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Fixing leak and repairing gelcoat and gelcoat cracks

wjejr

Active Member
Hello fellow Sunfishers. I hope you are all safe and well.

I've had my 1971 Sunfish for more than five years, and for the first three it never leaked a drop. A couple of summers ago, however, after returning from a sail I discovered that the cat bag from the inspection port was wet. Hmm. I first thought I must have thrown something in the bag that was wet, but after looking a little more closely, sure enough, water had leaked in. Thus began my off and on, mostly off, search for the leak.

I tried the pressure method a couple of times using soapy water, and although I did find a leak under the bow handle, that wasn’t the problem. I also tried taping the dagger board slot and filling it up with water, likewise the mast step, and the cockpit, but no luck. The water sat for hours, but not a drop leaked into the boat.

BTW, pressuring the hull scares me to no end. Even using a hose on a Shopvac exhaust has me terrified that I am going to crack the bond, now 49 years old, between the foam blocks and the hull.

I had sort of given up on ever finding the leak, but now with stay at home mandates and time on my hands, I decided to have another go at it. I’d been thinking that since water was getting into the boat even on the calmest of days, the leak must be somewhere on the bottom. With that in mind I decided to fill the boat up with a couple of inches and see what happened.

Picture 1: My boat up on sawhorses

Picture 2: The boat filled about two inches deep with water. The dark brown near where you see the reflection of my phone is from damage that has since been repaired. The black strips are stringers that make the hull stiffer.

Picture 3: Drum roll please, is the leak. Yay! You can see I marked it with a green squiggle. That spider crack, as it will turn out, is more than it seems.

More to come...
 

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Wavedancer

Upside down?
Staff member
Glad you found the culprit.
The picture/image shows more than a spider crack; no surprise that that area is leaky.
Should be relatively straightforward to fix that, I would think.
 

beldar boathead

Well-Known Member
For the reference of others who see this, that isn’t a spider crack. That is a decent hole in the boat. Looks like someone took a pickaxe to your hull!
 

wjejr

Active Member
Honestly, the enlarged picture makes it look much worse than in real life. The picture makes it look rough, but to the touch, it is actually quite smooth. It looks like a small rock hit the hull and cracks emanated from the point of impact.
 

wjejr

Active Member
Next step in the process was to remove the gelcoat to see what the problem was. I used a palm router with a cheap 1/4 round nose bit to carefully remove the gelcoat. Picture 1

When I started removing the gelcoat, it was obvious what the problem was. Instead of only being a coating, the gelcoat layer was deeper over an area of about 1/2" square. Picture 2

Digging that 1/2 square inch out, I found a small hole, probably about 1/8" round. Picture 3

Note that I have started, to route out the hairline/spider cracks emanating from the hole. To repair these cracks and have the repair last, IMHO, you need to route out the gelcoat down to the glass and provide enough surface area for the new gelcoat to adhere. If you don't get down to the bottom of the crack, the crack will "telegraph" and reappear. I used to do this by hand, but having the palm router makes it much easier.

Now that I knew what the problem was, it was apparent that the deeper gelcoat repair had initially plugged the leak, but that over time the gelcoat had cracked and started to leak due to flexing of the hull. BTW this hole is under the foot-well. Pressing on the damaged area it only flexes about 1/8" maybe a little more before the hull hits the foot-well.

Stay safe and well fellow Sunfishers.
 

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wjejr

Active Member
Next Step: Getting ready to repair.

Now that I know what the problem is, the next step is get everything ready.

Picture #1 I used a compressed air gun to blow out the dust. Alternately, I could have used a dry paintbrush to dislodge any small particles of gelcoat

Picture #2 With a clean rag, I washed the area with acetone to remove any dirt or oils that could interfere with adhesion

Picture #3 For the patch, I cut out two 1/2" circles of fiberglass. I think the weight was 4 oz. You want to use something light as the circles are so small that the glass wants to unravel.

Picture #4 I mixed a small amount of epoxy using a scale. One of the reasons that I like MAS epoxy so much is that the 2::1 ration makes mixing small amounts easy.

Picture #5 Here's everything I need: Mixed epoxy, disposable brush, patches in one plastic cup, chopped glass in the other, tweezers to place the patches West 404 high density filler. Also in this picture you can see another set of spider cracks that I have ready for repair, and other that have been repaired in the past. Also notice that I don't worry too much about color matching. If I was repairing on the deck I would try and match the color. On the bottom, I'm the only one that knows. :)
 

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wjejr

Active Member
Ok, so I have been delinquent if following through.

Picture 1: I wet the area with epoxy without any thickener so that I don't have to worry that the glass patch will be resin starved. It also helps hold the patch when I first put it in place.

Picture 2: The patch is so small that I used tweezers to place it. The hole is about 1/8" and the patch 1/2". Once the patch was in place, I used the flux brush to wet it out and then placed the 2nd patch on top of that. The second patch was slightly larger, but again the patches are so small that the cloth unravels, and so it is not like a bigger patch where there is much more size variation between the layers. Before adding the second patch, I also added the West 404 high density adhesive filler to give the patch more strength as well as viscosity.

Picture 3: Once done, I taped a piece of wax-paper over the patch. I did this so I could smooth it out, again because the patch was so small and I found it hard to smooth the patch without moving it, but it also offered another advantage which was:

Picture 4: I live in Massachusetts, and it isn't all that warm here yet. To cure the epoxy faster, I taped a piece of wet dry sandpaper with the black side up.

Picture 5: By the end of the day, the epoxy had cured.


A note here is that the distance between the full and the foot well is only about 1/4". Part of why I didn't grind out more, and also another reason for using the adhesive filler, was that I didn't want the patch to touch the foot well. My feeling was that having the hull adhere to the foot well would introduce a small pressure point on the hull. Once the patch was cured the hull still flexed, so I a seem to have succeeded in my goal. It it had not flexed, likely I would have ground out the patch and tried again.

Hope this helps someone in the future.

Stay safe and well my fellow Sunfishers.
 

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wjejr

Active Member
Finding it hard to find time to post, but here's the next step: Reapplying gelcoat.

Picture 1: All the stuff I need to do the repair which includes
  1. Polyester gelcoat and hardener from Total Boat
  2. West 406 thickener (colloidal silica)
  3. Syringe (blue) to measure drops of hardener
  4. Larger irrigation syringe for applying gelcoat
  5. Good quality mixing cups (the cheap ones dissolve on me)
  6. Hotel key card to smooth gelcoat (turned out I didn't need it)
Picture 2: I poured one ounce of gelcoat into the small cup and added thickener until it was thick enough that it wouldn't run. I then added ~25 drops of hardener. I added a little more hardener than usual as the outside temperature was in the middle 60's. I tried to stir as gently as possible to keep the air bubbles to a minimum.

Pictures 3 -5: I filled the irrigation syringe with the gelcoat and applied it to the routed out grooves. In hindsight I didn't need as much thickener, as I thought. This error resulted in more sanding later and probably added more air bubbles.

Picture 5: This is the gelcoat applied to where the hole was. I routed out the patch so that the gelcoat could form a thin layer. You can also see that while the gelcoat isn't running it's also a little too thick.

Picture 6 & 6b: The gelcoat has wax already added, so you don't have to wax paper over the repair, but I did anyway to help with curing, smooth out the gelcoat and...

Picture 7: I could put the wet dry sandpaper over top to help heat the repairs using the sun's rays.

Picture 8: I missed some spots as the sun was so bright, it was hard to see. I went back the next day and filled those areas. It was cloudy and cool, so I used heating pads over the repairs and they gave off enough heat to cure the gelcoat.
 

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wjejr

Active Member
Hello again fellow Sunfishers. Well it took about a day for everything to cure, and then it rained for a couple of days, and then I finally got around to have at it again.

Picture #08z Peeling off the wax paper left me with a bit of a "blob". I think next time I will use less filler. Also removing the wax paper proved to be more of a challenge than I remembered from the last time I fooled around with this stuff. Not sure if wax paper has changed, but the paper did not release well. Anyone know?

Picture #9 Next step was to wet sand the gel coat down to the hull level. I started with 220, better to err higher than lower, but quick found that was much too fine a grit. BTW I use a sanding block and water with a little dish washing soap. I suppose you could sand dry instead, but I find the sandpaper doesn't clog with water.

Picture #9a I switched to 150 grit and that worked well.

Picture #10 Once the gel coat was sanded level, I found a few pinholes here and there from bubbles. I will go back and reapply another light layer of gel coat without any thickener to fill them in, but first, I am going to wait until it warms up into the 60s. Until then, I won't bother smoothing the patches using further with finer grits. I usually go up to 600 or 800 grit, which I think is more than sufficient given to overall age and condition of the hull.

Picture #11 Here's a repair where I sanded through the gel coat a little. If I get motivated I will rout out the dark area ever so slightly so that I can fill it with gel coat. If I just paint over it, I am likely to burn through it when wet sanding again.

Hope all this helps someone.
 

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L&VW

Well-Known Member
Reapplying gelcoat.

Picture 1: All the stuff I need to do the repair which includes
  1. Polyester gelcoat and hardener from Total Boat
  2. West 406 thickener (colloidal silica)
  3. Syringe (blue) to measure drops of hardener
  4. Larger irrigation syringe for applying gelcoat
  5. Good quality mixing cups (the cheap ones dissolve on me)
  6. Hotel key card to smooth gelcoat (turned out I didn't need it)
You get all that stuff out before you start? :eek:
 
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