Gelcoat stress crack(s)

[Sailor Ray]

Here is the cabin trunk on the forward starboard side. (The port side has a similar crack.) The crack is severe in the front and extends back about 12" or so. Looks like a previous owner attempted some sort of repair, the grey looking material. I was thinking of grinding out and filling with fiberglass matt/roving using polyester resin and re-gelcoating. I have read wonderful things about using epoxy but can I bond polyester gelcoat if I use epoxy instead? What would you do? You can also notice smaller cracks in non-skid portion of deck. Loaded with these cracks as well.

Help.

[Tim]

It is possible to apply polyester gelcoat over epoxy resin if you take proper precautions and follow the correct procedure.

Here's an article covering a test program using polyester gelcoat over epoxy resin (West System, in this case). I have done this, and it worked out well enough as far as that goes, but I wouldn't make a habit of it. Still, it's good to know that one can use superior epoxy resins and still patch the cosmetic surface with gelcoat afterwards in situations where painting isn't called for.

Link: Polyester over Epoxy (PDF File)

The cracks you show are typical features of many boats, and are rarely harmful to the overal integrity. You could leave it alone. The previous "repair" is clearly a poor application of some cheap gelcoat "repair kit" that a previous owner bought at the marine store; not only did it not "repair" the problem, but it looks worse t han if it had been left alone.

If you want to repair these cracks for real, however, it will require grinding out the crack until you reach solid material in all directions. What material you use to fill the resulting gouges will depend in part on how deep the areas end up being. Some fiber reinforcement will help prevent the same cracking from reappearing, but in these natural stress points isn't unusual for some form of a crack to reappear (depending on the extent to which one goes to repair them in the first place).

I don't advocate using polyester resin as a repair system. The quality of the adhesion (bonding) simply isn't as effective as epoxy. For a simple cosmetic repair like this, particularly where you want to use gelcoat over the top, though, I suppose you could get by with polyester if you preferred. But I didn't tell you to.

[Quetzalsailor]

Many older glass boats have that failure. The vertical sides of the house are far stiffer than the deck as it continues forward and the boat bends up at the ends under shroud loads.

When I fix that problem on our 1970 North East 38 I will grind out the top face of the deck and house sides by perhaps 4" and I will have to continue the repair out to the toerail (following my cracking). I will grind a scarpf in the thickness of the top face, scoop out the Airex foam core, grind the top of the bottom face clean. I will make a judgement about replacing the Airex as it was when I see how bad everything looks; I think I will want to transition from 'glass-Airex-glass' to solid 'glass at the corner and back to 'glass-Airex-'glass on the house side and front. I'm thinking about gradually thickening the 'glass faces and correspondingly thinning the core and get to solid at the corner. I don't think I'd put Airex back in the corner, if that's what's there. In other words, I want to spread the stiffness out farther on the flat surfaces and transition from shape-stiffened to flat-flexible more gradually and let a larger part of the deck take the flexure. There are dandy pourable lightweight corestuffs made for this type of repair so the transitions might not be so difficult.

No doubt, I'll use epoxy in order to get a better bond to the old polyester. When I layup the top face, I'll scarpf to the old top face. My taste would be to duplicate/restore the pattern of the nonskid and make the repair invisibly, however, the better course might be to grind the whole deck smooth and apply new nonskid throughout. I've got cracking at cockpit corners, some delamination between Airex and 'glass, lots of sundamaged nonskid, some original and ugly repairs, and telegraphing Airex blocks.

I doubt my skills at applying gelcoat, and anyway you can't onto epoxy, so the finish will be paint.

[Sailor Ray]

Beautiful day on Long Island, New York to get some work done. I started by grinding into the crack to prepare for new gelcoat. I eventually ground down to a sizable void in the deck. I continued grinding the crack aft till it ended. I ground down to the balsa core in some spots. Unfortunately I found some wet core in spots. My intention is to let it dry a few weeks before effecting my repair. I plan on using some thickened epoxy and fabric laminate for the larger areas.

Do I need to lay new glass mat over the areas where the core is exposed? How far should I fair the edge back in order to lay the fabric?

[Tim]

If you found wet core, now is the time to determine whether it extends beyond the area you've opened up or not. Maybe you've already determined this.

Your repairs will be most effective if you are able to install new fiberglass so that it has the appropriate overlap with the surrounding areas for strength. For the most serious structural repairs, 12:1 is the appropriate bevel, but for an area like yours, and the conditions which caused the initial damage, I think you can get an effective repair with less overall contact area. Still, you may find this hard to do while trying to stay within the confines of the narrow white gelcoat band, and without extending any of your repair work into the nonskid. I assume, however, that you are trying to avoid touching the nonskid areas.

Given this, for the worst area you show, I'd bevel the existing glass back as far as you can inside the white area, and then laminate a few layers (determined by the thickness of the surrounding areas) of fiberglass into the area, being sure that it adheres well. When cured, clean, sand, and fair as appropriate. How effective this all ends up being depends on too many factors to predict.

If you find that you seem to be making too many compromises to your potential repairs by attempting to stay within that 1" band along the edge, I suggest that at that point you come to terms with the possibility of extending your preparations outward to allow for the best repairs, even though this will affect your molded nonskid. This may not be necessary, but don't sacrifice a proper repair to save the adjacent areas--this will come back to haunt you in the end. Unfortunately, it's not always possible to effect a proper repair without adversely affecting the cosmetics of other areas of the boat.

[Sailor Ray]

Indeed I was disappointed to find wet core. I was hoping to only have to fix the cracks on the cabin trunk and not have to intrude on the non-skid areas. Finding the wet core changed that approach. I certainly do not want to visit this task again in the future. So after mulling over the situation I think the best route will be to do it right the first time. My plan is to:

1. Obtain core samples around suspect wet areas until dry core is found
2. Remove top layer of glass and bevel edges
3. Glass new top layer in epoxy
4. Sand down entire top layer in preparation for Dynel as anti-skid
5. Prep for paint
6. Prime and paint

I will post pics when I get the wet areas opened and core removed.

Thanks so much for the insight.

Tim,
I read your entire Pearson Triton rebuild and have found the information priceless. Thank you for taking the time to document the entire process. Its helps and inspires us newbie?s to get the job done right. Your work sets a standard at can be done with hard work and determination. Going through some of your posts I can?t imagine where you had the time to even type on keyboard with all the work you must have gone through.

Thanks again!

Ray