How to apply polyurethane to concrete flooring

Written by ian kelly
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How to apply polyurethane to concrete flooring
Beautify your floor with a polyurethane finish. (cat licking its paw on a blue floor image by Inkkensix from

Preparation is the key to applying polyurethane to a concrete floor. Polyurethane will not form a chemical bond with concrete; however, it will bond readily with epoxy and epoxy will bond to concrete, so an epoxy undercoat is necessary. The second problem could be a damp floor. Basement floors typically attract moisture, especially if a plastic barrier was omitted when the slab was poured. If you have a damp basement, your best bet is to stain the floor instead of painting it.

Skill level:

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Things you need

  • Broom
  • Concrete patching compound
  • 100 grit sandpaper
  • Sanding block
  • Cat litter
  • Commercial floor degreasing agent
  • Soap
  • Muriatic acid-based concrete cleaner
  • Stiff bristle broom
  • Scrub brush
  • Mop
  • Medium nap paint roller
  • Paint brush
  • Polyurethane paint or varnish

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  1. 1

    Sweep the floor with a broom and inspect for cracks, holes and depressions. Follow the manufacturer’s instructions and repair any defects with a concrete patching compound. After it has thoroughly dried, sand the area level with 100 grit sandpaper wrapped around a sanding block.

  2. 2

    Degrease the floor. If you have heavy deposits of oil on a garage floor, cover the area with cat litter and leave overnight before sweeping off. Scrub the floor with a commercial floor degreasing agent and follow up with soap and warm water. Rinse well and leave to dry.

  3. 3

    Etch the floor with muriatic acid-based concrete cleaner to ensure proper bonding. Scrub a generous amount of acid into the concrete with a stiff bristle broom and leave for 15 minutes. Rinse and scrub the surface thoroughly with clean water and a scrub brush. Go over the surface twice to remove all traces of acid. Dry with a mop and leave overnight.

  4. 4

    Follow the paint manufacturer’s directions and apply two coats of stain blocking epoxy primer with a medium nap paint roller. Use a paint brush to paint clean edges against skirting boards and mouldings. Allow each coat to dry for three to four hours between applications.

  5. 5

    Apply two coats of polyurethane. Follow the manufacturer’s direction if your paint or varnish of choice needs to be mixed with a catalyst. Stir well and apply the finishing coats as described in Step 5. Allow 24 hour curing time before walking on the floor.

Tips and warnings

  • If the floor was previously covered with tile or a glue-down hardwood floor, remove all traces of adhesives with 100 grit sandpaper and a sanding block during the cleaning process. Any traces left will show through the painted surface.
  • When you etch the floor with acid, keep the floor wet. Dried acid deposits are hard to remove.
  • Use a paint fresh roller cover when applying polyurethane.
  • Open outside windows and doors to ensure proper ventilation while etching and painting the floor.
  • Wear a respirator, rubber gloves, rubber boots, and eye protection when etching the floor.
  • Wear a respirator during the painting process.

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