I bought this 0 - 75 lb. scale off eBay for about $33 delivered. The seller gave helpful advice. I haven’t stressed it heavily yet, but it seems very accurate and reliable. Has 3 ranges, accuracy in the lowest range is rated at 0.1 oz. The LCD panel is attached by a coiled cord and pulls out for weighing larger items. Container taring is trivially easy. I wish the SS tray was available when I ordered. It’s a little sensitive to static - doesn’t damage the scale but causes bizzare readings. OTOH, a little anti-static sray fixes it right up.
I don’t understand some of the responses on this thread. If anyone was suggesting weighing the resin and catalyst mixture, it went over my head. Weigh each component separately, after taring each container. With rare exceptions, measuring by weight is the standard approach for all industrial and laboratory processes…
-Samiam
im not a chemist but
epoxy doesnt actually use a catalyst though
a catalyst sets off a chemical reaction(chain reaction)
with epoxies
its a hardener that fills in the blanks of a chain of molecules (if that explains it clearly)
so unlike poly which will cure over time .
epoxy will never properly cure if you dont use correct amounts
likewise if you use to much it weakens the lam as well as there is areas where there is just excess hardener
whether it be by volume or weight
just get it right.
i use medicine cups and there fine
although 4 to 1 maybe more forgiving
hey Daklaw
i used to be pretty casual with amounts for ages
(never a problem)
until i had to spend
two days scraping uncured fairing resin off the side of a boat?
I use the plastic measuring tubs sold at my local boat shop, but can be found at most paint stores. I use the same method I saw use at surf expo: fill to the desired mark with resin, then add hardener to the same tub to the proper mark. I then mix for at least two minutes. There must be some room for error, but this way gets me close enough. I think improper mixing of the two may be a bigger problem…jim
Nice scale… I may have to look into those for other stuff. Like making bread, for instance…
Me, I have had enough disasters with trying to measure by volume that I wouldn’t do it again with anything other than lab-grade graduated cylinders or the like. On the cheapo cups the gradiations are just stencilled on ‘someplace on the cup’, and who knows how accurate those might be on a given run of cups. I suppose you could calibrate your cups, but eventually it’s a ‘why bother’ scenario.
Then…does the amount that stays in the measuring cups when ya pour it out to mix stay at the same ratio and such? Doesn’t look like it to me. So for small batches, you have problems, no? It’d be less of a problem with big batches, but I don’t do those.
The closest I come to mixing by volume is using the pumps ( mustard pumps or whatever you want to call 'em) for very small batches to do repairs. The setup I use is two pumps and the one in the hardener has that cute little stop-insert that limits pump travel to half a stroke - accurate enough for small stuff. but I also prime the pumps carefully first, taking a partial stroke with 'em and stopping when it stops being air coming out - that’s when I put a cup under it all.
Granted, there’s some slop in what you can get away with- if it’s 2:1 resin:hardener you can probably get away with 1.9 -2.1:1, but too much or too little hardener and the stuff doesn’t go off, at least not for me.
Measuring both together… oh dear. I can see how it’d seem to be a good move, but I know I’d measure out, say, 50 grams of hardener, then try to add 100 more of resin to that container but screw up and put in 150 and have to add 25 more of hardener but screw that up and need to add more resin…you can see where this’d wind up. About three times the resin mix you need or else pitch it out and start over.
Nah- the scales are the way to go.
doc…
I do it the same way… adding the hardener first, then the resin. Haven’t had a problem yet. I use the graduated buckets West Marine sells.
Hey Doug,
but the bottom on the board was SOFT!
-
what was your foam and glass schedule?
-
what’s wrong with a soft bottom? Thats what I prefer. Unless Im making a strong board…
I ended up with too little hardener.
hmm, too little H might make it a bit brittle…to a point…
inaccurate mixing? Ive made flexible E from regular’ole 2k…wouldnt necessarily put it on top tho…but its interesting, the complaints that epoxy boards are too stiff
if youre concerned, sand the sh_t out of the bottom with 100 and put on another 2 or 4oz layer…problem solved
oh yeah,
if you live anywhere where its consistently cool it could take a couple of weeks before full cure…a little post cure helps
ps - I have a 1 pound digital scale…accurate to 1/10 gram…I never use it to mix RR…never had a prob
Craftee, Actually, last night as I contemplated stripping the bottom and reglassing, I had the same idea: Sand down to the original fabric then lay down one layer of 4oz. I can’t see why it wouldn’t work.
Post cure wasn’t the problem. After one week of room temp and seeing it was soft, I cured it in my board oven at 125 degrees for 10 hours. The extra temps helped some, but my buddy came back from Hawaii and the board had a rail split from the airline, and multiple dents on the bottom.
Thanks to all for the useful input. Now I need to decide between volume measure or weight.
Greg Loehr, are you out there? What do you think? Doug
Hey Paul,
Haha. That story of yours reminds me of my first poly job. It just wouldn’t harden, and my house smelled like a poly resin factory. Gawd awful. But anyways, when I say I eyeball it…i try to get pretty accurate. I don’t just dump resin and hardener randomly. I just never had a problem. But I’m getting a postal scale for free so I’m hoping that’ll work for epoxy measuring. Goodbye eyeballing, hello better glass-resin ratio! woohoo!
Cheers
Rio
I’ll through in my $.02 here. I have used epoxies for about 7 years. My one experience with poly resin is something I do not wish to repeat. I’ll never use it (poly resin) again… nasty stuff!! Have used both volume and weight to measure the product and find that by weight measurements are much easier to do.
The pumps are not accurate by them selves. I’ve tested that many times and found them to be lacking in accuracy and constancy. Measuring in a cup is a PITA.
Measuring in volume, in general, is a PITA for epoxies, and is very wasteful. How do you measure the right amount with out too much waste for a leash cup or fin box? It’s so easy to measure out 10 grams, or less, than it is to measure out ¼ oz. AND get the ratio right. If your using two cups to measure (one for resin one for hardener) how do you get all of the product out of the cups into a mixing bowl. Some always sticks to the sides/bottom. One of data sheets I found tells me their product only has a 2% allowance before the resin’s qualities are compromised. They also suggest to error light on the hardener if you have a choice.
Until I started measuring by weight I would get lots of little epoxy pucks around the shop. Waste epoxy I didn’t have a use for when I mixed up some for a small glue up. This adds up fast. The other problem is clean up. The measuring cups need to be cleaned to use again or you use a new one each time. How much do accurate measuring cups cost again…?
I use a 300 gram digital scale. It measures in .1 grams, .01 oz, karats and grains. Set a paper bowl on the scale tare it out add resin. Multiply that by 1.44 and you have a total for the mix. Add hardener to the calculated amount. Use paper bowls that do not have wax coatings. About $.05 each for the small ones $.09 for the large ones. If I have to mix large batches (for me anything >10 oz mixed resin) I measure it in two bowls and dump the hardener in with the resin so I can use the hardener bowl again if needed. Use a small plastic scrapper to get as much hardener into the resin as I can. These bowls are a good indicator to know if you have mixed the resin properly too. Since they are disposable I can leave that one I just emptied on the work bench and let it cure. The epoxy in the bowl will be done about the same time my project is done and if there are no sticky spots in the bowl when everything is cured I know that I mixed everything right. Then I don’t have to go into panic what the hell do I do now/where did that end up mode.
The biggest problem I’ve had since I started using weight is that I’ll get a in a hurry to see what something looks like wet out and not mix the epoxy properly. Good thing I’ve only done that once… yea right!
Hafte
Medical dixie cups have never failed me. 4:1 or 2:1.
Warm the resin if it’s cold, cut your stir sticks square to get into the corners, stir 100 times then scrape the sides & bottom.
Don’t make it more difficult than it needs to be. 
yah i can do a accurate 20 gram batch with medical cups
any thing smaller i use two to one or 5 min epoxy
lately ive been gap filling with 5 min and also ding repairs
OK, hardener - you are absolutely correct, “catalyst” was sloppy usage on my part. A calalyst causes a reaction but is itself unchanged, where if I understand this correctly, both components of the epoxy mixture are consumed in the process. As you can tell, my vocabulary is strongly oriented to Poly tech. MEaKulPa? I still don’t see how measurement by weight can be considered less reliable than measurement by volume. Weight is not susceptible to the density altering effects of temperature or to parallax and meniscus sighting errors. The only reason I can see for preferring volume is if the ratios by weight were flatly not available, and that doesn’t seem to be the case.
-Samiam
Quote:
Nice scale… I may have to look into those for other stuff. Like making bread, for instance…
Me, I have had enough disasters with trying to measure by volume that I wouldn’t do it again with anything other than lab-grade graduated cylinders or the like. On the cheapo cups the gradiations are just stencilled on ‘someplace on the cup’, and who knows how accurate those might be on a given run of cups. I suppose you could calibrate your cups, but eventually it’s a ‘why bother’ scenario.
Then…does the amount that stays in the measuring cups when ya pour it out to mix stay at the same ratio and such? Doesn’t look like it to me. So for small batches, you have problems, no? It’d be less of a problem with big batches, but I don’t do those.
The closest I come to mixing by volume is using the pumps ( mustard pumps or whatever you want to call 'em) for very small batches to do repairs. The setup I use is two pumps and the one in the hardener has that cute little stop-insert that limits pump travel to half a stroke - accurate enough for small stuff. but I also prime the pumps carefully first, taking a partial stroke with 'em and stopping when it stops being air coming out - that’s when I put a cup under it all.
Granted, there’s some slop in what you can get away with- if it’s 2:1 resin:hardener you can probably get away with 1.9 -2.1:1, but too much or too little hardener and the stuff doesn’t go off, at least not for me.
Measuring both together… oh dear. I can see how it’d seem to be a good move, but I know I’d measure out, say, 50 grams of hardener, then try to add 100 more of resin to that container but screw up and put in 150 and have to add 25 more of hardener but screw that up and need to add more resin…you can see where this’d wind up. About three times the resin mix you need or else pitch it out and start over.
Nah- the scales are the way to go.
doc…
I must admit that my old eyes are a factor in my bias on the volume/weight question. And with my luck I’d be treated to the smoke and flames reward before I reached the end of that “mixture juggling” scenarios.
-Samiam