Is eco resin waterproof? Out of the mould, no. Eco resin is water-resistant: it handles splashes and brief contact without damage, but prolonged water exposure will dull the surface and leave staining over time. Apply a sealer and it becomes fully waterproof. That is the complete answer. Everything below is the practical detail.
I'm Anirudh, founder of Artriso. We make CALSO ONE, a water-based eco resin produced in Hyderabad. This is one of the questions I get most from first-time buyers, and the answer matters because it changes how you finish a piece before you sell or use it.
What "water-resistant" actually means in practice
A fully cured CALSO ONE cast is a dense mineral-acrylic composite. The surface is not porous in the way that unglazed ceramic is, but it is not sealed the way fired ceramic or glass is. Under a microscope, there are micro-pores in the surface.
In everyday use, this means a coaster handles a cold glass fine for the first few minutes. Leave a wet glass on an unsealed coaster for an hour and you will see a faint ring. Leave it overnight and the surface will be dull in that area. The mineral filler has absorbed a small amount of water, and the surface has slightly degraded.
For coasters, trays, planters, and anything that contacts water or moisture regularly, the unsealed finish is not sufficient for production use or for selling. Sealing is not optional for functional pieces.
For purely decorative objects that will not contact water, the unsealed matte finish is fine and requires no coating.
How sealing makes eco resin waterproof
A sealer closes the micro-pores on the surface and creates a continuous film that water cannot penetrate. After sealing, the same coaster can sit under a wet glass for hours with no effect on the surface underneath.
The sealing process for a cured eco resin piece is straightforward. Wait the full 24 hours for CALSO ONE to reach full mechanical strength before sealing. Do not seal at 45 minutes just because the piece has demoulded. The cure is ongoing internally. If you sand the piece, do it before sealing, not after. Apply sealer in thin, even coats. Let each coat dry fully before applying the next.
Two coats of a water-based acrylic sealer is the standard for coasters and trays. Three coats for pieces that will hold water directly, like planters.
Which sealer to use
For decorative eco resin casting, use a water-based acrylic sealer that is compatible with mineral-acrylic substrates. GlazeSeal is the sealer we supply alongside CALSO ONE and is formulated specifically for this purpose.
For a high-gloss finish that also deepens pigment colours and makes marble and terrazzo effects read more richly, a gloss acrylic sealer is the right choice. For a matte or satin look that preserves the natural stone feel, a matte or satin topcoat applies over the same base.
Avoid: industrial-grade concrete sealers, oil-based coatings, and construction-grade sealants. These are designed for concrete substrates with different chemistry and can yellow, peel, or fail to bond correctly to eco resin.
The detailed application steps for both concrete and eco resin pieces are in the sealing guide.
Does sealing change the appearance?
Yes, in ways that are usually improvements.
A gloss sealer deepens pigment saturation, makes terrazzo chips and marble swirl patterns read with more contrast, and gives the surface a refined, high-end look that reads differently from the raw matte cast. The piece looks finished rather than raw.
A matte sealer preserves the natural mineral texture but adds a slight sheen that suggests the surface has been treated. It also closes the pores, so the piece photographs better and handles better.
Some studios seal everything as a standard production step regardless of end use, purely because sealed pieces look more intentional than unsealed pieces. That is a reasonable position for a commercial operation.
Does sealing affect the colour?
Gloss sealers will deepen and saturate colours slightly. A pale grey coaster reads slightly richer and darker under a high-gloss coat. This is almost always a positive outcome for decorative work, but worth testing on a sample before sealing a large batch.
Matte sealers have minimal effect on colour and hue.
Neither sealer type will cause the eco resin base to yellow if you are using a water-based formulation. This is one of the practical differences from sealing epoxy: water-based acrylic sealers remain stable over time, while some oil-based or solvent-based topcoats can contribute to the yellowing that epoxy pieces experience.
What to do with planters
Planters are the use case where sealing matters most. A planter that holds soil and is watered regularly will experience continuous moisture exposure. Three coats of gloss sealer inside the planter cavity is the minimum. Let each coat cure for the manufacturer's specified dry time. A fully sealed planter will handle regular watering without issue.
For outdoor planters in Indian conditions (monsoon, direct rain), add a fourth coat and allow a full 24-hour cure between the final coat and first use.
The complete eco resin guide covers the full material properties of eco resin in Indian conditions.
Frequently asked questions
Is eco resin waterproof without sealing?
No. Out of the mould, CALSO ONE and mineral-acrylic eco resins are water-resistant, not waterproof. The cured surface is dense but micro-porous, and prolonged water exposure will cause surface dullness, staining, or moisture absorption. For coasters, trays, planters, and any piece that will contact water regularly, sealing is required to achieve waterproofing.
How long after casting should I wait before sealing eco resin?
Wait the full 24 hours for CALSO ONE to reach full cure before sealing. The piece may feel hard and demould cleanly at 45 to 60 minutes, but the internal cure continues for 24 hours. Sealing before full cure can trap moisture in the piece and affect the bond between the sealer and the substrate.
How many coats of sealer does eco resin need?
Two coats of a water-based acrylic sealer is standard for coasters and trays that will experience normal moisture contact. Three coats for planters or pieces that will hold water directly. Apply each coat in a thin, even layer and allow full dry time before the next coat.
Can I use any acrylic sealer on eco resin?
Water-based acrylic sealers formulated for decorative casting work reliably with eco resin. Avoid industrial concrete sealers, oil-based topcoats, and construction-grade sealants. These are designed for different substrates and can fail to bond correctly, yellow over time, or peel. Use a craft-grade sealer compatible with mineral-acrylic substrates for production results.
Anirudh Rapole is the founder of Artriso, the Hyderabad studio behind CALSO ONE. Sealing questions? Email contact@artriso.com.
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