Mixing Epoxy Fairing Compounds
If using the recipe method, follow these directions.
- Combine the accurately measured resin and hardener in a clean container and mix thoroughly for approximately three minutes.
- Working quickly, add the thickening agent and mix thoroughly. The reason you want to work quickly to mix the thickening agent (and the microballoons in Step 3) is that the mixture starts curing once the resin and hardener are combined in Step 1. Don’t be surprised if the epoxy resin absorbs a decent VOLUME of thickening agent before you achieve the desired consistency. For fairing purposes, the desired consistency is typically like peanut butter.
- Add the glass microballoons and mix thoroughly.
For best results, measure and mix only as much putty as you can apply according to the indicated working life (pot life) and temperature specified by the resin manufacturer.
Use clean, dry tools and work as quickly as you can to mix fairing putty thoroughly when using the recipe method. The mixing of the resin and hardener creates an exothermic reaction which begins the curing process, so you’ll only have a small window of time to apply the fairing putty before it becomes unusable.
After adding and mixing in the thickening agents to the mixed epoxy resin, use the mixing stick to "wrap" the mixture evenly around the inside of the mixing cup. This action will reduce the amount of exotherm (heating process the resin goes through while curing), and increase the time you have to work with the fairing compound.
If using a two-part, pre-mixed epoxy fairing putty, combine the resin (Part A) and hardener (Part B) according to the mix ratio by volume or by weight specified by the manufacturer because not all pre-mixed putties are the same. Some specify a 2:1 mix by volume. Others, such as TotalBoat TotalFair use an easy, 1:1 mix by volume, and a blue plus yellow mixes to an even green color as an indicator to let you know when it’s thoroughly mixed.
Always be sure of your measurements in order to achieve the proper cure. If improperly mixed, the unwanted results include no cure, soft cure, or shrinkage from too much heat caused by an excessive exothermic reaction.
To create larger quantities of fairing putty, you can gain greater accuracy measuring by weight. Before you begin, know the working time (pot life) of the product and mix only as much compound as you will be able to use in that time, or it’ll be wasted.
Note that even though the mix ratio by volume of a certain pre-mixed fairing compound might be 1:1, 2:1, or 3:1, the mix ratio by weight will not be equal ratios because the resin and hardener are different densities. Be sure to read the product technical data to determine the proper mix ratio by weight.
As an example, we’ll use the mix ratio 100A(resin):90B(hardener). To measure a two-part, pre-mixed epoxy fairing compound by weight, start with two clean measuring containers and a scale, and do the following:
- Measure the resin (Part A) quantity first. Place a clean, empty container on the scale and adjust the scale to zero so the weight of the container is not counted. Dispense the desired quantity of resin paste (Part A) into the bottom of the container, taking care to keep it off the sides. Take note of the weight and remove it from the scale. For this example, let’s say you have measured 12 ounces of resin.
- Calculate the amount of hardener (Part B) you’ll need according to the manufacturer’s specified mix ratio by weight of hardener. Here’s a calculation you can use to determine the needed weight of hardener. Note that PHR means parts per hundred.
- PHR of Part B/PHR of Part A x Weight of Part A measured = Weight of Part B needed
- In this case, the equation would be: 90/100 x 12 oz. = Amount of hardener needed
- So, 1080/100 = 10.8 oz.
- In this example, in Step 1 you measured 12 oz. of resin (Part A), so you would need to measure 10.8 oz. of hardener (Part B) into the second clean container (making sure the scale is set to zero again before adding hardener).
- Place the two weighed amounts of resin and hardener on a clean surface and mix as indicated below.
Easy Steps to Combine a Pre-Mixed Epoxy Fairing Compound
- Use a clean tongue depressor to dispense and place the correct mix ratio of Part A and Part B on a clean surface.
- Use a plastic spreader to mix the two parts together.
- Mix thoroughly until the putty is a uniform color, with no swirl marks.
Mixing Polyester or Vinyl Ester Fairing Compounds
If using the recipe method, follow these directions.
- Combine the accurately measured polyester finishing resin and MEKP catalyst in a clean container and mix thoroughly.
- Add the thickening agent and mix thoroughly. Don’t be surprised if the polyester resin absorbs a decent VOLUME of thickening agent before you achieve the desired consistency. For fairing purposes, the desired consistency is typically like peanut butter.
- Add the glass microballoons and mix thoroughly.
For best results, measure and mix only as much putty as you can apply according to the indicated working life (pot life) and temperature specified by the resin manufacturer.
If using a polyester laminating resin (which typically doesn’t contain wax), you need to mix wax in thoroughly first, then the MEKP catalyst. After those three are thoroughly mixed, you can add your thickening agent and filler.
For best results, measure and mix only as much putty as you can apply according to the indicated working life (pot life) and temperature specified by the resin manufacturer.
If using a premixed polyester or vinyl ester fairing compound: These products typically contain a thickened polyester or vinyl ester resin compound and separate hardener. They provide easy instructions for mixing resin and hardener in precise amounts. Premixed compounds are typically faster and easier to mix and apply, cure faster than recipe compounds, and are easier to sand.
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