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
- Concrete patching compound
- 100 grit sandpaper
- Sanding block
- Cat litter
- Commercial floor degreasing agent
- Muriatic acid-based concrete cleaner
- Stiff bristle broom
- Scrub brush
- Medium nap paint roller
- Paint brush
- Polyurethane paint or varnish
Sweep the floor with a broom and inspect for cracks, holes and depressions. Follow the manufacturer&rsquo;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.
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.
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.
Follow the paint manufacturer&rsquo;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.
Apply two coats of polyurethane. Follow the manufacturer&rsquo;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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