Curing With & Without PRO ACCELERATOR

Curing Instructions for “The Coolest Resin!”  
       PRO EPOXY and PRO HARDENER   
       With and Without PRO ACCELERATOR

Summary: 

• Our 24 hour gel time with PRO EPOXY & PRO HARDENER (without PRO ACCELERATOR) is the longest in the industry. This allows for the coolest, thickest clear castings ever: up to 4 inches in one pour! (at 72°F or 21°C). Most thick casting epoxy resin systems gel in 6-12 hours and are limited to 0.5-2” thick in one pour.
  
  
• 1-4% PRO ACCELERATOR speeds the gelation time to as short as 6 hours. This is still a slow gel time, but enables the system to be more practically used for countertop epoxy coatings, bar tops, seal-coats for the live edges of River Tables prior to the main pour, and castings under one inch in thickness. It can also be used to fine-tune the gel times of your deep pour epoxy projects. There is no longer any reason to stock one "deep pour" epoxy for 1.5" deep pours, and another for 2-3" deep pours. 
  
  
• 4% PRO ACCELERATOR added to our mixed resin system is ideal for River Table edge seal-coats because you can coat the edges one day, and it will remain tacky for 24+ hours, thus ensuring good bonding. The next day, make the  deep pour (with zero PRO ACCERATOR in the mix of PRO RESIN & PRO HARDENER) and it will bond very well to the still-tacky seal coat. 
  
  
• With or without PRO ACCELERATOR, our Clear DEEP POUR PRO epoxy system is substantially cured in 5-7 days, but only reaches full hardness (~79-81 Shore D) after 10-21 days cure at room temperature. 10-21 days for full cure is typical for all commercial thick-casting epoxy resins
  
  
• Caution: As a rule of thumb, the speed of reaction (& rate of heat generation) DOUBLES for every 10 °C (18°F) rise in temperature! A thick resin casting that is problem-free when cured starting at 72°F (22°FC) may get way too hot if cured starting at 80°F (27°C). Likewise, if your thick casting is too well insulated from heat loss during cure, it too may get way too hot and crack or even burn. It’s important to experiment with small quantities (100g, 4 0z) of resins first when you first encounter new curing conditions, or at least monitor the situation EVERY MINUTE until well past peak exotherm. When run-away heating happens, it happens very quickly.

• Liquid Densities

Clear-THICK-Cast PRO RESIN density:              1.10 g/cc    9.19 lbs./gal

Clear-THICK-Cast PRO HARDENER density:    0.95 g/cc    7.93 lbs./gal

MIXED 3/1 vol. PRO RESIN/PRO HARDENER   1.06 g/cc    8.86 lbs./gal.

PRO ACCELERATOR density:                            ~1.0g/cc     8.34 lbs./gal.

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Details

Curing Thick Epoxy Castings Without Cracking, Simply Explained, With or Without PRO ACCELERATOR (for Thin Coatings & Castings Under 1 Inch Thick): 

When each epoxy resin group reacts with an amine hardener, it always releases the same fixed amount of heat, called “the heat of reaction.” To fully cure, all of the epoxy groups need to react. Hence, whether an epoxy cures fast, or slowly, the same amount of total heat GETS released. Heat released is called an “exotherm.”

Highly reactive amine hardeners react very quickly, gel quickly and get very hard quickly: in say, 15-20 minutes at room temperature. All of their “heat of reaction” is released in that short time! They get HOT! (They are VERY “Exothermic.”) Even in a small 100 g mass (~4 oz.), this can easily melt a poly beaker, turn the resin yellow or dark brown, & even smoke and burn in a larger mass. For this reason, creating thick-casting epoxies that don’t crack & char is a real technical challenge.

Practically, the only way to do it is to identify hardeners that react VERY slowly, giving the resin mass time to slowly cool during cure, gradually releasing all that heat to the room, through conduction (through the walls of the mold) and convection (to the air). Fans help. 

The thicker the casting, the more the resin insulates itself, the slower the conductive & convective heat losses, & the more the temperature rises. As noted, the reaction rate then increases, further increasing the temperature. At some thickness (which varies with each resin system and curing conditions) for any resin system, the heat becomes so great that the curing resin overheats, cracks, and will char or burn. 

For thick casting resins, the longer the gel time when starting at room temperature, the better.  

Gel Time:

There are many ways to define “gel time.” We define it as the point at which you cannot stir the mixed resin. It can still be semi-liquid, but feels more like a clear “tar” – stringy, and it pulls up when touched with a wooden tongue depressor, but then it very slowly levels back down. We record the temperature during gelation and cure. The highest temperature reached during that time is the “Peak Exotherm Temperature.” This usually occurs shortly after gelation. At this point, most of the heat of reactions has been released into the resin mass.

The gel time of Clear-THICK-Cast PRO EPOXY RESIN mixed 3 to 1 with Clear-THICK-Cast PRO HARDENER is the longest in the industry: 24 hours (100g mass). Since it has more time to release heat from its mass during cure, our system also has one of  the LOWEST peak exotherm in the industry: only ~80 deg F (27 deg. C) for 100 g mass cured at 72 deg. F (22 deg. C). All good. The slowest gelling epoxy will also be the coolest (i.e. it will have the lowest peak exotherm.)

Most commercial competitors have significantly shorter gel times (6 hours+) and therefore much higher peak exotherm temperatures than PRO EPOXY and PRO HARDENER.

In practical terms this means that thicker castings can be made with our resin system than any most any other thick-casting epoxy system in the industry:  up to 4 inches. Others may claim this, but can't do it in one pour.  (We may be slow and thick, but we’re cool!)

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Using PRO ACCELERATOR           (“C-Side”) with

          PRO EPOXY                           (“A-Side”) &

          PRO HARDENER                   (“B-Side”)

Sometimes a faster gelling system is wanted, as for sealing the live edges of a River Table prior to the main pour (to minimize bubbles rising out of the wood), or for a bar top coating, or a casting under 1” thick. Our epoxy system can be made to gel in as little as 6 hours (vs. 24 hours) by adding up to 4% PRO ACCELERATOR to the mix of PRO RESIN & PRO HARDENER. The density of PRO ACCELERATOR is close to 1 g/cc so it doesn’t matter if you use wt. % or volume % in your calculations for PRO ACCLERATOR (only).

In effect, we have developed the first “3-Part” Epoxy System for River Tables, where the same base resin system can be used for Thick Casting AND Thin Coatings/Castings! It is the most versatile system available.  You no longer need purchase & inventory a “Fast Epoxy” for thin coatings or castings, in addition to a “Slow, deep pour epoxy.”

4% PRO ACCELERATOR with PRO EPOXY and PRO HARDENER is ideal for a River Table edge seal coat because you can coat it on one day, and wait until the next day to do the deep pour, since it will remain tacky for 24+ hours  - thus ensuring good bonding. The next day make the main pour (with zero PRO ACCERATOR in the PRO RESIN & HARDENER mix). It’ll adhere very well to the seal coat.

Lower levels of PRO ACCELERATOR can be used to "tune" the gel times of deep pour PRO EPOXY + PRO HARDENER.  Maybe you want to cure a little faster than 24 hour gel times, if your casting or river table is only 1-1.5" thick.  Then add 0.5-1% PRO ACCELERATOR.  In short, you no longer need to inventory two or three different versions of deep pour epoxy, plus a coating epoxy resin.  Now, one resin system can not only meet all your deep pour resin needs, but also many of your thin epoxy coating requirements as well.

One (epoxy) ring to rule them all!
Deep pour epoxies, countertop epoxy coating, seal coat epoxy...

VOLUME %: Example of River Table Edge Seal Coat or Bar Top Coating, using VOLUME % (3 to 1 mix ratio by volume): If you mix 1 quart (32 liquid oz) of PRO RESIN with 1/3 quart (10.7 liquid. oz.) of PRO HARDENER (3 to 1), that’s 42.7 liquid oz. resin mix. 4% PRO ACCELERATOR equates to 1.7 oz added to the mix (for a total of 44.4 liquid oz., or 1.4 quarts).

A simpler example is if you have 100 ml of our PRO resin mix, just add 4 ml of PRO ACCELERATOR

WEIGHT %:  Example when using WEIGHT %: the proper ratio of PRO RESIN to PRO HARDENER is: 3.48 parts PRO RESIN to 1 part PRO HARDENER by weight; (or 1 part hardener/4.48 parts final mix  = 22.3 wt.% Hardener in final mix, and 77.7 wt.% Resin in final mix.) 

The table and graph above both show that with or without ACCELERATOR PRO, it still takes 10-21 days for final cure to be achieved.

Depending on how much PRO ACCELERATOR you add to the PRO EPOXY+ PRO HARDENER mix, you can adjust the gel times and peak exotherm temperatures (for 100 g mass) anywhere between 24 hour gel time (with peak exotherm temperature of 27°C) to 6 hours (with peak exotherm of around 45°C). See graph below.

We have found no benefit of going above 4% PRO ACCERLERATOR in the mix (see graph below). In a similar manner, while adding up to 4% PRO ACCELERATOR does speed up initial gelation and cure, ultimate cure at room temperature still requires 10-21 days.

Speeding-Up Final Cure Through Post-Curing At Elevated Temperatures: 

If you want to speed up final cure to get to highest ultimate Shore D hardness, then only after the PRO RESIN & PRO HARDENER resin mix is hard to the touch (with or without PRO ACCELERATOR), & only after virtually all of the heat of reaction has already been released, you can post-cure it for 1 day at up to 120°F (49°C), for example if you have a wood-drying kiln or a heating blanket. That too will complete the cure, giving you the ultimate Shore-D Hardness.  

• Make sure it is well supported during the elevated temperature cure so there is no sagging of the part. 
• Longer post cures, or more elevated temperature post cures will accelerate resin yellowing.  That's OK if the part is very dark, or yellow to begin with.