Epoxy Mixing Ratio and Pot Life of the Mixture

Epoxy coating is a two-component paint: the resin and the hardener must be mixed in the correct ratio to cure into a hard paint film. Mixing in the wrong ratio is a mistake that cannot be fixed by applying another layer on top, because the faulty film lies at the bottom and will undermine the whole system. This article explains what a mixing ratio is, what pot life is, and how to organise mixing so as not to waste material or ruin a floor.

Mixing ratio: read it correctly and mix it correctly

The mixing ratio is the ratio between the resin component and the hardener component, specified by the manufacturer for each product. There are two common ways of stating a ratio: by weight and by volume. The two are not equivalent, because the densities of the two components differ. Taking a weight ratio and mixing by volume, or vice versa, is wrong from the start, however carefully the measuring is done.

The hard rule is: mix to exactly one type of ratio as stated in the technical data sheet, mix the full product set in its packaging proportions when the manufacturer requires it, and do not add thinning solvent on your own or reduce the hardener to save material. Adding thinning solvent may make the coating easier to roll, but at the same time it reduces the dry film thickness and hardness, and can cause surface pitting.

The common consequences of a wrong mixing ratio are: excess resin leaves the film soft, slow to dry, and easy to scratch; excess hardener leaves the film brittle and easy to crack; a large error leaves the coating uncured, with a surface that stays tacky for a long time and must be ground off and redone. There is no cure by coating a correctly mixed layer on top, because the faulty layer underneath remains the weak point of the whole system.

What pot life is

Pot life, or the working life of the mixture, is the period from the moment the two components are mixed together until the mixture can no longer be applied. Within this period, the mixture is still fluid enough to roll or self-level evenly. Once pot life has expired, the mixture gradually thickens, heats up, and cures right in the container, and can no longer be poured onto the floor.

Pot life is not a fixed number for epoxy materials in general. Each product has its own pot life, and that pot life is only correct at the reference temperature published by the manufacturer. This article does not give a common number, because applying one product’s number to another product is a direct way to ruin a mixed batch.

The three factors that shorten pot life fastest

• Temperature: the higher the temperature, the faster the curing reaction and the shorter the pot life. The same product, applied at midday in hot sun and on a cool evening, can give clearly different working times. Storing materials in the sun before mixing also shortens pot life.
• Batch size: the curing reaction gives off heat, and a large mass retains heat better than a small mass. A full container of mixed coating will heat up and thicken faster than the same amount of coating spread thinly on the floor. After mixing, therefore, the mixture should be poured onto the floor and spread as soon as possible, rather than left sitting in the container.
• Mixing and induction time: some products require an induction period after mixing, so that the two components react preliminarily before application. Skipping the induction step, or inducting for too long, both affect the quality of the paint film. The induction time, if any, is stated in the product technical data sheet.

The correct mixing procedure

1. Prepare all tools before opening the lids: a scale or measuring jug matched to the ratio type, a low-speed mixer, a clean mixing container, and a stopwatch.
2. Stir each component separately before mixing them together, because the heavier component can settle to the bottom of the container during storage.
3. Pour the hardener component into the resin in the correct ratio, and mix evenly with a low-speed mixer to limit air entrainment. High-speed mixing creates air bubbles, which become pits on the floor surface.
4. Scrape the sides and bottom of the container while mixing, because material clinging to the container walls that is not mixed will make the paint film patchy.
5. Write the mixing time on the container, and size each batch to the team’s actual application speed, so that even the last batch is spread on the floor before its pot life expires.

Signs that a mixture has passed its working time

When a mixture starts to heat up abnormally, thicken, form strings, or become hard to spread evenly, that is a sign that its pot life has expired and it must be discarded. Trying to keep applying it by adding solvent or mixing in fresh material only creates a non-uniform film, hard in places and soft in others. The cost of one discarded batch is always cheaper than the cost of grinding off an entire coated floor area that has failed.

For a multi-coat roller system such as RollCoat, sizing batches to the team’s rolling rhythm is an application-organisation skill no less important than rolling technique itself, because every rolled coat starts from a fresh batch and is subject to the same pot life rule.

Note: this article presents the general framework of epoxy coating materials, not Kadier-specific specifications. The specific parameters of each coating system are valid only as stated in the official technical data sheet of that product.

Request a consultation on the coating system suited to your floor condition.

Illustration: Pexels / Pavel Danilyuk.