Crystalization of Epoxy

Epoxy can be "off" a little in mix ratios, but you where grossly off and the result can't be unexpected.

If you mix 10 ounces of a 2:1 ratio goo and happen to be off a few drops on one or the other, the percentage is quite low, so no big deal. On the other hand if you are a few drops off on the 1 side of an 8:1 mix, the percentage is much higher, so higher ratio formulations need to be more precise.

I have no doubt that your 8:1, mixed properly, will yield a cured goo.

 

what PAR said above is very true and I point I like to make too.

that is a good reason for using epoxies with a 1:1 or 2:1 or similar mix ratios.

Also the curing agent side of the epoxies (part B) is the expensive part so when companies formulate with a 5:1 or 8:1 etc. they are doing it to maximize their profits with little concern for the welfare of the customer.

--- Paul Oman MS MBA ---
Member: NACE & SSPC (National Assoc. of Corrosion Engineers& Soc. of Protective Coatings)
----------------
Progressive Epoxy Polymers, Inc.

 

Guys,
Thanks to all of you for your assistance, it's appreciated. It's a given I'll be giving the 8:1 ratio a try ASAP.
The reason I started this post is my Epoxy Experience has been with only a single source, West System. I had no problems with it, as I called West's Tech advisor the morning of the day I glassed a16 ft. canoe (13 hrs. start to finish). We talked for close to a half-hour discussing possible issues. The result was as I hoped, very good!
Maybe I should ditch the Dow Stuff and drop a wad on more of Wests' Epoxy. i still have their pumps so it's a no brainer, eh. That's not gonna happen.
phil w.

 

My experience is very different. Epoxies are all different, 5to 1 are stronger than 2 to 1 or
1 to 1. They cost the same if of similar quality, I find 1. To 1

 

unlike polyester resins, epoxy hardeners are the other half of a chemical reaction. A certain amount of part a reacts with a fixed amount of part B. Any excess part A or excess part B is 'off ratio mixing' and will not be used. that said , most epoxies can be off 10-20% and still step.

there are dozens of different curing agents and even more 'additives' including those that 'dilute' part A or part B to create whole number mix ratios.

by the way the oldest epoxy use I've come across was a customer that used 28 year old epoxy from his dad's old work shop. They had built a boat when the guy was a teenager. 28 years later dad died and the guy was cleaning out the dad's shed.

paul
progressive epoxy polymers inc

 

Interesting, Paul, I used 7 year old epoxy and wasn't willing to use it on a structural part, but it cured fine, though being in a metal container had gone nearly black. That was the oldest previously opened use I was aware of, but your customer smashed my uneasiness 4 X over. I've oven wanted to test really old batches, to see how much difference in physical properties there might be.

Phil if you want to toss the 8:1, send it down here. I'll put it to work.

 

I do not feel that mixing ratio (proper mixing ratios used, that is) is of influence on the mechanical strength.

I have stuff that is 1:1, which is rubbery, as it has a low Tg, but I also have a 100:90 version that has a Tg well over 200 degrees C.
Same for strength. My 100:50 stuff is not extremely strong and stiff, but my 100:38 stuff is one of the best I have.

Pauloman is try that for ease of use a 100:50 version or even a 100:100 version is easier than a 100:13 version. If people were to accurately dispense and mix, it would not be a problem, but if they make a small error, percentage-wise the error is much smaller as the mixing ratio goes to 1:1.

Which is why at this moment my consumer-targeted epoxy resin is 100:50. Even when people "eyeball" the mixing ratio, at least it still cures.

 

I have found that it's easier to first measure the hardener (by weight) because it's the smaller part. Then calculate the amount of epoxy base that's needed depending on the actual amount of hardener I poured. Re-zero the scale and then pour in the epoxy base. The accuracy I get depends on the accuracy of the scale at the weight of the hardener.

I've never understood why some find it easier to measure by volume. I just find it messier.

Erik

 

Indeed. I never trust the small pumps that screw on the containers.

However, the gear pumps in for instance Resix dosage machines are good and accurate. It is a bit fiddly to get the mixing ratio you want (changing chain gears) but once setup it is a "set it and forget it" thing. Open the valves, operate the crank, and there you have your dispensed resin and hardener. Especially suitable for smaller amounts.



When such a unit is not available, a scale works perfectly, just make sure the mixing ratio is known and checked, and install a calculator nearby. Cover everything with plastic film to protect from spills. Replace weekly or even daily.

For continuous larger amounts I like one or more buckets, where after careful weighing in the resin, a mark (sharpie) is placed on the outside. (white or transparent bucket needed). Then add the hardener, and mark again. Use this bucket for quickly dispensing large volumes of resin and hardener. Mix in the bucket, transfer to another bucket, and mix again. (when infused, then degass). I prefer to assign this job to one person, who shall not be distracted by other operations.

 

Informative thread. I have to agree about the hand pumps, though I still use them. I am considering the purchase of a scale and demoting the pumps purpose to only despensing the resin and hardener.

Other than the change in mechanical properties of a mismix (brittle or soft), can a slight mismix also promote excessive blush formation and would it be in the too much hardener or too much resin category? I've experienced a lot of blush formation recently need to tune my operation before starting any serious builds.

My build environment has changed from warm-hot and mostly dry to cool and humid. I had changed to a faster hardener, but will be returning to a slow hardener and use heat for the cure. I will also be focusing on higher end low-blush formulations. Along with mixing by weight, I think I'll get the blush issue whipped.

 

cold and humid might trigger blushing. Usually when there is a surplus of hardener. (can also affect water resistance)

There are plenty of blush-free systems available, also in the low end range.

 

blush is caused by CO2 and moisture reacting with some of the common curing agents during cure. The 'greatly reduced blushing' curing agents cost more so most vendors go the cheap route to make more profit and offer the non blushing versions at much higher prices.

- Our Basic No Blush (tm) is a good quality and lots of our customers (DIY and commercial) have switched over from the major brands over the last 10 or 12 years. --- LP send me a private email (info@epoxyproducts.com) - we are in NH so shipping is not bad.

paul/progressive epoxy polymers inc.

 

Regarding heating a batch before use: Take your time, approach it very carefully. The "Kick" can be quite dramatic, and you're left with a pot of useless hot goo.

 

PAR,
You are correct. Thus week I separated a quart of the Dow D.E.R. 331 Resin and a Small plastic Container of the D.E.H. 24 Hardener from the metal 5 USG containers and mixed 2.0 grams of Hardener in a plastic cup, zeroed the scale and added a correct amount (calculator) of Resin. My digital scale is good to 0.1 Gram. I was carful to get the amounts 100:13. After mixing for 1 1/2 mins. scraping the sides , etc. I let it set and after 15 hrs. at ~ 65 degrees F. It cured nice and hard in the cup.
Not being 100% convinced, I then mixed another sample and wet a prepared piece of Ash. It curred over night and looks good, too. I thickened a portion of the second sample and used it to bond two samples of Ash together. I put the curred piece in a vise today and I (1.95 M and 120 kilos) hit the sucker with a wood mallot. It broke the joint but took wood from one of the pieces with it. I guess I'll keep the epoxy and use it to finish the drift boat I am building.
A couple of notes: I determined, after close inspection of the worn label, the date on the Hardener is 8-XX-1988. I can only assumne as the material hasn't been opened to the elements or stored where it might have frozen (Dow advertises 24 months shelf life). The resin is the viscosity of Honey, lots thicker than what I've seem before. it ook the better part of an hour to run the resin through a paint/varnish strainer. There were some very small partiicles in the resin. The Hardener is the viscosityh of water. I wasted a small batch, due to the hardener spilling over the side of the cup due to my stirring to fast. So slow and easy was the ticket!

Herman,

Nice thought, taking all the pills at one time. Just think, it might work faster (curing what ails ya), eh.
For the record, I spoke to a Tech Support prior to my first "test". He was at Dow World Hdq. (45 Km from my residence). He wouldn't commit to the 100:13 as gospel. He said most customers do their own develpoment depending on the application. They sell this stuff to many different industries, I can only assume Marine applications arn't one of their big users.
I am a Retired Mechanical Engineer (41 yrs.) and not that comfortable with chemicals. Seen too many oops'. Thanks for your opinions, they are appreciated, from you and all!
phil w.
ce fini