Polyurethane is a clear sealer known for its durability and long dry time. If the coating turns sticky, how to fix it?
To fix sticky polyurethane, expose the finish to heat using a hairdryer or heat lamp. The increased heat will speed up the evaporation rate of the solvent (oil or water), and make it dry faster.
To prevent a sticky finish, prep the surface properly, wait until one coat dries before applying another one, sand between coats, and apply light coats.
Why Does Polyurethane Turn Sticky?
Polyurethane turns sticky if you re-coat it too soon, if the humidity is high when you apply it, if the surface has oily deposits, or if you apply thick coats.
If you re-coat too soon and don’t allow enough time for the coating to dry, the new coating won’t stick over the existing wet coating. The solvent in the existing coating will be trapped between two coatings and prevent both from drying, resulting in a sticky finish.
Dirt and filth will prevent a new polyurethane coating from sticking if you don’t sand between coats. Sanding will remove imperfections, dust, and filth from the coating and leave behind a textured surface.
High humidity will prevent a polyurethane coating from drying as the evaporation process is slower and the moisture in the atmosphere will settle over the topcoat. If you apply a new coating before the existing coating dries properly, the finish turns tacky.
If you apply polyurethane over a stained surface (material) with high oily deposits, the oils will bleed through the finish and prevent it from drying. Wood types such as Mahogany, Bloodwood, and Rosewood have a high deposit of oils.
Thicker finishes take longer to dry and tend to turn sticky more.
How Long Does Polyurethane Take To Dry?
It takes water-based polyurethane 6-8 hours to dry enough for a re-coat and 24 hours to cure. It takes oil-based polyurethane 24 hours to dry enough for a re-coat and 48-72 hours to cure.
The dry time refers to the time it takes for the solvent (oil or water) to evaporate from the coating. The cure time refers to when the paint particles harden and the coating turns from liquid to solid. Once the paint cures, it can be used and cleaned.
Polyurethane takes longer to dry than regular paint because it is a sealer and is formulated with several chemicals and resins to improve its durability, water resistance, and UV resistance. All these chemicals and resins need time to react and harden, making the cure time longer.
Also, polyurethane is plastic in liquid form, and it will take longer for the plastic to form and harden.
How To Fix Sticky Polyurethane?
To fix sticky polyurethane do the following things.
- Dry the coating using a hairdryer or heat lamp.
- Open all windows, vents, and doors for improved circulation. This will get the coating to dry more quickly.
- Use a dehumidifier to remove the excess moisture from the room.
- Apply Talcum powder to the polyurethane coating.
Even if the coating dries it won’t be as strong as it should be. It will get damaged by moisture. So it’s better to start from scratch.
If polyurethane remains sticky after 24 hours, it’s best to remove it with a solvent such as turpentine or paint thinner and re-apply it. Once it is removed, clean the material, apply stain-blocking primer, and re-apply it.
When polyurethane doesn’t dry or remains tacky, it’s because of poor preparation before applying it or not allowing enough dry time between coats. There’s nothing you can do in both scenarios, so removing it and starting from scratch is better.
How To Know If Polyurethane Is Dry?
The following signs will indicate if polyurethane is dry.
- The texture will be hard and silky-smooth.
- The top layer will not be cool but warm when touched.
- The top layer will be glossy.
Try bending the polyurethane coating with your finger (push the finger into the coating) — the coating isn’t dry yet if there’s a dent.
Sprinkle water over the coating, if it absorbs the water the coating is still wet. If the water stays over the glossy finish, the coating is fully dry (cured) — polyurethane becomes water-resistant once it dries.
Polyurethane shouldn’t be sticky after it dries — at most, it can be sticky for 6 hours. Once the 6 hours pass the coating must be hard, non-porous, and glossy.
If your polyurethane coating remains sticky or wet several hours after application, it’s usually due to one or more of the reasons below.
Related Read: How To Fix Yellow Polyurethane?