Which Epoxy Resin to Use Low Vis or FLAG?

Once you've decided to use the MAS non-blushing system, the next question we get asked is which resin to use. Here are a few pointers.

Mixing ratio and hardener choice

Both Low Vis and FLAG are part of the MAS non-blushing, no-wax epoxy system. They're a 2-part system, mixed 2 parts resin to 1 part hardener by weight or volume. Hardeners come in slow, medium, and fast.

Both resins offer a low-odour, clear-finish, non-blushing epoxy system that we've found very simple to use, giving predictable, excellent results time after time. The Low Vis and FLAG systems are castor-oil based, which gives them great flow-out, and if you do get any on your skin it doesn't burn — the over-exposure problems that have plagued many older systems simply aren't there. In practical terms, the sensitising effect of older epoxies doesn't seem to be an issue for people using MAS's low-odour, non-blushing system.

Both resins and all three hardeners can be measured out in any of three ways, but make sure you use the same method for both resin and hardener, and keep to the 2:1 ratio.

Three ways to measure your mix

In the workshop we use all three methods, depending on the job at hand:

1. Pumps. We use pumps for small mixes and one-off jobs. Our pumps are precalibrated — blue for resin, red for hardener — so one pump of each gives you the correct 2:1 ratio.
2. Scales. For larger jobs where two or three people might be mixing, or just a large area where we want the mix as accurate as possible throughout the work, we use digital scales, which we cover with cling film to keep them readable and usable. Our most popular mixes are 200g to 100g, and occasionally 400g to 200g — good amounts to use without the pot life running out.
3. Measured beaker or jug. We use this on large areas with a number of operators working on the project, or one person who can work quickly over a large area. We normally mix 2 litres of resin to 1 litre of hardener, using the slow hardener for these mixes.

You can use this non-blushing, low-odour epoxy anywhere you'd have used older-type epoxies, but with more ease of use and a quicker job.

MAS Low Vis Resin: for penetration and saturation

"Low Vis" is short for low viscosity, meaning it's thinner than FLAG resin — it flows more easily and soaks into cloth and substrates. That's a big advantage over older-type resins, which, unless worked and forced into the substrate material, would just sit on top like a patch.

The flow, or viscosity, of liquids is measured in centipoise (cP): water has a cP of 1, and molasses a cP of 10,000, so our Low Vis resin is thinner than most on the market.

Watch our video of MAS Low Vis resin being used to glass a wooden cedar canoe.

What are the advantages of a Low Vis resin system?

When coating, you'll get an easier flow and deeper penetration into the substrate. We recommend all porous substrates be coated with a Low Vis resin and hardener mix. When using cloth or carbon fibre, you get full impregnation through the material with minimal work and fewer voids. Low Vis can be easily injected into voids and cavities, and is ideal for vacuum bagging — remember to add our part-three unit for vacuum bagging, which prevents the chemical reaction starting until the whole job is wet out.

We also use Low Vis resin with fast hardener when making epoxy foam. You can always thicken Low Vis by adding powders to the mix if needed. For an easy, perfect varnish finish: clean the wood back and sand with 120-grit paper, then coat with one or two coats of Low Vis to seal the wood. Once cured, cut back with a light sanding to bring the surface to a grey, opaque state, then apply one coat of your favourite varnish — you'll be impressed with the result.

MAS FLAG: for gluing, fairing and building up

FLAG stands for Filleting, Laminating And Gluing. It's a thicker resin than Low Vis, with dissolved fibres added, meaning you don't have to add as much powder when making up slurries and filleting blends for gluing and tabbing. You can use FLAG simply with its hardener to glue up and laminate.

Where we use FLAG in the workshop

1. Straightforward gluing, and gluing with thickening agents such as Workshop Mix.
2. As a fairing compound: mixed with any of our powders and medium or fast hardener, FLAG makes a great fairing compound on vertical and horizontal surfaces, and its built-in anti-slump agents mean it gels evenly and quickly.
3. As a barrier coat, when coating over a substrate already treated with Low Vis, or over a clothed project, we use FLAG to build up the thickness of the barrier coat evenly and quickly. A workshop tip: Low Vis and FLAG can be mixed together, so if you have some Low Vis left over, you can add FLAG with its hardener to complete the job — or, as we do, cut FLAG and Low Vis together to get a mixture we like to use when building up barrier coats.
4. FLAG also makes a great moulding material when we need to repair broken furniture and similar items.

FLAG has a cP of 2,300, though remember these figures change with the temperature of the resin.

So FLAG can be used for

Fairing — add powders such as Workshop Mix, glass balls, cab-o-sil, etc.
Laminating — use on its own with the relevant hardener, or add powders to achieve peanut-butter or ketchup thicknesses.
And virtually anything else you can think of, from barrier coating to bonding hardware.
Gluing — on its own, with hardeners and additives.

Which one should you choose?

If you need maximum penetration and saturation — coating porous wood, wetting out cloth or carbon fibre, or vacuum bagging — reach for MAS Low Vis. If you're gluing, fairing, laminating, or building up a barrier coat on a vertical or overhead surface, MAS FLAG is the better tool for the job. Many of our own builds use both, one after the other, on the same project.