Mixing Chemicals

[Velocity]

I had purchased some epoxy to make into pistons, but it cost me $15 to buy 9 oz of epoxy. I went out and spent $40 to get 128 oz of fiberglass resin and hardener. A much better deal I think. However, I see that the ratio of resin to hardener is not 1:1, as it had been with the epoxy; the ratio of resin to hardener is 72:1. This poses a bit of a problem to me, for I do not know how I will measure out the hardener accurately. I am fairly certain that it does not have to be exactly a 72:1 ratio; but it should be pretty close. Can anyone suggest a good method that I could use to have accurate measurements of resin and hardener? I do not really have any good measurement tools; I can buy some basic ones if necessary. Thanks.

In case you are wondering, it is the same fiberglass resin and hardener that Gippeto used in his stirrup pump how to.

[clide]

I don't know if it would be as accurate as you want, but you could estimate it based on the volume of simple shapes. For example, if you wanted to mix about a golfballs volume worth of resin you could estimate that much resin by eyeballing it and calculate the size that a sphere with 1/72 of that volume which would be about .4 inches in diameter. Using something like sphere diameters as a reference would be easier than trying to estimate volumes directly. It is hard to visualize how much volume one thing is compared to another, but it isn't very hard to visualize spheres of certain sizes.

Alternatively a scale with a high resolution would probably be the easiest way to get a more precise mixture.

[elitesniper]

Well, mabey two syringes might work?

[Velocity]

I think that in the end, I would just have to use syringes. I could calculate how much I would need of both the resin and hardener by doing a density equation (m=pV). I would still probably need several different sizes of syringes, some large for the resin, and some small for the hardener.

[jackssmirkingrevenge]

I use syringes, I had looked up the density of the particular brand of epoxy I use and the hardener is only slightly denser than the resin so I mix them by volume and it works well.

[Gippeto]

Might as well put this here.


From: Gippeto
To: Velocity
Posted: 04/23/2008 21:30 PM
Subject: Re: Fiberglass Resin+Hardener

I'm glad you enjoyed it and are finding it useful. I don't have the resin handy to read the label for volumes, so I'll "wing it".

In this application, the epoxy is not structural, so if you don't get the mix "perfect" don't worry.

Buy a cheap syringe, and use it to fill a yogurt container with water to a known volume. (for example 62ml)

There are 8 fluid ounces in 1 cup. 1 cup = 250 ml, so 1 fl.oz. = ~31 ml

Mark the container, you now have a calibrated measuring cup.

Add the resin to your new measuring cup.

Add the recommended amount of hardener. (this is usually in "drops")

Mix thoroughly (very important) and pour into the mould.

[jrrdw]

Me, when I mix this stuff for auto body work I pure out the desired amount of resin and then squirt a X of hardener across the resin pile. Same way with Bondo, works well for me and I been working with this stuff for years. It's a easy quick way to do it.

[Ragnarok]

so 1 fl.oz. = ~31 ml

Correct me if I'm wrong, but is a fluid ounce not 28.4 ml?...
Or I suppose, in the US system, 29.6 ml.

Ugh. As if the Imperial system wasn't complicated enough, it has to be different depending on the country (not to mention wet and dry US pints)

A cup is a bad measurement to use, as it varies so much around the world:
- In Australia, Canada and New Zealand, it's 250 ml.
- In the UK and US, it's half a pint (although, half of which ever pint is appropriate to that country, so it's different in each)
- In Japan, it's 200 ml or 180 ml depending on context.

That means a cup can be 250ml, 284ml (10 Imperial fl.oz.), 237 ml (8 US fl.oz.), 200 ml or 180 ml.
That can result in a difference of over 100 ml between countries.

As for my suggestion... As an approximation, adding a volume of hardener approximately a quarter of the dimensions (in each direction) of the resin would result in a fairly close mix of 64:1.

[Gippeto]

Ragnarok is correct, I made a mistake and "ass u m ed"

A (US) fluid ounce is indeed 29.6 ml.

I checked the can this morning, and it says 12 drops of hardener per ounce of resin.

It also says the volume is 32 ounces or 946ml. (thus the 29.6 above)

Thank you for the correction.