I'm curious if anyone has any specs on the relative hardness of epoxy versus poly. I did a very unscientific test today on the Swamp Girl I built this past spring, and my bass boat. (which I assume is made with poly resin) I scratched the Swamp Girl with my trusty Uncle Henry in an inconspicious place. It scratched fairly easily. I tried the same thing on my bass boat in a storage compartment without gelcoat. It was several times harder to scratch. I know this is not an scientific test, but the results were very obvious. The bass boat has had several years to cure, but this is a pretty dramatic difference. There is no way the epoxy on the Swamp Girl is as hard as the stuff the bass boat is built of. That boat is made of some really tough stuff.
Relative hardness of poly versus epoxy resin
- Thread starter tw541
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There are hundreds (maybe thousands) of different formulations of epoxies and esters so the resultant hardness of the cured resins can vary. Hardness is only one of the properties that must be considered when choosing a resin system because with all properties there are trade offs. For example, harder materials are generally more brittle and not as flexible, thus more prone to breakage. Consider a knife made from very hard steel. You probably have to go back to manufacturers' specs to find hardness of different resin systems.
Just for fun, you can greatly improve your hardness testing capability cheaply. It's called the pencil hardness test and it uses pencils of different grades.
Grading pencils come in an assortment of both hard and soft, and can be found in most art or office supply stores. The 'H' stands for hardness, the 'B' stands for blackness, and HB is for hard and black pencils. The hardest is a 9H, followed by 8H, 7H, 6H, 5H, 4H, 3H, 2H, and H. F is the middle of the hardness scale; then comes HB, B, 2B, 3B, 4B, 5B, 6B, 7B, 8B, and 9B, which is the softest. Another grading method uses numbers; the equivalents would be #1=B, #2=HB, #2-1/2=F, #3=H, and #4=2H. The most commonly used writing pencil is the #2 (HB grade), which is fairly soft, contains more graphite, and leaves a dark mark.
Basically you use the pencils to determine the minimum hardness that will scratch your coating.
not totally scientific, but better than a knife blade.
Just for fun, you can greatly improve your hardness testing capability cheaply. It's called the pencil hardness test and it uses pencils of different grades.
Grading pencils come in an assortment of both hard and soft, and can be found in most art or office supply stores. The 'H' stands for hardness, the 'B' stands for blackness, and HB is for hard and black pencils. The hardest is a 9H, followed by 8H, 7H, 6H, 5H, 4H, 3H, 2H, and H. F is the middle of the hardness scale; then comes HB, B, 2B, 3B, 4B, 5B, 6B, 7B, 8B, and 9B, which is the softest. Another grading method uses numbers; the equivalents would be #1=B, #2=HB, #2-1/2=F, #3=H, and #4=2H. The most commonly used writing pencil is the #2 (HB grade), which is fairly soft, contains more graphite, and leaves a dark mark.
Basically you use the pencils to determine the minimum hardness that will scratch your coating.
not totally scientific, but better than a knife blade.
I emailed System Three and West and asked for some technical data/studies. I'll pass on any info I get back.
Don'tcha just HATE it when we're sitting here arguing about how many teeth there are in a horse's mouth - and some smart alec want to go out to the stable and actually COUNT them?? HERESY!
Good call Matt.
I would be more concerned with the strength and bonding to wood properties than hardness. It will be coated in varnish anyway.
Hardness on the bottom is increased with the addition of graphite powder.
I would be more concerned with the strength and bonding to wood properties than hardness. It will be coated in varnish anyway.
Hardness on the bottom is increased with the addition of graphite powder.
I had access to a Brinell tester a few years ago, but not now. If I can find the pencils, I am going to do a few tests. It would be interesting to see how different compounds affects the actual hardness. The toughest mix I have seen yet is the fumed silica mix I used in the end pours of the two boats I am building now. I drilled them for the bow eye bolts and quickly dulled a 3/8" bit getting through. I wouldn't like to sand that stuff. I used graphite on the Swamp Girl, and it has scratches that I do not think would have happened with something as hard as the material on the big boat. It may not be practical or even possible to get results like that on these boats. I am not planning to stop using epoxy. I have always been really good at finding complex and expensive solutions to problems that do not exist. :lol:
Terry
I think you will find polyester is a lot harder than epoxy,but is not nearly as flexible.
I paddle with several guys with epoxy and graphite bottoms on there boats, mine is polyester with a good grade of paint over it, and so far my boats may be standing up to the wear a little better.
I use my boats rougher than they do, some of them carry there boats more than they paddle them.
Ron
I know Polyester is not on par with epoxy, :lol: and I have to say I don't build my boats where they flex and bend
PS Just thought of something funny , I would have to laugh if folks started putting on a polyester and graphite coat over there epoxy :twisted: :twisted: :lol:
I think you will find polyester is a lot harder than epoxy,but is not nearly as flexible.
I paddle with several guys with epoxy and graphite bottoms on there boats, mine is polyester with a good grade of paint over it, and so far my boats may be standing up to the wear a little better.
I use my boats rougher than they do, some of them carry there boats more than they paddle them.
Ron
I know Polyester is not on par with epoxy, :lol: and I have to say I don't build my boats where they flex and bend
PS Just thought of something funny , I would have to laugh if folks started putting on a polyester and graphite coat over there epoxy :twisted: :twisted: :lol:
JD
Already in the foxhole ,flack jacket on steel pot pulled down low.
INCOMINGGGGGGGGGGGGGGGGGGGG
Ron
Already in the foxhole ,flack jacket on steel pot pulled down low.
INCOMINGGGGGGGGGGGGGGGGGGGG
Ron
Unless the formulations have changed a lot in the last seven years, applying polyester over epoxy doesn't work out well. We found that when gelcoat was used to paint the insides of lockers, etc., wherever epoxy remained, like along glue lines, the gelcoat would never cure properly. It would sometimes dry up, but never chemically cure.
Also, polyester does not bond nearly as well to wood as epoxy. Vinylester is a little better than polyester and can tolerate more flexing without fracturing, but is still inferior to most epoxies. Many aircraft components are now made from epoxy/carbon fiber. Most of those use formulations that have to be baked in autoclaves, so aren't practical for home use. There may be some room temperature curing epoxy formulations that sacrifice flexibility for hardness that would be useful for an outer abrasion coat, especially with graphite added.
Also, polyester does not bond nearly as well to wood as epoxy. Vinylester is a little better than polyester and can tolerate more flexing without fracturing, but is still inferior to most epoxies. Many aircraft components are now made from epoxy/carbon fiber. Most of those use formulations that have to be baked in autoclaves, so aren't practical for home use. There may be some room temperature curing epoxy formulations that sacrifice flexibility for hardness that would be useful for an outer abrasion coat, especially with graphite added.