TOPIC: Spider cracks v. stress cracks

Here are thoughts on classic fiberglass boats.

Polyester fiberglass gelcoat "moves" as it cures. Some say 7%. It also hardens over time and some tell me it really never stops curing. Warm weather, cold, freezing, and sunlight also seem to cause it to "move". Perhaps these are all reasons for spider cracks in the gelcoat of classic boats.

Stress cracks and damage from hits look different and are different. They almost always do go deep under the gelcoat and into the actual fiberglass structure under that gelcoat. Even tight radius corners in the boat's design seem to stress crack when the boat goes into use. (tight corners are hard to properly get a real good, void free layup in them as the boat is being laid-up) and these voids create problems.

By the way, it seems that epoxy does not shrink like polyester and has additional flex in it before it cracks.

What do you think?

By the way, I think pro restorers who would not want to "re-do for free" a paint job if spider cracks come back tend to drive the conversation towards a longer, harder process as that is what they must do when they bid a job.

I firmly believe that there are no shortcuts to fixing a stress crack if you do not want it to come back.Stress cracks are into the fiberglass layup under the gelcoat. You must fix the underlying layers of fiberglass as well as the gelcoat to rid a boat of a dock bump stress crack. I do not think that a too tightly radius corner in the basic design of the boat can be fixed, as there are deflects pretty well through the boat at that location.

I feel I am on the track of going to explore the idea that spider cracks are only in the gelcoat.

Still, it will be interesting to see (to keep spider cracks from coming back) if one has to take all the gelcoat off or only take it down enough to allow new material to adhere to the old gelcoat.

Uhmm, most spider cracks do NOT involve the underlying glass. If the cracking was caused by Impact then yes the glass may also need to be repaired but basic gelcoat spidercracking from aging is a gelcoat issue and not associated with the underlying polyester resin and glass. Once the Old, Aged gelcoat is removed down to the glass the glass can be recoated with gelcoat and if the gelcoat is applied properly the glass will not cause further spidercracking for years to come. This is all on the premise that the glass is in good condition and not suffering from delamination or any other issues that could be caused from years of exposure to the elements.

If I understand what you are saying, one must remove all of the boat's gelcoat which is what is often done in a yard when a cruising boat's bottom is full of blisters.... only on the hull bottom rather than the deck. After that one puts on new gelcoat onto the old glass. Did I understand you correctly?

Do you use this?

www.gelplane.co.uk/gelplane/product.asp

Yep, blisters are often also in the laminates of glass behind the gel, so it too must be dealt w/ to prevent blisters from coming back, even if you removed & re-apply all the gel.

Some have used a grinder w/ a flap wheel, large diameter sanding disc or other means to remove large areas of gelcoat. Sucks, IMO, but if the gel's badly crazed & cracked, seems to be the 'best' way to prevent the cracks from telegraphing thru any new coatings, gel or paint...

And deck, cap or hull bad gel's bad gelcoat....

I have no blisters or other than a few stress cracks from tight radius corners that were designed in by Glasspar.

What I am addressing is hairline crazing lines in the gelcoat. I am making the point that I am going to try to re-finish the deck without removing 100% of the gelcoat.

Do you agree with part removal of the gelcoat or 100% removal of gelcoat?

seabuddy wrote:

I am going to try to re-finish the deck without removing 100% of the gelcoat.

Do you agree with part removal of the gelcoat or 100% removal of gelcoat?

I can't answer that accurately w/ out seeing pix. Remotely via the internet makes it really tough to do. I tend to err on doing too much, rather then not enough.

Even w/ pix, until you attempt to grind/sand/remove the crazing/cracking, and see how badly the crazing/cracking really is, hard to say for sure that all the gel in the affected area has to come off, completely.

Here's a pix of my FireFlite's gel damage:




All that ^^^ probably started as crazing: small hairline, super fine cracks. Now they are definitely cracks.

Compare to these:

Which ^^^definitely look like impact cracks.

Or these that are still fairly small, hairline cracks (Crazing):


In the instances of very fine, hairline crazing, you might get away w/ only removing a little gelcoat, perhaps w/ a sander, fill, fair & recoat. Gel isn't really much thicker then paint when you hit it w/ a grinder w/ a wheel. The grinder will burn thru them both fairly quick.

Where mine has developed large, deep cracks, the gel really needs to come of the entire area. Until you can see the actual fiberglass behind the gel, you won't know if the glass has also cracked, esp at the suspected impact site. I've seen gelcoat crazed so badly that when those cracks start to open up, UV as compromised the underlying fiberglass in a weird spider web pattern 'etched' into the fiberglass.

If you look really closely, where the cockpit coaming that separates the 2 cockpits attaches to the port side of the gunwale, you can just make out some yellow lines on the glass. These were cracks in the gelcoat. That have been burned into the glass by UV:


Just to the right & down from the center of the pix. It's in the slightly darker area of exposed fiberglass.

Specifically on my Fireflite, when you start to really look & inspect the gelcoat closely, I'd guess 65%+ of the gel is actually compromised, in 1 way or the other. When you grind, you feather the edges back a good ways. So for estimation only, lets say that's another 25%+ of my total surface area.

Dang, that's 90%+ of the cap's gelcoat. I don't think you could find a 6" circular area that's not compromised in some way. And when you're feathering the edges of a repair area, I also suspect that 99% of them will overlap into another affected area's grinding area.

So yep, it's all coming off. Even though I rally don't want to do that.

Help any ^^^ &/or answer your question?

Thanks for your very detailed response! Just what I need.

These that are still fairly small, hairline cracks (Crazing) in my boat. Like your last photo.

Thanks again.

Awesome topic and help full information! I was actually thinking about sanding my gelcoat down on the hull and rolling some thin epoxy over the whole bottom then resand,prime,paint.The hull i'm working on has only small spider cracks covering the bottom and sides nothing that appears to be from impact.The cap is in great condition and should only require sand,prime,paint. Probaly dreaming its always worse once the grinder starts the dust flying! My thought is that the thin epoxy will seep into the small cracks and seal/glue them together after an extensive sanding and cleaning session? This isn't a show boat just a fun glassic to be enjoyed in the sun? Any thoughts would be greatly appreciated and again this is a nice staight boat with no heavy damage. Redoing floor, even the stringers, and trasom are solid with no heavy water saturation.

Production classic (and modern) boats are made in a female mold. The finish part that we see is the image that the highly sanded, polished and buffed mold gave it. A boat was laid up (gelcoat first and fiberglass structure after that) against a near perfectly surfaced mold and its finish reflects that.

Putting new epoxy on top of the old surface of the gelcoat (whether taken down half way or all the way off) will result in a lumpy hi-low rough finish. Roll or brush on new epoxy on top of that surface means that the boat needs to be made fair, smoothed, and buffed prior to any new finish put on top.

That smoothing process is a lot of work.

Now, besides doing enough hard work to end up with a pretty boat(all of the above),... one has to make a judgement as taking the proper steps BEFORE the new finish is started to insure that the old very-thin (hair-line) crazing tight lines do not come back after a season or two of use and show though the new finish.

That is what this thread is all about. Not about bigger cracks. I, too, want a conversation of this.

My G3 had what I cll spider cracks and I wasn't sure what to do. I finally decided to sand out what I could without getting into the glass as I had decided to paint instead of re-gelcoat. Quite a few disappeared before the gelcoat was gone the remaining bit I ground out with a Dremmel tool and filled with epoxy and micro-balloons. After fairing I sprayed all with high build epoxy primer and sanded again. Next step is sealer then topcoat with Awlgrip. I hope the cracks don't reappear, guess I'll find out next summer. For what it's worth, that's my story.

My G3 had what I call spider cracks and I wasn't sure what to do. I finally decided to sand out what I could without getting into the glass as I had decided to paint instead of re-gelcoat. Quite a few disappeared before the gelcoat was gone the remaining bit I ground out with a Dremmel tool and filled with epoxy and micro-balloons. After fairing I sprayed all with high build epoxy primer and sanded again. Next step is sealer then topcoat with Awlgrip. I hope the cracks don't reappear, guess I'll find out next summer. For what it's worth, that's my story.

Yep, that's the rub really, until a light grind, fill & fair (even w/ epoxy) fails, or doesn't, it's hard to predict 1 way or the other.

If it's going to fail, when? 1st season after repair wouldn't be acceptable to me, a 5yr or longer wait for the cracks to reappear might suit some, but not others.

It is more likely, IMO, to fail then removing it all & 'starting from scratch' but it's also significantly less work. A trade off I suppose.

It also is of note that no matter how similar a crack looks from 1 boat to the next, there are a ridiculous amount of variables that could have 1 repaired as JK describes last a very long time. While another boat, w/ a different maker, from a different period in glass boat building history, w/ a different restorer using the same process & materials could get different results.

And that's ^^^ my primary motivation for suggesting aggressive crack removal rather then another method. As well as why I often spend a lot of time doing research, try provide lots of info & encourage others to do their due diligence, not to just take 1 guy's opinion, mine alone or others.

It is often also a matter of time, skill level, access to the necessary tools, equipment & adequate work space and the boat rebuilding budget. Which are all widely variable.

I agree that more is better, but THE WORK!

Well if i'm understanding correctly then i should sand all gelcoat thats cracked completely off down to the glass, inspect,repair,then start the fairing and refinish process. That even applies to just the fine spider cracked areas. That does seem like a ton of work but when theres only one way to do the job correctly then why short cut? Of course i understand that every hull, make, year, model,etc. is going to have its own flaws and weaknesses. It is hard to compare ones boat to anothers and expect the same problems and results, but if the job is done properly than long lasting great results can be expected. So much for me trying to think there was any way easier than days of grinding and more grinding before the refinishing begins!! LOL , as always thanks for all the helpfull and inspiring insight and information.

Before you go and make more work by grinding all the gel off unless its beyond saving and you are going to re-paint or re-gel . You can fill most spider cracks and crazing with epoxy and a heat gun with very good lasting results . First lightly sand the area with a medium grit like 120 then clean off with compressed air and acetone trying to flush out the cracks as best as possible . Mix a small batch of Epoxy , a couple of ounces ( this is for a small area repair) get a chip brush a heat gun ( not a hair dryer) . Heat the area good and hot dont burn it though then brush the epoxy on the cracks then reheat . It works much like sweat soldering copper pipe , the epoxy gets drawn into the crack and fills and bonds the crack . It might take a couple times to fill the cracks/crazing but it beats filling and faring the whole thing . This is for small area repair not whole decks and such . Dont try this with polyester or vinylester unless you want the fire dept to visit and your project ruined . Epoxy resin is fire resistant .
P.S wear a respirator , epoxy may have a somewhat pleasant smell but it is a sensitizer and it could affect anyone at anytime .

Very nice tip about the heat gun! Thanks.

This video may help ^^^

And here's a link to similar info:
www.boatrepairvideos.com/id9.html

Like many things, different stuff will work for different folks. I can't say a good epoxy fill & fair on small hairline cracks will fail to prevent recracking, but it might. Same for removing the gelcoat & filling/fairing before reapplication of gelcoat. I can't say it won't fail, but it probably won't.

In that video, it's not a complete removal of all gelcoat, but there are LOTS of places ground down to glass.

the epoxy heat gun trick isnt for that kind of repair lol

Very good video. I looked at all three parts, which was easy from using your link. I highly recommend my fellow buds on FiberGlassics get a cup of coffee and learn a lot. Thanks..

here is a still from the re-finished 1958 boat.

And another photo from the video that was posted above. Just over-the-top work.

that is the clear coat finish after it dried.

This is a show boat. Not a user boat.In fact, this boat may never be used as a boat, just as a static car and boat display.

Just be aware that Epoxy and Gelcoat don't mix. Epoxy and Paint A-OK!!!!

Do you think that this issue applies to trailer kept boats? I thought it was limited to the longer term exposure to water that the boat bottom on a slip kept boat was the only issue.

seabuddy wrote:

Do you think that this issue applies to trailer kept boats? I thought it was limited to the longer term exposure to water that the boat bottom on a slip kept boat was the only issue.

?Does what apply to trailer kept boats?

The issue that MyFlamingo is bringing up?

seabuddy wrote:

The issue that MyFlamingo is bringing up?

Gelcoat over epoxy has marginal results, slipped or not. That problem?

EDIT: Waterwings is correct, I have corrected my typo ^^^

What type of marginal results?

Poor adhesion

read thru this thread: forums.iboats.com/boat-restoration-building-hull-repair/gelcoat-over-epoxy-can-done-yes-no-531342.html

Specifically search that site for ondarvr's responses. I've never seen him give bad advice, or be vague (and then easily misunderstood) in his replies. He's the resident coatings expert on that site.

No it's not the epoxy on gelcoat, it's the gel coat applied over epoxy. Epoxy will adhere to gelcoat to fill holes, deep scratches etc but once you do that you will not be able to apply gelcoat over it. If you use vinylester you can gelcoat over it. Once you epoxy your pretty much stuck with painting over it.

Bob

Thanks Bob, corrected my typo..... You are correct..

How is the odor comparison of Polyester, Vinylester, and epoxy. Some of us work in a confined space and in the winter do not want to open up the space.

Epoxy the lowest?

seabuddy wrote:

How is the odor comparison of Polyester, Vinylester, and epoxy. Some of us work in a confined space and in the winter do not want to open up the space.

Poly is bad & requires a mask, vinyl I've never used, epoxy isn't nearly as bad as poly, but I'd wear a mask in most situations, if working in close proximity to the resin &/or work surface. Like leaning over a large panel when applying epoxy to it.

You should protect yourself & others from epoxy similar to any other. Google epoxy allergy. Some become VERY allergic to it after even limited exposure.

Vinyl and poly stink , Epoxy has a very mild odor which is a wolf in sheep's clothing . It is a sensitizer which means at some point your body is going to say no more , it may be thirty years of bathing in it or it could be thirty minutes breathing the pleasant epoxy aroma that brings you to your knees or worse . Better safe than sorry WEAR A RESPIRATOR regardless of the smell , at least poly and vinyl let you know very quickly its not good stuff to breath .

Yep what they said. Never work with any of these products without a respirator, just good safety. If you plan on doing this in a basement, I hope you have plenty of ventilation to the outside so it doesn't seep into the rest of the house. Some kind of fan drawing the fumes outside.

Bob

Thanks.