that, then sand out some (most of) of the interior strand to minimize weight gain. But that sounds like a lot of work :smile: My understanding is that the puncture strength of these chopper gun layups is low - so adding a woven skin would improve that, as well as skin over the myriad of patches.

#4

Assuming you are going to be applying patches to both the interior and exterior of the damaged areas you cut out, I would shape the edges of the hull in a way not shown in your diagram with both the interior and exterior sides of the hull beveled. The cross section of the void in the hull would then resemble the contour of an hourglass. Beveling the edges of the hull will increase the bonding surface for your patches.

If the majority of the repair is going to be done with interior patches, you could use method “C”.

The old epoxy should probably work although often times the hardener turns red with age. Shouldn’t matter since you plan to paint over the repairs. It might be a good idea to mix up a small batch of epoxy and use it to bond together some fiberglass scrap just to be sure it cures properly, however.

I use unthickened epoxy to wet out cloth. If you need to thicken epoxy for structural repairs such as filling in small voids, I think silica powder (cab-o-sil) works best. The fairing fillers are designed to be easily sanded smooth.