Slow curing epoxy question ...

[trawler10]

Am using Graham's magic potion  ... two pumps of A, one pump of B plus some wood flour to thicken, but in some batches the cure process has been mighty slow.  When thickening for fillets, etc., I use wood flour if little sanding required, or his micro-balloons if the area must be sanded such as fairing, etc.  Normal glassing, the stuff sets up and hardens just fine, but when using eitherr of the two aforementioned thickeners in some cases it has been a couple of weeks and the thicker areas are still a little soft inside.  I am in the Seattle area, temps in the low 50's during the day, and have used a heater to keep the work area warm at night after glassing sessions.  Any thoughts as to why the thicker mixes are not fully hardened, or is this a normal occurance in cooler climes. 

Cut the boat in half yesterday (Two-paws 9) and everything held together just fine so now am spending much of my spare time sanding, fairing, preparing finish items etc.

[paul_stewart]

Bob,

You want to mix A and B very very well before adding anything else.  Are you doing that?

--Paul

[Ken_Potts]

  In addition to what Paul said - Don't change the ratio in an effort to get a faster cure.  Epoxy isn't like that other stuff (polyester, vinylester etc).  If you add too much hardener it will not cure.  Too little hardener and it will be brittle.  I don't think you changed the ratio, I'm just warning against it 

  Temps in the 50s will give you a long cure time with slow hardener.  The good news is if it is mixed properly it will eventually cure.

[Joe Nelson CS#35]

Aside from the wrong temperature range of epoxy...inaccurate mixing is almost always the answer.  Dont add more than specified...just get it right.  Low temps also make the pumps hard to regulate.  Are you getting any air bubble pops when you pump?

[Garry]

I wonder... The pumps I got from Graham were set up for ONE stroke each, but one pump was limited to half of the stroke of the other so I was getting a 2:1 mix. I didn't notice when I apparently broke the stop on the short stroke pump and got a couple of batches of 1:1 mix. Then, to accommodate, I began using two strokes of one to one stroke of the other to maintain the 2:1 mix.

Are you sure you should be using two strokes to one stroke? If one pump has a shorter stroke, maybe you should be using one stroke each to get the 2:1 mix.

[Tom Lathrop]

My first thought was the same as Garry.  You did not make that mistake, did you :

Even if your pumps have equal volume per stroke, it's an easy way to make a mistake.  Much better to have double volume for the resin pump and religiously pump them in sequence. Always one at a time.  Never try to pump several strokes from each.  Way too easy to lose count.  I always place the two containers in the same relative positions, left to right, and always start pumping on the left one every time.  That way, I don't have to count.

This epoxy will set up in a few days, even in a freezer.  A couple weeks to set up -- never.  Something is wrong with the ratio.  Improper stirring will not cause the set up to be that bad either.

There is no recovery from an improper ratio.  It's the one unforgivable sin with epoxy. 

Graham is having some problem with access to the forum so he has not read anything for a few days.  I am of no help with that.

[Charlie Jones]

If you have pumps from Graham, it's ONE stroke of each. Otherwise you get the wrong ratio, and it won't cure properly OR to the correct strength.

Having said that, in cool weather ALL of the 2-1 ratio epoxies cure slowly. Just a fact of life. I've been using some of Graham's epoxy on the bottom job currently underway on our 25 foot sloop, and having to heat it with a heat gun to accelerate the cure, because I'm pressed for time.

Just count on this- if it's around 50 degrees or cooler, it's gonna take about 2 days for properly mixed 2-1 ratio epoxy to reach cure to a sandable state.

[Greg Luckett]

I have been using West Systems and the respective pumps.  I believe the actual ratio is 5:1 but it might be 3:1....I just cannot recall now.  I use the fastes hardner because I am usually working in cool climate, even in the summer.  When the temperature is below 60F the closer to freezing it gets, the longer it takes, and will take hours to cure and overnight to harden.  This slows me down a great deal.  I can build more in two weeks in July than I can get done in 6 months in the winter.  I heat my shop with electric heat now and it helps but can take all day to raise the temperature from 20 to 60 in the shop and also warm up everything in the shop.

[Oyster]

This is a side note for you guys working in the areas of extreme seasons. You can microwave your resin for a couple of minutes before mixing it, especially if you are using a 2 to 1. The advantage of this ratio is that you do get more working time and more material at a lower cost per ounce too. For those that are working out of a can, buy some Glad containers, retangle in shape with a lid thats used for freezing foods. I nuke resin in small quantities for about one to two minutes in larger quanities using the ratio. Of course the lightbulb in a small cooler is the old standby method.

[cdunc]

I have the pumps from Graham and both pumps are identical.  They both pump the same amount.  I use a digital kitchen scale to measure out the epoxy.  One pump puts out 30 grams.  So two pumps from the resin and one pump from the hardener gives me 90 grams.  I can mix up smaller batches using the kitchen scale.

I am using Graham's epoxy and the slow hardener.

Craig

[wkisting]

One tip on speeding up the curing in low temps... I found that draping a tarp over the entire boat and putting a small, thermostatically-controlled (for safety) space heater underneath can heat the interior very effectively to speed up curing. At temperatures outside of 50 deg F, I was able to heat the interior of our CS20 to nearly 80 degrees this way. Depends on the size of the heater, of course. And don't leave home with the heater plugged in... even with a thermostat-equipped heater, you should take care to check it every 45 minutes or so to ensure nothing is burning or potentially at risk of causing a fire. At those temps, the fillets cured rock-hard for us in about 6-8 hours (using Raka 606 slow hardener)... though probably not 100% cured for another day or two.

[paul_stewart]

Craig,  Does "1 pump" of resin weigh the same as "1 pump" of hardner? 

--Paul

[paul_stewart]

DeeR SanTa,  ....

[cdunc]

Yes.  One pump of the resin is 30 grams.  One pump of the hardener is also 30 grams.  I checked that the first time I mixed the epoxy.  I usually mix up a small batch at a time.  Which is 2 parts(pumps) resin and 1 part(pump) hardener.

[Apteryx]

Probably best to keep the resin and the hardener at the same temperature if you're measuing by volume.  Heating the jug of resin and then measuring the mix by volume of warm resin versus cold hardener might not be accurate if the resin expands much.  Measuring by weight, that's probably the way to go, anyway.

I really like long cure times, being a slow-moving klutz, but I've avoided shop temperatures below about 68.

It's OK to work in cold temperatures?  If it takes a day or two to harden enough to unclamp, I'm OK with that, just so long as I can start making regular progress.

[PAR]

I use the tarp over the work with a space heater trick often this time of year (the next 6 weeks are the coldest of the year). I use the silver ones, which are heavier and reflect the heat back inside. I use the heated oil style of heater. They look like a steam radiator from up north, but it's stamped sheet metal. I got a few of them from Wal-Mart for less then 20 bucks each.

I did a transom replacement last week on an old 'glass bow rider. It was moderately warm (mid 70's) during the afternoon, but a clod front moved in and it dropped into the upper 30's at night. I rigged up the tarp, which completely covered the boat. I pinned it to the ground with concrete blocks and 4x4 posts, with a single heater inside. I checked when the 11:00 news was on and it was almost 90 degrees inside. The slow hardener I used was well cured in the morning.

These little heaters kick butt and one will keep my garage (oversize two car) in the high 60's with 30 degrees outside. Two of them can make it darn uncomfortable inside, but it does kick goo fast.

[John Burritt]

A couple of thoughts - the pumps measure volume, not weight.  Hardener will float on resin, so its lighter.  Does each pump give you the same volume?  2nd thought - could possibly be the thickener.  Microballoons, being hollow, might not cure real hard.  Fairing shouldn't be very thick.  Not sure about the wood flour.  I usually use it as an additive to cabosil.  Try cabosil (fumed silica) for filleting.  If this doesn't get hard, you've got some kind of epoxy problem.  I regularly do epoxy work with a shop temp in the 50s to 60s without a problem.  Obviously cure times increase.

[cdunc]

True that the pumps measure volume.  So if the hardener and resin are of different density then doing it by weight would be bad.  Since I am using the same pumps for both parts and a full pump puts out the same volume and they both weigh the same then the density is equivalent, correct?  density = mass/volume.

I emailed Graham to ask about my pumps and they are identical, but apparently there is a spacer under the pump handle on the stem that can be used to restrict the handle to a half pump.  I did not notice the spacer when they arrived.  I will have to check them when I get home.  Both my pumps travel the same distance so they are both pumping their full volume.

I will try to do some measurements to prove my theory that the density is the same.

[John Burritt]

If one liquid floats on the other, they're not the same density.  Unless there's a dramatic difference, this probably isn't the problem.  The mixing tolerance of the resin/hardener mix (+/- 5%, I think) should accomodate the difference.  (How's that for changing my mind?)  I'm still curious about using a different thickener and/or what happens if things are warmed up.

[Howard]

I haven't used a pump to measure epoxy and hardener in a long time. Too many partial spurts to be a reliable way to measure. And for a large batch, it's a lot of work. Pop the cap and pour it.

I use graduated measuring cups to measure by 2:1 volume:

I have them marked out for all occasions, all the way down to 7.5 ml batches. One "master" of the quantity I want that is measured. Another of the same size that fits inside the master. Just cheap disposable plastic cups. Get the little medicine cups at a drug store and mix straight in them. Volume measures are marked on the side. I enhance the marks with a Sharpie so I can read them better.

What everyone else said about temp control. At 50 degrees, most slow hardeners are going to be too slow. If fast is too fast, mix your fast and slow hardeners to get the cure rate you want. Mixing is easier if you are measuring and not pumping.

If you mixed your epoxy well before adding the thickener, the presence of the thickener won't make any difference in cure rate. That is all a function of temperature. Epoxy cure rates are all temperature dependent. External and internal to the mixed epoxy, which starts generating it's own heat as it starts to cure. At 50 degrees, you could mix and spread a thin layer of slow cure and it may take days to cure past a tack stage. On the other hand, 100 ml of epoxy mixed with some fast hardeners, and left in the mixing cup will start to heat, then go off in a matter of minutes.....probably smoking and melting the cup it's sitting in.