FlowCast vs. UVPoxy: Which EcoPoxy to Use, How Much to Buy, and Pouring Tips

We stock two EcoPoxy formulas, and nearly every epoxy question we get at the counter comes down to which one to use. Here is the short version, followed by the details that matter once you start mixing.

Which epoxy do I need?

The short answer

It comes down to how much epoxy you are pouring at once, not just how deep. For a river, a large void or any pour deeper than about 1/4 in across a big area, use FlowCast. For coating a surface or filling small holes, use UVPoxy. Most river tables use both: FlowCast for the river, then UVPoxy as the clear finish coat over the whole top.

Why volume matters: epoxy makes its own heat

Epoxy is a two-part liquid that cures through an exothermic chemical reaction. When the resin and hardener are mixed, the reaction gives off heat, and that heat is what drives the epoxy to cure from a liquid into a solid.

The more epoxy in one place, the more heat it builds. Past a certain point, too much heat causes problems: the epoxy can bubble, turn cloudy, and worst of all shrink too much and crack.

That is why the two formulas exist:

• UVPoxy mixes 1 to 1 and cures fast, setting up within about 4 to 6 hours, and even faster when it is hot. A thin coat spreads that heat out, but a large, thick pour of it can overheat.
• FlowCast is formulated to cure slowly so the heat builds gradually. Even so, its cure time depends on volume: a 1/2 in layer might take a week or up to two weeks to fully cure, while a 2 in pour in hot weather can "flash cure" overnight or within two days, and that is when it is at risk of cracking.

There is no exact formula for the limit, but the volume and the temperature of your shop decide how fast the epoxy cures and how hot it gets. When in doubt, pour thinner layers.

Small holes: tabletop epoxy is fine

Because it is the volume that builds heat, a small fill does not need deep pour epoxy, even when it is deeper than 1/4 in. A common knot hole about 1 in across and 1/2 to 3/4 in deep can be filled with UVPoxy in a single pour. There is so little epoxy in it that it will not get hot enough to cause trouble. Larger voids and long cracks can be filled with UVPoxy too, as long as you build them up in several thin pours instead of one, or fill them in one go with FlowCast. Save FlowCast for rivers and other big pours.

FlowCast: the deep pour epoxy

FlowCast is a slow-curing casting resin made for thick pours. It runs thin, so air bubbles rise out on their own, and it builds heat slowly as it cures, which helps prevent cracking and warping in a big pour.

• Use it for: river tables, filling voids and cracks in live edge slabs, casting and embedding objects
• Pour depth: 1/2 in to 1-1/2 in per layer, and no more than 20 liters in one layer. Past about 12 liters, thinner layers help keep the heat down
• Mix ratio: 2 parts resin to 1 part hardener by volume
• Working time: about 8 to 12 hours
• Cure: depends on the volume and temperature; a 1/2 in layer can take one to two weeks to fully cure, while a thick pour in hot weather can cure much faster and risk cracking
• Kits: 6L, 12L and 30L

Going deeper than 1-1/2 in? Pour in layers. Pour the next layer while the last one is still tacky (about 20 to 44 hours), or wait at least 72 hours, scuff the surface with 220 grit and then pour. Do not use FlowCast for anything thinner than 1/2 in; it is too slow and thin for a coating.

UVPoxy: the tabletop epoxy

UVPoxy is a thicker, faster-setting epoxy for clear coats. It levels itself into a glossy finish and has UV stabilizers that help it resist yellowing.

• Use it for: tabletops, bar tops, countertops, small knot holes and checks, larger voids and cracks in several thin pours, a seal coat on wood before a deep pour, and the top coat over a river table
• Coat thickness: up to 1/8 in per coat; build up with more coats
• Mix ratio: 1 to 1 by volume
• Working time: about 30 to 40 minutes
• Cure: sets up within about 4 to 6 hours, faster when it is hot
• Coverage: about 3.4 sq ft per liter at 1/8 in thick, or about 26 sq ft per liter as a thin seal coat
• Kits: 1L, 2L, 4L, 8L and 20L

For more than one coat, pour the next coat while the last one is still tacky. Because it cures fast and builds heat in the bucket, mix anything over 4 liters in separate batches rather than one big bucket.

How much do I need, and which kit size?

Use the epoxy calculator near the top of this post (it is also on our EcoPoxy page). Enter the length, width and depth of your pour and it gives you liters and gallons (with a little extra for waste), the resin and hardener amounts, and the cheapest combination of kits. If a pour is over 20 liters, it tells you how many layers to split it into.

A few rules of thumb:

• Size up if you have more projects coming. Larger kits cost less per liter, and leftover epoxy keeps if you seal it.
• A river needs more than you think. Live edges are irregular and wood soaks some resin up. Measure the river at its widest points, not the average.
• Do not forget the seal and top coats. A typical river table uses FlowCast for the river plus a 1L or 2L UVPoxy kit for the seal coat and finish.

Before you pour

• Start with dry wood. Wet wood keeps releasing moisture and air into the epoxy. All of our slabs are kiln dried.
• Seal the wood first. A thin coat of UVPoxy on the live edges and any open grain stops bubbles from rising out of the wood into your pour.
• Tape cracks and line your mold. We press sheathing tape over the underside of cracks, knots and voids so resin cannot leak through, and use it to line river table molds. Cured epoxy peels right off it.
• Dark fills. For a hole on a vertical edge, or where you want a fill that looks like a dark knot, black epoxy sculpting clay packs in and stays put.

Measure carefully

The ratio is a chemical recipe, not a suggestion. If you are off even a little, the reaction will not finish and you end up with a gooey mess that never cures.

• Measure the larger part first. FlowCast is 2 parts resin to 1 part hardener, so measure the resin first, then the hardener.
• Check your math. A 2 to 1 ratio does not always land on round numbers. Work it out before you start pouring.
• Use marked cups. Graduated mixing cups with the mix ratios printed on the side make this much easier. We use EcoPoxy's in our shop and carry them at the store.
• Mix thoroughly and scrape the sides and bottom. Unmixed resin along the walls of the bucket is the most common cause of soft spots.

Bubbles and cloudiness in tabletop epoxy

The most common complaint we hear about tabletop epoxy is bubbles and a cloudy look. Some cloudiness is normal at first: when the two parts are mixed, the epoxy turns cloudy, and it should clear up as you keep mixing. If it never clears, the problem usually is not that it is under-mixed. It is full of tiny trapped air bubbles.

That comes down to viscosity, which is how thick a liquid is, or how much it resists being stirred. Water has very low viscosity. Syrup has high viscosity. UVPoxy is much thicker than FlowCast, and thick liquids trap air easily. Those trapped bubbles make the epoxy look cloudy, or they rise and pop at the surface and leave it pitted and rough.

How to avoid it:

• Warm the epoxy before you mix. Cold epoxy is thicker, harder to stir and traps more air. We keep ours in a heated cabinet so it stays at least 75°F.
• But not too hot. Because the reaction makes its own heat, starting with epoxy at 100°F or more can make it flash cure in the cup while you are still mixing.
• Mix tabletop epoxy slowly, by hand. Do not use a drill mixer or any power mixer on UVPoxy. It whips in air and you end up with a cloudy, bubbly coat. It sets up in a few hours, so trapped bubbles do not have time to escape.
• A mixer is fine for deep pour. FlowCast is thin, almost like water, and takes days to cure, so bubbles have plenty of time to rise to the surface and pop on their own.

Popping surface bubbles

A heat gun or small torch passed quickly over a fresh pour pops bubbles at the surface. Keep it moving. Holding it in one spot cooks the epoxy and can flash cure that area, turning it white and cracking the surface.

Color and swirls

• Liquid dyes: it takes very little, so add a few drops at a time.
• Mica powders: they come in lots of colors and give a shimmer you cannot get from dye. A little Eye Candy mica powder goes a long way, so try a sample cup before you color a whole river.
• Swirls take timing. FlowCast stays liquid for days, so swirls you make right after the pour will settle and disappear within a few hours. For a specific swirl shape, work it in by hand with a stir stick close to the point where the epoxy starts to thicken, so the pattern holds.
• Natural clouds. In a thick deep pour, the heat of the cure often creates slow convection swirls on their own, which leave soft cloud-like patterns in colored epoxy.

Don't like the gloss? Change the sheen

Tabletop and deep pour epoxy both cure to a high gloss. A lot of people, us included, don't love it: gloss shows every scratch, speck of dust and fingerprint. What many people don't know is that cured epoxy can be sanded and refinished just like wood.

• Sand it smooth. Work up through the grits to 220 or 300.
• Topcoat it. Spray a satin polyurethane for a durable satin or flat look, or use a natural oil or wax if you prefer.
• Go light. Epoxy is not porous, so it won't soak up finish the way wood does. Thin coats are all it takes.

Our finishing guide covers choosing between film finishes and oils.

Watch the temperature

The working and cure times above are for a room at 68 to 77°F. Colder slows everything down and thickens the epoxy. Hotter speeds the cure up, shortens your working time and raises the risk of a flash cure, so on hot days pour thinner layers.

River tables from our shop

Back to the epoxy calculator
Enter your length, width and depth and it works out the liters you need and the cheapest kits.

Always follow the instructions that come with your kit. If you are planning a big pour and want a second opinion, call us at 1-864-GOT-WOOD (864-468-9663). If you would rather have us build the table, M2 Furniture Company builds custom epoxy river tables.