RJ Burns
One common and easily prevented problem inspector’s notice during routine inspections is water saturation (high moisture content,) leading to de-lamination of cored fiberglass hulls and structures. The most common areas for trouble to develop are the Rub-rail fasteners, Stanchion Mounts, Antenna Bases, Outboard Motor Brackets and Through-hull Penetrations. If these problems are not identified and corrected early they can be quite expensive and potentially dangerous. There can be several reasons these problems begin and future articles will cover them. In this article I will discuss the most probable cause: improperly preparing the attachment points (fastener holes.)
It normally goes something like this when you want to mount or move a bracket or cleat. After determining its location you carefully mark the position of the fastener holes, remove the part, and drill the appropriate size hole for the fasteners. Squirt some good’ole RTV in the holes, line the part up with the holes, put the fasteners in, slide on some washers and nuts if you’re using bolts, tighten the heck out of them and you’re done, right? Yes and No.
You’re done for the immediate future but you’ll be back, probably to do more than tighten the loose part or fastener. Here’s why. The RTV will cure and remain effective for a relatively short period of time. This is assuming that most of it wasn’t displaced by the fastener. No doubt the core material was compressed and if only washers and no Backing Plate were used the load or compression has not been distributed evenly. This flexing causes voids which allow condensation to form or moisture to enter through the gaps. Eventually the sealant loses contact completely due to the wet core material thereby allowing more moisture to enter. The core material becomes weak or “punky” and the fastener looses its effectiveness. The core material in the immediate area becomes saturated (this is where it gets expensive) and begins to migrate; not always in a consistent direction. This causes a host of trouble along the way. The freeze and thaw cycle continues to create voids; etc, etc.
The only way to remedy the problem is to remove or dry-out the wet core material before attempting to reattach or reseal anything. If the problem covers a large area several holes may have to be drilled to allow the moisture to drain over a long period of time while also using heat to dry out the material or removing either the inner or outer skin to replace the core material. Ouch.
If the wet/delaminated area is localized here is one way of removing the core material without too much trouble. You’ll need about six inches or less of a welding rod or stiff coat hanger. Put a 90 degree bend in the end of the welding rod or hanger. The length of this leg should be as long or as deep as you think the core is wet. Start short and work out as you see fit. Place the other end of the rod or hanger into a drill. Work the bent end into the fastener hole. With the drill in vertical position turn it on and route out the bad stuff occasionally vacuuming out the hole. This will also help remove some of the moisture.
For a through bolt hole, after you’re sure the area is dry, proceed as follows. Tape off the lower hole and completely fill the void with thickened epoxy resin making sure there are no hollow spots. After the resin has cured lightly sand and rinse the exposed resin to remove the residue. The epoxy forms a rigid barrier between the core material and any potential moisture through the fastener hole. Drill the fastener holes, coat the mating surface of the part with a sealer, and using a backing plate attach the part. Incidentally, if you used a permanent type of sealer like 3M5200 a hot putty knife can be used to remove the part. If the repair area involves a blind (screw type) hole the procedure is the same. If a new devise is being installed in sound or new material, this is how it can be done. Drill the fastener hole using a bit approximately twice the diameter of the fastener. Fill with thickened epoxy and precede the same as previously described.
Bonding the contact surface of a part and the use of a properly sized backing plate will contribute quite a bit to load distribution over the maximum possible area. By better distributing the load movement and flex are minimized. This allows a stronger and secure attachment point, provides a better seal, and greatly decreases the chance of moisture intrusion through these areas.