The Technique article in this issue, “Checked Plywood Repair” by Kent and Audrey Lewis, is one that I took a special interest in. Several of the boats I’d built, and the teardrop trailer I’d built using the same materials and methods, have been showing areas of plywood that had checked. Work that had held up for years was being undone and I wasn’t sure why.
The oldest of the boats is the gunning dory I built for my father in 1980. John Gardner’s The Dory Book, published in 1978, was my guide for both my introduction to boatbuilding and the plans for the dory. It was the second planked boat I’d built, the first being a Marblehead dory skiff. With the exception of the garboards, both were traditionally built with red cedar planks on oak frames, all finished bright. I had taken Gardner’s advice and used plywood for the garboards to avoid the splitting he noted that happens to the short grain at the ends of natural lumber garboards.
Several years ago—after the dory was kept at my dad’s rowing club, outside, under a tarp that I frequently found not fully covering the boat—the inside faces of the painted fir plywood garboards developed pronounced checks. Looking back again at my copy of The Dory Book, I saw I had underlined “plywood garboards,” but I did not mark what followed: “…plywood does not stand prolonged soaking and drying as well as natural lumber. However, this fault in plywood may be overcome to a large extent by sealing it with plastic.” I know now that by “plastic” Gardner meant “epoxy,” but 44 pages separate his garboard advice from his description of epoxy, and that description only indirectly connects it with “plastic” and covers only the use of epoxy as a bonding adhesive. So, I had only primed and painted the plywood.
I no longer have the dory skiff. In the mid-’80s, I think, I had sold it to a man who took it to Alaska. It last turned up on eBay in Connecticut in 2013, and the pictures posted with the ad seemed to indicate the boat was in very good shape. If it had been stored out of the weather, the plywood garboards might have been in good shape, even after 40-plus years. While building the skiff, I had studied Gardner’s 1977 volume, Building Classic Small Craft. In it, he notes that when using plywood for dory construction, “…coat the surface of the wood with paint and special sealers to prevent it from soaking up water too fast or drying out too quickly.” While several of the boats detailed in the book are made of plywood with joints covered with fiberglass tape set in epoxy, none of them are given overall saturation coats of epoxy. Instead, “before any paint goes on the plywood…the boat should be thoroughly soaked inside and out with a good wood preservative.”
In Gardner’s defense, at the time he wrote these two books, epoxy was still fairly new to amateur boatbuilding. The Gougeon Brothers on Boat Construction, which introduced wood/epoxy composite construction, was published in 1979 and provided a better understanding of the uses of epoxy. In the chapter, “Wood as an Engineering Material,” the Gougeons wrote, “our basic approach is to seal all wood surfaces with WEST SYSTEMS resins. This includes those that come into contact with air as well as those in contact with water.” Later books on composite construction, such as Devlin’s Boatbuilding, published in 1996, offered similar advice: “And always be sure to seal all plywood edges and surfaces with epoxy to ensure maximum longevity and help prevent moisture invasion and veneer degradation.”
For most of the boats I built in later years, I used a traditional approach and rarely used plywood. Then in 2003, I switched to glued-lap plywood construction to build Iain Oughtred’s Caledonia Yawl. I used his 1998 book, Clinker Plywood Boatbuilding Manual, as a guide and finished the BS-1088 with plywood primer and semigloss alkyd enamel, without first sealing it with epoxy. Oughtred was of the same mind and noted “I have never coated a boat with epoxy.” My Caledonia’s finish held up well during the 16 years the boat was kept in my garage, but it had to give up its place for another boat and spent 3 years outside under tarps. The paint has now developed a barely discernible pattern of fine checks.
In 2009, when my son Nate and his high-school pal decided to build an Escargot canal cruiser, I steered them to marine-grade fir plywood because it was less expensive than the mahogany options. The instructions called for sealing, priming, and finishing with marine or deck paint. Nate and I had seen another Escargot—built of fir plywood and painted—and noticed that the finish had checked. We would prevent that by sheathing the exterior surfaces in fiberglass and epoxy. After a dozen years of being parked on the driveway on the sunny south side of the house, covered with poly tarps, the Escargot’s plywood is without checks, with one exception: a 1”-wide gap between spans of fiberglass where the wood was protected by epoxy alone. Some significant cracks in the paint have appeared there.
The following year, 2010, I built HESPERIA, my garvey camp-cruiser, using BS-1088 plywood and finished with primer and paint. Only the cabin roof got a layer of fiberglass to give its 1/4″ plywood additional strength. The boat spends its time outside under tarps, and the painted surface is now covered with fine but easily noticed checks.
A teardrop trailer that I built in 2013, and now parked in the back yard, is in even worse condition. I’d built it with the same materials I’ve used for boats, and the plywood on the roof cracked so severely that a couple of years ago I had to peel loose veneer off and fill the voids with ’glass and epoxy before sanding the whole top to bare wood and applying 6-oz ’glass cloth and epoxy. The varnished mahogany plywood sides are badly checked in spite of being sanded and revarnished at least twice; the painted front end looked fine when I ’glassed the top, but it is now checked. I noticed one small area flanking a joint between plywood panels that was still in good shape. It had been protected by the epoxy I’d squeegeed alongside of the seam.
Two of my boats have survived for decades without any evidence of checking. One is a plywood Greenland-style stitch-and-glue kayak I built in 1994. It is sheathed inside and out with fiberglass cloth and epoxy, primed, and painted. While the kayak’s red topcoat has been worn away in places, there is no evidence of checking despite being stored outside for decades, sometimes covered with a tarp, other times exposed to the weather.
The other boat with its finish still unchecked is a decked lapstrake tandem canoe I built in 1988. I got the design from Canoe and Boat Building by W.P. Stevens, published in 1889, and followed the construction method describe by Thomas Hill in his 1987 book, Ultralight Boatbuilding. He, too, wasn’t in favor of an epoxy coating, writing “I do not recommend epoxy saturation for these canoes. Some people believe epoxy applied to plywood prevents checking. I’m not convinced.” He cites two boats that were badly checked in spite of five coats of epoxy on a transom in one case, and epoxy and fiberglass on the deck in another. I followed his advice and finished my canoe with primer and enamel.
Aside from the wear and tear caused by use, the paint and varnish on the canoe I built in 1988 has never been refinished and yet is still in good shape and So why did HESPERIA, which had received the same finish, fare so poorly after just 11 years? What differentiates the two is how they have been stored. That canoe has always been out of the weather, either in a basement, under the eaves on the shady side of a house, or in a garage. The cruiser has had only tarps to shelter it and they’ve done little to mitigate the effects of hot summer days.
While the advice I’d gathered over the past about using plywood fell into two camps—pro-paint and pro-epoxy—the experience I’ve gathered from the boats I’ve built says they can’t both be right, but there is a part of the discussion that seems to be missing from all of the books I’ve read: Where is the boat going to be stored? Primer and paint are inexpensive, get a boat finished quickly, and can last decades if kept out of the weather. Sunlight and moisture will take a toll on the plywood of a boat kept outdoors, even if under a tarp, and for those boats, epoxy saturation and fiberglass sheathing will add to the weight, cost, and labor but will buy time.