What Is the Best Sealer for Fountains? A Material-by-Material Guide

Walk into any hardware store and you'll find dozens of sealants claiming to be waterproof. But not all of them are safe for fountains, compatible with your fountain's material, or effective when submerged. Using the wrong product can peel, discolor, or even leach harmful chemicals into the water. Here's how to choose the right sealer for your specific fountain.

The 3 Non-Negotiables for Any Fountain Sealant

Before looking at specific products, every fountain sealant must meet these criteria:

• Waterproof when submerged — not just water-resistant on the surface
• Non-toxic once cured — safe for plants, birds, and any wildlife that drink from the fountain
• Flexible — able to expand and contract with temperature changes without cracking

Best Sealers by Fountain Material

Resin and Fiberglass Fountains

Best choice: Polyurethane waterproof sealant or two-part epoxy

Resin fountains like our FountJoy collection bond exceptionally well with polyurethane-based sealants. Look for products labeled for fiberglass or marine use — these are formulated for continuous water contact and temperature cycling.

• Excellent adhesion to resin surfaces
• Remains flexible after curing
• UV-resistant formulas available for above-waterline repairs
• Cure time: 24–48 hours before water contact

Concrete and Cast Stone Fountains

Best choice: Penetrating masonry waterproofer + surface-applied pond coating

Concrete is porous by nature and benefits from a two-step approach:

1. Penetrating silane/siloxane sealer — soaks into the concrete to waterproof from within
2. Brush-on pond and fountain coating (such as Drylok or similar) — applied over the surface for complete waterproofing

For cracks specifically, hydraulic cement is the fastest fix — it expands as it cures to fill gaps completely and can even be applied to actively leaking cracks.

Ceramic and Glazed Pottery Fountains

Best choice: Aquarium-safe clear silicone sealant

Ceramic surfaces are smooth and non-porous, making adhesion challenging. Aquarium-safe silicone (the same product used to seal fish tanks) is the most reliable option:

• Bonds well to glazed surfaces
• Completely non-toxic once cured (24–48 hours)
• Remains flexible and waterproof indefinitely
• Available in clear for invisible repairs

Natural Stone Fountains (Granite, Slate, Sandstone)

Best choice: Stone-specific penetrating sealer + flexible polyurethane for cracks

Natural stone varies widely in porosity. Sandstone and limestone are highly porous and benefit most from penetrating sealers. Granite and slate are denser and may only need crack repair rather than full sealing.

• Apply penetrating sealer annually to porous stone
• Use flexible polyurethane or epoxy for visible cracks
• Avoid silicone on rough stone surfaces — adhesion is poor

Cast Iron and Metal Fountains

Best choice: Epoxy-based metal repair compound + rust-inhibiting primer

• Clean and sand the area thoroughly before applying
• Apply rust-inhibiting primer first if any rust is present
• Use two-part epoxy for structural crack repair
• Finish with a waterproof metal paint or coating for above-waterline areas

Full Basin Waterproofing: When to Use a Coating

If your fountain basin leaks in multiple places, or if you want to proactively waterproof a new concrete or stone fountain, a brush-on pond and fountain coating is more efficient than sealing individual cracks:

• Apply 2–3 coats with a brush or roller
• Allow each coat to dry fully before applying the next
• Cure for 72 hours minimum before filling with water
• Reapply every 3–5 years as part of routine maintenance

Products to Avoid

• Standard bathroom silicone caulk: Contains mold inhibitors that can be toxic to wildlife
• Exterior latex caulk: Not designed for continuous submersion; will peel within weeks
• Roofing tar or bitumen: Toxic and will leach into water
• Expanding foam: Not waterproof and will absorb water over time

Final Thoughts

The best sealer for your fountain is the one matched to your specific material and situation. Take 5 minutes to identify your fountain's material before buying — it's the difference between a repair that lasts years and one that fails by spring.

Our FountJoy resin fountains are precision-molded for excellent inherent waterproofing — but when repairs are needed, polyurethane sealants bond beautifully to our UV-resistant resin construction.