I'm running out of answers... RR epoxy

I’ve made about 2 of these posts so far, so this is going to be lucky #3 hopefully. I did a hotcoat this morning and 6 hours later it still has not cured fully. I can still scratch it with a fingernail, just like the hotcoat I put on the deck the day before. I used roughly 12 oz of RR, measured in grams with a scale though because that was a possible reason it wasn’t curing before. Fast Hardener, and the appropriate amount of Add F. In the previous hotcoat I used no Add F and used X-55 hoping it would cure faster. The shop is around 70 for the most part, I used brand new brushes, gloves, and wiped everything down with denatured alcohol beforehand. I can’t understand why this keeps happening. I’ll leave it for another day, probably put it in my car tomorrow in the hot sun to see if I can postcure it maybe. But this is really cutting into “production time.” I need to have this board done before this weekend and if I have to do more hotcoats or wait longer for fins it’s going to kill me.

Anybody have the ResinX guy’s email? I think it might be time for a switch.

You’ll be able to sand tomorrow. Are you using glass ons? Also, don’t know why you used denatured for a wipe down. Using additive F in the laminate eliminates that step. X-55 isn’t a replacement for Add F it’s just an excellerator. Makes it so you can sand in about 3 hours. If your building that many boards you could set up an oven. Guy7s that do can sand in about an hour and a half.

I feel totally out of line talking about RR with Greg’s post right on top of mine, but…

The 2:1 ratio is by volume. Measuring by weight is close, but that’s not the intended ratio. I don’t understand why some insist that measuring by weight is somehow more accurate, when measuring by weight makes sure you get it “perfectly wrong.”

Humidity will interfere with cure times, just as temperature. What’s the air like in the shop?

Postcuring works wonders for shortening flip times and sanding schedules. It also makes all boards postcured remarkably stronger. This should be standard practice with RR.

I hope you didn’t just glass this board and expect to get it in the water this weekend. You gotta wait several weeks after lamming before riding or you’re taking a huge risk. If you’re just hotcoating over fully cured lamination, you’re ok…

The DNA wipe is a good idea if you and your buddies have been groping it up for the past month. It can’t hurt…

I always leave a little puddle of the stuff in the bottom of the bucket to guage curing rates. If it gets hard, your board will get hard, too. Just in a bit longer time.

I’ve measured both by volume and by weight. I figured if I was getting it wrong with the volume then it certainly couldn’t hurt to try by weight. I’ve heard both sides of the argument and I don’t really think one is better than the other, I just need my boards to cure. Relatively low humidity, I work inside my house and the A/C is on. I will probably plan on postcuring but it wasn’t until about 6 boards ago that I started having all these problems. Before then everything cured just fine.

I don’t plan on getting it in the water by this weekend. I have to deliever it by this weekend. The girl I shaped it for doesn’t have a wetsuit and isn’t planning on getting in the water until it warms up a bit, but I promised her this board back in March and haven’t had a chance to finish it until now.

I usually leave a puddle too, and it’s curing just as slowly as the board.

I know nothing about epoxy, and probably shouldn’t be commenting here, but I was intrigued by your statement.


The 2:1 ratio is by volume. Measuring by weight is close, but that’s not the intended ratio. I don’t understand why some insist that measuring by weight is somehow more accurate, when measuring by weight makes sure you get it “perfectly wrong.”

Aren’t weight and volume proportional here? In baking you have to watch out when measuring flour by weight or volume, since flour compresses when it sits around. RR is a non compressible liquid with constant volume – right?

Try to look at what you may have changed to cause the problems. I usually hot coat one day and sand the next. Unless it’s very cold that always works. You didn’t switch to slow hardener did you? Having issues with colder temps? That can really slow things down. 72 is fairly cool for curing … not too cool but that temp is slow.

Measuring by weight is 45 to 100. 2 to 1 by volume. Neither is better if done right.

Hi Rachel,

Post curing is the go.

My oven consists of a big cardboard box ( the one my blanks come in ) and a small fan heater run through a waterheater thermostat. I bake a board for about 4-5 hrs at 50 degrees C. sands just like poly afterwards.

I dont use epoxy below 20C. (70 F ? in that other crazy scale ).

If you are friendly with a sparky (electrician) you’re sweet.



Do you have any recommendations for what temperature is too cool for room temperature curing?

Hello there Entity,

have you had any problems with condensation? 70 degrees is 21 degrees celsius by the way, so I can’t see the temperature being a huge issue myself.

I’ve done boards down to about 50F. It cures down there but slow. Add F really improved that because when things are that slow the surface comes out like crap. Add F made it so we could go down a bit and still get good results.

Im wondering if the AC has something to do with your curing problem.

I dont have any problems with R&R epoxy

except when I eye ball the ratio’s or add extra hardner to get a faster kick

That only happened once each, eye balling = bad, extra hardner = bad

the extra hardner will give a slower and incomplete cure

I mix as the lable say’s 2-1 by volume

in my garage, ambiant air temp, So Cal

The key is density. If the resin and the hardner have different densities, which apparently they do, then the volume ratio and weight ratios will be the different.

Ditto…I can barely even get the 2:1 by volume right using dixie cups and low light (under the redwoods outside here)…and I still have no problem getting the epoxy to kick - even in winter when it’s super humid and cold! My biggest problem is, you guessed it, dirty batches which fish eye…Even so, I’m stoked on RR (and the FH before that when I could get my stuff in town) and will never go back to PU…

I will probably plan on postcuring but it wasn't until about 6 boards ago that I started having all these problems.

Was 6 boards ago when you first opened your new bottle of resin? I’ve had two gallons of resin that were suspect and another bottle of hardener that I wouldn’t use. I go into the habit of constantly using X-55 just to make sure that it cured, even in summer.

by weight is 45 to 100 if i am not mistaken…

That’s the ratio. Taking a clue from BammBamm, what I do is decide how many grams I’m using (easier when using smaller quantities) and divide the total grams by 3.22. Resulting number is grams of hardener. Add this to the cup on a scale (that’s been zero’d for the cup) then add resin until you’re at your total number of grams. Very simple, and it’s easier to eyeball the numbers climbing on the scale than making sure I’m right on the line of my measuring cup, plus, I don’t have to scrape the inside of the measuring cups a zillion times trying to get all the resin and hardener into the mixing pot.

For me, this has been a tried and true formula for mixing RR epoxy by weight:

45% hardener to resin

Total amount resin/catalyst mix, divide by 3.22 gives you amount of catalyst to use

For example:

9 oz equals 252 grams

252/3.22=78.3 g which is 45% of 173.7 (the difference between 252 and 78.3). I just round down and up in this case, so 78 g of hardener to 174 g of resin. Haven’t had a bad batch yet.


I work in materials testing. I weigh stuff, I measure stuff by volume, I sit on committees the write procedures on how to do that stuff. Weight (mass) is a more accurate method of proportioning than volume by sight. It is. I’ve got scales that are calibrated to, and indicate at, 0.001 grams. That’s 1/1000th of a gram. They require isolated bases and draft screens but they are damn precise. We don’t need those scales for resin but there are cheaper, less precise scales that are more accurate than sighting a miniscus on a line through a translucent, screen printed, plastic cup that’s got it’s own issues of accuracy.

The point is not which is more accurate, the point is how accurate you need to be and how you can acheive that accuracy reliably. If you can acheive that by sight, which most people here seem to be able to do, more power to ya.

The finer the resolution on the scale, the more precise you can be. The narrower the column of the volumetric measure, the more precise you can be. It’s the margin for error that comes into play with both methods.

Lots of things can come into play to screw things up. Did you zero the scale? Is it working right? Is it precise enough? If so, it will be the more accurate method. Volumetric is pretty fool proof. Fill it to the right line and you’ve got it. But! You might be on a slant, you might be tricked by the miniscus, you might be trying to measure too little for the cylinder which increases your error.

Both methods work, and both can be plenty accurate for the task. It’s a matter of knowing how much you need, being sure your methods are sound, and your margin for error is acceptable. In other words, pay attention.

Rachel, my apologies for the hijack. I needed to vent.

I think I figured out the problem. I went back and read the orginal post twice and it hit me…

“…I did a hotcoat this morning and 6 hours later it still has not cured fully…”

I expect a “flip” time in 2-3 hours but “fully cured” and ready to sand is another story. With a room temp over 70 degrees F and without a post cure I always wait at least 24 hours before sanding. ( Greg already said that every thing would be fine tomorrow).

Rachel…Keep up the good work

And for Ryan…

Thanks for the post! You made me smile. I use PPG mixing cups from the Auto Body Supply Store. Pour it in ,stir ,lam…never had a problem…No scale, no tare wieght ,no conversion chart, no headaches… Make sure you use the PPG brand mixing cups.


You’re absolutely right… you get a more accurate ratio if you use a good, accurate scale. No arguement there.

But so many people do the same 2:1 ratio by weight. That’s a problem…

Amen, Ryan. Your post should be an epoxy sticky.