Gelcoat cracks -
http://www.passagemaker.com/channels/gelcoat-cracks-should-you-be-worried/
"Not long ago I received an e-mail from a reader requesting assistance with a seemingly serious problem. His late model trawler had developed cracks in the foredeck. He was deeply concerned that this would lead to water penetration of the fiberglass substrate or, worse, the core. His concerns were understandable, stories of saturated composite core, particularly balsa core, are legion in the world of recreational boat ownership, and with good reason, wet core leads to a host of maladies, including diminished rigidity, unsightly oozing brown stains, and diminished resale value.
The Mechanics of Gelcoat
Before understanding how and why it cracks, and the consequences thereof, it’s important to why it’s used and how it’s applied. For most production boat builders, gelcoat is the first item used in the construction process. It is sprayed onto the inside of a female mold (usually about 1/50th of an inch thick); fiberglass laminate is then applied over this, then core is installed in the case or cored composite construction, and finally more layers of fiberglass laminate, creating a sandwich-like structure which, when properly executed, is both stiff and light.
For all its durability and abrasion resistance, gelcoat has its weaknesses, primary among which is its inability to tolerate movement and stress. This deck would likely benefit from increased stiffness, which would reduce flexing and prevent cracks like these.
For all its durability and abrasion resistance, gelcoat has its weaknesses, primary among which is its inability to tolerate movement and stress. This deck would likely benefit from increased stiffness, which would reduce flexing and prevent cracks like these.
Once the part, anything from a deck or hull to a cabin top or hatch, is removed from the mold, the gelcoat is all that is visible on the side that is normally visible. The inside may also be “painted” with gelcoat as a sort of rough finish in areas that might be used for storage, or areas that are visible from inside the vessel, engineering spaces, chain lockers etc.
This approach has two primary goals, the gelcoat provides pigment, and if done properly, a smooth appealing and durable finish. Additionally, and to an extent for below the waterline applications, it also prevents the laminate from absorbing water—although its ability to do this is limited and it should not be relied upon as a true, below the waterline barrier or osmosis (which can lead to blisters) prophylactic. For that, laminates should be skin-coated using vinyl ester resin, which is osmosis resistant, and/or an epoxy barrier coat applied.
Because of the leverage they impart on the deck, stanchion bases are notorious for causing gelcoat cracks. These can be prevented by ensuring the structure to which the stanchion is attached is rigid and utilizes an ample backing plate to properly distribute the load.
Because of the leverage they impart on the deck, stanchion bases are notorious for causing gelcoat cracks. These can be prevented by ensuring the structure to which the stanchion is attached is rigid and utilizes an ample backing plate to properly distribute the load.
When gelcoat becomes damaged, however, either in the form of stress cracks or due to impact or other stress, its aesthetic appeal is obviously diminished. However, does this also diminish its ability to resist water absorption? In fact, this is, or should be, of less concern; for the most part gelcoat is cosmetic, and it has no structural properties what so ever. If, on the other hand, the damage is more than skin deep, if the cracks penetrate the laminate, then it’s another matter entirely. Water may enter the fiberglass laminate as well as core material beneath.
It’s also important to note that while gelcoat shares some attributes with paint, the two are more different than they are alike. Gelcoat is essentially pigmented fiberglass resin. It’s tough and abrasion resistant, however, it is not very flexible; more on that in a moment. Additionally, unlike paint, other than in repair scenarios, or for areas where aesthetics and water absorption are not critical, it should not be applied wholesale, over large areas and without the benefit of a mold—hulls, cabins and decks should not be sprayed with gelcoat after they are complete. Gelcoat, when allowed to cure while exposed to air, tends to be porous, making it dull and prone to water absorption. Two-part linear polyurethane paint is far better suited to this role.
Reading Gelcoat Cracks
Because gelcoat is primarily applied for cosmetic purposes, cracks and other defects are especially irksome. The causes are varied and in some cases worthy of concern. In the majority of cases, cracks occur for a few possible reasons. One of the more common reasons for cracking is applications that are simply too thick. Because it is comparatively brittle and, unlike fiberglass laminate, unreinforced, it will crack if applied too heavily; thin gelcoat is more flexible than thick gelcoat. In the vast majority of cases, gelcoat is applied by hand using a pneumatic spray gun by, hopefully, experienced applicators who, to my never ending amazement, manage to get it right the vast majority of the time.
The places where it often becomes too thick are in fillets and low areas, where (when in the mold, all angles are inverse—any component that is concave while in the mold becomes convex when complete) gelcoat tends to pool. Once the part is complete, these problem-prone areas often manifest themselves on rounded, convex surfaces, in and around hatch gutters.
Gelcoat can crack for a variety of reasons: some are benign and strictly cosmetic, others are indicative of more serious structural issues. This crack is likely the result of gelcoat that is too thick; however, it’s very unlikely that it extends into the laminate and is, therefore, of no concern other than aesthetics.
Gelcoat can crack for a variety of reasons: some are benign and strictly cosmetic, others are indicative of more serious structural issues. This crack is likely the result of gelcoat that is too thick; however, it’s very unlikely that it extends into the laminate and is, therefore, of no concern other than aesthetics.
Alternatively, if the applicator is inexperienced or simply hasn’t been properly trained, or if his or her equipment is not functioning properly, gelcoat could potentially be applied too thickly in any location. When this happens, cracking can occur anywhere and everywhere. In extreme cases repair becomes impractical, the only solution being wholesale removal of the gelcoat, by peeling and/or sanding, fairing and then painting with two part linear polyurethane.
Even when everything about the installation is right, highly stressed hardware like this cleat can be hard on gelcoat.
Even when everything about the installation is right, highly stressed hardware like this cleat can be hard on gelcoat.
Yet another area where gelcoat cracks can and often do occur is adjacent to hardware installations. If fastener holes are not properly sized or relieved, or if the laminate beneath the hardware is insufficiently stiff, allowing excessive flexibility, the gelcoat will crack even if its thickness is correct.
Initially, if cracks appear it’s important to first determine the cause. If it’s the result impact damage, repairs are straightforward enough and, if carried out properly, should be long-lasting. If, on the other hand, cracks are the result of improper or over-application, there’s nothing to be done other than carry out repairs and hope for the best, it’s possible that cracks will re-appear. As soon as practical, a determination must be made regarding the depth of the cracks. If they extend into the laminate, then the problem, and its solution, become necessarily more complex and carries with it a greater sense of urgency.
In many cases, gelcoat cracks begin at holes drilled for fasteners. If the holes are too small or if they are not stress relieved, cracks can begin here and spread considerable distances.
In many cases, gelcoat cracks begin at holes drilled for fasteners. If the holes are too small or if they are not stress relieved, cracks can begin here and spread considerable distances.
There is yet another possibility; cracks can result from incorrect hardware installation, or inadequate substrate rigidity. If holes drilled in gelcoated fiberglass for fastener installations are improperly sized and stress relieved or chamfered, cracks may result. Similarly, if the fiberglass structure beneath and adjacent to hardware installations, particularly those that are stressed such as cleats, stanchions and windlasses, lacks adequate rigidity, it will flex, which in turn often results in gelcoat cracking. In either of these two latter cases, if the underlying root cause is not corrected, with fastener holes stress relieved or the addition of support, cracks will often reappear shortly after repairs are complete.
Overall, in most cases gelcoat cracks are a cosmetic rather than a structural issue, and, again broadly speaking, of little concern from a water penetration point of view, unless the cracks extend into the laminate beneath. In order to avoid reoccurrences, analysis and evaluation of the cracks should, however, precede any attempt to make repairs."
