The Body Filler Hardener Dilemma: How Much is Too Much?

Hot Topic: What’s the best body filler hardener mixing ratio in a high-heat environment?

Summertime heat is a body filler nightmare, and our latest Evercoat Optex video clip generated a hot-button question: What’s the best hardener mixing ratio in a high-heat environment? We asked Evercoat’s Tim Mckinney for advice. See his response below.

body filler hardener mixing ratio dilemma on facebook

“The topic of catalyzation has been an ongoing subject, and probably since the beginning of polyester filler. The technician from the dealership in the video was correct for the amount of BPO Cream Hardener used. However, the technician was a bit heavy for his initial application and technique.

We have been placing stickers on the tops of the cans to help guide technicians on the proper ratio for some time now. Most technicians see that the filler has hardened and so therefore it must be the ‘correct’ ratio. When actually, if the filler is not fully catalyzed it leads to post-curing and repair mapping. 

Some of the technicians referenced the amount of hardener related to pinholes, and there is some degree of truth to that. Generally, when a filler is over-catalyzed there is an urgency to get the material on the panel, so therefore the proper application technique is bypassed for sake of time. For high heat conditions, I recommend keeping the product AND the hardener at a cooler temperature (in the office, away from the hottest area in the shop, or possibly on the floor). If nothing else to keep the hardener at a cooler temperature to help slow down the reaction. 

Next, spread the product out over the mixing surface to help dissipate the heat. Polyester cures with an exothermic reaction, so by increasing the surface area it can help to reduce the heat. If none of those slow down the filler/putty, the next option is to mix in a small amount of Rage Ultra XTRA #100144. This is a standalone filler with a working time above 40 minutes at 72°F (22°C) and an extended sanding time of almost 2 hours. Because of the slow working/sanding time, it can be added in to slow down the reaction, and also help to thicken the product(s) as their viscosity will thin out in high heat, so it helps for both time and viscosity.

With regard to the application surface, Rage OPTEX meets the  ASTM B117 Corrosion test and provides 500 hours of salt spray protection. This may be why the technician applied it over bare metal knowing that he had that level of protection. It can also be applied to over properly prepared factory clear for smaller repairs and factory primer and e-coat to work with the factory coatings as part of the factory corrosion protection.”

Interested in trying Rage OPTEX? Contact Your Local Jobber for Pricing & Availability

Visual examples of best-practice mixing ratios for Rage Optex

In ideal conditions, Rage Optex body filler should be mixed with the corresponding Evercoat Blue Cream Hardener at a 50:1 (fifty to one) ratio, or 2% by weight.

rage optex hardener mixing ratio 50:1

If you have a two-inch puddle of Optex on your board, create a bead of hardener from the center of the puddle to the edge.

optex 4@2x

If you have a four-inch puddle of Optex on your board, create a four-inch bead of hardener across the center from one edge of the puddle to the other.

optex 8@2x

If you have an eight-inch puddle of Optex on your board, create an eight-inch bead of hardener across the center from one edge of the puddle to the other. Then create another bead of hardener next to the first bead starting in the center of the puddle and ending at the edge of the puddle.

Watch this video for more information about how to apply Rage Optex body filler

Interested in trying Rage OPTEX? Contact Your Local Jobber for Pricing & Availability

Rage Optex TDS

Click here to download the Rage Optex TDS document

Additional Resources

Evercoat Body Filler Basics: Prepping, Applying, and Sanding

Easily ID Low Spots with Evercoat OPTEX Super Build 4:1 Primer

Evercoat Light Speed: Ultra-Fast, LED-Cure System

Try Evercoat’s New Online Courses: Lessons Are Free

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