July 17, 2021

What To Do When Polyurethane Won’t Dry

Many of us have suffered from the dreaded “polyurethane won’t dry!” problem and have been left with a sticky, shiny mess. So what’s the answer?

Why is The Polyurethane Not Drying?

When the polyurethane does not dry, the wood you are finishing contains natural oil, or you have applied the oil, and it has not dried. Exotic woods do not dry since they contain oil that you even feel when looking at the wood. Only wood like Mahogany allows polyurethane to dry with ease. 

Polyurethane contains mineral spirits that act as solvents for the resin. When you apply the polyurethane to the wood, the resin, and the polyurethane mix, it slows down the process. Oil-based polyurethane dries in two stages. If you are not aware, you will mess it up, and it will not dry. 

The solvents take time to dry, and you should not apply the polyurethane before it dries. Failure to master your weather also makes the polyurethane fail to dry. Avoid low temperatures and high humidity since these slow down the process. Cross-linking is the second drying process that involves molecules reacting in the presence of oxygen. 

The process allows the molecules to bond together, and mastering the second process determines the durability of the surface. The second process takes weeks to dry and if you are not sure how long, refer to the label of the finisher. Sealing polyurethane makes it last longer than the standard period. 

How Long Should You Wait for Polyurethane to Dry?

Polyurethane takes 24 to 48 hours to dry, and that is if the weather is warm enough not to slow down the process. Drying time depends on the type of polyurethane, temperature, and humidity. 

Polyurethane products have instructions at the back written on the label. That specifies the exact time a brand takes to dry. If you are not sure, consult the manufacturer or your local supplier. Two types of Polyurethane take different times to dry. 

The oil-based polyurethane takes more time to dry since the resin has to dissolve and evaporate after pouring it onto the surface (Source). The resin remains on the wood as varnish, and it has to dry. 

The idea that it takes more time makes it more durable than water-based polyurethane. Water-based polyurethane takes less time to dry, and that is why less ventilation is required. What shows you that polyurethane is dry is when it is no longer tacky. 

How Long Do You Wait Between Coats of Polyurethane?

Knowing the type of polyurethane to use gives you details on the period you have to wait before the next coat. The manual contains details about the waiting time between coats. Thinning out the first coat of Polyurethane using paint thinner speeds up the drying time. 

Apply the polyurethane in full strength and sand between each coat. The 24 to 48 hours of drying the polyurethane gives the surface time to cure. The last coat of polyurethane does not allow you to sand. It has to harden before applying wax or any other sealer. 

What Happens if You Recoat Polyurethane Too Soon?

  • The first coat remains sticky.
  • The finish does not last.
  • Polyurethane will not dry.
  • Polyurethane sticks to the application brush, and it becomes difficult to move.
  • The wood keeps bleeding.
  • You cannot apply a sealer properly.
  • The finish becomes rough.

How To Apply Polyurethane To A Wooden Floor

Gather your tools for the application that include white vinegar, tack cloth, polyurethane sealer of your choice, bristle brush, roller with a handle, roller cover, and a respirator with a vapor cartridge only if you are using an oil-based polyurethane. 

Use a cloth to sweep the wooden floor with water and white vinegar, use the brush to apply the polyurethane on the wooden flooring edges, and use the roller or pad to apply the polyurethane at the center of the floor. Stir the polyurethane and avoid shaking it since that creates bubbles. 

Apply a coat of wax as you rub it onto the wooden floor using a soft cloth in a circular motion. Cover the whole surface with the wax and allow the wax to set for 30 minutes. 

Sand the surface, clean the dust and dirt using a soft and dry cloth on the entire piece and allow the wax to set for 30 minutes. Apply two to three coats of polyurethane using the same method. Dust the wood floor regularly with a soft cloth or feather duster so that it lasts longer.

Applying the edges

The edges require a formula when applying polyurethane. Start from the corner, far from the doorway, and dip the brush with enough polyurethane to cover half of the bristles. Clear the polyurethane from the tip of the paintbrush to avoid dripping. Start with 10-14 inch strokes and repeat the strokes. 

The center

The center of the floor requires one to start from the edges of the first corner. Back and forth sweeps using a roller pad are the starting point and do not wait for other parts to dry. Sand between coats if you are applying multiple coats. 

What to do when polyurethane won’t dry

If the polyurethane will not dry, heat the surface with a heat lamp or blow dryer. However, the speed is not too much. If you want an effective way that leaves less room for polyurethane not drying, strip the surface off using a strong solvent such as lacquer thinner or acetone. 

Before you start applying the polyurethane, wipe off the surface with naphtha or acetone to get rid of the natural oil. Apply the polyurethane after the solvent dries completely. The first coat of shellac seals the oil inside the wood, and it is quick to dry on exotic trees. 

Drying the oil takes a week. You are allowed to sand back the surface as you restart the process. That process creates a strong bond between the wood and polyurethane. There are factors to take into consideration so that you rectify your previous mistakes. 

Check your weather if it is appropriate for drying the polyurethane, look for the details of the previous stain and find out if it is compatible with the polyurethane, check the expiry date, stir the contents well and avoid heavy coats and stick to several thin coats.

David D. Hughes
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