How to Clean Fire Damaged Concrete: Tips & Tricks

House fires can cause immense damage, not just to the structure and interior of a home, but also to exterior surfaces like driveways, patios, and foundation walls made of concrete. The intense heat from the fire often scorches and discolors concrete while the smoke and soot leave behind oily black stains. Even the chemicals used to extinguish the flames can eat away and deteriorate the concrete finish. 

While repairing fire damage on concrete surfaces can seem daunting, it is possible to restore the appearance and integrity of the concrete using specialty cleaning methods and equipment. With proper cleaning, sealing, and a good deal of elbow grease, you can bring fire damaged concrete back to life.

Causes of Fire Damage on Concrete Surfaces

During a residential or commercial building fire, concrete surfaces are subjected to extremely high temperatures that can alter the finish and composition of the material, leaving behind obvious signs of damage:

• Scorching: Concrete exposed directly to flames or indirect heat can appear dried out and extensively discolored, usually with a burnt orange or yellowish tone. The dehydration and oxidation processes weaken the surface.
• Smoke and Soot Stains: The oily residue left behind by smoke will stain and discolor concrete, usually leaving a black or dark gray cast. Soot stains can penetrate deep into the pores of concrete if left untreated.
• Chemical Deterioration: Fire retardant foams, powders, and other suppressants used for extinguishing flames contain harsh chemicals that can eat away at the cement paste and aggregate in concrete, deteriorating the surface.

Safety Precautions for Cleaning Fire Damaged Concrete

Before starting the concrete cleaning process, it is important to take safety precautions to avoid inhaling potentially hazardous fumes or irritating chemicals:

• Wear protective clothing including gloves, long sleeves and pants, and closed toe shoes. Avoid skin contact with cleaning products.
• Work in a well-ventilated area to prevent concentration of chemical fumes. Take frequent breaks for fresh air.
• Carefully read and follow all usage instructions provided on cleaning product labels. Never mix chemicals.
• Keep spray and splash contained by closing off or masking any drains.

Equipment Needed to Clean Fire Damaged Concrete

Having the proper equipment on hand will make the cleaning process much easier:

• Pressure Washer: A heavy duty gas pressure washer with at least 3000 PSI of cleaning power is ideal to lift smoke stains. An electric pressure washer over 2000 PSI can also work.
• Non-Metallic Brush: Use a stiff bristled brush or broom with polypropylene or other non-metallic bristles to avoid scratching the concrete when scrubbing. 
• Bucket, Rags, Putty Knife: For hand cleaning and scrubbing tough stains in crevices.
• Degreasing Chemical Cleaner: Look for heavy duty alkaline degreasers containing sodium metasilicate or ammonium hydroxide to lift oily smoke deposits. 
• Neutralizing Chemical: Such as sodium carbonate, sodium bicarbonate or other solvent to neutralize and remove traces of cleaning agents. 
• Concrete Sealer: To apply as a protective finish over cleaned concrete.

Cleaning Steps for Scorched and Discolored Concrete

For concrete that appears dried out, oxidized and discolored from flames or excessive heat exposure:

1. Lightly pressure wash affected areas to remove any loose concrete particles, dust or debris on the surface.
2. Apply a degreasing cleaning compound to scorched areas, allowing it to soak for 5-10 minutes. This will help lift stains from burnt organic compounds.
3. Vigorously scrub stains with a non-metallic stiff bristle brush, applying moderate pressure.
4. Rinse thoroughly with clean water using the pressure washer wand held 6-8 inches away to avoid further damage.

Repeat this process as necessary until the discoloration has been removed. Heavily scorched concrete may never return to its original color but scrubbing will dramatically improve appearance.

Removing Oily Smoke and Soot Stains

For smoke stained areas of concrete walls or flooring:

1. Mix a cleaning solution of 1 part household ammonia to 3 parts water and apply it to stained concrete using a bucket and brush or rag. 
2. Allow the ammonia solution to sit for 3-5 minutes. This gives it time to penetrate and dissolve the oily soot deposits.
3. Agitate the solution using a non-metallic brush or rag, scrubbing in a circular motion to lift the stain from the pores of the concrete.
4. Once scrubbed, rinse thoroughly with clean water using moderate pressure from the pressure washer nozzle. 
5. Repeat this process as needed until smoke stains have been removed. Several rounds of scrubbing and rinsing are usually required.

Neutralizing Concrete Surfaces After Chemical Exposure

 If concrete appears eroded or etched from fire suppressant chemicals used during extinguishing:

1. Sprinkle granulated sodium carbonate lightly but evenly over the affected areas of concrete.
2. Using a garden hose on a low pressure setting, lightly wet the concrete surface to activate the sodium carbonate. 
3. Allow the sodium carbonate solution to sit for 15 minutes before thoroughly rinsing off the area with clean water.

The sodium carbonate will neutralize and remove any remaining harsh chemicals that may be residue on the concrete surface.

Sealing and Protecting Cleaned Concrete

As a final step after the pressure washing, scrubbing, and neutralizing process:

1. Allow concrete to dry fully for at least 24-48 hours. Sealing damp concrete can prevent proper bonding.
2. Apply a concrete sealer using a paint roller and brush evenly across the surface. This will help prevent smoke stains from absorbing into the concrete pores again in the future. 
3. Choose a sealer suited for your needs such as a penetrating or acrylic-based sealer.
4. Allow sealer to fully cure for the time recommended on the product instructions, typically 24-48 hours.

Proper cleaning and sealing are essential to restoring fire damaged concrete and preventing further deterioration. While the process requires an intensive investment of time and labor, bringing your concrete back to life is well worth the effort and will help your home recover from this unfortunate event.