Boat Building

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Boat Building

This is a general resource page for people who BUILD boats... QUESTIONS?

I have been building boats since 1962 and I have collected a lot of information about the subject. I will organize. Sometime. Maybe soon.

A lot of the stuff I had collected last 20+ years is here: I'll try to update it here...

From Dave Carnell

Dave was an amazing guy, a DuPont chemist who built many boats and did extensive experiments with wood, fiberglass and epoxy. I enjoyed talking with him occasionally on boatbuilding forums and occasional email. He is gone now but some of his knowledge and information remains for us that Make Stuff. I have tried to grab it all over the years; what I have is HERE:


By: Dave Carnell

In 1978 I first used a plywood butt joint of fiberglass cloth and epoxy resin to avoid having to make a scarph joint (not easy and loses length)or use butt blocks (hard to work around). The joint is so thin that careful feathering of the edges makes it invisible.

In 1986 I wrote about the joint in Small Boat Journal. About the same time "Dynamite" Payson wrote in Boatbuilder about a similar joint concept. Years later I discovered that Joe Dobler had used the principle well before our publication, as had Jack Chippendale in England.

A piece of plywood bent around the side of a boat is carrying most of the load in its outer and inner plies. The load (stress) on the convex side (usually the outer) is a tension load trying to pull the wood apart. On the concave side (usually the inner), the load is compressive-the wood is being pushed together. The invisible butt joint makes two pieces of plywood one by building a skin of fiberglass and epoxy on each side. When you flex the joint, the load is carried entirely by those two skins you have built.

I made joints in various thicknesses of plywood and tested them by breaking them in flexure with the maximum stress applied at the joint. Joints that passed were ones where the plywood, not the fiberglass-epoxy resin joint broke.

My design basis for invisible joints in plywood is:

  • for 1/4" plywood, 1 layer of 6 oz. fiberglass cloth on each side;
  • for 3/8", two layers on the top (outside of bend) and one layer on the bottom;
  • for 1/2", three layers on top and two on the bottom;
  • for 3/4", four layers on top and two on the bottom.

Make the first fiberglass strip on top 2" wide and each succeeding one an inch wider. On the bottom side make the first strip 2" wide and the second one (if used) as wide as the widest strip on the top side. After you lay up the joint cover it with a piece of 4 mil polyethylene film and squeegee or roll it out. This presses the cloth layers together and feathers out the excess epoxy onto the plywood. Peel the film off after the joint cures and the surface is smooth and faired so that very little filling or sanding is required. If you use woven tape instead of pieces cut from cloth, the selvage may make a ridge at each side of the joint. A joint with a single layer of 6 oz. cloth on each side is about 0.020 in. thicker than the plywood at its thickest point and tapers off to zero at each side. Two layers on each side adds about 0.030 in. at the thickest point. The joint in 3/4" plywood with four layers outside and two inside is only about 0.045 in. thicker at its thickest point.

These joints are designed to use a minimum of material to get the ultimate strength. I would only make them with epoxy resin (not polyester resin) because: 1) epoxy bonds the glass cloth to the plywood in a stronger joint that will not peel apart; 2) epoxy will always eventually complete its cure; 3) there is no fire hazard with epoxy; and 4) there is less of a toxic hazard with epoxy.

Originally, both Payson and I made the joint on one side and turned the piece over to complete the joint. The turning over is fraught with danger of destroying the joint that is very weak at that point.

I have gone to laying polyethylene film on a smooth surface, laying the wetted out fiberglass tape (I use cloth to avoid the selvage) on that, epoxy coating the face of the plywood that goes against that, laying the plywood on the wet tape, filling any least void between the plywood edges with thickened epoxy (this is critical, as any voids between the butting plywood edges can make the joint weak), epoxy coating the upper plywood joint surface, laying on fiberglass and wetting it out, covering with poly film, laying on a smooth board, and weighting the assembly with concrete blocks. In fact, the last time I did it I laid up a sandwich of two 16' by 20" pieces for the side planks of a sailing skiff and cured them all in one operation.

If you are making joints in plywood thicker than -1/4", make the bottom side of the layup the one with the fewer number of fiberglass strips.


Here is an example of butt joints in 1/4" plywood for the sides of a JonBoat. Directions in previous section.

Preparing Layout --- Weights on joints --- After sanding before overall layer of fiberglass (CLICK Photo for larger)

JonBoatBuilt005.jpg JonBoatBuilt007.jpg JonBoatBuilt008.jpg



This is a distillation of my experience in using epoxy for 30 years and improving my techniques. I started using epoxy for boatbuilding in the 1960s. This was before Gougeon came out with their West® system. I was using generic epoxy from Defender and an amine hardener that was mixed 1:10 with the resin. Later I switched to Epon® resin and Versamid® hardener from a surplus outfit in CA. This was a 2:1 mix and far easier to use.

Then, as now, all resins and hardeners were made by a few major chemical companies. The companies selling products at retail develop their formulations from commercial products.

Resin and hardener are ingredients that have to be mixed in the correct proportion to cure to a solid with the desired strength and hardness. If you want the mix to cure faster or slower, you pick a different hardener. You don't change the mix ratio.

Epoxy is far superior to polyester resin because it sticks to just about all materials, while polyester is not even a reliable adhesive for laminating glass cloth to wood.

If you mix your epoxy in the correct ratio it will eventually cure. If the catalyst you add to polyester does not kick it off, it will never cure.

Epoxy resin and hardeners have shelf lives of many years. I am still using a two-part surplus military epoxy putty that was manufactured almost 25 years ago. The only exception to unlimited shelf life I have found with epoxy resins is that the hardener for 1:1 mix systems thickens and cannot be used after about a year.


The most important use of epoxy resin is as glue, including gluing fiberglass to wood. Its advantage over most other glues is that it will fill gaps; in fact, there always has to be some gap. If you clamp too tightly the epoxy will be squeezed out so that the joint will be weak. Adding filler to epoxy used as glue makes stronger joints, perhaps because the filler keeps too much resin from squeezing out of the joint. One-inch boards edge glued will break apart in the joint when it is flexed; add about 20% pulverized limestone and the glued joint breaks in the wood. I add about 10% limestone to resin when laminating fiberglass onto wood, also.


Fillers are added to epoxy resin to make putties for two kinds of uses that have greatly different requirements. Those used for structural joints alone or in combination with fiberglass should be as strong as possible. Putties used for filling and fairing must sand easily.

The best filler for structural uses is pulverized limestone (flour fine, not gritty as ground limestone is). It mixes to a putty that doubles the resin volume and is dense and strong. It is universally available as a fertilizer material at under a nickel a pound. It is difficult to sand. Portland cement is pretty much equivalent. Talc, another mineral, is almost as strong and sands easily. It also is thixotropic (the putty does not flow, but will spread). It is available from fiberglass supply houses at around a dollar a pound. For filling and fairing applications hollow bead type fillers sand most easily because they are hollow and break. There are three kinds of beads: thermoplastic (Microlight®) which can soften with heat; phenolic, which are usually dark-colored; and glass (Scotchlite®), which are white. The glass beads make the lowest density filler and are the lowest cost. White wheat flour from the kitchen is a pretty good filler for finishing putties.


A fiberglass-epoxy butt joint of plywood can be as strong as the plywood itself. See "Invisible Butt Joints" above. Right-angle joints in -1/4" plywood for rowing seat boxes, etc. can be made with just a 1/4" radius bead of epoxy putty on the inside of the joint. I tack such a box together with brass brads and then make the epoxy fillet joints. For angle joints such as chines in -1/4" plywood a 1-1/2" fiberglass strip laid over a -1/4" radius epoxy fillet on the inside and a 1-1/2" strip on the rounded outside edge gives a joint that breaks by pulling the plywood apart. Bulkheads secured by a 1-1/2" glass strip over a -1/4" radius epoxy fillet on each side fail in the plywood. All joints must have the weave of the glass cloth filled smooth for maximum strength. Many designs specify much more glass than needed. Make up short specimens of your joints, cure them, and test them-in a vise, by standing or jumping on them, or by running your truck over them. If the joint holds and the material breaks, your joint is strong enough.


The principal hazard of working with epoxy resins is from skin contact. The hardeners are the offenders. As a general rule, the lower the mix ratio, the less the hazard (2:1 is less apt to irritate than 4:1), but you should avoid all skin contact and wash thoroughly after any contact. Wash thoroughly before eating, drinking, or going to the bathroom. Gloves and clothing help protect you, if they are clean.


Vinegar - it's the best non toxic cleanup for non cured epoxy.

Zip lock bags - sandwich size are great for mixing by kneading, add thickener of choice, cut off the corner and used like a little cake decorator. Perfect for laying down small fillets.

Thinned with 10% to 33% lacquer thinner after mixing, makes a penetrating epoxy good for pre coating ply panels while they are still


You will note that I have not mentioned epoxy encapsulation; i.e., coating both sides of everything with several coats of epoxy resin. It has no advantages and is a waste of money and time that adds useless weight. It won't turn lauan underlayment into marine plywood, though it will make it cost nearly as much. It does not keep the water out of the wood boat that lives in the water and a dry sailed boat doesn't need it.


By: Dave Carnell

WARNING: Warning this article contains material that may be offensive if you think painting is more fun than boating.

When I bought my first yacht (27’ auxiliary sloop) for $300 in 1951 I quickly learned that if its for a boat, the same material costs several times as much as if it is for your house. Oakum was $1/lb. at the marine supply store; five pounds for a dollar at the plumbing supply store. Marine paint cost several times as much as house paint of similar composition. I worked for a major chemical company that also made paint and knew that their paint that made the most money and on which they spent the most on research was house paint. Houses are out in the weather all year-no winter cover or inside storage. Their owners expect to repaint them infrequently, such as every ten years or so. They also expect a good paint job will require little preparation before repainting. Back then the only house paints were oil paints, so my yacht was painted with top quality oil-based house paint.

All paints consist of binders or resins, pigments, solvents, and additives. The binder forms the film that sticks to the boat and holds the pigment there. The pigments color the paint, make it opaque and have a good deal to do with UV resistance. Solvents keep the binder dispersed or dissolved and the pigments dispersed in an easy to apply state. They allow the paint to be applied in the correct thickness and then evaporate from the paint film as it dries. Mineral spirits, a petroleum distillate fraction, is the most common solvent in oil-based paints. In latex paints, water is the major fluid. It does not dissolve the latex particles, but disperses them in suspension. Small amounts of special solvents are present to control the coalescence of the latex particles into a tough, tenacious film and to slow down the drying of the latex paint.

Through the years latex paints have developed to the point where 100% acrylic latex paints are better than oil paints on all counts. They are more durable and tougher. They resist chalking and fading, retaining their color especially well when exposed to bright sun. They are easier to apply, going on more smoothly and with less brush drag. They have less tendency to grow mildew. They have almost no odor and no fire hazard. Cleanup is with water. They can be recoated in as little as one hour.

The 100% acrylic latex is the key to the outstanding latex primers and paints now available. The weather resistance of these polymers parallels that of the acrylic molding powders that make red automobile taillight and stoplight lenses that last forever without fading. I checked out all the top quality exterior primers, paints, and porch and deck paints at both Lowe’s and Home Depot-they are all 100% acrylic latex products (the Glidden latex exterior primer at Home Depot used an organic nomenclature I hadn’t worked with for 50 years, but my Handbook of Chemistry and Physics translated it to 100% acrylic copolymer latex). All of the products are available as custom colors mixed to your desire.


Your new boat went together pretty fast-instant boat or tack and tape construction. What kind of a paint schedule can you use to get it in the water next weekend. Let’s say the inside will be all one color and the outside all one color, not necessarily the same as the inside. You can do the outside in one day, the inside the next, and give it a couple of days before you launch it.

Here is the schedule. Sand it all over with 60 grit and clean up the dust. Put on a coat of latex primer. That will raise some hairy fuzz, so after drying a couple of hours give it a once over with 60 grit to defuzz it. Put on a coat of your exterior latex paint. Gloss is the toughest and most durable, but also shows surface imperfections best. Semigloss is almost as tough, durable, and easy to clean as gloss while not showing surface imperfections. For me, it is the usual pick. I have stayed away from flat paint.

You won’t have to sand after the first coat of finish paint and you can easily recoat in the afternoon. That finishes half of the boat. The next morning turn it over and repeat the schedule for the other half of the boat.

If you use two colors on the outside of the boat, you will add another day to the painting. If you use different colors for the bottom and the side on the inside and have a steady enough hand to cut it in at the chine you can do it in one day.

While it is best to wait a week for the paint to dry hard, don’t let it keep you from getting in the water before next weekend.

A posting on the newsgroup on the Internet asked if latex paint was good below the waterline, as if it was going to wash off. Look around your neighborhood. All those houses painted with latex paint sit out in the weather all the time. My boats live in the water with their latex paint jobs. Platt Monfort recommends for waterproofing the Dacron® skins of his Geodesic Airolite boats “...the simplest method being a good quality exterior latex house paint.”

How long is the latex paint job going to last? My sailing skiff that lives in the water was three years old this spring. The inside, especially the bottom, was scroungy from bilge water and having been through two hurricanes, so I gave it a one coat repaint job this spring. It looked great until Hurricane Bonnie messed it up this year.

The 16-year old Uncle Gabe’s Flattie Skiff (Sam Rabl) built of ¼” fir plywood was painted when new and then about 9 years ago. It looks pretty scroungy, but the interesting thing is that while the paint on the wood has been scoured off by hurricane winds and general wear the paint on the epoxy-fiberglass joints in the sides is perfectly intact and looks great.

A fellow who was donating a boat to our local museum told me he had the real secret to boat painting. He had painted a production plywood boat with latex primer and latex paint. He was sanding the paint off and found it was almost impossible to remove the last traces of the latex primer because it had penetrated the wood to some degree. Well, nothing soaks into wood like water and some of the pigment particles are bound to be carried along with the water vehicle of the latex paint.

When I rebuilt my 1964 Simmons Sea-Skiff 20 I used a heat gun and a wide chisel to remove about a dozen layers of old oil paint. To repaint I used latex primer and then two coats of Lowe’s “Severe Weather” 15-year guarantee semigloss latex exterior paint custom colored to match the “Simmons blue” that was next to the wood. It has been three years and three hurricanes ridden out on the mooring since the boat was launched. Except where the boat has rubbed fenders or the edge of the float and on the cockpit floorboards the paint is in first class shape. I do need to repaint the floorboards. In my survey I found that Lowe’s has an exterior 100% acrylic latex skid resistant paint (Skid-Not®) that can be custom colored. I believe I will try it.

I am not alone in appreciating the outstanding performance of 100% acrylic latex paints for boats. Thomas Firth Jones, boat designer, boatbuilder, and author of Boats To Go wrote in Boatbuilder several years ago that he preferred latex paint over oil paint for boats for all of the reasons cited above. He did comment that he paints his tiller with oil-based paint because the latex paint stains there.

I was talking with “Dynamite” Payson one May weekend a couple of years ago and he told me he was going to repaint his skiff with latex paint that weekend.

Jim Michalak, boat designer and builder, uses latex paint on his boats.

Phil Bolger reported in Messing About in BOATS that his personal outboard boat is painted with semigloss latex house paint.

Boatbuilders are traditionalists and it has been a hard sell to get them to accept plywood, stitch-and-glue construction, epoxy adhesives, and other similar innovations. Don’t let tradition keep you from benefitting from the ease of application and outstanding performance of 100% acrylic latex paints.


by Dave Carnell

Once rot gets a toehold in wood it is difficult to cure completely--- it is like a cancer. Digging out the rotted wood will still leave spores and water in the sound wood. After you fill in the cavity with something like epoxy, the rot continues to flourish underneath. Products promoted to make rotted wood sound and stop rot penetrate only until they meet water, with which they do not mix. Under the solid repair rotting goes on. With one exception (more later), the commercial products sold to treat dry wood to prevent rot are completely ineffective against established rot in wet wood because they are dissolved in petroleum solvents and oil and water do not mix.

There are two commonly available inexpensive materials that will kill rot in wood and prevent its recurrence. First, there are borates (borax-boric acid mixtures) which have an established record in preventing rot in new wood and in killing rot organisms and wood-destroying insects in infested wood. Second, there is ethylene glycol, most readily available as auto antifreeze-coolant. Glycol is toxic to the whole spectrum of organisms from staphylococcus bacteria to mammals. All of the published material on its effectiveness against wood-destroying fungi and insects that I am aware of is the result of my investigations over the past 15 years.

Both borate solutions and glycol penetrate dry and wet wood well because they are water-soluble; in fact, penetration by glycol is especially helped by its extreme hygroscopicity-its strong attraction for water. For both, the fact that they are water-soluble means they are not permanent solutions to rot in wood that is contnually exposed to water-below the waterline and in ground-where they will eventually be extracted-dissolved out.

I first was interested in glycol as a wood-stabilizing agent, where it is in many ways superior to polethylene glycol (PEG), and it was during this work that I realized the useful effect of glycol on organisms, though I was pretty dense in interpreting the first experiment.

The ladies immerse the stems of greenery such as magnolia branches in glycerin to keep them green. Glycol is very similar to glycerin in all its physical properties and much cheaper, so I stuck a magnolia branch in antifreeze. The next day it was brown. After the third attempt I tumbled to the fact that the glycol was killing the greenery.

This was the reason that glycol never replaced glycerin in applications such as a humectant for tobacco and an ingredient of cosmetics and pharmaceutical ointments, though it had all the desirable physical properties.

I had two 2" thick slabs of a 14" diameter hickory tree that had just been cut. I treated one with antifreeze and left one untreated. I was looking at wood stabilization, not rot prevention. After about six months stored inside my shop the untreated control was not only cracked apart, but it was sporting a great fungal growth, while the treated slab was clean.

The local history museum wanted to exhibit two "turpentine trees", longleaf pines that had many years ago been gashed to harvest the sap that made everything from turpentine to pine tar. The trees delivered to us after cutting were infested with various beetles and had some fungal growth. I treated them with antifreeze outside under a plastic tarpaulin every few days for three weeks. They were then free of insects and fungus and have remained so after being moved inside and installed in an exhibit over four years ago.

I took three pieces from a rotting dock float that were covered with a heavy growth of fungus, lichens, etc. I treated one with antifreeze painted on with a brush, the second with a water solution containing 23% borates (as B2O3), and left the third untreated as a control. They were left exposed outdoors and were rained on the first night. By the next morning the growth on the antifreeze-treated piece was definitely browning and the borate-treated piece showed slight browning. After two months exposure to the weather the growth was dead on the antifreeze- and borate-treated pieces and flourishing on the control.

I have a simple flat-bottomed skiff built of plywood and white pine, which has little resistance to rot. After ten years some rot developed in one of the frames. It may have begun in the exposed end grain. It consumed the side frame, part of the bottom frame, and part of a seat brace fastened to the side frame. The plywood gusset joining the side frame to the bottom frame was not attacked. I excised the rotted wood, saturated all with ethylene glycol antifreeze to kill all the rot organisms, and there has been no further deterioration in four more years afloat with wet bilges. I have not replaced any pieces, as I am building another boat that can replace it; that is more fun, anyway.

I have a 60+ year old case of the fungus infection known as "athlete's foot". Many years ago it infected the toenails extensively. The whole thing was pretty grotesque. My dermatologist and druggist both assured me there is no known cure. About six years ago I started using antifreeze applied under the nails with a medicine dropper about every five days. The professionals are technically right. I have not completely cured it, but the nails have grown out pink and thinned almost to the ends and I never have any trouble with blistering, peeling, or itching between the toes as I had had for six decades. No drug company is going to have any interest in this because the information has been in the public domain for so long that there is no opportunity for any proprietary advantage. The various wood-rotting organisms cannot be anywhere near as tough.

Glycol by itself has one big advantage over solutions of borates in either water or glycol. Glycol penetrates rapidly through all paint, varnish, and oil finishes (except epoxy and polyurethanes) without lifting or damaging those finishes in any way. You can treat all of the wood of your boat without removing any finish. The dyes in glycol antifreeze are so weak that they do not discolor even white woods. Once bare wood has been treated with glycol or the borate solutions and become dry to the touch it can be finished or glued. If a borate solution leaves white residues on the surface, it will have to be washed off with water and the surface allowed to dry.

This is my preferred process to treat rot. Once you find soft wood or other evidence of rot, soak it with antifreeze even if you cannot do anything else at the moment. Paint it on or spray it on with a coarse spray. Avoid fine mist-like spraying because it increases the likelihood that you will breathe in unhealthy amounts of glycol. Put it on surfaces well away from the really damaged wood, too. Use glycol lavishly on the suspect wood, which will readily absorb 10-20% of its weight of antifreeze.

Next dig out wood that is rotted enough to be weak. Add more glycol to wet the exposed wood thoroughly. Then add the 25% borate solution of the recipe below so long as it will soak in in no more than 2-3 hours. Then fill in the void with epoxy putty and/or a piece of sound treated wood as required. The reasons I use borates at all are: 1) it is a belt-and-suspenders approach to a virulent attack, and 2) over a long period glycol will evaporate from the wood; especially, in areas exposed directly to the sun and the high temperatures that result.

If there is any question about water extracting the glycol or the borates, you can retreat periodically with glycol on any surface, painted or bare, and with borate solutions on bare wood.

Glycol's toxicity to humans is low enough that it has to be deliberately ingested (about a half cup for a 150 lb. human); many millions of gallons are used annually with few precautions and without incident. It should not be left where children or pets can get at it, as smaller doses would harm them, and they may be attracted by its reported sweet taste that I have confirmed by accident. The lethal dose of borates is smaller than of glycol, but the bitter taste makes accidental consumption less likely.

Borate Wood Preservatives

Commercial and Home-Brewed

Tim-Bor®: about $3/lb. plus shipping.

Ship-Bor®: Same as Tim-Bor®; $19.95/lb. plus $2 shipping.

Bora-Care®: $70/gal. plus shipping.

Home-Brew Water Solution of Borates:

Based on U.S. Navy spec. of 60% borax-- 40% boric acid (this ratio gives the maximum solubility of borates in water); 65% water, 20 %borax, 15% boric acid; 15.8% borates; borax costs 54 cents/lb. (supermarket), boric acid costs about $4/lb. in drug stores (sometimes boric acid roach poison, 99% boric acid, is cheaper in discount stores); equiv. to Tim-Bor® or Ship-Bor® at 30 cents/lb. To make this solution mix the required quantities and heat until dissolved. The boric acid, in particular, dissolves slowly. This solution is stable (no crystals) overnight in a refrigerator (40°F.), so can be used at temperatures at least as low as 40°F.

Home-Brew Glycol Solution of Borate:

This is equivalent to Bora-Care® diluted with an equal volume of glycol to make it fluid enough to use handily; 50% glycol antifreeze, 28% borax, 22% boric acid. To make a stable solution you mix the ingredients and heat till boiling gently. Boil off water until a candy thermometer shows 260°F. This removes most of the water of crystallization in the borax. This solution is stable at 40°F and has a borate content of 26%. With antifreeze at $6/gal. and borax and boric acid prices as above, this is equivalent to Bora-Care® at about $15/gal.

FROM Jim Michalak: Plywood


This from Jim Michalak's April, 2002 newsletter

I hear Jim is about to publish a book. Judging by the quality of information in his newsletters, I say, buy it!

Blame it all on the late Pete Culler. He was talking about making boats and boating things with Weldwood glue, which is a powdered glue that you mix with water. Very easy to use but the manufacturer says it is water resistant, not waterproof. The usual way to test glue quickly for waterproof is to boil it for an hour. Culler said something like "If you're going to boil your boat, don't use Weldwood" and was widely quoted thusly, including by Harold Payson who has done more to educate us about plywood boats than anyone. So I made several boats using Weldwood and still have several around and don't worry about it. But one of them, a Bolger Jinni that was my second homemade boat, had to sit outside for several years and it often filled somewhat with rainwater in storage. After a few years of this treatment I noticed the internal chine logs were getting spongy where they were constantly wet and little leaved plants were growing out of them at times. One year I chopped out the bad parts and noticed there was no sign of any glue in those joints, they were held only by nails and the external fiberglass tapes. I gave it little thought thinking that I didn't get enough glue in the joints during assembly. I repaired the chines with fiberglass/epoxy taped seams and made a cover for the boat and improved the drainage. But a year or two later the mainmast, which was laminated from two pieces of wood, came apart at the base where it stuck out from under the cover. The Weldwood there was also gone. And I came to the conclusion that Weldwood, indeed, was not totally waterproof. And the boil test was perhaps not a lot of hooey after all!


Plywood glue has always caused worries and since it varies so much from load to load I began to advise that builders boil a piece if they were at all suspicious. I got a letter from one builder who had boiled some "good buy" plywood and it delaminated after 20 minutes in the boil pot. Was that good enough? I didn't really know since I had never boiled anything!

So I rounded up some different plywoods that I had out in the shop, all of which were supposed to have "exterior" glue. I put them in a pot and, when my wife was away, boiled them on the stove. My first sample was a piece of cheap 3/8" BC pine. After an hour in the boil it showed no sign of delamination.

My second sample was a piece of 3/8" (actually slightly less) exterior plywood that I had used for the bottom of my AF4 which I built four years ago. This had two thick crude looking plies of fir (I think) with a thin skin facing of a flawless mystery wood. After an hour in the boil it showed no sign of delamination.

My third sample was a piece of cheap 1/4" lauan underlayment which was sold at a real lumberyard, not a depot type of store. The sheet was unmarked but the yard said it had waterproof glue. After an hour in the boil it showed no sign of delamination.

So the builder's plywood that was delaminating after 20 minutes in the boil was clearly not the same stuff I had. And now more than ever I think the boil test is a good quick way of checking glue.


With the plywood testing done I thought to test in the same way some glues that have been used in cheap boatbuilding. Here are my results. Weldwood. A few years back I cut a small section off the edge of my Birdwatcher's centerboard and I tested that piece. The board is laminated from layers of 1/4" plywood using Weldwood water mix glue. After an hour in the boil pot it was still quite together which is interesting since this is the glue that caused all the furor in the first place. I was able to pry it apart with a knife but I'm still not sure what that means.

Tightbond2, it says "not for use below waterline" right on the bottle. Guess what? After an hour in the boil it held up as well as any glue tried. PL Premium is a construction glue that you use in a caulking gun. Very handy and thick so exact fits or lots of pressure aren't needed. I had a piece of an old project, about 3 years old, that had a 2x2 glued to 3/8" plywood with this glue and it had been outside the entire time with no sign of failure. After an hour in the boil pot it looked quite solid but when I gave the glue line a pry with a knife it popped apart cleanly where the glue met the wood. Strictly speaking I suppose that is a failure.

But here is another test result from a recent email I got: " First, I am using PL premium for the glue. I tested the strength by gluing up two small 2 X2's, letting it dry and I soaked it in water for a week(submerged). I then took a 5 lb sledge and commenced on beating it soundly. It held. I was impressed. I did the same with a liquid nails product and it broke apart with handstrength." Epoxy, in this case a bit of "DC7" which is an epoxy paste in a little can from the hardware store. I've used it with total success to stop rust holes in old fuel tanks. After an hour in the boil it held well but clearly was getting very soft, as did the PL Premium. Epoxy is well know to have strength problems at higher temperatures.


Like Pete Culler I think all the glue are sufficient for a boat that is stored under cover. As for the long term effect of water on the glues, I'm not sure the test proves anything. The idea of " I soaked it for a few weeks" may not be good enough for a boat that will sit in the water (or fill with rainwater) for months at a time. I would not use any plywood that didn't pass the one hour boil test. After all, the pieces I used passed and they were from very cheap sheets. And just because the plywood passes the boil test, it may delaminate in places where not enough glue was used. The lauan I tested was like that - bubbles and peels at edges where there isn't enough glue. A Final Thought..... I saw this posted by Dave Carnell on "....the real advantageof interior glue is that it is a cold press operation vs. the hot press operation required for exterior glues. The durability of the interior glues is surprising in some ways. I once tested lauan underlayment by soaking in water until it sank, drying at 150°F. in an oven, resoaking, and redrying. It didn't delaminate. I also tried freezing it while wet and it held together. When I bent it for boat planking on a hull being built outdoors, it came apart as soon as it got rained on. Once it is stressed, the whole game changes. I have seen people talk about testing in a dishwasher, but that isn't good enough. Boil it for an hour or two. If it doesn't hold together, it is no good."



This is the ~gallon 126.6 oz size with the West supplied pumps

Example: Will publish spreadsheet later

Caption text
FULL 105B with Pump 167 167
EMPTY 105B with Pump 15.50 15.50
105B NOW 63.50 47.00
Remaining 48.00 31.50
Per Pump(Both) 0.88 0.88
Remaining Pumps 54.55 35.80


  • GLOVES - Nitrile