How to Fix Blooming in Polyurethane

Polyurethane should be shiny with no bluish tint from blooming.

Blooming in polyurethane is a condition that creates an iridescent quality in the finish on doors, floors or woodworking projects. It is a bluish tint inside the polyurethane that cannot be fixed unless it is completely sanded off. It is caused when the polyurethane is not completely cured and another coat is applied over it, trapping the bloom inside. The only sure way to fight blooming in polyurethane is to make sure that it is completely dry before adding a top coat.

Things You'll Need

• 1 qt pressure pot paint gun
• Hardwood blank
• Lacquer thinner

Instructions

1. Spray a thin layer of polyurethane onto the surface of a hardwood blank using the pressure pot canister and gun. Wait the recommended time for it to dry according to the manufacturer's direction on the can.

2. Hold the blank up at a 30-degreee angle and examine it carefully. You should see a clear, consistently glassy finish. If you see any signs of bluish qualities in the finish, double the drying time and check again.

3. Hold the blank up at 30 degrees and examine. If you still see blueish tints in the finish, thin the polyurethane. Add 1 pint lacquer thinner to 1 gallon of polyurethane.

4. Spray another test piece of hardwood. Wait the required time according to the manufacturer's directions, and double the time if you see bluish tints after checking it first.

5. Add another pint of thinner to the polyurethane if you continue to see blooming and repeat Step 2.

Tips & Warnings

• Temperature can also create blooming problems in polyurethane. Keep the temperature above 50 degrees when applying polyurethane. It works best when the temperature is approximately 72 degrees.

• Wear breathing protection, and use polyurethane in well ventilated areas only.