Repair Case Study: Whisper Hull Crack

This Whisper CL was brought into the factory for repair after an unfortunate drop of about five feet onto a sharp rock. We’ll take a look at the process for repairing the 5″ crack.

*Remember to work in a well ventilated area and always wear appropriate personal protective equipment.*

Materials used:

  • Isopropyl alcohol
  • Cleaning cloths
  • ~14″ of 3″ fiberglass cloth tape
  • 1.2 tubes of Devcon Plastic Welder White (47ml)
  • 3 static mixer nozzles for 50ml cartridges
  • Tongue depressors
  • Latex gloves (the adhesive will dissolve nitrile gloves)
  • Single-sided razor blade
  • 180, 400, 600, and 800-grit wet/dry sandpaper.

Tools used:

  • Dispensing gun for 50ml cartridges
  • Rotary tool with engraving cutters

Total time was a bit more than two hours (not including time waiting for adhesive to harden).

 

Examine the crack.

Fortunately, this crack was easily accessible from the inside through the cockpit.

Crack from the exterior.

 

Realign the crack (if necessary).

You can see that there is a significant offset between the two sides of the crack. This needs to be realigned as best as possible for the most effective repair. Sometimes the crack is easy to realign and other times it can be quite difficult.

This one was quite difficult. We first tried to shave the edges of the crack with a razor blade so they might move past each other. Use extreme caution as the edges of the crack can be just as sharp as the razor.

Unfortunately, that was not enough and we resorted to using a rotary tool to open up the crack. We will use a rotary tool to open up cracks on most repairs to fill them later, but usually not to the extent that was needed here.

The crack needed to be opened up significantly and it still didn’t want to align very well. We tried to align the edges as best as possible and then stabilized the area before patching the inside.

 

Prepare for the repair.

The Devcon Plastic Welder (# DA291) adhesive we used in this repair has a relatively short working time of about five minutes in a cool shop. On a hot summer day, the working time can be extremely short. Therefore, it’s important to have the repair area and materials organized and prepared.

We begin by cleaning the repair surface with isopropyl alcohol.

Then we cut the fiberglass cloth to be about 1″ longer than the crack on either side. We cut two of these since we’ll be doing two layers.

We mask the perimeter of the repair area to keep it looking clean once the adhesive is spread around.

Finally, we prepare and organize our work station. We like to use scrap cardboard as it makes clean up easier and we have plenty around the shop. Parchment paper or polyethylene plastic can make a nice work surface as the adhesive won’t stick to it and can be peeled off after it hardens.

 

Patch the interior.

We connect the mixing nozzles to the adhesive cartridge and dispense it onto the fiberglass cloth. It’s better to start with less as it’s easier to add more than it is to reuse excess. Five minutes is a good amount of time for a small patch with easy access, but the clock is ticking once you mix the adhesive.

The adhesive is spread smooth with a tongue depressor or other spreader (e.g. rubber squeegee). Flip the cloth over and repeat for the other side. We then put the second cloth on the first and repeated again. Depending on the location of the repair, it may be easier to put the first layer in the boat and then apply the second layer over it. In this case, we put both layers together and then applied it to the boat.

We carefully pick up the patch, lay it over the crack (within our previously masked area), and press it onto the hull. We then try to smooth it out. It is a good idea to try to leave an adhesive coating over the fiberglass cloth rather than wiping it away. The adhesive can be sanded later, but not the fiberglass cloth. Your end result can be better if there is a thin layer of adhesive to sand smooth.

The masking tape is pulled up before the adhesive dries or it will be glued there. Any fiberglass strands that stick out can be trimmed with a razor once the adhesive hardens.

After some trimming and some quick sanding, the interior patch is essentially complete.

 

Fill and polish the exterior crack.

With the inside patched and hardened, we turn our attention back to the exterior. The edges of the crack are cleaned up and the area wiped with isopropyl alcohol.

With a new mixing nozzle attached, the bulk of the crack is filled with adhesive.

We then smoothed it with a gloved finger and wiped away overflow with isopropyl alcohol and a cleaning cloth. Aesthetics aren’t very important at this stage.

We again tape off our working area.

This time we overfill and smooth out the adhesive. You’ll want to leave the adhesive a bit higher than the hull’s surface as it will shrink down a bit as it cures. This way you can then sand it down to be flush with the hull.

Once the adhesive has hardened, it can be shaved/sanded down flush with the hull.

After some time sanding and polishing the repair is complete and the kayak is ready for the water. More time can be spent on the aesthetics of the repair, but there is a point of rapidly diminishing returns for the time investment and it can be important to call it done. There will almost always be a visible scar and the severity of the scar depends on the severity of the damage. It’s also important to note that the white Devcon Plastic Welder is a bright white and will not immediately match the white of the hull, especially on aged kayaks. A touch of acrylic paint (such as brown or black) can be added to the adhesive to better match the hull color and not have as much contrast.

We hope you found this case study useful.