March 2002 Telltale page 3 - by Tom Winlow and Marcel Laroche.
De-lamination is the separation of the deck skin laminate from the core. The problem is almost always between the top skin and the core.
As far as I can determine, most of the problem seems to originate during the construction of the deck. Because the core material is opaque, it is difficult for a workman to ascertain that there is an intimate contact between the core and the top skin. In some instances, it seems that not enough resin was used between the core and the top skin during the lay-up. This would account for de-lamination in flat areas. In curved areas, it seems that the core material was not pressed down hard enough to achieve full contact with the top skin, or that it sprung back before the resin hardened, leaving a gap between the core and the skin. Delamination could also be caused by people jumping on the deck or cockpit floor, resulting in an over-stressed resin poor bond between the core and the skin.
It is very rare to find the bottom skin de-laminated from the core. This may be because it is easy to see through the translucent bottom skin, areas that require more resin during the lay-up. The bottom skin is also thinner and sometimes porous in places. The latter can cause a leakage problem when injecting the deck with epoxy resin; so beware.
Suspect de-lamination when the deck emits a cracking sound, flexes underfoot, or cracks are found in flat surfaces, like the cockpit floor or areas of the deck away from fixtures. Cracks found in corners and running parallel to them are not caused by de-lamination, as there is no core material behind the corners proper. Those cracks are caused by the flexing of the laminate at the corners due to expansion and contraction (heat + cold), and by the weight of people standing in the cockpit. The fissures are usually only in the hard and brittle gelcoat. Cracks around stanchion bases and cleats indicate local overstressing of the deck laminate and often the fittings are loose. The fitting should be removed, rebedded and larger washers/backing plates installed. The deck should be checked for wetness.
The suspected area of de-lamination can easily be confirmed by sounding with a plastic hammer. A small inexpensive plastic hammer works much better than a screwdriver handle, because it can deliver more consistent blows. Begin by "tapping" the deck on one side of the crack proceeding towards the crack and onto the other side, while delivering even light blows to the deck. A "TOCK" sound indicates no de-lamination, a "THUD" sound indicates de-lamination. Once you have determined on which side of the crack the de-lamination is, tap from the delaminated area towards the non-delaminated area, and mark the border with a pencil (not a pen). Often the outline of the delaminated area looks like a lake with bays and creeks connecting it to other delaminated areas.
Tap areas where there is a cracking sound underfoot. Sometimes, the sound is made by the loose top skin contacting the core. If de-lamination is present, sound it and mark it as above.
Areas that flex underfoot are also likely to be delaminated. This is because the deck depends on both top and bottom skins being bonded to the core for rigidity. However, large flat expanses of deck must give a little. Again resort to the plastic hammer for the answer.
While you still have the hammer in hand, you might as well sound the whole deck. Most likely there are other areas needing attention. A "TICK" sound indicates a void between the gelcoat and the top fiberglass laminate. This is another can of worms and the subject of a future article. Delaminated areas should be repaired ASAP, because they often lead to wet decks ($$$). The flexing of the top skin that occurs at the border between the delaminated and non-delaminated area, manifest itself at first by a crack in the gelcoat. Continual flexing will eventually break the laminate and water will enter the core (snake pit and future article).
Begin by drilling three 1/16inch holes about 3 or 4 inches apart, into the core but not through the bottom skin , starting at the lower end of the delaminated area. Drill the holes about one inch on the delaminated side of the line. Assuming that the core material clinging to the drill bit is dry, start injecting epoxy in the lower hole until epoxy comes out of one of the other two holes. Wipe the overflow with lots of acetone and plug the hole with a large round toothpick. Continue injecting until epoxy flows out of the third hole, wipe the overflow and transfer the syringe from the first hole to the third hole. Wipe off overflow around the first hole and insert a toothpick. Now drill two more holes and repeat the procedure until the delaminated area is completely filled. Once in awhile, press down on the top skin; this will help the epoxy resin flow into all areas. The idea here is to inject from one end of the delaminated area towards the other end, while providing an escape hole for the trapped air being replaced by epoxy resin. Once the epoxy has started to gel in the lower holes, remove the toothpicks, otherwise they will be part of the boat and they will need to be drilled out. After removing all the toothpicks, thoroughly wipe off the epoxy resin from the surface before it fully hardens. Using a 3/32inch drill, gently redrill the holes oversize to remove the epoxy from around the rim of the holes. Next, using a toothpick, fill the holes with gelcoat, working it well into the holes for a good bond. A second gelcoat application is usually required. If the gelcoat colour is a near match, the 3/32inch holes will be hard to detect. Once the epoxy has hardened, sound the delaminated area again and inject any unfilled areas.
If the core material is dry, there will be a very good bound and the deck will be restored to its original strength. If on the other hand, the core was humid or wet, the strength of the bond will be inversely proportional to the amount of moisture in the core. This is because wet core can absorb little or no resin to complete the gluing process. Epoxy injection will not dry a wet deck. As far as deck repairs are concerned, epoxy injection is a fun job. Take your time and it will come out fine.
Do not use excessive pressure on the syringe plunger in order to force more resin into the deck. This could cause the top skin laminate to rise above the surrounding surface.
Cover the area below deck with a plastic sheet in case of a leak through the bottom skin of the deck. Bottom skins are not as thick and are porous in some areas.
If an inordinate amount of resin is required in some areas, stop and suspect a leak.
Use epoxy resin because of longer setting time and better bonding strength.