working with epoxy resin

The first and most important thing to know about epoxies is that they are chemicals that can cause allergic sensitisation through over-exposure. Generally, once you are sensitised there is no going back, and there are many stories from people who can no longer work with epoxy. This is not intended to be alarmist; with basic precautions, you should not have a problem.

All Australian CLC kits are supplied with WEST System epoxy resins and fillers. The mixing ratio of WEST System is 5 parts resin to 1 part hardener (5:1).

Any reference to MAS or other brands of epoxy, or other mixing ratios in the manuals, should be ignored.

We provide digital scales in place of pumps for measuring the correct resin/hardener quantities and use exactly the same method and scales in our workshop.

When thickening epoxy for filleting or filling holes where the boat will be bright finished (varnished), use mostly 413 Microfiber with small amounts of 405 Filleting Blend or wood flour mixed in to match the colour to the plywood/timber. Where thickened epoxy is specified where you plan to paint, omit the 405 completely and use only 413 (403) for thickening your epoxy resin.

In our experience, even “non-blushing” epoxy can produce blush. See the Amine Blush section for further details and guidance on avoiding secondary bonding and finishing problems.

Please read the WEST System manual provided, as well as the rest of this document on working with epoxy resins, before commencing in order to produce the best results.

The Gougeon Brothers on Boat Constuction

For those using WEST System, you can view the Gougeon Brothers book on wood/epoxy boat construction as a downloadable PDF (below). This book is the “Bible” on wood/epoxy boat building and is well worth a read before any project.

the-gougeon-brothers-on-boat-construction-book.pdf

PPE – Personal Protective Equipment

Whenever working with epoxies, follow the manufacturer’s material safety data sheet (MSDS) and keep epoxy off your skin and vapours/dust out of your lungs. This means wearing a good quality respirator fitted with appropriate filters, and always wearing good quality nitrile-based gloves. Do not use disposable supermarket gloves, as they can allow epoxy through onto your skin.

At Denman Marine we use Sundstrom brand respirators (SR100), which are comfortable for extended use. We also use Mediflex MX12 heavy-duty long-cuff nitrile disposable gloves and change them regularly on longer jobs (every ~30mins).

We recommend wearing a good quality respirator with an ABE1 filter (organic vapour + inorganic vapour + acid gas) whenever doing any work whatsoever with epoxy, regardless of the manufacturer’s claims. Epoxy is a hazardous material, and we advise exercising caution.

Always wear a respirator while working with epoxy, including application, filleting, fibreglassing and sanding. Where possible, use a respirator together with dust/fume extraction, such as a vacuum sander.

In addition to thick nitrile gloves, changed often (approximately every 30 minutes), we also recommend wearing full-coverage clothing to avoid getting epoxy on your skin.

Problems

Epoxy resins are generally straightforward to work with. Most problems people have when using them come from:

Incorrect mix ratios
Mixing in contaminated containers
Not mixing the product thoroughly enough before use
Using the wrong hardener for the conditions
Applying epoxy to greasy/oily timbers
Amine blush and secondary bonding
Ambient temperature

Let’s look at these in turn.

Mixing ratios

Most epoxies can be mixed either by weight or by volume. In this case, the ratio is the same.

WEST System used with 205 or 206 hardener uses a 5 parts resin to 1 part hardener ratio (5:1 – see the table at the end of this document). These are the only hardeners we use in our workshop and supply in our kits. We don’t use (or deem necessary) West System’s 207/209 hardeners.

However, some builders may choose to also purchase West System’s 207 or 209 Hardener separately. It is very important to note that these hardeners use a 3:1 ratio.

While you can buy pumps to dispense epoxy, we have found that over time pumps can get out of calibration, gum up due to the viscosity of the resin/hardener, or fail to raise fully, dispensing partial pumps and throwing out the all-important ratio. This is especially evident in cooler climates. Pumps can also be slow to return to the top of the stroke, and it is easy to get distracted and lose count of how many pumps you have dispensed. We find a much easier and simpler way to dispense epoxy/hardener is by weight. In our workshop, and in the kits we supply, we use small digital scales (5 kg capacity) to weigh the epoxy. We keep a mixing chart on our epoxy hot box that tells us exactly how much resin and hardener are required for a total mix quantity. Simple, accurate and effective.

Containers

While it can be tempting to re-use dog food tins, margarine containers and similar items, residual product in those containers can affect the epoxy. We use plastic takeaway food containers because they are cheap, clean and have smooth sides, allowing the epoxy to be mixed thoroughly. You can buy a sleeve of 50 or a box of 500+, and the most useful ones are the round containers designated BS20 and BS30 or similar. A box of 500 will set you back about $60. These are a single use item and are discarded after each mix.

Mixing

Pay special attention when mixing epoxy to ensure the sides of the container are scraped down and the mix is thoroughly combined before use. Stir the resin and hardener together thoroughly for at least one minute, and for longer in cooler temperatures. To ensure thorough mixing, scrape the sides and bottom of the pot as you mix. Use a square-ended mixing stick to reach the inside corner of the pot. If you are using a power mixer, occasionally scrape the sides and corners of the mixing pot while mixing.

The right hardener

Most epoxy systems have hardeners for warmer weather and hardeners for cooler conditions. These hardeners have a lower temperature limit below which they will not cure. WEST System 205 Fast Hardener is suitable for ambient cures down to 4°C, and 206 Slow Hardener down to 16°C. You can use this to your advantage when adjusting cure times. We get cold weather in Tassie during winter, but we do not stop using epoxy. The main hardener we use in winter is 205 Fast Hardener. We also use 206 Slow Hardener on larger glue-ups to give a longer working time, then apply supplemental heat to raise the epoxy to the required curing temperature.

As the ambient temperature changes, and if your kit requires multiple kits of epoxy (e.g. 2x 4.8L kits), you may receive both slow and fast hardener with your order. These can be used interchangeably, or even mixed together to create a “medium” hardener. When both are provided, we recommend using the slow hardener for larger or longer jobs, such as filling fibreglass weave or large-quantity filleting, and the fast hardener for everything else. As the temperature approaches the lower end of the hardener’s recommended curing temperature (see the WEST System manual), the epoxy may need supplemental heat to complete the curing process. See the Ambient temperature section for more information.

Oily timbers

Oily timbers such as teak, Huon pine and white beech can be difficult to glue with epoxy. The key is to prepare the surface thoroughly before gluing. We “key up” the surface with an old saw blade, then wipe the surface down a couple of times with acetone and a clean rag around 5-10 minutes before glue-up. This removes surface oil, and the keyed surface promotes mechanical bonding.

Amine blush and secondary bonding

Amine blush is a by-product of the epoxy curing process. It is a waxy film that forms on the surface of the epoxy during cure and is more prevalent in cooler or humid conditions. Blush will clog sandpaper, so if in doubt, try sanding the cured epoxy with 80/120 grit. If the paper clogs with a waxy substance (often appears as a hard white substance stuck in clumps to sandpaper), you have amine blush. Luckily, it is easy to remove with plain warm water and a Scotch-Brite pad. Scrubbing and then drying by wiping down with paper towels or clean rags (discarding often) will remove it, although you may need to repeat the process a few times to ensure it is all gone. If you are secondary bonding anything to cured epoxy (epoxy, paint/varnish, etc.), sand the area with 80/120 grit sandpaper after de-blushing to key the cured epoxy and allow optimal bonding between layers.

Recoating with epoxy

There are several methods you can use when applying several coats of epoxy. We recommend the methods below for all epoxy products, regardless of claims, including WEST System, Kinetix, MAS, etc.

Long re-coat – more forgiving

Apply a coat, wait for it to fully cure (approximately 24 hours), de-blush, lightly sand to key the previous coat, then recoat.

Short re-coat – less forgiving

You can apply coats one after the other before the epoxy has fully cured. Apply a coat, then wait until it has tacked off. This is when it feels like the sticky side of sticky tape, and little to no residue should come away on your gloved finger. Timeframes for this reapplication window will vary depending on the hardener used, ambient temperature and other conditions. While not always possible, we aim for this method in the workshop due to the time it saves. Once the final coat has cured, de-blush and sand.

Other Tips

Clean up – Use methylated spirits to clean uncured epoxy off tools and the job, but not off your skin. If the epoxy has cured, use a heat gun to warm the cured resin and scrape it off with a triangular paint scraper.
Filleting tools – The best filleting tools give a clean, crisp edge to the fillet, making clean-up much easier. We use metal flat-blade paint scrapers for our filleting tools, and a set will last you a lifetime. You will need a few of them for various fillet radii, and it is easy to file or grind the radius on them. If you forget to clean them, apply a little heat from a heat gun and the epoxy comes off easily.
Epoxy and fibreglass cloth – In modern wooden boat building, fibreglass cloth of various weights is used to reinforce the timber substrate. Epoxy is the resin of choice because polyester resin does not adhere to timber as well, particularly if the timber gets wet, and is less protectant than epoxy.
Epoxy viscosity – Epoxy resins are usually thicker, or more viscous, at room temperatures below approximately 25°C than polyester, and they do not wet out cloth as easily. This is particularly noticeable in cooler climates because the substrate is usually cooler as well, adding to the problem. At Denman Marine (Tasmania) we work with epoxy resins year-round and have found that, in the cooler months, certain techniques are needed to ensure top results when working with resins and cloth. First, we keep our resin and hardener in a hot box, which is a simple MDF box with a filament style light bulb inside (LEDs don’t produce enough heat). The inside temperature sits at approximately 20-25°C year-round. If you think of epoxy like honey, the colder it is, the thicker or more viscous it is; conversely, the warmer the epoxy, the runnier or less viscous it is.
Using heat to lower viscosity – The second, and probably the best tip you will learn about working with epoxy is to use a variable-temperature heat gun to locally lower viscosity. We use cheap Ryobi or Ozito heat guns that allow the user to vary the temperature from 50-600°C. When wetting out cloth with resin, pour the resin onto the cloth, or apply it with a roller, then use the heat gun in one hand, set between 50-100°C, and a squeegee in the other. Gently warm the resin and work it around the cloth. With the viscosity lowered, it will wet out the cloth quickly and easily, even if it is only 5°C in the workshop. As the epoxy is spread out in a thin layer, the heat gun has minimal effect on the total cure time. You can use the same technique when clear-coating timber components. Try it; you will be pleasantly surprised.
Wood flour, 405 Filleting Blend and 413 (403) Microfiber – Another difference you will notice with CLC’s method of thickening epoxy is that the manual will often talk about using a straight wood flour to thicken the epoxy when gluing or filleting. In place of wood flour, Denman Marine now supplies WEST System 405 Filleting Blend in our kits and prefers to use a majority 413 (403) Microfiber mix with a small amount of 405 to colour the thickened epoxy if you intend to bright finish the boat. Straight wood flour is much harder to work cleanly, is harder to sand once the epoxy has cured, and is often a very dark colour compared with the plywood. If you are planning on painting your boat, you can forgo the wood flour/405 completely and use only the 413 (403) agent to thicken your epoxy.

“When thickening epoxy for filleting or filling holes where the boat will be bright finished, use mostly 413 (403) with only small amounts of 405 Filleting Blend to match the colour to the plywood.”

Epoxy cures faster or slower depending on the ambient temperature, hardener used and other conditions. See WEST System’s Epoxy Chemistry page to learn more about the effects of temperature and hardener on curing times.

Ambient temperature

We attempt to tailor the epoxy supplied to your location and the time of year. See our tips below on working in cooler or warmer temperatures.

205 Fast Hardener is formulated to cure at temperatures as low as 4°C, but this requires an extended cure time before removing clamps or sanding. 206 Slow Hardener should not be used below 16°C unless you elevate the working temperature to allow the system to cure properly.

Allow additional cure time before removing clamps or stressing joints. As a general rule, double the cure time for every 10°C drop in temperature. Allow additional cure time beyond the 10°C rule for pre-stressed joints, such as bent laminations, and joints that will be subject to high loads.

The time required for final cure depends on the hardener used and the temperature the epoxy is exposed to. Generally, higher temperatures require shorter cure times. Do not exceed 60°C, and do not remove clamps or load the joint until the epoxy has cooled. CAUTION: heating a porous material may cause air within the material to expand and out-gas. This will be particularly prevalent in epoxy exposed directly to sunlight during application/curing. Allow the epoxy to reach a partial cure before elevating the temperature. If an epoxy coating applied over the material has not gelled, bubbles from the out-gassing material may show up in the cured coating or glued joint as it warms. These can be knocked down with a foam brush as they appear, although you will need to keep an eye on them. Alternatively, these bubbles can be sanded down once cured and a subsequent coat of epoxy applied.

We use WEST System epoxy throughout the year, with temperatures varying from the negatives to 30+°C, and simply tailor our methods to suit the ambient temperature.

If you are still having trouble managing epoxy due to high temperatures, you could look at getting some of WEST System’s 209 – Extra Slow Hardener. Note this uses a 3:1 ratio rather than 5:1. For a WEST System distributor near you, see WEST System’s distributor information.

Cooler temperatures

Use 205 Fast Hardener
As above, keep your epoxy in a hot box.
Use a variable-temperature heat gun to locally lower viscosity during application.
Use supplemental heat to ensure a full cure (increase ambient temperature). Think space heaters, air conditioning, etc.
Use heat lamps to apply heat directly to the area.

Warmer temperatures

Use 206 Slow Hardener
Save large epoxy jobs for the coolest part of the day, or for a day you know will be cooler than others.
Mix small batches of epoxy at a time, such as 50-150g batches.
Pre-prepare as much as possible, and work quickly on larger jobs such as fibreglassing.
Possibly the most important tip: get the mixed epoxy out of your mixing cup as quickly as possible and spread it out. The larger the volume of epoxy, the quicker it will cure. A batch left in a mixing container or bag will cure quicker than when it is spread out. CAUTION: Curing epoxy creates an exothermic reaction (creates heat) and will go off faster as you increase the stored volume. We have seen many a forgotten mixing cup full of mixed epoxy start smoking due to its exothermic reaction. Worst case scenario – if left unattended this may even lead to a fire.
If working with thickened epoxy, spread the thickened epoxy thinly across a clean board, such as a plywood scrap. You can then take a bit more time for precision when applying the epoxy to the job from the board due to the longer curing time compared to a bag or mixing cup.
If working with fibreglass, mix a small batch, e.g. ~100g, pour it straight onto the fibreglass and spread it out for a nice even coat. If required, mix another batch, pour it straight onto the fibreglass and spread it out. Repeat until no more batches are required, rather than mixing larger batches and dispensing slowly from a mixing cup.
Store your resin and hardener in a fridge or cool box to lower the epoxies temperature.
Caution: when cooling epoxy, try to avoid condensation as much as possible, as this may cause curing problems.