Friday, February 4, 2011

This Old Hull – Laser Deck Repair with Air Pressure

Somewhat housebound after yet another New England snowstorm this winter, I’ve had the chance to work on my 23 year-old Laser hull with decks adjacent to the cockpit so soft and sagging that they seemed to be structurally unsound. My good friend and fellow Laser enthusiast, Yarg, told me that the problem might be delamination of the fiberglass-foam sandwich deck structure. Pictured below is a piece of the 1/2” thick deck material which I had cut out for an access port some years ago in order to repair a cracked mast step tube.

Inspecting the underside of the deck, using a mirror, and an existing access port next to the centerboard revealed what appeared to be perfectly intact fiberglass. However, pushing on the deck seemed to suggest an airspace as the upper deck surface made a crunching sound when it touched the rough foam surface below. My findings probing through a 1/16th inch test hole were consistent with the delamination theory as well. Perhaps the deck might be repaired by injecting epoxy into the space between the layers, but without easy access to the inside of the hull, clamping the two sides together would be problematic. Pushing from the top only would leave a seriously sagging deck. The answer appeared to be pressurizing the hull with an electric air mattress pump.

I began the repair by cautiously connecting an electric air mattress pump to the stern drain hole applying just enough pressure to cause the sagging deck to rise. Too much pressure, causing the hull to explode, would be counterproductive. Drilling holes in the tubing reduced the air pressure as necessary. After covering the deck with masking tape, I drilled an array of 1/16th inch holes into the soft areas of the deck using a hexagonal pattern, 2 inch hole to hole spacing, and 3/8th inch depth. The hand drill had a stop using a piece of dowel to prevent drilling too deep. Five 1x2s clamped across the deck prevented the deck from rising above its normal flat position when the air pressure was applied.

West Marine extra slow curing epoxy allowed enough time for me to inject all the holes before it thickened. I injected the epoxy using a West Marine syringe with a tapered nozzle that fit snugly into the 1/16th inch holes. I loaded the syringe by removing the plunger and pouring in the epoxy. It takes way too long to try to suck it into the syringe. I injected one syringe-full (about ½ ounce or 15 ml) into only 1/3 of the holes which worked out to holes with a 4 inch spacing pattern. The other 2/3 of the holes allowed for excess epoxy and air to escape. The average epoxy thickness was about 2.2 mm or 3/32th inch. It was comforting to see the excess epoxy and air bubbles flow out of almost every hole when the air pressure was turned on indicating that the epoxy had spread out well. I injected some extra epoxy into any hole that was not oozing.

After leaving the air pressure on for 24 hours (praying the pump wouldn’t conk out before the epoxy hardened) the deck appeared to be quite solid. A few of the holes were leaking air, so the pressure was turned off, and the leaking holes were sealed by injecting a little more epoxy. By the way, pressurizing the hull is a good way to find other leaks as well. Running my hand under the joint between the deck and the hull revealed a previously unknown large leak near the bow with air blowing out. I’ll do a search for smaller leaks at some point. The final step for the deck project was to apply some Gel Coat repair material to the 1/16th inch holes.

The soft, sagging deck is now flat and solid, but will it be good for another 23 years (or even 23 minutes of sailing in rough conditions)? Time will tell.