bad mix ratio?


ThanksFor various reasons, my resin and hardener sat in a box for almost a year before I was able to break my kit open and get to work.  For part of that time the resin wa in a cold garage.  When I opened the resin it seemed to have settled to the bottom and would not pump.  I placed the container in a tub partly filled with warm water (as previously suggested by CLC) and after  30 min or so it began to flow well.  I proceeded to mix the epoxy (with cell-u-sil) to apply to the puzzle joints (Chesapeake 17) and after I began to do so I noticed that the mix began to thicken raather quickly.  I decided to stop after putting the two hull panels and one bottom panel together and at that point I noticed the resin pump was sticky and not rising all the way to the top.  That makes me wonder if I wasnt pumping an adequate amount of resin in the first place and thereby ended up with a bad mix.   If that were the case is there a way to test?  And is there anything I can do about it now to the 6 joints I have put together? Thanks



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RE: bad mix ratio?

If the fiberglass in the joints you have already put together hardens, I suspect you are OK. If the joints don't dry, your hardener may no longer be any good, but the resin supposedly lasts almost forever.

In the future I'd try two things.

First, be sure to let the resin pump rise all the way up between pumps. Use that time to start mixing the resin and hardener.

Second, mix up small batches (I kept to no more than 20 pumps of both resin and hardener, about 10 ounces) and mix the epoxy in a relatively large container. If the epoxy gets more than about 1/2 inch deep it will harden faster than you'd like.

I express these opinions cautiously. I've almost finished building my Northeaster Dory and I've done bits of fiberglass work in the past, but I'm no expert!

RE: bad mix ratio?

if you are dealing with resin and hardener that has been in storage for a while, you certainly can test to determine if it is still good to work with.   as i understand it and based on my own experience, if a proper ratio of hardener and resin cure properly, then you can assume that the resin and hardener are fine.   by cure properly, i mean that at the right temperature and after an adequate amount of time, it forms a solid, no tackiness and not subject to indentation by a fingernail.

if you have a mixture that you have applied that is not curing (per the test above), you need to remove it and start again with good epoxy.   at the stage you are at, that should not be too hard.  a heat gun and scraper are good tools for getting epoxy off the okoume or other plywood.

all that said, it is easy also to mix a bad batch if you get distracted or a pump starts to fail.  i always double check my pumps by allocating a disposable plastic cup for hardener and a seperate one for resin with little marks i make with a sharpie i know how much of each i have.  this way if i lose count on the pump or the pump malfunctions....i know how much i have or need to add to get to the correct amount i am trying to get to for resin and hardener (remember it's two to one).  so basically i pump into the calibrated cups first.  and then once i confirm i have the right amount/ratio....i pour the contents of the resin cup and the hardener cup into a final cup where i actually mix them.

i hope that helps


RE: bad mix ratio?

   If the resin and hardener sat all that time unopened, it should be fine.  (assume it's the Mas brand CLC sends in most of their kits?) I've used Mas that was several years old w no prob.  If it has started to crystallize you may need to really heat it up.  Use very hot (not boiling water) and leave it to sit until the water cools. My pumps got gluey after being left to sit in the containers for months.  Cleaned them with alcohol and let dry completely before reusing and they were fine.  The resin is always more viscous than the hardener and I always seem to miss a drip or two, so I put a little cup under the pump to catch drips.  In the summer, it thins out a lot, so you could put it in a box w/ a light bulb overnight to thin it out in the winter (my garage is unheated but protected from freezing).  

RE: bad mix ratio?

   Also, I got to where I was just measuring into mixing cups for my larger batches. It can get more accurate than counting pumps since there is always a little error with each pump.

RE: bad mix ratio?


RE: bad mix ratio?


   So if Anything I erred in adding too much hardener to the mix.  Are there adverse consequences to that other than more rapid curing (if that)?   Will the bond that results still be OK?


RE: bad mix ratio?

I have built two CLC kits and found early on that the pumps are a challenge.  Do you alternate resin and hardener until you get enough, or do you put in all resin and then add hardener?  Either way there is some dripping from the pump spout which is messy.  The pumping is also very time consuming, waiting for the pump to retract before pumping again.

I ditched the pumps and just poured into a graduated, disposable plastic cup (with mix ratios printed on the side).  I placed the cup on a digital electronic scale, like one used for weighing food ingredients.  This type of scale measures to 1/100 th of an ounce.  The cups that I used are called E-Z Mix cups.  There is a 24 oz.and a 7 oz. size.  Put the cup on the scale, tare out the cup weight.  Then weigh out resin and then add 1/2 the weight in hardener. You can also double check the mix ratios by the markings on the cup.  This has to be much more accurate than pumping, where each pump stroke is subject to some variation.

In any event I found it much faster, easier and more accurate than pumping.  Never had a batch that failed to cure properly.


RE: bad mix ratio?



   I've not had any batch go bad yet (knock on wood) with Mas epoxy in a CLC kit, and I know I've not always been the most accurate.  I HAVE had WEST epoxy cook off on me...the 4 to 1 ratio means you have to be spot on with the hardener.

The pumps are great for the small steps IMO.  I have reserved measuring cups for the larger batches either clear coating or making fillets.  I also reuse lots of small plastic caps and containers like laundry detergent caps, Chinese takeout, sour cream,  cheese dips, olives, yogurt containers, you name it.  You can mix in them, or if you have a scale, measure out in them, and not feel guilty about tossing them when done.  I keep one decent paint cup with graduated markings each for the resin and hardener, wiping them as needed, and unmarked recycled containers to mix and toss.

The nice thing about epoxy resin is that it doesn't eat most plastics like the old polyester resins did.  Still don't use waxed cups or styrofoam.

RE: bad mix ratio?

   If using a scale, research the densities of your resin and hardener. Almost none are going to be 2:1 by volume AND weight. The resin I use most is 43 parts hardener to 100 parts resin, by weight. I've made a handy chart above the scale in these multiples.

RE: bad mix ratio?

   Some builders make a balance beam with the fulcrum adjsuted to get the correct wieght/mass ratio. Put 2 cups that weigh the same, one for hardner and the other for  the epoxy. Pour the epoxy you need into the appropriate cup and then hardner into the hardner cup until the beam balances. Now mix the 2 cups into a 3rd cup or one of the cups and mix. This shoud aways get the correct ratio for any size baertch. If needed the ratio could be checked using a scale and any material.

RE: bad mix ratio?

   Oh, nice idea with the ratioed beam balance.  Especially for bigger jobs, it should make for good consistency batch to batch.  

RE: bad mix ratio?

  No, don't use a three cup solution. Epoxy cups on tippy fulcrums is also silly. And if this process starts with an eyeballed splash of resin, you are making a wild guess at your total quantity, unless you are using calibrated cups.

If using a weight based method (digital scale or rube goldberg fulcrum), I'd suggest dispensing the hardener first, since the larger resin quantity added 2nd gives you a less finicky target as you match the smaller hardener amount. Basically, a drop of resin has a smaller ratio effect than a drop of hardener.

Another benefit to having and using a scale is the ability to weigh one's cloth first, then using that same amount of epoxy will almost always yield a proper amount to wet out the glass- a 50:50 resin:cloth ratio is a good goal for hand wetting glass on wood.

RE: bad mix ratio?

>>No, don't use a three cup solution. Epoxy cups on tippy fulcrums is also silly.

Why not? Why? Without a reason it just sounds like an opinion. Otherwise, good tips, especially starting with the hardener.

BTW, the resin:fiber ratio can be made even better by blotting the fully wet-out cloth with paper towels. That will get rid of any excess that hasn't been soaked into the wood. Blotting a hand layup gives a good approximation of vacuum bagging and peel-ply.

Have fun,




RE: bad mix ratio?

   The reasons against a 3-cup solution are first the waste, unless you save your two starter cups which will have never curing goo in them. And, the precision of the scales is lost when resin and hardener are left in the measuring cups, which can have a big effect when mixing small batches. Last, it is a waste of time and effort and worry to have such a goofy procedure to do something you must do nearly a hundred times in one build- simplify this repetitive and crucial job instead of complicating it.

And the "tippy" objection hopefully needs no further explanation, to anyone that has ever launched a small child into the air by sitting on the other end of the see-saw...

RE: bad mix ratio?

One thing I like about MAS epoxy is that it doesn't seem all that finnicky. I know that my pumps aren't especially accurate because I ran out of hardener way before I ran out of resin. But the epoxy still worked very well. And it has also worked well in quite varying temperature conditions. I like the temperature to be about 60 when I apply the epoxy, but my garage does get colder at night and the stuff still cures. When it is likely to get down into the 40's at night, I have set up shop lights to heat the curing epoxy. But even those pieces that weren't getting much (or any) supplemental heat, came out fine eventually.

RE: bad mix ratio?

The use of a balance beam was posted as an alternative to using the measuring pumps or use of poorly crafted measuring cups. It is simple and if used correctly can be vary accurate and easily be reallocated if necessary.

This type of scale has been in use for centuries by alchemist and chemist.

If you are concerned about accidental splashes of the the chemicals, then one shoule be wearing protective eyeware. It might not protect the skin but it should keep the chemicals out of the eyes.

Epoxy Ratio Scale

A Simple Beam Balance

Updated Epoxy Ratio Scale

Today I am thankful that I can respond to this post. 35 years ago today I was away ffom family and firends waiting to board a plne on a direct fight to Camron Bay Yacht Club.


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