Epoxy dilution: what you need to know

Epoxy dilution: what you need to know

How to dilute epoxy and what to consider before the dilution process

Reducing the viscosity of WEST SYSTEM® epoxy by adding a solvent can facilitate the application process, as well as deeper penetration into porous surfaces such as partially rotted wood and faster saturation in glass cloth. For these reasons, a lot of people are attracted to the idea of ​​epoxy dilution. However, what should not be overlooked is that reduced viscosity can change the composition of epoxy, which affects strength as well as moisture resistance. It will also affect the time it takes for the epoxy to turn into a gel. Before you decide to dilute epoxy, it is important to consider the benefits and potential risks. If you decide to dilute, the next thing you need to consider is whether to use heat or solvent to dilute your epoxy.

Common misconceptions about epoxy dilution

The technical staff at West System International often talk to customers who believe epoxy needs to penetrate deep into the wood to be effective. While this may be the case, it is generally not necessary, which means that users often consider diluting epoxy when it is not actually useful.

The rarer it is, the more likely it is to be more porous.

A non-diluted epoxy coating on a surface, for example, provides much better water resistance than a diluted epoxy because the rarer it is, the more likely it is to be more porous. Similarly, adhesion depends on the surface of the joint, the strength of the wood, and the strength of the adhesive used, not how many think how deeply epoxy has penetrated. When it comes to rotten wood, although diluted epoxy will surely harden it, it will not regain its original strength. If you are considering diluting epoxy for any of these reasons, you should be aware of the possible implications and whether it is really necessary. If you think it is necessary, then our guide will tell you what you need to know to dilute epoxy effectively:

Epoxy dilution using heat

There are two options if you want to dilute the epoxy with heat. You can heat the resin and hardener separately and then mix them together to get a diluted epoxy; or you can heat the surface — such as wood — and apply your mixture of resin and room temperature hardener to the heated surface.

The heated mixture of resin and hardener retains all the characteristics but the hardening is faster. Using WEST SYSTEM 206 Slow Hardener® or WEST SYSTEM 209 Extra Slow Hardener® can help, as these two hardeners harden more slowly giving you more time to work with heated epoxy.

If you are coating wood, the best method is to heat the wood rather than epoxy. Remove the heat source just before applying the epoxy and the mixture will dilute when it comes in contact with the wood. As the wood cools the epoxy penetrates deep before the “Gell” phase, and expels air from the wood fibers. Whichever method you use, you should be able (without any interference) to touch epoxy containers or wood, so heat them to a maximum of 35 ° C. Overheating causes the epoxy to harden too quickly. If you notice smoke from hardened epoxy, it is very likely damaged and should be replaced as a precaution.

Dilute epoxy using a solvent
Adding solvents … can make drastic changes.

While heating the epoxy can allow you to retain the original characteristics of the same, adding solvents such as acetone, varnish thinner or denatured alcohol can make drastic changes. We by no means recommend diluting epoxy with a thinner at any time, and here’s why:

-Adding 5% thinner to the epoxy varnish reduces the epoxy’s compressive strength by 35%. As such, it is no longer compatible as a structural adhesive.

-Adding solvents can extend the curing time, making your job unpredictable.

-Addition of solvents can cause the epoxy to compress and crack over time. This happens if the solvent does not evaporate before the epoxy hardens, but comes out of the mixture after a while.

-Adding solvents such as acetone can change the color of the hardened epoxy.

-Adding solvents can damage substrates such as styrofoam – so test your solvent on the substrate before diluting your epoxy.

-Adding solvents can increase the risk of fire and damage your health.

-Adding solvents to soak the glass reinforcement faster can create parts without enough resin if excess epoxy leaks out of the vertical surfaces.

Our recommendation is to always dilute the epoxy using heat as this allows you to retain the original characteristics of the epoxy and make it as unpredictable and risky as diluting with a solvent. This recommendation comes with a caveat, though: by diluting the epoxy, you are changing the composition of WEST SYSTEM products that have improved over the years. That doesn’t mean you should never do it, but it does mean you should think and act


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Comment (1)

  • Peter Reply

    If a solid component is added to the epoxy, which already will encourage it to cook off faster, and it is diluted with heat, cook off times may become so short as to render the work very difficult to impossible.

    18/08/2022 at 3:08 AM


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