Hull crack repairs

Recently I painted a 40 yr old boat. In the prep work we dremeled out a bunch of small checks and cracks. Under each was a small air bubble form the original layup i guess.

After repair and paint, and a few weeks in the sun, the repairs are slightly noticeable. Can anyone critique the method so I can never have that happen again. I currently have constructed a 1/2" thick fiberglass test panel to try suggestions out.

The process:
1) dremel the disturbed area until the crack disappears or until the air bubble is located. For however deep i am, bevel the surface out about 7X. Most are about 1/8" to 1/4" deep.
2) overfill the gouge with Awl Fair.
3) wait about a day for the stuff to harden
4) heat lamp until surface is hot to the touch
5) longboard or block sand smooth to 120 grit
6) epoxy prime (awl grip 545)
7) sand primer to 320
8) fill any pinholes
9)topcoat (in this case awl craft Flag Blue with 2 coats clear on top)


About 2 weeks after I put it outside it started to show.

I spoke to one guy that mentioned priming the surface before filling.

Your comments are appreciated.
Regards.

 

What you are doing is ok. Some people prime the surface before the filler stage but this is just to guarantee the adhesion of the filler. (primer will seal any dodgey layers better than filler is the theory). In your case I am not sure if it will be benefit.

I have seen this before on some vessels. It isn't a system fault or this would mean that you could never repair anything.

I presume when you say you see the repair, you mean you see the original hole/filler as opposed to somethingelse eg sandscratch marks?

My comments would be as follows:-

1) "wait about a day" - what does this mean exactly? The longer you let the filler cure the better. Depending on temperature the filler will take 2 days to get sandable. I see you are using a heatlamp but this may not be really making much difference depending on other factors eg heating the surface to 70C is good but it will quickly cool back down again. Just leave it for 3-4 days at 20C. Bake then if you want.

2) how soon did you prime the filler patches? Leave them as long as possible. I think awlgrip say minimum 48hours ie 2 days at 20C. Longer is of course better

3) Awlgrip prefer High Build primer on the filler before the 545. I know this seems a pain but it seal the surface much better. No guarantees here but we used to fill whole boats with the 545 on filler system till we got too many problems. We have changed to using high build under the 545 and we have much less problems

4) The real cause of problem is the difference in hardness/hdt between the filler and the original gel. Sometime there is no solution except burying the repair under HIgh Build and 545. These seems to shield it. The Highbuild is like concrete when fully cured. You can try to build upo the 545 in lots of coats (over 2 days) but there is no real gain. Just apply 150microns of the high build and then 50-75microns 545. Block sand the High Build with something like 120-180.

best of luck

ps I wouldn't recommend use of clear over the flag blue, a) it will change colour over time b) it is pig to repair due to a). Just mix it 50% or more in last coat. We've just finished the latest J-Class in Black...mixed with clear and it looks very nice.

 

Thanks Colin. I think the issue must be on the time we wait before sanding. I had an issue once before (smaller mind you) but we had done the repairs and ran high build over the whole boat before 545.
I have a small panel that we are playing with and I am going to do as you describe and what I had done and see how it comes out.
The time factor is incredible since it really slows down a repair process!

What are you using to fill pinholes after priming the boats?

PS ; i've done the mixing of the color on the final coats. In this case the customer insisted on it.
Thanks again.
Todd

 

the laminate, substrate, is flexing and the gelcoat is brittle and cracking. Open up the stress fracture with your dremel, epoxy fill with micro fiber then fair in is the typical repair.

 

Thanks Michael,
Are you waiting X hrs or days before fairing the epoxy? I thought of using that as the time for Awl Fair would have me doing nothing for a couple of days. Also, what are you using to fill the pin holes? More epoxy with high density filler added?
Todd

 

keep your method, but try similar products for different vendors. Differences in type of filler, brittleness, etc. from brand to brand may improve (or worsen) your results.

 

Awlfair is good filler. The problem with old glass boats , pinholes and stress cracks, is that its a whack a mole repair game. Fix one then another pops up.

Pin holes must be made big enough to fill.

In areas with many stress cracks get aggressive with a grinder and remove as much gel coat are practical. Other than that..whack a mole is standard proceedure.

 

What I like to do for cracking in gel coats:

Try to discern if the crack is created by a gel coat problem or a stress riser in the glass work.

In both cases the gel coat should be removed down to glass.
I have absolutely no confidence in dremel repairs to crazing. Remove the gel coat over the entire checked area. If that is the whole hull, get ready for a big job.
If a stress riser is present, reinforce the area with more glass. If the gel coat is just too thick/brittle etc, just removal, filling/fairing priming will do.

You are not stating if "showing through" means crack reprinting or other?

Flag blue is the worse case for dissimilar material such as new epoxy fairing compounds on old hard gel coats.
Having gouges filled with fairing compound is not what you want under a topsides paint job.

I bid a flag blue paint job just this last fall.
I forget the make, but heavy cracks/crazing all about a midships that someone had tried to get by dremeling out and covering with bog primer etc.
The owner is in denial- he will find someone to prime and paint again- LOL