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Old 27-06-2016, 21:25   #31
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Re: Epoxy .... "What", is a "Drop"?

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Originally Posted by mawtty View Post
POLYESTER RESIN!
Use a little less catalyst and the reaction is slower.
Temperature: the reaction is exothermic. With too much catalyst it can 'boil' in minutes.

+1

Besides, epoxy DOES NOT use catalyst as does PE.
Epoxy uses hardner which takes part in the reaction in FIXED RATIOS as opposed PE where the amount of catalyst only dictates the SPEED of hardening.
PE will set by itself over time.
Epoxy won't unless its premix and taken outa the cold.
If instructions include drops, donuts to $'s its PE.
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Old 27-06-2016, 23:04   #32
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Re: Epoxy .... "What", is a "Drop"?

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Originally Posted by lateral View Post
+1

Besides, epoxy DOES NOT use catalyst as does PE.
Epoxy uses hardner which takes part in the reaction in FIXED RATIOS as opposed PE where the amount of catalyst only dictates the SPEED of hardening.
PE will set by itself over time.
Epoxy won't unless its premix and taken outa the cold.
If instructions include drops, donuts to $'s its PE.
The PE commonly used in boat building does not use a catalyst. It is a free radical reaction where the MEKP is an initiator that creates a chain reaction and is eventually used up.
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Old 28-06-2016, 00:28   #33
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Re: Epoxy .... "What", is a "Drop"?

Your right, my bad, MEKP is incorrectly termed a catayst.
Well it is here anyway.
So what are cobalt, dimethyl aniline(sp) promoters? (DMA)
Reagents or catalysts?
With UV curing PE, does the UV form the free radicals with promoters?
Obviously, mekp is not present.
Long time since I used this stuff.
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Old 28-06-2016, 09:38   #34
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Re: Epoxy .... "What", is a "Drop"?

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Originally Posted by cal40john View Post
The PE commonly used in boat building does not use a catalyst. It is a free radical reaction where the MEKP is an initiator that creates a chain reaction and is eventually used up.
You just described MEKP as a catalyst.
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Old 28-06-2016, 14:48   #35
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Re: Epoxy .... "What", is a "Drop"?

Whatever the subtleties of the semantics, what i should have said is that if the proportion of reactant (catalyst, initiator, whatever) is in the vicinity of 1% (ie 1 drop per table spoon) it is likely to be PE as opposed > 20% for epoxy.
And, as someone mentioned, PE's hardener is flexible in quantity to a degree & relates more to rate of reaction.

I remember an order for a dozen large elephant tusks for an Indian restaurant.
I think we finally arrived at 0.43% in a water bath to control the exotherm.
A couple of the first ones cracked with the heat.
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Old 28-06-2016, 15:02   #36
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Re: Epoxy .... "What", is a "Drop"?

I had posted this before MEKP can blind you with only a couple parts /million. Keep kicked off poly out of your eye. It may not be immediate but long term.
MEKP if stored should be refrigerated. Why I don't know. I borrowed a qt. or so from a boat mfg.. It was in a reefer. as was all of their supply. For what ever it may of may not be worth
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Old 28-06-2016, 16:07   #37
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Re: Epoxy .... "What", is a "Drop"?

Because its a strong oxidising agent and will degrade in the light/heat.

Yep, treat with utmost respect. Here has to be in a dangerous goods store . Special transport etc.
When you are stirring a mix, bubbles become airborne and can be breathed in or settle in your eye--be aware.
Been there.

Cobalt/MEKP bombs are unpredictable. Don't ask how I know.
DMA is also a known carcinogen. Found ,IIRC, from use in footware industry.
Not talkin about speed here either.
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Old 28-06-2016, 16:21   #38
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Re: Epoxy .... "What", is a "Drop"?

Quote:
Originally Posted by lateral View Post
Because its a strong oxidising agent and will degrade in the light/heat.

Yep, treat with utmost respect. Here has to be in a dangerous goods store . Special transport etc.
When you are stirring a mix, bubbles become airborne and can be breathed in or settle in your eye--be aware.
Been there.

Cobalt/MEKP bombs are unpredictable. Don't ask how I know.
DMA is also a known carcinogen. Found ,IIRC, from use in footware industry.
Not talkin about speed here either.
That was the reason I had to borrow it. My supplier couldn't mail it or UPS it. It had to be trucked which was a little slow. In retrospect I believe they gave it to me and said the supplier would make it good.
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Old 28-06-2016, 16:31   #39
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Re: Epoxy .... "What", is a "Drop"?

I've just been using epoxies for the repairs/upgrades on our boat. More expensive, yes, but easier to work with, and a superior material in terms of strength, bonding, and workability.

Re polyester over epoxy - the WEST System people have confirmed that gelcoat will adhere just fine over an epoxy repair. Basically, unless you add successive polyester layers within a short timeframe, the bond between layers is going to be mechanical not chemical anyway. I haven't yet found a problem with the spots where I put gelcoat over epoxy.
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Old 28-06-2016, 16:39   #40
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Re: Epoxy .... "What", is a "Drop"?

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I've just been using epoxies for the repairs/upgrades on our boat. More expensive, yes, but easier to work with, and a superior material in terms of strength, bonding, and workability.

Re polyester over epoxy - the WEST System people have confirmed that gelcoat will adhere just fine over an epoxy repair. Basically, unless you add successive polyester layers within a short timeframe, the bond between layers is going to be mechanical not chemical anyway. I haven't yet found a problem with the spots where I put gelcoat over epoxy.
Epoxy will give you a far superior chemical bond to cured polyester. Polyester needs to be green to have much bond.
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Old 28-06-2016, 17:36   #41
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Re: Epoxy .... "What", is a "Drop"?

If you are mixing resin ang acellorator by drops I suspect you are using polyester resin, not epoxy. I suggest you use US Composites.com 635 THIN resin and fillers. This is epoxy 2 to1.
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Old 04-07-2016, 09:21   #42
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Re: Epoxy .... "What", is a "Drop"?

Jeezus, drops? Get some syringes, the small ones diabetics use are good for small batches but bigger ones sold at marine supply places work too. 22cc per quart is 2%, which is what your catalyst ratio is supposed to be @ 70F. Most use less for more working time. Do not exceed 3% in low temps, or use less than 1% in high temps (though many use as little as .5% for very large batches). To simplify the math most work off 20cc per qt. Thus, 10 per pint, 5 per cup, 2.5 for a 4 oz batch. Use less for large batches, more for small batches, never exceeding the stated limits either way. Only a casual user would ever use drops. Temp variation causes viscosity variation which causes drop size variation. Plus it's silly! Use a pro catalyst beaker if possible for 90% of your mixing, FOR SAFETY! They only cost a little. Keep the lid on and empty it back into the bottle when not in use. Only need a syringe for very small batches. MEKP is no joke, I've seen way too many industrial accidents with it. Your vision is worth $9 for a beaker.



http://www.fibreglast.com/product/ME...FZNafgodw1QOfw


http://www.tapplastics.com/product/s...p_catalyst/177
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Old 04-07-2016, 09:30   #43
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Re: Epoxy .... "What", is a "Drop"?

Quote:
Originally Posted by Lake-Effect View Post
I've just been using epoxies for the repairs/upgrades on our boat. More expensive, yes, but easier to work with, and a superior material in terms of strength, bonding, and workability.

Re polyester over epoxy - the WEST System people have confirmed that gelcoat will adhere just fine over an epoxy repair. Basically, unless you add successive polyester layers within a short timeframe, the bond between layers is going to be mechanical not chemical anyway. I haven't yet found a problem with the spots where I put gelcoat over epoxy.



How long has it been? Does the boat live under cover?
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Old 04-07-2016, 09:33   #44
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Re: Epoxy .... "What", is a "Drop"?

Note that 10cc is 300 drops! By the time you are done counting out 300 drops, the resin has kicked.



http://www.fiberglasssupply.com/pdf/.../mekpchart.pdf



Also note that there are many different types of catalyst, it's not just MEKP after all. I use Hi Point 90 for laminating, which has long open time but short gel time. A less hot catalyst is called for for finish gelcoat, or you may experience discoloration.



And the safety note-


Caution:
Organic Peroxides can decompose explosively.
Always wear safety glasses and protective gloves.
Keep away from heat, sparks and open flame.
Keep away from acids, sanding dust, copper, brass, iron, bases and
promoters.
After use, inspect area for spills.
Store in original closed container at recommended storage temperature.
KEEP AWAY FROM CHILDREN




Always remember that MEKP is a common ingredient in explosives. I have seen some crazy stuff happen with it. It burns bright green, and you don't want to go there!
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Old 04-07-2016, 11:14   #45
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Re: Epoxy .... "What", is a "Drop"?

If this is redundant sorry. They make what looks like shot glasses marked in ccs and oz.s for the pharmaceutical industry.
They are great for measuring MEKP.
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