# Converting Mix Ratio by Weight to Mix Ratio by Volume

1. The Mix Ratio of a two part resin
system is extremely important in achieving a proper cure. Epoxies,
Polyester, & Vinyl Ester Resins use a chemical reaction between a
resin and hardener which have a ratio that determines the relative
proportions in which the two substances react for this reaction. This
ratio can vary from product to product and is reported on each Technical
Data Sheet.
2. Why Is It Important? An error of no
more than +/- 5% from the mix ratio is a good guideline. Larger errors
in the mix ratio can allow un-reacted components to remain within the
resin and may lead to an increase in outgassing, a decrease in Tg and
decreased resistance to chemicals and moisture.
3. For some processes, however, a
customer may find it more convenient to measure and mix by volume rather
than weight. Using the reported mix ratio by weight to mix by volume
can cause products not to cure properly.
4. How To Convert
The volumetric mix ratio can easily be determined from the weight mix
ratio by using the specific gravities of each component also reported on
each data sheet. Specific gravity is a unitless quantity defined as the
ratio of the density of a material to the density of water. Because
water has a density of approximately 1 g/cc, the specific gravity can be
considered the density in units of g/cc for the purpose of these
calculations.

Consider
INF-114 & INF-210 where the mix ratio by weight is 3.65:1, and
specific gravities are 1.14 for Part A and 0.94 for Part B.

Divide the number of weight parts by the respective density:
Weight parts PART A = 3.65 g = 3.20 cc
Specific gravity PART A 1.14 g/cc

Weight parts PART B = 1 g = 1.06 cc
Specific gravity PART B 0.94 g/cc

This yields a volumetric mix ratio of 3.20 : 1.06, which can then be
normalized to a more convenient ratio. To create a ratio in the form of
100:b, divide the volume parts of Part B by the volume parts of Part A
and multiply the result by 100.
Volume parts PART B X 100 = 1.06 cc X 100 = 33.1
Volume parts PART A 3.20 cc

This yields a volumetric mix ratio of 100 : 33.1 The ratio can also be
normalized to the form a:1 by dividing the volume parts of Part A by the
volume parts of Part B.
Volume parts PARTA = 3.20 cc = 3.01
Volume parts PART B 1.06 cc

This yields a volumetric mix ratio of 3.01 : 1