Once the deck or cabin core decomposition becomes severe you'll know it: Things get a bit springy up there. Mild decomposition may not be so evident, but can be detected by pulling bolts/screws and inspecting the holes, or by tapping the deck and listening for tonal differences. If there a lot of air under there, it sounds hollow. You can also test drill through the deck to take a look. More often than not you'll be right so the test hole is no issue. If the wood turns out to be good, squirt it with some CPES and then after the CPES cures fill in with an epoxy filler. Our Fill-It dries just off white and smooths nicely.
Repairing Rotted Cores
Method 1: Removing Deck Skin and Replacing Core
How you repair rotted cores will depend on a lot of variables: How large the rotted area is, what it is, where it is, where the boat is and what kind of weather protection it has - and how patient you are.
There are two basic problems: 1) Accessibility to the deteriorated area and 2) drying things out. Epoxy will not effectively penetrate wet wood; the wood has to be reasonably dry. So, obviously, the best solution is always to pull the top off the deck and scoop out the bad wood and replace it. Easier said than done, right? On sailboats, especially, this can be a nightmare, with all the hardware scattered around. Still, it might in the end be worth it because things happen a lot faster this way. You treat the edges of the bad wood area with CPES, and the new wood if it's ply, and then re-install. With balsa you must put it in place first because the backing compound is dissolved by the CPES, or you can order the balsa core without the film backing. For bonding use our Layup & Laminating Resin, but wait until the CPES on the treated wood has cured. In a perfect world you would replace with a plastic honeycomb instead of wood, but we've been told many times that plastic core material is hard to get in limited quantities. Below is a rough schematic for removing outer glass deck skin. There are various ways you can accomplish this task; this is just one of them.
Removing Outer Skin
Removing Inner Skin
On some boats, especially the smaller ones, it is sometimes possible to get at the deck core from inside. Removing the inner skin is the preferable way of gaining access to the damaged core because it leaves the exterior surfaces unmarked. The schematic (right) shows steps for inner skin removal. Once again, old remaining wood and new wood core material should be CPES treated and bonded with our Layup & Laminating Resin.
TIPS FOR REMOVING THE INNER SKIN
Replacing the Core
Replacing the Deck
How you replace the outer deck skin will depend on how large the area is and how it relates to the hull structure. Ordinarily the skin section can be placed back over the new core with L&L Resin bonding and the cut edges later filled with our Epoxy Filler and then sanded smooth. However, if you are concerned that this will not present the same strong structure as it was originally, we recommend you use the steps shown below to restore the deck. Use only epoxy resins for re-bonding, and we can suggest our Layup Laminating Resin as being an excellent choice. It has a long pot life, is a simple 1:1 mix, and remains slightly flexible after curing. After major repairs you may elect to cover the deck with one of the non-skid flexible coverings. It'll hide all your cut and scratch marks.
(1) Fit outer skin over new core.
(2) Bond with thickened L L Epoxy Resin. The core should be solidly bedded in the thickened epoxy, and epoxy should squeeze out the cut line all around the new section.
Cure thoroughly (at least 24 hours), compressed with weights. (Place polyethylene plastic sheeting between weights and skin).
3. After resin mix has cured, sand/bevel seam areas into a shallow v-shaped depression with the original cut line in the deepest part of the 'v'.
4. Cut fiberglass cloth into narrow strips (or use fiberglass tape) and laminate them into the depression with straight L L Epoxy Resin. Each strip should be about 1 inch wider than the previous one.
Finally, sand the cured surface, then paint with a water-barrier coating or cover with non-skid flexible covering.
Repairing Rotted Cores
Method 2: Treating Core Without Removing Fiberglass Skin
Many of you will elect to repair the core without removing the deck skin. On smaller areas especially this will be the case. Sometimes, though, the glass skin is just too difficult to remove, or, it's an old boat and you just don't want to expend the time and effort. It's possible in these cases to perforate the outer skin with drilled holes, dry the area underneath, and then inject with Clear Penetrating Epoxy Sealer (CPES), Layup and Laminating Epoxy Resin, and then close the holes with Fill-It Epoxy Filler.
The key here is drying the core material. Epoxy will not displace water in and around wood cells. Although CPES will partially displace light moisture, in almost all instances it will be necessary to use some sort of drying method. It can take awhile. Ideally, this is a project that can be started in the winter when boating is less frequent. The deck can be opened, covered, and then left to dry out over a few month's time. If slow drying is not possible, there are ways to speed up the process. Here's the procedure: