How to use polyurethane? Tips, drying times, and painting advice.

• June 19 2025, by Carola Straccali
• 6 min reading time

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Are you working on a mold, model, or protective coating? Then applying polyurethane correctly is essential for a strong final result. Whether you want to know how long polyurethane takes to dry, whether you can paint over it, or whether it's waterproof—this guide tells you everything you need to know.

How do you apply polyurethane for casting and sealing?  

Polyurethane is a versatile material used for casting, coating, sealing, and insulating. At Siliconesandmore.com , our PU products are primarily used for casting detailed models, prototypes, and technical components .  

Before pouring:  

• Prepare your workspace well – clean, dry and well ventilated.  

• Mix components A and B – most systems, such as our PU Casting Resin D70 , use a 1:1 ratio.  

• Add filler (optional) – for better heat control and thicker casting layers.  

• Add pigment or UV stabilizer (optional) – for color and protection against aging.  

• Pour slowly into the mold – this way you avoid air pockets.  

• Allow to cure – follow the indicated de-mould and curing times.  

Looking for a strong, fast-curing resin? Try PU Casting Resin D70 or the extra-strong D80 version.  

For sealing:  

• Use a polyurethane sealer to protect surfaces from water, abrasion, or chemicals.  

• Apply with a brush, roller or spray.  

• Allow each coat to dry completely before applying the next.  

Need extra protection for a PU casting? Contact us for recommended sealers compatible with our polyurethanes.  

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How long does it take for polyurethane to dry?  

Drying time depends on the product and application.  

For casting resins (such as D70/D80):  

• De-moulding time : 15–90 minutes, depending on filler and thickness.  

• Full cure : 24–48 hours for maximum strength.  

For sealers and coatings:  

• Dust dry : approx. 2 hours  

• Can be painted over : after 4–6 hours  

• Fully cured : up to 7 days (for maximum hardness and water resistance)  

Tip: For best results, work in a room with a constant temperature.  

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Can you paint over polyurethane?  

Yes — but good preparation is essential:  

1. Allow the polyurethane to cure completely.  

1. Lightly sand with fine sandpaper (220–320 grit) for better adhesion.  

1. Clean with a damp cloth or adhesive cloth.  

1. Use a suitable paint: acrylic or enamel paint works best. A primer is necessary for smooth or greasy surfaces.  

Want to add color right away? Mix pigments into the resin before pouring for an even result.  

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Is polyurethane waterproof?  

In short: yes , polyurethane is waterproof — after full curing.  

• It forms a hard, moisture-resistant layer.  

• Widely used for exterior coatings, water-repellent applications and flexible molds.  

• For outdoor projects, always use a matching PU sealer for extra UV and water protection.  

Our PU Casting Resin D80 offers high strength and minimal shrinkage — ideal for outdoor use (when sealed).  

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Which polyurethane should you choose?  

Our recommendations:  

• PU Casting Resin D70 – For small to medium-sized castings, prototypes and rapid processing.  

• PU Casting Resin D80 – For larger, structural castings with minimal shrinkage.  

• Impact-resistant PU – For castings that need to withstand a blow.  

• Flexible PU – For rubber-like products with wear resistance.  

• PU Foams (flexible and hard) – For light, cushioning applications.  

• PU Sealers – For extra protection in damp or outdoor environments.  

Not sure which product is right for you? Contact our experts or browse our full PU range .  

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The best results thanks to smart application  

Those who know how to properly apply, dry, and finish polyurethane will get the most out of this versatile material. Whether you're an artist, maker, or professional user, polyurethane offers strength, flexibility, and durability —when applied correctly.  

Ready to start pouring?
Discover our complete range of polyurethane products and realize your ideas with the quality of Siliconesandmore.com.  

Fast curing. Waterproof. Durable.  

Tags

Polyutheraan PU PU Gietresin D70 PU Gietresin D80