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Epoxy Tricks


Howard

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Back to my mention of thinner epoxies. I think most of us would be hard pressed to find clear evidence based on scientific research that can point to one aspect of epoxy (or for that matter.....construction techniques in general) being better than another. So what most of us do is default to anecdotal evidence, either our own or from someone else, and of course it is hard to avoid the influence of marketing. In the epoxy world, System 3 has probably taken the marketing aspect farther than anyone else. They have developed products for every occasion.

 

Faced with all these choices, and having been cursed with a curious and skeptical mind, early on I developed a pattern of taking recommendations, either from manuals, website, individuals, and of course the manufacturers, and testing them.  My shop is cluttered with all manner of crap I've messed with over the years. Everything from busted fillets to the mil thickness of various weights of wetted out glass cloths.

 

One of my tests was of the lamination strength of various epoxies. I simply glued up some joints using various epoxies, then broke them, measuring the pounds of effort it took to get the piece to fail. I did the same thing on various types of wood. Certainly NOT up to scientific methodology standards, but for the purpose of satisfying my curiosity, good enough. Anyway, MAS markets their FLAG product (which stands for Filleting, Laminating And Gluing) for those specific purposes. Their other product is Low Viscosity, which is recommended for surface coatings, glassing, etc. FLAG is thicker and Low Vis is thinner. Other than being formulated to be thicker or thinner, are they the same? I don't know. Unless a person had access to the technical specs (and ability to understand and comprehend their meaning), you would not know, so the average consumer is likely going to simply default to the marketing information and leave it at that. The marketing implication is, though, that one is better for those uses than the other.

 

So my assumption going in was that FLAG would give me the strongest joint and all others something less. I was simply curious how much less. Imagine my surprise when the B&B stuff surpassed it.......and not by a little, but by a lot.

 

Could it be that much stronger? Probably not. What was different was the thinner stuff soaked in a lot farther. The yellow pine wood failed before the joint did and deep inside the margin of the joint. The FLAG failed at the joint, and it appears to me, because it was thicker, never got past the surface. I would imagine each to be equally as strong given a fair test to measure them.

 

Bottom line is, as Paul suggests, most of these 2:1 marine epoxies, from reputable sources, are plenty strong and as long as the builder does a good job of measuring, mixing and applying them, they will be stronger than the wood they are joining. And contrary to some marketing claims, experienced users can take the various additives and use one base epoxy resin for a whole variety of uses.

 

PS: Black Locust is an incredibly strong, dense, rot resistant wood, but none of the epoxies I tried on it worked. They all failed at the joint and with remarkable ease. If a person wanted to use that for something, they better be thinking mechanical fasteners.

 

The unsung hero was plain old S-P-F construction lumber. It glued well with everything and failed at almost the same levels as yellow pine and fir.

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Moving on to additives and thickeners, not much new here. Each of us probably has our own favorites.

 

This video is instructional on many levels:

 

 

First is the mixing process.......standard cup and stirring stick. The second is how the guy goes about measuring his wood flour.......by hand and by trial and error. Of course, no discussion about this can be complete without reference to ketchup, mayonnaise, peanut butter, etc.

 

What I have found worked better for me was to find a volume of additive, relative to the volume of epoxy, that gave me the consistency I wanted. Consistency as far as the thickness I wanted, but also consistency batch to batch. I have found that somewhere around 1:1 volume of epoxy to additive (depends on which additive) makes a pretty good adhesive. Around 1:1.25 to 1:1.5 epoxy to additive for a non-sagging fillet mix. So if I have a single pump batch of 45 ml of epoxy and I'm making fillets, I have about 60 ml of additive in a cup ready to go. Speeds the process along and the end result is pretty consistent.

 

Stirring sticks work OK on small batches, but on larger ones, I'm not above using a paint stirring contraption on the end of an electric drill. For larger batches, my goal is to get it mixed and out of the cup. The faster I can get it mixed, the faster I can get it out of the cup or get the additives started. With larger batches, and especially in warmer weather, a large batch can go off on you before you are ready.

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I built a Black Locust raised panel door for a Concordia 39 yawl, the one that goes to the foc'sle.  Abeking and Rasmussen seem to have used Mahogany and Black Locust interchangeably with total randomness.  Many Concordia owners have removed that door as it is really in the way.  The door opens into a small hallway adjacent to the head door that also opens into the hall.   As a result, some are lost and now some boats don't have one at all.  This was the case with my customer.   I did a lot of gluing, and some laminating for rails and stiles as I could not find sufficiently thick stock.  I used West Epoxy for all of the gluing and had no issues at all.  I have never had issues gluing Teak with epoxy either.  The only thing I do when working with both of these that may be different than common practice is to clean the mating surfaces with acetone immediately before gluing.  So I guess another trick or technique for gluing oily woods with epoxy, or anything for that matter is to remove the oil from the gluing surfaces first.

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The other thing I ran into during my last build was that certain finishes do not play well with an epoxy substrate.  A polyurethane varnish softened up my nicely epoxied gunwales and I had to the whole job again. Switching to a traditional spar varnish with a high UV content solved the issue and looked great when done.  Maintenance has been a simple sand and recoat with varnish each year for the past 5 years.  

 

David:

 

I was of the opinion that fully cured (reacted) epoxy is more or less inert. Once it is fully cured, even the normal solvents used for cleanup, such as alcohol and vinegar don't affect it. Some will even wipe cured epoxy down with acetone after sanding and prior to painting or finishing (probably a bad idea and not necessary.....I'd rinse it with water instead). I can't imagine there is anything in polyurethane varnish that would harm it. On the other hand, if it were still green, and not fully cured, it might. The only thing I can think of that will soften fully cured epoxy is heat.

 

The idea of using epoxy as a base coat for varnish probably came from the companies selling the stuff. I seem to recall System 3 mentions it in their literature. A couple coats of epoxy was supposed to replace 5 or 6 coats of varnish. Then varnish over the epoxy to give it UV protection (of which epoxy has none).

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My favorite trick is to get rid of the pumps and measure the ratio with a scale. I don't remember where I got it, but I have a 2:1 epoxy weight chart next to my cheap harbor freight gram scale. It is so easy to mix without those silly pumps. Put about 2/3rds of what you think you need and get the weight, look at the chart and squirt enough of part b until the weigh adds to the total and mix it. Done. I replace my caps with mustard style caps and you can meter out a single drop if you need to. I cover the scale with a piece of waxed paper and it works great.

 

One other thing. I do all my epoxying in a basement that is about 58 degrees F year round. I think because of that, the first gallons of Epoxy I bought from B & B crystalized within a month, including the epoxy in the pumps. What a mess! I though maybe it was something in B & B's mix. Heating it was a pain and didn't score many points with my wife when I did it in the kitchen! I bought the next couple of gallons from Duckworks. Same thing! I now keep the epoxy nicely snuggled up next to my hot water tank and my infrared thermometer says it all stays around 75 degrees and hasn't crystalized again. Of course when I'm ready to buy again I will buy the Epoxy from B & B. It wasn't their fault.

 

Take Care,

Steve 

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I know of no paint of varnish, nor even solvent that harms cured epoxy either Howard.  My cleaning solvent of choice to remove dust and such after sanding, whether sanding epoxy or varnish or paint is alcohol.  The reason being that it is fairly cheap and evaporates completely and quickly.  The problem with water is that it takes a good while to dry completely and even if it appears dry to the touch, it may not be.  Any moisture will significantly damage a coat of a solvent based coating or epoxy.  I do not advocate alcohol to remove blush, this is where water is called for.  And then I simply wait a loooooong time before applying anything else.  Or if I am in a hurry,  I wipe again with alcohol as moisture is absorbed into in solution and then dries virtually as fast as the alcohol would alone.

 

I think the most common reasons for wanting to use epoxy as a base for varnish are one,  that it gives one a sense of making the coatings bomb proof.  This I believe is a fallacy.  The other is that it goes on thick and replaces several coats of varnish in the build up process.  So people are looking to alleviate or at least minimize  maintenance  and be lazy in the process.  I am all for that, but I just don't think it works over solid wood detailing, spars or other such non-flat or fair curved surfaces.  And like I said in my last post; when there is damage, the repair is extremely difficult to do well.  With varnish one simply removes the varnish with a heat gun, sands out the blemish and recoats.

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My favorite trick is to get rid of the pumps and measure the ratio with a scale. I don't remember where I got it, but I have a 2:1 epoxy weight chart next to my cheap harbor freight gram scale. It is so easy to mix without those silly pumps. Put about 2/3rds of what you think you need and get the weight, look at the chart and squirt enough of part b until the weigh adds to the total and mix it. Done. I replace my caps with mustard style caps and you can meter out a single drop if you need to. I cover the scale with a piece of waxed paper and it works great.

 

That sounds like a good trick that I had completely forgotten about. As I recall, System 3 was a strong proponent of this, and especially so for some of the special products, like Gel Magic and perhaps their fairing compounds, that do not work well when measured by volume.

 

I did a quick search and found plenty of information on weighing epoxy by volume. Some of it kinda scary.......but that is nothing new. Seems Duckworks has a chart similar to what you describe. First thing that pops out is the epoxy and hardeners do not have the same weight per volume, so the weight is not in the same 2:1 ratio as it is by volume. The Duckworks chart has the hardener at 43%. On the Progressive Epoxy Polymer's jugs, Paul actually lists the mix ratio by weight as well as volume (2:1 and .422 hardener to epoxy). So that would be an easy calculation.

 

? grams epoxy x 143% = total weight of the batch.

 

If a person wanted to test this with an unknown brand, and was now using pumps, they could put in one pump epoxy, weigh it. Then one pump hardener, weigh the combined batch. Do the math to get the percentage.

 

I'm going to try it.......and I already have the gram scale.

 

BTW, most serious bread bakers measure their ingredients by weight. A much more accurate way (weigh?) of assembling a recipe.

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When I think back to the epoxy gooping up under the polyurethane, I know it was very humid, and I was not using my favorite brand of epoxy.  The combination of humidity, poor mixing or ratios, and inadequate time most probably led to the problems encountered.  I know that after I scraped it all off and did it again it was MUCH better.  

 

Dave - 

I promise to NOT put epoxy on the mahogany gunwales, and will use straight spar varnish this time around.  If I don't like it...then I can always retreat to my old stubborn ways.  

 

I like the idea of mixing by weight rather than volume.  

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Dave-

I promise to NOT put epoxy on the mahogany gunwales, and will use straight spar varnish this time around.  If I don't like it...then I can always retreat to my old stubborn ways.  

LOL, well said Dave.  A truly intelligent person listens to the ideas of others yet always remains a skeptic. 

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Fillets. If you have not yet downloaded the West Systems Epoxy Book, I suggest you do so. Fillets are mentioned in detail starting around page 101 or so. This is certainly one area were the West and S3 literature differ.

 

While most of us recognize that there are scantlings for plywood, etc, what may not be as well know is there are also scantlings for the size of the epoxy fillets, depending on the size of the plywood. Those appear to be much larger than I knew.

 

I have two sources that are suggesting the radius of a structural fillet to be as much as 3x the thickness of the plywood. So for 1/4" plywood, that would be a radius of 3/4" and meaning the diameter of the fillet tool would be twice that, or 1.5 inches. That is much larger than I have been using, and if this is true, I need to beef things up considerably. A similar version of this story places the run out of the fillet up the side of the panels to be 2x the thickness of the plywood. That is less than 3x the radius, but is still bigger than I have been using.

 

Years ago I did a fillet test, as the West literature suggests and glued up a number of fillets on 3/4" marine fir plywood. These were done with fillets alone (no tape), but also with various levels of tape over the joints. In every case, the fillet held and it was always the wood beneath it that gave way. The radius of these fillets was no more than 1/2".....much smaller than suggested above, and about all tape did was to increase the area of plywood being peeled off. Of course that was with fir and other plywood would be different. Best advice I can see is to make them big enough the wood always fails first and can't see how making them bigger is going to help beyond that.

 

This is one are I'd like to see considerable discussion on.

 

 

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Years ago I did a fillet test, as the West literature suggests and glued up a number of fillets on 3/4" marine fir plywood. These were done with fillets alone (no tape), but also with various levels of tape over the joints. In every case, the fillet held and it was always the wood beneath it that gave way. The radius of these fillets was no more than 1/2".....much smaller than suggested above, and about all tape did was to increase the area of plywood being peeled off. Of course that was with fir and other plywood would be different. Best advice I can see is to make them big enough the wood always fails first and can't see how making them bigger is going to help beyond that.

This is one are I'd like to see considerable discussion on.

 

Interested in more specifics of your test failures... referring to Figure 11-18: cross section A (wood failure) and cross section B (joint failure) as shown on Page 103 (Chapter 11 of "Gougeon Bros on Boat Construction").

Would you comment and compare your testing failures to those shown. 

 

I found it very interesting that the "good" results (sketch A attached) are described as there being no failure at all in any part of the fillet-to-wood join. This was totally unexpected by me, having read that information many times over during the 1970's/ 1980's - I still had not retained just what an acceptable failure mode would look like.

 

As far as System 3 vs West... I switched to System 3 because I liked the "less brittle" character of that product and, besides being surprised, also find it interesting that the difference in fillet size is so pronounced.

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Tom:

 

The failures in my test were of the type in Figure B, with the wood peeling up from below. Except it never broke free at the top.......the plywood face always failed at the tip of the fillet on the bottom or along the base. Even with tape and fillets on both sides, the face of the bottom or horizontal plywood the vertical piece was glued to always peeled off and lifted up. Again, this was with fir plywood. Would be a good idea to repeat this with the Meranti I'm using for the Princess. And do it with fillets of ever increasing size to see if it's possible to get a piece of plywood to snap off as shown in Figure A. Structural wood, such as pine, might, but not sure about plywood.

 

The other question I had after conducting this test was the need for multiple layers of tape. If one layer of tape was strong enough to peel the face up, what more would additional layers do? Chain is being only as strong as it's weakest link......in short, no need to over build things.

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I build in a detached, unheated garage and have installed a night-light socket and bulb in the cabinet I keep all my products that are damaged by the cold. Just turn it on when the nighttime temps are going to be below 40.

 

I heat my epoxy that has been idle for a few months before I use it, stirring well before measuring out amounts.

 

My preference for measuring epoxy is by weight using a scale. This method seems to use more hardener but a little hotter mix works well when it's cold.

 

Bill

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Storing epoxy hardener in the same cabinet as solvent based materials is dangerous.  The resin is a solvent based material and is flammable.  The hardener is an oxidizer.  Adding electricity and heat to that cabinet makes it significantly more dangerous.  OSHA prohibits all of those (stored together, heat in the cabinet, electricity in the cabinet) in commercial establishments. It wasn't clear what exactly you stored in the cabinet, but thought you might want to know Bill.

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Speaking of fillets, when one is making fillets with radius 3x where x is the thickness of the ply, we're talking significant volumes of goo to be extruded into (sometimes) hard to reach corners.  Do the smart guys use the fillable caulking tubes such as West sells for this?  These would seem to get a little awkward to reach into some of the nooks and crannies once one starts installing nooks and crannies..  Could we get some comments on these tubes and maybe as well on any alternative methods, cake frosting bags perhaps.  At the stage I'm at on my build haven't needed to do a lot of that yet but have tried zip lock bags with some success, but very messy and a good deal of wasted goo.

 

I know that the early fiberglass boats were very flammable.  I'm talking way back yonder.  I saw one go up in smoke.  This was in the mid fifties and I'm guessing this boat was built using polyester resin.  The West System manual mentions that curing epoxy can get hot enough to ignite nearby combustibles but doesn't seem to say that the  epoxy itself is combustible either cured, uncured or the separate components.  This question crossed my mind a while back when, having a pump full of crystallized epoxy, not wanting to bother the dear wife for her hair dryer, I (tenderly) warmed it up with my heat gun which i believe is 1500 watts.

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Storing epoxy hardener in the same cabinet as solvent based materials is dangerous.  The resin is a solvent based material and is flammable.  The hardener is an oxidizer.  Adding electricity and heat to that cabinet makes it significantly more dangerous.  OSHA prohibits all of those (stored together, heat in the cabinet, electricity in the cabinet) in commercial establishments. It wasn't clear what exactly you stored in the cabinet, but thought you might want to know Bill.

 

Dave:

 

Are you saying OHSA prohibits storing epoxy resin Part A and hardener Part B together in a heated cabinet? The West System's epoxy book suggests doing that very thing by storing them in an old refrigerator with a light left on. If true, they need to revise their book and get that out of there. A lot of people are doing it. Mine are stored side by side, but on an open shelf.

 

Edit: It was not the West System's book that talked about using a refrigerator to store epoxy. It was Devlins book on Stitch and Glue construction. Has a picture and everything.

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Speaking of fillets, when one is making fillets with radius 3x where x is the thickness of the ply, we're talking significant volumes of goo to be extruded into (sometimes) hard to reach corners.  Do the smart guys use the fillable caulking tubes such as West sells for this?  These would seem to get a little awkward to reach into some of the nooks and crannies once one starts installing nooks and crannies..  Could we get some comments on these tubes and maybe as well on any alternative methods, cake frosting bags perhaps.  At the stage I'm at on my build haven't needed to do a lot of that yet but have tried zip lock bags with some success, but very messy and a good deal of wasted goo.

 

I expect you will get a lot of suggestions on this one. For larger areas, the plastic bags work best for me. Once the panels are fixed in place so they won't move, I wet out the fillet area with mixed, but unthickened epoxy. For me, this serves two purposes: first, I figure epoxy thickened enough so a fillet won't sag is not going to soak very deep into the wood fibers, so any endgrain isn't going to get coated and what contact there is will only be to the surface. Second, thickened epoxy will tend to slide around on the unthickened stuff, so I stand a better chance of forcing it into those nooks and crannies you refer too if it's sliding around on liquid goo. That is also helped by squeezing it from the bag into the direction I want it to go. The bags are more compact than the tubes would be and serve the same purpose.

 

Some of the mess seems to come from filling the bags. I'm generally using sandwich size, or no larger than quart sized and I use the type with the slider on them........not the type that "zips" together. (Great Value brand from Walmart are a great value for this). In my experience, if you get anything on the "zips", they tend to not stay closed. With sliders, it doesn't seem to matter. Also, to load them, put the bag inside a tin can or mixing cup and open them up, draping the top of the bag over the rim of the cup.....the larger the holding cup the better, as it really forces the mouth of the bag open. That helps eliminate any spillage and any chance of getting epoxy on the closing edge. Get it in the bag, zip it shut, snip a corner and get busy pushing it out. With a little practice, you can get the vast majority of it out of the bag, so there is very little waste. Depending on the hardener used and ambient temps in play at the time, this is a race between getting it mixed, bagged and into place before it starts heating up on you. If you feel any heat at all, you are at the limits of what you can do. Once epoxy starts heating up to the point you can feel it, you have a wildfire on your hands that likely can't be stopped. Since the speed at which it reacts (cures) is dependent on heat, and once it starts generating it's own heat, the reaction progresses at an ever increasing geometric rate. Regardless of what method you use, this is the always present factor you have to be mindful of. Until you get a feel for what you can do, start with smaller batches and work you way up to the limits of what you can handle.

 

Instead of bags, I believe others recommend using a large flat surface........get the thickened epoxy out of the cup and onto what is essentially the same thing as a brick layer's hod for mortar. That spreads it out to give you some operating time and they will use paddles or stirring sticks to spread it and work it into place.

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My preference for measuring epoxy is by weight using a scale. This method seems to use more hardener but a little hotter mix works well when it's cold.

 

Bill

 

Bill:

 

Measuring with a scale should give you the exact same usage rate as with volume, unless you are mixing 2:1 by weight. The hardener is slightly lighter, so you use less of it by weight. (Five gallon bucket of ping pong balls will weigh less than a five gallon bucket of rocks......but both fill an equal volume). Depending on the epoxy (all mix in similar but different ratios by weight), most 2:1 epoxies by volume will work out to 1:0.43 by weight. (Example........100 grams Part A : 43 grams part B ). After you have weighed those out, measure the volumes. The hardener should be half the volume of the resin. And they should always be in this proportion, regardless of temps or conditions.

 

The "hotter mix" theory comes from using polyester resins, where you can alter the reaction rate of the cure by adding more drops of catalyst to speed up the reaction rate. That is verboten with epoxy and doing so may result in a failed batch.

 

If you want a faster cure rate in colder temps, switch to a different hardener, or find a way to increase the ambient temps of your work area.

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Still scratching my head on the issue of the size of epoxy fillets. The West chart Tom referenced up above suggests the radius for a structural fillet for 1/4" plywood to be 7/8", which translates into a diameter of a fillet tool to be 1 3/4" inches. That isn't a radius of 3x but 3.5x. And a tool for a cosmetic fillet to be almost 4 inches in diameter. For 1/4" plywood? Ouch.

 

An extension of the rule of thumb for the runout to be 2X the thickness of the plywood is for the depth of the fillet itself to be equal to the thickness of the plywood. On a 90 degree (perpendicular) joint, that would place the depth of the fillet at 45 degrees to be 1/2" for 1/2" plywood. That results in a radius of about 1 1/8" vs. 1 1/2"  that the 3X radius rules suggests to join 1/2" plywood. That seems a bit more reasonable and realistic, but is probably still larger than what a lot of folks are using. BTW, the 3X rule leaves a fillet that calculates to a depth of about 5/8" when using a radius of 1 1/2 inches.

 

Complicating this even more is that unless the angle of the fillet is perpendicular, or 90 degrees, the angles will either be obtuse or acute (more or less than 90 degrees). If the panels to be joined are at an angle (as would be the case joining fore and aft panels to a V bottom hull), the same fillet tool would leave you with a fillet depth of much more and much less depth than the thickness of the plywood, so if you want to maintain that depth rule, you would use different sized tools to shape your fillets, depending on which side of the joint you are working on. I doubt many of us are doing that, but if you wanted to maintain that rule, you would need to.

 

Of course all this could be calculated into a chart for different thicknesses of plywoods and angles, which I doubt anyone has done.... including the authors of the references. About all they show are graphics explaining it, leaving it up to readers to figure it out for themselves.

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