Its all in the mix

[Andy J]

A lot of the products we use in building our models requiring a two part mix. Whilst epoxy is easy to judge by eye having dispensed two similar size blobs its only a matter of twizzling the mix together to form the adhesive. However a bit lost on how liquid two part mixes such as fiberglass and fuel proofer can be accurately dispensed to ensure a correct chemical reaction.

 

It would be possible to buy several different disposable pipettes but one would need a whole range of sizes dependent on the amount of product required. So how do most overcome this issue. Assume weight is one method but are there any alternative methods?

[Graham R]

Hi Andy, Invest in a decent set of digital scales https://www.easycomposites.co.uk/precision-mini-scale .

Hope this helps.

[Andy Stephenson]

If the two parts are to be mixed by volume and they of different densities, then weighing them instead would lead to inaccurate proportions.

However, if the densities are known then weights can be calculated.

[Graham R]

All the resins Iv'e used give the weight ratio which is very helpful.

[Ron Gray]

1 hour ago, Graham R said:

Hi Andy, Invest in a decent set of digital scales https://www.easycomposites.co.uk/precision-mini-scale .

Hope this helps.

They are the same as the ones I use and are invaluable! I agree with Graham, weight ratios are usually given.

[Andy J]

Did dig out my micro scales a couple of days ago with the intent of trying to use it to measure out a batch of epoxy but unfortunately found the unit was no longer working. Have already placed an order for a replacement unit measuring up to 500gr but with hindsite it would have been far better to have gone for the one as recommended by Graham.

Had not noticed that several manufactures post the mix ratios by weight on their instructions so will now go looking for this info.

[Brian Cooper]

Having been mixing various epoxies over the last 60+ years, it has become apparent that mixing the EXACT quantities is not overly crucial. .  . Yes, you want to be as close as possible but there is some leeway to the percentages. 

 

Basically, don't drive yourself mad being pedantic about measuring to the last gram.  

[Andy J]

Agree Brian as have been mixing epoxy by eye for the last 50years.  It was more the issue on mixing up fuel proofer that range between 4:1 and 10:1 dependent on brand as to the reason I started this thread.

[John Lee]

13 hours ago, Andy Stephenson said:

If the two parts are to be mixed by volume and they of different densities, then weighing them instead would lead to inaccurate proportions.

However, if the densities are known then weights can be calculated.

If you weigh the two unopened bottles at the start you can get a good enough mixing ratio (it's not exact, for that you should deduct the weight of the bottles from the total, but as I said good enough).

 

I use this little scale: https://www.amazon.co.uk/gp/product/B075VM7TJH/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

[Ron Gray]

2 hours ago, Brian Cooper said:

Yes, you want to be as close as possible but there is some leeway to the percentages. 

Ah but getting as close as possible has the other advantage, you run out of both glue and hardener at the same time, rather than ending up with some of either left over!

[Andy Stephenson]

Laminating epoxies tend to be more critical on mix ratio than the run-of-the-mill 5 minute epoxy glues.

[Martin Harris - Moderator]

I do know that in the full size glider world, great emphasis is given to accurate weighing of laminating epoxy mixes. Whether our (usually) over-engineered applications need such precision is arguable but it certainly won’t hurt to measure as accurately as practical. 

[Don Fry]

Weigh stuff. E bay does the miniature scales beloved of drug dealers. Accurate to 0.1 g, not expensive.

[Andy Stephenson]

I bought an ebay one for about 7quid, it works well and it even comes with a calibration weight. They call it a jewellers balance but we all know what they are really used for.

[Andy J]

This is the one I have purchased. All of them are pretty much the same I assume, its only the price that changes. 

[Geoff S]

There was a balance around at home when I was a youngster - it had pennyweight calibrated weights 🙂  My grandfather started the business in the late 19th century as watchmakers and jewellers. 

 

On a more practical level I've been using a digital scale intended for weighing food for dieting I bought at Boots perhaps 20 years ago.  It's a bit course for measuring small quantities as the minimum reading is 1gm. 

[Andy J]

Just to close off this thread I have now tried using the weight measurement a couple of times for mixing Aerokote.

Resulting mixture was far easier to apply than previous applications and has certainly resulted in a good finish on a small engine cowl I have been working on.

On the negative side could not find any weight ratio mixing quantities on this product labeling.

Also given I only needed a small amount of mixed product I did find dispensing only 1gr of the active accelerator difficult, so a couple of small pipettes would be useful to use in conjunction with measurement of weight.

Edited February 1, 2023 by Andy Joyce