Working with Epoxy Resin

Denman Marine's hints and tips for working with epoxy

Working with epoxy resins

The first and most important thing to know about epoxies is that they are chemicals that can cause allergic sensitisation in people from over-exposure. Generally, once you are sensitised there is no going back and there are hundreds of stories from people who can't work with epoxy anymore. I don't mean to be alarmist but if you take some basic precautions you shouldn't have a problem.    

PPE

Whenever working with epoxies follow the manufacturer's material safety data sheet and keep the epoxy off your skin and the vapours out of your lungs. This means wearing a good quality chemical respirator and using good quality nitrile based gloves. Do not use the disposable gloves you buy at the supermarket as they let the epoxy through and onto your skin.

At Denman Marine we use Sundstrom brand respirators which are really comfortable. We also use Mediflex MX12 heavy duty long cuff nitrile disposable gloves and change them regularly on longer jobs.

We always recommend wearing a respirator with an ABE1 filter (Organic vapour + inorganic vapour + acid gas) when doing any work what-so-ever with epoxy, regardless of the manufacturers claims. Epoxy is a hazardous material and we always advise exercising caution.

Always wear a respirator while working with epoxy (application, filleting, fiberglassing, sanding etc.), preferably a combination of respirator and dust/fume extraction (e.g. vacuum sander) where possible.

In addition to thick nitrile gloves (and changing them often - ~30 mins), We also recommend wearing full coverage clothing to avoid getting any on your skin.

Problems

Epoxy resins are generally pretty easy to work with and most of the problems people have with 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 temprature

Lets have a brief look at these in turn:

Mixing ratios
Most epoxies can be mixed either by weight or volume and 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 (see table at end of document).

Kinetix uses a 2 parts resin to 1 part hardener ratio.

Whilst you can buy expensive pumps to dispense the epoxy, we have found that over time the pumps can get out of calibration, gum up due to the viscosity of the resin/hardener and not raise fully only dispensing partial pumps which throws out the all-important ratios (especially evident in cooler climates). This also results in a slow pump action (taking forever to return to the top of the stroke), not to mention it being easy to get distracted when dispensing and forgetting how many pumps you have put into the container. A much easier way to dispense is by weight. We use in our workshop, and supply with the kits, small digital scales (5kg capacity) to weigh the epoxy and keep a mixing chart on the epoxy hot box that tells us exactly how much resin and how much hardener is required for a total mix volume. Simple, accurate, and effective.          

Containers
Whilst it can be tempting to re-use dog food tins, margarine containers etc, there can be residual product in the containers that can affect the epoxy. We use plastic take away food containers as they are cheap, clean and have smooth sides so the epoxy can be mixed thoroughly. You can buy a sleeve of 50 or a box of 500+ and the most useful ones are the round ones designated BS20 and BS30 or similar. A box of 500 will set you back about $60.

Mixing
You should pay special attention when mixing the epoxy to ensure the sides of the container are scraped down and that the mix is thoroughly combined before using. Stir the resin and hardener together thoroughly, at least one minute, longer in cooler temperatures. To assure 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 will have hardeners for warmer weather and some for cooler conditions. These hardeners will have a lower temperature range that they will not cure below. West System 205 fast hardener is good for ambient cures down to 4 degrees Celsius and 206 slow hardener down to 16 degrees. You can use this to your advantage when adjusting cure times. We get pretty cold in Tassie during winter but we do not stop using epoxy. The main hardener we use in winter is 205 fast hardener but we will also use 206 slow in winter on larger glue ups to give a longer working time and then apply supplemental heat to raise the epoxy to the cure temperature.

Often as the ambient temperature starts changing, and if your kit calls for multiple kits of epoxy, 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, however when both are provided, we recommend using the slow for larger/longer jobs (filling fiberglass weave, large quantity filleting, etc.) and the fast for everything else. As the temperature approaches the lower end of the hardeners recommended curing temperatures (see West System manual) the epoxy may need supplemental heat to complete the curing process. See the ambient temperatures 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 properly prior to gluing to ensure success. We "key" up the surface with an old saw blade and then wipe the surface down a couple of times with acetone and a clean rag around 5-10 minutes before glue up. This removes the 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 and it is a waxy film that forms on the surface of the epoxy during cure. It is more prevalent in cooler/humid conditions. The blush will clog sandpaper so if in doubt, try sanding the cured epoxy with some 80 grit and if the paper clogs with a waxy substance you have blush. Luckily it is easy to remove with some plain warm water and a scotch brite pad. Some scrubbing and wiping down with paper towels or clean rags will remove it although sometimes you will need to go through the process a few times to ensure it is all gone. If you are secondary bonding anything to the cured epoxy then give the area a sand with 80 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 implement when applying several coats of epoxy, we recommend the below for all epoxy products regardless of claims (West System, Kinetix, MAS, etc.).

Long re-coat – more forgiving          
Apply a coat, wait for it to fully cure (~24hours), de-blush, light sand to key previous coat, then recoat.

Short re-coat – less forgiving
You can apply coats one after the other before the epoxy has fully cured, simply apply a coat then wait till it has ‘tacked off’. This is when it reaches a point when it feels like the sticky side of sticky tape, you should have little to no residue come away on your gloved finger. Time frames for this window of reapplication will vary depending on the hardener used, ambient temperature etc. While not always possible, we always aim for this method in the workshop due to the time saved. Once the final coat has cured, be-blush.

For those using WEST System, you can view the Gougeon Brothers book on Wood Epoxy boat construction as a downloadable .PDF file

https://www.westsystem.com/instruction/the-gougeon-brothers-on-boat-construction-book/

This book is the "Bible" on Wood/Epoxy boat building and is well worth reading for any project.

Other Tips

• Clean up - use methylated spirits to clean uncured epoxy off tools and the job (not off your skin!)   If the epoxy has cured, use a heat gun to warm the cured resin and scrape off with triangular paint scraper.

• Filleting tools - The best filleting tools give a clean, crisp edge to the fillet making clean up a lot 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/grind the radius on them.  If you forget to clean them up you can 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 are used to reinforce the timber substrate.  Epoxy is the resin of choice here as polyester resin does not adhere to timber well, particularly if the timber gets wet.
• Generally speaking, epoxy resins are "thicker" at room temperatures (below about 25 degrees) than polyester and do not wet out cloth easily if the resin is too thick.  This is particularly noticeable in cooler climates as the substrate is normally cooler as well, adding to the problem.  At Denman Marine we work with epoxy resins year round and have found that in the cooler months certain techniques are needed to help work with resins and cloth.  Firstly, we keep our resin and hardener in a "hot box" which is a simple box made from MDF with a light bulb inside.  The inside temp sits at approx 20-25 degrees year round.  If you think that epoxy is like honey, the colder it is the more thick or viscous it is and conversely, the warmer the epoxy, the runnier or less viscous it is.
• The second and probably the best tip you will ever 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 temp from 50-600 degrees. When wetting out cloth with resin, pour the resin onto the cloth (or apply with roller etc) and then use the heat gun in one hand (set on between 50-100 degrees) and a squeegee in the other.  Gently warm the resin and work it around the cloth and with the viscosity lowered, it will wet out the cloth very quickly - even if it is only 5 degrees in the workshop.  As the epoxy is spread out in a thin layer, the warming really has minimal effect on the 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.  One difference you will notice with CLC's method of thickening epoxy is the manual will often talk about using a straight wood flour/resin mix to thicken the epoxy when gluing or filleting. In place of wood flour, Denman Marine now supplies West Systems 405 filleting blend in our kits and prefer to use a majority 413 (403) microfiber mix with a small amount of 405 to colour the mix 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 very dark in colour comparatively to 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 and the hardener used etc. See West System’s Epoxy Chemistry page to learn more about the affects of temperature and hardener on curing times etc.

Ambient temperature

We will attempt to tailor the epoxy supplied to your location/time of year. However when working in cooler or warmer weather, please see below for a few tips.

205 Fast Hardener is formulated to cure at temperatures as low as 4°C, but this does require 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 more than 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.” 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 simply be knocked down with a foam brush as they appear, however you will have to keep an eye on it. Alternatively these bubbles can be sanded down once cured and a subsequent coat of epoxy can be applied.

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

West System have an excellent article on Epoxy Chemistry here which describes using epoxy in different ambient temperatures. If you are still having trouble managing epoxy due to high temperatures, you could look at getting some of West System’s Extra Slow Hardener, however please note this uses a 3:1 ratio rather than 5:1. For a West System distributer near you, see here.

Cooler temperatures

• As above; keep your epoxy in a hot box
• Use a variable temperature heat gun to locally lower viscosity
• Apply supplemental heat to ensure a full cure
  • Heat your workspace with some form of heater
  • Use heat lamps to apply heat directly to the area

Warmer temperatures

• Try saving large epoxy jobs for the coolest part of the day or a day that you know will be cooler than others
• Mix up small batches of epoxy at a time 50-150g batches
• Pre-prepare as much as possible, and work quickly on larger jobs (e.g. fiberglass)
• Possibly the most important tip; get the mixed epoxy out of your mixing cup as quickly as possible and spread out. A batch of mixed epoxy will cure a lot faster when left in a volume, e.g. mixing container or bag. Curing epoxy creates and exothermic reaction (creates heat), and will go off faster as you increase the stored volume.
  • If working with thickened epoxy, you can spread the thickened epoxy out as thinly as possible on a clean board (e.g. plywood scrap), you can then take a bit more time for precision when applying the epoxy to the job from the board rather than a bag or mixing cup.
  • If working with fiberglass, mix a small batch (e.g. ~100g), pour it all straight onto the fiberglass and spread it out for a nice even coat. If required, mix another batch and pour it straight onto the fiberglass, spread out. Rinse and repeat until no more batches are required. Rather than mixing up a large batch and dispensing slowly from a mixing cup etc.
• Store your resin and hardener in a fridge or cool box to lower its temperature
• You can put together a makeshift cool-box, simply put some ice in a small insulated box and store the mixed epoxy you are working with at the time. E.g. a container or bag of thickened epoxy can be placed in or on ice as you are applying it to the job
  • This can be used in conjunction with storing the resin and hardener in a fridge/cool box

Caveat; when cooling epoxy, try to avoid condensation in your mixed batches as much as possible as this may cause final cure problems.

Please ensure you read the WEST System manual provided with your kit on working with epoxy resins.