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Thread: Epoxy question

  1. #1
    Join Date
    Nov 2006
    Austin, Texas

    Epoxy question

    Over the past few months I have used a lot of epoxy (primarily filling flaws in mesquite lumber). In fact a quart of System 3 Resin with a pint of System 3 medium speed hardener, mixed a fraction of an ounce at a time. It is rather fluid, which is great for soaking into cracks, and by the next day it is ready to sand or process (or add another layer if the crack was deeper and the soaking slow). Mixing involved 44% as much hardener as resin, by weight.

    General discussion of epoxy, that I have seen over the years, suggest that some brands or types have a more flexible formulation - use more hardener to harden faster, use less to harden slower. If I have a deep crack, I am delighted to allow time for it to flow, but if I am just filling a small flaw on the surface, I would like to harden faster so I can get on with the process, not wait until tomorrow. No hint of that flexibility with the System 3. Am I not remembering right (at my age that happens too often), or are there other brands of epoxy, that are more flexible in cure speed, that I should consider?
    Charlie Plesums, Austin Texas
    (Retired early to become a custom furnituremaker)
    Lots of my free advice at

  2. #2
    Join Date
    Jul 2011
    The Gorge Area, Oregon

    Selected quotes:
    "Cure time of an epoxy system is dependent upon the reactivity of the amine hydrogen atoms."

    "Cure time for any given epoxy system can be altered only by adding an accelerator in systems that can accommodate one, or by changing the temperature and mass of the resin/hardener mix. Adding more hardener will not “speed things up” and adding less will not” slow things down”."

    "The cure rate will vary by about half or double with each18F (10C) change in temperature. For example, if an epoxy system takes 3 hours to become tack free at 70F, it will be tack freein 1.5 hours at 88F or tack free in 6 hours at 52F. "

    I know there are some accelerators for some types of system 3 (not sure about the general purpose, haven't found any...) but haven't tried any so I don't know how well they work in practice.

    they also sell a 5 and 15 minute epoxy which might fit the bill:

  3. #3
    Join Date
    Feb 2008
    S E Washington State
    When building my little sail boat I bought epoxy from here. They have fast, medium and slow hardeners, and thin, medium and thick resins.
    "We the People ......"

  4. #4
    Join Date
    Jul 2007
    Florida Keys
    Charlie, I would consider West System. Hardeners come in slow, medium and fast. Not only that but they use a pump system to measure the ingredients. Very hard to mess it up. They also have many filler additives available. I've used this product for many years. While it is a product for fiberglass repair, I have used for all kinds of wood projects. I would have to say that it is a little more expensive than other products, but it just can't be beat. The pumps can be left in the product until the can is empty and they are reusable. Very good shelf life even in the heat of South Florida.

  5. #5
    Join Date
    Aug 2008
    Reno, Nv
    For off the shelf, casual use, I like Devcon. different c olors and cure times...which taught me to read labels! 90 minute cure time isn't really needed for pen segmenting.
    Your Respiratory Therapist wears Combat boots

  6. #6
    A little trick I learned. It starts with, if you are going to stain use epoxy, if you are leaving the wood natural, use whatever finish you are going to use. With epoxy thin with acetone 25% or more. The acetone thins whatever epoxy you are using, thus allowing deeper penetration. Then add dust to the thinned epoxy and pack in the crack and wet sand until even. With natural wood use the same process, but with the final finish. Epoxy leaves a noticeable spot on natural finished wood. Using the finish as your epoxy leaves it almost unnoticeable.

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