Mixing SMALL amounts of gel

[Riverman]

I have a gram scale (alright, no crack jokes) to measure small amounts of gel, does anyone know how many drops of MEKP there are in a gram or millilitre?

[hsbob]

last i recall the specific gravity was close to water. thats what i would use.

test the batch before you use it. they spraied my sons boat last month and the gel was bad. they forgot to put the cobalt into the gel.

[Riverman]

Hey I found it! 20 drops=1ml

[TeamHART2]

be careful with that drops method of measuring, depending on what you are dropping out of it can be way off. I was measuring MEKP at 16 drops for a milliliter, and then when I actually measured it in a syringe I was using way less MEKP than I had thought..... had been wondering why my cure times were so slow.... Id try to get some syringes if you can and keep it accurate.

[Riverman]

I did an experiment with a graduated cylinder, and it is 28 drops/gram of MEKP.

[Six Four]

so thats 28 drops to how much gel?

[Riverman]

so thats 28 drops to how much gel?

Depends on the percentage you want to mix at. If you want to mix 20 grams of gel at 2% you will need 0.4 ml of MEKP. Thats 11 or 12 drops.

[johnnyrotten]

go to fleet and farm or farm and fleet whatever they call it in canada or local coop they should have a cow seringe for about 5.00 for 2 of them they work great clean them out when done !!!!

[Wile E. Coyote]

you also need to be careful, many chemicals have a minimum amount you can mix in order for it to cure properly, there are many epoxy resins which give a ratio of say, 4:1 and if you tried to mix for example 2:1/2 it wouldnt cure.....so I guess what im sayin is if your mixin a small batch, mix a test batch and apply it to something other than your finnished product, you may be in for a suprise.....
Bill

[Riverman]

This is about polyester gel with MEKP hardener. Epoxies are much simpler to get a good ratio by weight. Polyester requires a 1-2% hardener ratio depending on temperature, so mixing 10 grams of gel at 1.5% means you have to measure 0.15 grams of MEKP. That's really hard to weigh! Using the drop method, 4 drops are used. Easy!

[GregAdams]

hi Riverman
Forget the drop method. It is too unreliable. Get yourself some syringes from a pharmacy or agricultural supplyer for the larger sizes. A 2 ml syringe is ideal for what you are trying to do. You don't need to, but if you attach a large bore needle or a small piece of clear hose, it will be even easier to draw the MEKP out of its container. On a safety note, MEKP is a peroxide. Wear safety glasses. It can damage your eyes. Squirting catalyst into resin with a syringe may cause it to splash back into your face. Rags contaminated with MEKP may undergo spontaneous combustion. Not good when your bin catches alight in the middle of your workshop at 3am . No! it didn't happen to me!
Best way to get rid of contaminated rags is to burn them. MEKP is flammable.
good luck
Greg

[GregAdams]

One more thing. Trying to save money by mixing tiny amounts of gelcoat, like 10 g, often results in wasted time and money because, as you said, mixing very small amounts is not very accurate. It is even worse if you have to pigment the gelcoat as well.
Good luck

[Six Four]

whats the smallest amount of gel that should be mixed to get good results

[Riverman]

Greg, this about experimentation! If you go to the trouble to get a good match on pigmented gel, why waste it? A ratio is a ratio, there is no reason you can't maintain accuracy using small amounts if you take the time to develop the process.

Drop size is based on the viscosity and surface tension of the liquid. Conversions I have found use 20 drops/ml, that is probably using water. Using a 5 ml graduated cylinder, I can consistantly get 70 drops to 2.5 ml of MEKP. That's real accurate if you ask me.

Six Four, I suspect the answer to that is a large enough quantity that the whole number of drops falls within the percentage range of the mix you want, depending on temperature.

[GregAdams]

I am all ears Jeff Experimenting is what this game is all about. I was just giving you my perspective from inside the industry. Much of which was learnt by experimenting like you are. You are on the measuring side of the fence, and not the guessing side of the fence, which indicates you are smarter than the average glasser. I may be buying gelcoat in larger quantities, so 10 or 50 grams is neither here nor there. Accuracy is the key, so you are on right on the mark there.
I had a look through your restoration thread. Your boat looks great. I like the white too. That boat has some bold contours in its shape and the white highlights that.
Greg