Thread: Calculating Resin and Catalyst

wrote a reply here. realized, that although you were talking about polyester resin i somehow ended up in the pen turning section which i know nothing about. so, i withdrew a whole bunch of drivel about resin and catalyst believing it was for fiberglass layup or something. sorry about that...
maybe the ratios are the same or maybe theres totally different recipes in for polyester resin in the world of pen turning that i dont know about. but, i will say anyway that for iso/ortho polyester resins used for laying fiberglass the rule of thumb is 2% catalyst to resin.

The resin I got said 1.5%. But thats besides the point. But its 1.5% by weight, not volume. so 100 gms gets 1.5 gms of catalyst.
300gms will get 4.5 gms.

I use electronic scales that go in grams and its worked ok for me.

Converting oz to ml will depend on the product. Might be right for water but resin will be different.

Peter

Excellent reply for a first post alex, thank you for the awesome advice and safety info, I had no idea. Really appreciate your input. Thanks also _fly_, I was thinking by weight also so might invest in some digital scales.

Whilst electronic scales are very handy for weighing out resin and pigments, most are simply not accurate enough to weigh catalyst. Most of us use the electronic kitchen scales which have a resolution of 1 gram. That means they don't indicate anything between 1 and 2 grams. For small quantities of resin where you may only need to weigh 2 or 3 grams of MEKP, it is far more accurate to use the plastic pipettes available from places like Barnes. They can measure down to 0.5ml, the difference between volume and weight as far as MEKP goes is neglible.

Catalyst ratios vary not only with temperature, they vary even more with the size of each cast. If you are casting say an individual 18mm square resin blank using 60 grams, or a solid block the size of 4 of of these blanks using around 250 grams, you cannot use the same quantity of MEKP for the bigger block due to the increase in exothermic reaction in this quantity of resin.

The pigment used also has a bearing on the amount of catalyst needed, you will learn with experience that some pigments require more catalyst, others less.

So, use the 1.5% volume/weight ratio as a starting point and vary according ot conditions.

Here is a link to an indicative chart with some more info, bear in mind the gallon referred to there is a US gallon, which is 3.8 litres rather than our Imp Gallon which is 4.5 litres.

http://www.silpak.com/products/47-po...kp-ratio-chart

when i first started casting i bought some "jewellery" scales off ebey cost around $3 from memory. they weigh to 500g in .1g increments. they make it very easy to get an accurate measure of resin and catalyst. i have mixed catalyst down to .5% with no issue.

Originally Posted by sjt

Ok, so I've bought some Polyester Resin ready to cast my own blanks and decided to do a little research in to the ratio of resin to catalyst. Let me know if I've got this calculation right.

From the research, you need 7 drops of catalyst per ounce.
1 ounce = 295 mL.
7 drops = 0.35 of a mL.

So here's how I worked it out if I had 500mLs of resin.

(500 divided by 295) x .35

Equals .59 of a mL.

Does this sound right?

your formula is wrong. decimal off. 1 ounce liquid is 29ml not 295. that would make your MEPK a little more reasonable dont you think. for 500 ml you would 41ml not .59 using your numbers. i personally use 8-9 drops for smaller pours and 5-7 for larger ones.

Originally Posted by cwolfs69

your formula is wrong. decimal off. 1 ounce liquid is 29ml not 295. that would make your MEPK a little more reasonable dont you think. for 500 ml you would 41ml not .59 using your numbers. i personally use 8-9 drops for smaller pours and 5-7 for larger ones.

Yep, you're right, thanks. I was trying to convert ounces to mLs and was way off. I must admit I even had trouble veggie math at school.

Here in Brisbane I am mixing my resin either in 30ml or 60ml cups.
I use 5 - 6 drops MEKP per 30ml of resin and that works for me. The resin cures with heat so even if you go a drop or two either side of that it will not matter too much, might just cure a little quicker or slower.
As was said before temperature does play a part in the curing so when temperature is cooler a little more MEKP might be required. You will soon get a feel for it after doing a couple of castings.
I am also finding that the solid colour pigments when mixed with the resin and catalyst take a little longer to gel than the Pearl Ex.

Hope that helps,
Cheers
Tony.

I have used small amounts of acrylic paint (like artists use) in small amounts to colour resin. A match head of it in the 60ml of resin does no real damage. Didn't want to buy lots of colours at the start while I learn (real pigments are not cheap if you make mistakes). Yes I did buy 5 proper ones (solid and translucent).
I tried to get leather (shoe) dyes but you can only get black, blue and brown, the rest are basically paints as well.
Now I have a question, How long do you leave the resin to gloop up before you pour into moulds? Some of the batches I have done I poured right away as I didn't want to get air bubbles and I thought the thinner the resin the better. But you don't get a nice mixing of colour. I've seen one youtube thing where the guy left it to gel up a bit before he poured. He then push a copper wire corkscrew down into it and pulled it back out.
What are the differences in pouring watery stage, thin yogurt stage, honey stage?

Peter

depends on the effect you are looking for. the longer you let it set, the more separated your colors will be. if you mixed right away they would just blend into a mixed single color. so, what you do with trial and error, heavy on the error, you learn just when to add the different colors to achieve your desired results. now the white alumilite is different. it cures so fast that i pour them immediately after mixing and it stays almost completely separated. PR resin and alumilite clear you need to wait longer and experiment.

using PR (Polyester Resin) for casting with a temp of between 20-34degC will notmally need the same MEKP

heres how I run with it ... weigh the resin on 0-3Kg 0.5gram scales, don't forget to zero for the cup,
Now if you have 350gm of Resin I add 2x MEKP HOWEVER the MEKP is measred in Millileters,,

so 359grams = 7.18ml (or 7ml it's close enough) I mix the two and then add the dyes ...

After adding the MEKP, I set the countdown (time ranges from 15 mins to 25mins) once the timer is set and counting down I add the colours then at ZERO I pour, if time is too long the resin will set in the cup. so I cut the time back and remember it for next time ..

ratios can be as low as 100grams = 0.7mls or as high as 100grams = 2.5mls

More MEKP the faster it sets the hotter it gets and then more it shrinks - Tooo HOT and it will crack or catch fire

Less MEKP and it sets slower tooo little and not enough heat will be generated and it wont cure (a toaster overn might help you start the exothermic reaction and get it going again)

low outdoor temps= slower setting time = more MEKP (for normal timings)

High outdoor temps = Faster Setting times = less MEKP (for normal timings)

more MEKP = HARDER and more brittle blanks

Less MEKP = Softer and cleaner cutting blanks


PR resin = Cheap option = hard to turn blanks

Epoxy Resin = 3x price = better easier to turn blanks

hope this helped

Originally Posted by salty72

hope this helped

More than helped, thank you! I've received more information from this thread than what I have researched.