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Guide to casting solvent free epoxy systems

Rev07/20

GreenCast 160, Surf Clear EVO, GreenPoxy 33

GreenCast 160 – Bio-based, water clear, UV stable epoxy for thick castings

River tables, clear epoxy sculptures and encapsulations, wood and resin combinations such as furniture, chopping/serving boards and large pen blanks.

Surf Clear EVO – Bio-based, water clear, UV stable epoxy for thin castings and coatings

Tabletops and bar counters including with embedded items such as bottle tops and coins. High gloss finishing cast onto thick cast epoxy. Resin jewellery, pen blanks, knife scales, 3D layered resin art, water effects for architectural models.

GreenPoxy 33 – Bio-based, epoxy for thick castings (slow hardener) and coatings (fast hardener)

River tables, pigmented epoxy sculptures, wood and resin combinations such as furniture, chopping/serving boards and large pen blanks.

Introduction

Aerontec has a number of bio-based epoxy systems that are suitable for casting and artistic work. This guide will get you started in the exciting world of epoxy casting, noting that our technical advice is given in good faith but without warranty. All products are sold upon condition that purchasers will make their own tests to determine the quality and suitability of the product for their particular application and circumstances.

Have fun with these products but remember that in the liquid state, the resin and hardener should be considered toxic and handled with caution, such as using gloves and eye protection and working in a ventilated area. Once the resin and hardener have been correctly mixed and fully cured, the result is a stable and inert plastic that is not toxic. It is suitable for incidental food contact purposes (short term) such as cutting boards but these epoxies do not have FDA or Food Safe certifications which may be required for commercial applications.

GreenCast 160 / SD7160

Bio-based, clear, UV stable epoxy for thick castings using the SD7160 mega slow hardener. The resin has a light blue appearance. This system is easily pigmented with Aerontec’s range of epoxy pigments for translucent, opaque and luminous effects. This product has been designed as a casting resin, not a coating resin. The open surface typically needs to be flatted and polished to achieve a perfectly flat, glossy finish. The open surface can also be coated with Surf Clear Evo to produce a high gloss, flat finish.

UV Stability – This product will resist yellowing and is water resistant, however, it does not provide 100% UV protection and is not suitable for permanent, outdoor exposure. UV protection can be improved by overcoating with protective urethane paint such as Sicomin TopClear or UV resistant wax polish.

Curing Time – Depends on the ambient temperature but around 48hrs to touch-dry, but longer in thin castings. Allow at least 72hrs before demoulding or attempting to do any finishing work on the resin. The epoxy will take about 30 days to reach full hardness although this can be accelerated with a post cure of 24hr @ 40 to 60°C.

Kit – Each kit contains a bottle of resin and a bottle of hardener which are mixed together at 100:42 parts by weight or 2- parts resin to 1-part hardener by volume.

Coverage: 885 millilitres per 1 kg with 1 litre covering 1 square meter to 1mm of thickness

Surf Clear Evo

Bio-based, clear, UV stable epoxy for thin castings, surface coatings and laminating. The resin has a light purple appearance. This system is easily pigmented with Aerontec’s range of epoxy pigments for translucent, opaque and luminous effects. Evo has been designed as a coating resin or thin casting resin. It cures to a high gloss, level surface. It is not suitable for thick casting as it will exotherm.

UV Stability – This product will resist yellowing and is water resistant, however, it does not provide 100% UV protection and is not suitable for permanent, outdoor exposure. UV protection can be improved by overcoating with protective urethane paint such as Sicomin TopClear or UV resistant wax polish.

Curing Time – Depends on the ambient temperature but around 2hrs to gel. Allow at least 24hrs before demoulding or attempting to do any finishing work on the resin. The epoxy will take about 30 days to reach full hardness although this can be accelerated with a post cure of 16 h @ 60 °.

Kit – Each kit contains a bottle of resin and a bottle of hardener which are mixed together at 100:41 parts by weight or 2-parts resin to 1-part hardener by volume.

Coverage: 909 millilitres per 1 kg with 1 litre covering 1 square meter to 1mm of thickness

GreenPoxy 33 / SD477x

Bio-based general-purpose laminating and casting epoxy. The slow casting 4771 and 770 hardeners are clear while the fast 4775 and 4777 hardeners are yellow-brown. Typically used for sealing wood with the fast hardener and medium to thick castings with the slow hardeners.

UV Stability – This epoxy is not UV stable and must be pigmented to conceal UV yellowing.

Curing time – The various hardeners can be blended to change gel times. SD4771 hardener is touch dry in 11 hours (30°C) and SD4770 in 15 hours (30°C).

Kit – Each kit contains a bottle of resin and a bottle of hardener which are mixed together at 100:27 part by weight or various ratios by volume as per the data sheet.

Coverage: 909 millilitres per 1 kg with 1 litre covering 1 square meter to 1mm of thickness

Before you get started

You will need various ancillary items to make a success out of your epoxy project. It is recommended you have the following at hand before you open the epoxy containers.

  • Work Space – A dust free, ventilated room where you can mix, splash and spill sticky epoxy without care. For large pours that can get hot it can help to have air-conditioning or fans blowing air over the table to keep the resin temperature down.
  • Digital scale – nothing fancy, but able to measure 1-gram increments. Protect it with plastic if you’ve stolen if from the kitchen!
  • Nitrile or latex gloves – Epoxy is very sticky and the hardener component is corrosive to skin. Aerontec Tuff Gloves are thick, black nitrile gloves perfect for protecting your hands while having fun!
  • Eye protection – Epoxy hardener is corrosive so protect your eyes when mixing and pouring epoxy.
  • Dust mask – Wear a dust mask when sanding or machining epoxy. Don’t inhale epoxy dust.
  • Graduated Mixing Cups – Accurate measurement is extremely important to achieve the optimum cured properties. Even if you are using a scale, you’ll need plastic or coated paper mixing cups.
  • Clean Mix Sticks – Bamboo mixing sticks or wooden tongue depressors. Dirty sticks can cause contamination of the epoxy.
  • Plastic Squeegees – Great for spreading epoxy, they will not leave air bubbles behind as brushes can.
  • Brushes – Mostly for sealing wood before casting. Use a decent brush that won’t lose bristles in your artwork.
  • Flash tape – Very strong tape with pressure sensitive adhesive. Aerontec supply 12.5, 25 and 50mm width.
  • Solvent – Acetone for spill clean-up and cleaning surfaces before re-casting.
  • Propane Torch, Heat Gun or Hair Drier – Used by sweeping the heat or flame across the surface of the uncured
  • epoxy to pop air bubbles.

Beginners Tips

To avoid most of the common problems you should always do a trial run with the product to ensure you have a proper understanding of how to use the epoxy. The following guide covers casting with epoxy and is generally applicable to both casting and coating systems.

Epoxy quantity – To determine the quantity of epoxy you require, calculate the volume that you need to fill. If the cavity is an odd shape, filling it with rice and then pouring the rice into a measuring cup can work.

Otherwise estimate the volume by multiplying:

length (meters) X width (meters) x height (millimetres) = volume litres x 1.2 (specific gravity) = kg of mixed epoxy

Temperature – For best results the product should be used in conditions between 18° C to 25° C. Cooler resin will be thicker (more viscous) and more prone to air entrapment. Warmer conditions increase the risk that the epoxy could exotherm (overheat) during the cure which can cause it to crack, distort and discolour.

Work Space – The room you are working in should be clean, dry, dust and insect-free. Settling dust can often cause imperfections on the surface of the epoxy as it is curing. Make sure your project surface is level. If not level, the epoxy will pool at the lowest point. Epoxy often ends up on the floor, so take precautions.

Wooden Surfaces – For applications incorporating wood, the wood surface should be planed or sanded first and then cleaned until dust-free. It is also important that any prior stains or finishes be completely dry before beginning. Any types of moisture, oils, greases or uncured finishes can potentially cause fish-eyes or product curing problems. Oily hardwoods such as olive and teak require thorough washing in acetone to prevent fisheyes in coatings. Make sure the wood is clamped down, as it may float in the epoxy!

Measuring epoxy – Always make sure that your mixing container is clean and your measuring device is accurate. ACCURATELY follow the weight or volume mix ratio, using either a gram scale or graduated measuring cylinder. If you get the mix ratio wrong by a small amount the resin will cure but the mechanical properties will be decreased. However, if you were out by anything more than a few grams the resin would not be properly hard when cured and may have a tacky finish.

Mixing epoxy – Thorough mixing is the most important part of this procedure. Even if you have experience with other types of resins, it is very easy to underestimate the amount of mixing this product requires.

Depending on the quantity being mixed, it can take anywhere from 3 to 5 minutes of continuous mixing. During mixing the epoxy will turn cloudy and you must continue to mix until all signs of haziness and white streaks in the mixture have become transparent. To reduce air entrapment, mix slowly and purposefully without whipping air into the resin. Always scrape the sides of the mixing container and stick during the mixing process. As the epoxy at the bottom or sides of the container may not be mixed correctly, pour the mixed epoxy into a new container, that you will use to pour into the mould. This is termed double bucket mixing.

Pouring – Pour slowly, and preferably in the same place allowing the resin to find its own level. You can pour the resin through a flour sieve to break the surface tension to reduce bubbles. If any unmixed material remains on the side of the container and falls onto your surface while pouring it will leave an uncured sticky spot. While pouring the epoxy onto the surface, NEVER scrape or brush the sides or bottom of the container you just mixed in to remove every last drop. No matter how thoroughly you may have mixed, there will always be an unmixed portion which can be dislodged and will leave a wet or sticky spot.

Exotherm – Never leave mixed epoxy in your bucket unattended. The longer the epoxy sits in your bucket, it will increase the chances that the epoxy will exotherm and generate excess heat, begin to smoke and then cure quickly inside the bucket.

Mould materials and Release agents
A mould of some form is required when casting epoxy. The mould is a liquid tight form that prevents the epoxy from ending up on your floor! Note that when casting onto a wooden surface that the liquid epoxy can easily seep through the top surface to the bottom surface and thence onto the floor unless contained by plastic sheeting or a solid base. Moulds made from silicone rubber, polyethylene and polypropylene plastics do not need release agents although for multiple castings in silicone a suitable release agent will prolong the life of the mould.

For large castings such as river tables, melamine or polypropylene plastic sheet is typically used to make a box. The edges have to be waterproof using model putty, hot glue, adhesive, flash tape or similar materials.

Melamine must be coated with an appropriate release agent to prevent the extremely adhesive epoxy from bonding to it. Paste or aerosol wax, such as Mikon Mirror Wax or F-57 aerosol wax can be used while brown packing tape, normally made from polypropylene, makes an excellent low-cost release material.

Sealing porous wood surfaces
Before casting epoxy over porous surfaces such as wood, the surface should be sealed with epoxy to eliminate the risk of air bubbles coming out of the wood while the casting resin cures. The sealing coat is brushed onto the surface and fast gelling epoxy such as Surf Clear Evo or GreenPoxy 33 with fast hardener are ideal.

GreenCast 160 an also be used but it will take at least 48hrs before it has gelled sufficiently to seal the surface. Usually only one seal coat is required, however extremely porous wood or knots in the wood may need multiple coats in order to fully seal the surface. Ideally, warm the wood before applying the seal coat. This will expand the wood pores and release air and oils. Then wipe with acetone and paint the warm wood with epoxy. When the wood contracts, it soaks the epoxy into the pores, which leads to a better bond.

Pigmenting the epoxy
There are a wide range of epoxy pigments, typically sold in 50-gram containers. These can be used to produce translucent, opaque and luminous effects. The pigments are generally very powerful and only a small quantity is required to achieve great results. Thicker castings require a lower percentage of pigment because the colour appears stronger the thickness. Similarly, thin castings require a higher percentage of pigment. Note that in extremely slow casting systems such as GreenCast 160 pigment colours will disperse and combine during the very long liquid stage of cure. You can experiment with the amount of pigment you desire but ideally do not exceed 5% parts by weight of the mixed resin and hardener with liquid and paste pigments. Powder pigments can often be used at up to 300+% loading.

Filling with luminous powder
The epoxy resin can be filled with luminous powder. Any quantity of powder up to a maximum of 300% by weight can be cast. Note that the luminous powder has the consistency of sand and will settle out of the epoxy. It should therefore be cast in thin layers close to the surface of the part, where it will be exposed to light.

Casting
When casting onto wood, the insulating effect (particularly if you also have a wooden mould as well) can prevent the resin from cooling as it cures, increasing the resin temperature and possibly leading to exotherm. This is particularly important when working in high ambient temperatures. Often some sort of forced cooling is required such as metal moulds with fans used for cooling or even air conditioning the casting area. You need to assess the risk of exotherm based on your experience with the product in your environment and that will dictate the maximum casting thickness. If a single casting is not feasible, split the pour into multiple layers. The following layer can normally be cast as soon as the first layer has gelled to a sticky solid and the epoxy temperature in the casting has returned to ambient.

Coating
When coating a surface, such as a counter top, the flood coat should be poured onto the surface and allowed to flow and self-level. You can use flash tape around the edges to dam the epoxy. Use a plastic squeegee to help spread the epoxy. Generally, one to three flood coats are applied for most table and bar coatings. Deep pour resins such as GreenCast 160 can reduce this to a single pour but take a long time to cure in thin sections. You will need approximately 2kg mixed epoxy per square meter to ensure there is enough resin to self-level. The best way to apply the flood coat on tables, is to pour the epoxy in the middle and allow the epoxy to flow out. For counters, start on one end and pour the epoxy the entire length. Use a plastic squeegee or foam brush to help guide the material around.

Popping bubbles
Mixing the epoxy resin and hardener will introduce bubbles into the liquid. In commercial environments the mixed resin is normally vacuum degassed to ‘boil’ out the bubbles. This requires a vacuum pot and a vacuum pump. Pouring the resin will also entrap and introduce air bubbles. The best tool for removing bubbles is a small propane torch. By holding the heat source approximately 300mm away from the surface and quickly sweeping across the surface you will immediately see the bubbles start to pop. Don’t let the flame linger on the surface! Other tools that can be used to pop the bubbles are a heat gun or a hair drier. However, both of these tools move air around which increases the risk of dust settling in the coating. It is a good idea to continue popping bubbles every 30 minutes until the epoxy has gelled.

Re-Coating
Re- coating is often necessary when multi lay casting, repairing or using a faster epoxy such as Evo for a final high gloss finish. When re-coating onto a gelled but tacky epoxy layer, no surface preparation is needed. The layers will bond together as one. If you allow the previous layer to fully cure (i.e. hard surface with no tack), very light sanding with 120 grit sand paper is necessary to key the surface and promote adhesion. After sanding, you should wipe down the surface with a solvent such as acetone or denatured alcohol (not paint thinners, mineral spirits, benzine). The wipe down process with the solvent should be done with a clean rag that will not leave any lint on the surface. Our Aerowipe lint-free cotton cloths are perfect for this application. Continue cleaning until all sanding dust has been completely removed. You are now ready to re-coat. The next pour will fill in the sanding scratches and make them disappear.

Curing
After applying your final coat, the product should be kept in a clean and dust-free environment until cured. The time to cure touch dry varies with the epoxy type and the ambient temperature. For every 10° C rise in ambient temperature the cure time will halve (and vice versa, double the time if cooled). At temperatures below 18° C the product will take a very long time to cure. Once touch dry the epoxy is not yet fully cross linked and has not achieved its full mechanical properties, which typically takes up to 30 days unless post cured. The first couple weeks after curing the surface is therefore more prone to scratching, but as the product ages its hardness will increase.

Amine blush
In cool ambient temperatures and high humidity, the epoxy surface may develop an amine blush, leaving a waxy, oily, tacky surface. This will interfere with adhesion if overcoated. If amine blush is detected it should be removed by thoroughly washing the surface with warm water and detergent. Solvents will not remove amine blush.

Finishing to high gloss
The cast epoxy surface may end up with an orange peel effect if the final cast has taken a long time to cure (e.g. if a very thin layer of slow epoxy was cast), while a thick layer that gets hot will also produce a lumpy surface as the hot epoxy circulates toward the surface. In most cases, sanding and polishing work will be required to finish the cast surface to a high gloss. There are many approaches that can work compared to the options covered below and results will vary with the degree of experience and equipment used.  Remember, the cast surface is a plastic that will melt at low temperatures if excessive friction heat builds up.

Wear a dust mask and protective clothing when sanding epoxy! Epoxy dust is hazardous and should not be inhaled or allowed to settle on the skin.

The first method to achieve the final flat, gloss surface, is to sand the surface relatively flat and then cast a thin layer of Surf Clear Evo. Sand the surface flat with 100 sandpaper until no shiny dimples are visible anymore.

Round the edges where required and use flash tape around the edges as a dam if necessary. Apply Surf Clear Evo (2kg/m2 is required for a self-levelling coat) using a spatula and a roller on the edges. Cover the wet epoxy surface with a plastic tent to prevent dust contamination. If no dust is visible, wash with soap and polish with high quality plastic polishing compound. Otherwise remove blemishes with 1000 or 1500 water paper and then polish.

The second method involves cutting back the epoxy and wood to a perfectly flat surface. This contrasts the natural wood with the glossy epoxy but requires sanding or machining of the whole surface and then polishing the resin to high gloss. This is the normal approach for commercial river tables and similar products.

If the surface is very uneven, route the surface, removing less than 1mm per pass to prevent ripping into the surface. A drum sander can also be used to level the surface. Ensure there is no amine blush on the surface (wash with warm soapy water then dry thoroughly), to ensure the sand paper does not clog. Use 120-200 grit paper, removing 0.5-1.0mm maximum per pass.

An orbital sander can be used to flatten the surface. Begin with 100 grit until no shiny dimples are visible. Progress with water paper 220, 360, 600, 1000 and 1500 water paper. No scratches from the previous paper must stay behind. Use high quality plastic polishing compound and follow the recommend directions to achieve a high gloss finish. Swirl remover and hand glaze are typically used after polishing paste.

Health and Safety
As with any chemical, poor handling or misuse of epoxy could be potentially hazardous to health, therefore it is essential that the appropriate safety procedures are observed for the safe handling and use of these products. In general, the epoxy component of a solvent-free system is a skin irritant, while the hardener is a corrosive liquid.

  • Avoid skin contact by wearing appropriate clothing and latex or nitrile gloves.
  • Safety glasses are required to prevent resin or corrosive hardener splashing into the eye.
  • Wear a dust mask to prevent inhaling epoxy dust when working with cured epoxy, such as sanding or cutting.

Disclaimer
All statements, technical information and recommendations, including storage, contained in this publication are based on tests believed to be reliable, but their accuracy and/or completeness are not guaranteed. Our technical advice, whether verbal or in writing, is given in good faith but Aerontec gives no warranty; express or implied and all products are sold upon condition that purchasers will make their own tests to determine the quality and suitability of the product for their particular application and circumstances. Any information or suggestions are without warranty of any kind and purchasers are solely responsible for any loss arising from the use of such information or suggestions. Before using any of our products, users should familiarise themselves with the relevant technical and safety datasheets. The information contained herein is under constant review and liable to be modified from time to time.

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