How to Clean Cement Floor: Methods That Actually Lift Stains

Cement floors look indestructible, but the surface is more porous than people expect — about 12-18% air voids in standard mix designs. That porosity is exactly why oil, rust, and old wax soak in deep enough to laugh at most household cleaners. If you want to know how to clean cement floor the right way, you have to match the cleaner to the contamination type, not just blast everything with bleach.

I have cleaned hundreds of garage slabs, basement floors, and concrete patios over the years. The methods below work consistently, and most use products you can buy for under $20. Skip the wrong steps and you can etch the surface, embed stains permanently, or ruin a sealer that took three weekends to apply.

Step 1: Identify the Stain Before Reaching for a Cleaner

Concrete reacts very differently to acidic and alkaline cleaners. Use the wrong one and you can dull a polished slab or strip a sealer in under a minute.

• Oil and grease — alkaline degreasers (pH 11-13) like Simple Green Pro HD or Krud Kutter Original.
• Rust — mild acids (pH 1-3) like oxalic acid powder or commercial CLR.
• Efflorescence (white salt deposits) — diluted muriatic acid or RadonSeal Efflorescence Cleaner.
• General dirt and dust — neutral cleaners (pH 7-9) such as Bona Stone, Tile, & Laminate or plain dish soap.
• Mildew and algae — oxygen bleach (sodium percarbonate) at 1 cup per gallon of warm water.

Step 2: Sweep and Vacuum Before Anything Wet

Loose grit acts like sandpaper under a mop. Sweep with a stiff push broom, then go over the floor with a shop vac fitted with a HEPA filter. For a 400-square-foot garage, plan on 15-20 minutes of dry pickup before introducing water.

Pay special attention to corners and the seam where the slab meets the wall — that is where dust collects and turns into mud as soon as you start washing.

Step 3: The Standard Wet Wash for Routine Cleaning

For an unsealed but not heavily stained floor, a basic two-bucket method works great.

1. Mix 1/2 cup of dish soap or 1/4 cup of trisodium phosphate (TSP) into 2 gallons of hot water.
2. Apply with a stiff-bristle deck brush in 4×4-foot sections. Let the cleaner dwell 5-10 minutes.
3. Scrub in tight circles, then rinse with clean water from a second bucket or a garden hose with a spray nozzle.
4. Squeegee water toward a floor drain or shop-vac it up. Standing water leaves mineral rings as it evaporates.

For polished or sealed concrete, swap the dish soap and TSP for a pH-neutral cleaner. Anything alkaline above pH 10 will strip acrylic sealers in one wash.

Step 4: Removing Oil and Grease Stains

Fresh oil pulls out easily with cat litter or sawdust pressed into the puddle for 24 hours. Dried-in stains take more effort.

Mix a poultice of powdered laundry detergent and water into a peanut-butter consistency. Spread 1/4 inch thick over the stain, cover with plastic wrap taped at the edges, and leave for 24-48 hours. The poultice draws oil out of the pores as it dries. Scrape off, rinse, and repeat once if any shadow remains. For deep stains, switch to a commercial product like Pour-N-Restore (around $20 per quart) — it does the same job in 1-2 applications.

Step 5: Tackling Rust the Right Way

Rust looks like a forever stain but lifts easily with the right acid. Wear gloves and goggles, and ventilate the space.

Mix 1 tablespoon of oxalic acid powder per cup of warm water and brush onto the rust. Let it bubble for 10-15 minutes, then scrub with a nylon brush and rinse twice. For old, deep rust, products like Whink Rust Stain Remover ($8 per quart) or Singerman Laboratories Rust Remover work in 30 seconds without scrubbing.

Never mix oxalic acid with bleach or ammonia — the fumes are dangerous, and the chemistry cancels out the cleaning action.

Step 6: Pressure Washing — When and How

A pressure washer is the fastest way to clean a cement patio or driveway, but use it carefully on indoor slabs. Stick to 2,000-3,000 PSI with a 25-degree fan tip held 12-18 inches from the surface. Anything stronger or closer can pit the concrete.

For sealed floors, drop down to 1,500 PSI and a 40-degree tip. Pressure damage to a sealer often does not show until water beading disappears a month later — by then, you cannot un-blast it.

Step 7: Disinfecting and Killing Mildew

For musty basement slabs, use oxygen bleach instead of chlorine bleach. Chlorine evaporates fast and corrodes any nearby metal. Oxygen bleach (OxiClean, Stain Solver) at 1 cup per gallon kills mildew, brightens the surface, and rinses clean without residue.

For outdoor algae and mold on patios, Wet & Forget ($25 per gallon, mixed 1:5 with water) sprays on, requires no scrubbing, and works over the next 4-12 weeks with rainfall doing the rinsing.

Sealing After Cleaning

A clean cement floor is the perfect time to apply or reapply sealer. Wait 24-48 hours after the final rinse to let the slab fully dry — moisture meter reading under 4% is ideal. Use a penetrating siloxane sealer (Foundation Armor SX5000) on garages and patios, or an acrylic topical sealer for indoor finished spaces.

Plan on resealing every 2-5 years depending on traffic. A clean, sealed slab cleans 10x faster the next time around because contaminants stay on the surface instead of soaking in.

Dial in the right cleaner for the right stain, sweep before you wash, and finish with a sealer if the slab will see future spills. That is how to clean cement floor surfaces in a way that lasts longer than a single weekend project.