Why mix ratios are important for Epoxy coatings?

We have come across many times where contractors made a mistake in mixing the two components of an epoxy or polyurethane coating. Some of the common problems that occur of improper mixing are:

  1. No cure
  2. Soft cure
  3. Shrinkage caused due to high exothermic reaction

A mix ratio for a two component epoxy or urethane coating is the ratio used to determine the amount of resin and catalyst (also referred as hardener or curing agent) required to obtain a full cure 0f the coating. These ratios are determined b the chemicals that make up both the resin and the catalyst and must be followed scrupulously. Mix ratios can be expressed by weight, by volume, or PHR (parts per hundred). Due to differences in density between resins and catalysts the ratio by weight and the ratio by volume will be different in many cases. The most common expressions for mixing the resin and hardener is by weight but due to practical considerations on field many manufacturers recommend mixing ratios by volume. Please remember the volume changes with the change in temperature and pressure where the weight does not change due to the changes in temperature and pressure.

Improperly mixed epoxy coating

Improperly mixed epoxy coating

Recommended mixing procedure

  1. Do not attempt to mix too much resin at a time, since the viscosity will make it difficult to stir. Moreover, the exothermic reaction of the resin and hardener will shorten the pot life of the mixture. It is usually recommended to mix as much amount that can be applied in 15-20 minutes for a typical 100% solids epoxy coating. We recommend following technical data sheet of the specific product.
  2. For a large project, it is a good practice to have several smaller batches pre-measured and dispensed (but not mixed) with resin hardener ready to go so that there is no interruption during the application process.
  3. Dispense the epoxy resin (or polyurethane resin as the case may be) and the hardener into clean plastic or metal containers. Do not use foam or glass containers. The heat generated from the reaction of resin and hardener may soften the container or make it too hot to handle, and there is a danger of breaking glass containers for a potentially hazardous situation. It is recommended to use graduated mixing containers to speed up the mixing process.
  4. Over time the filler in the resin or hardener have tendency to settle. If they are not mixed prior to being used a catalyst rich or resin rich mix can occur.
  5. The resin and hardener is dispensed in two separate containers and then poured into a common mixing container; be sure to scrape all container surfaces into the mixing container to assure proper proportions.
  6. Once the products are dispensed into the mixing container, stir thoroughly with a slow speed mixing drill and paddle for stipulated amount of time. Clean sticks of wood or tongue depressors can be used for stirring quart or less than quart quantities.
  7. Thorough, careful and complete stirring of the mixture is extremely important for proper curing. Always stir contents in the mixing container before dispensing into shallow pans or other containers.
  8. It is NOT recommended to mix the resin and hardener in broad, shallow containers; it can’t be done properly and an improper cure may result. Incomplete mixing will result in spotty curing.

Keep things clean, keep products away from your skin and eyes, and provide adequate ventilation, mix the epoxy resin and hardener products thoroughly at the correct ratio. Prior to doing any mixing, ensure that all the tools you will need are ready for use, including cleaners and solvents.

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