Concrete that turns brown or becomes discolored can be an eyesore compared to the sleek, uniform look of newly poured concrete.
Your concrete may become discolored for several reasons, including inconsistent concrete mixtures, improper water ratios, and low-quality materials. Tracing the root cause can be time-consuming and delay construction projects.
It is often more practical to try remedies to improve the appearance and take preventive steps for future pours. This article covers common causes of concrete discoloration, ways to fix it, and best practices to avoid it.
Common Causes of Concrete Discoloration
Discolored concrete is a result of various factors during mixing, pouring, and curing. Knowing the most typical causes can identify why a slab or structure has an undesirable hue.
Explore common causes of concrete discoloration in the dropdown sections below:
Variations in concrete mixtures batch to batch can lead to slight color differences over a large pour. Using the same proportions of cement, aggregates, water, and admixtures is key for a uniform appearance.
Carefully following mix designs and frequently testing samples guarantees consistent batches. Reputable ready-mix concrete suppliers have rigorous quality control to prevent mix variations.
Too much water makes your concrete prone to segregation and a weakened surface called “bleeding.” This causes discoloration and uneven curing. Too little water also hinders cement’s hydration, affecting color.
Monitoring slump tests and sticking to the recommended water ratio for a mixture’s design avoids this issue. Adjust the water in the field only when necessary.
Impurities in cement or aggregates can introduce discoloring elements. Substandard cement may contain higher iron and manganese compounds that cause brownish tones.
Using trusted brand cement and aggregates from reputable quarries reduces this risk. Check certification data and do mix trials to verify materials meet specifications.
Certain admixtures, like calcium chloride — which accelerates concrete curing time — may lead to darker concrete shades. Higher dosages, above 2%, are more likely to cause discoloration.
Consider alternative non-chloride accelerators if color consistency is important. Otherwise, closely follow the admixture manufacturer’s recommended dosage guidelines.
Deicing salts and pavement deicers can sometimes cause your concrete to lighten or darken if the products leach chemical residues during manufacturing. Test any deicers on samples before wide application.
Contact the manufacturer if discoloration occurs — they may recommend less-prone alternatives. Pressure washing may also help remove residues.
Proper curing is critical for full cement hydration and strength gain. Insufficient moisture during this phase affects color consistency and makes concrete prone to future discoloration.
Ensure proper curing by leaving forms in place, covering the concrete with plastic, or frequently misting the surface for three to seven days per concrete curing standards.
Extreme heat, cold, or humidity impacts how concrete cures and alters its final appearance. For example, high heat may cause plastic shrinkage cracks that later become stained.
Carefully follow hot and cold weather concreting best practices, like regulating concrete temperature and using evaporation reducers.
Fixes for Discolored Concrete
While prevention is ideal, there are several ways to improve the appearance of concrete once it has already discolored.
Clean with Degreasers or Acid
Heated pressure washing using a strong degreaser removes residues or stains from deicing salts, excess oils, or admixtures. Mild acid washes dissolve discoloring compounds.
Always exercise safety precautions when acid-washing concrete — work outdoors with proper PPE to avoid chemical exposure injuries.
Apply Concrete Color Stain
Specialized opaque concrete stains mask discoloration by producing an alternative, uniform color effect. This is often cheaper than resurfacing or recoating methods.
Stains come in various hues, from earthy neutrals to bold primary colors. Multiple coats fully cover dark discoloration.
Grinding Wears Away Stains
Diamond grinding uses abrasive disks to wear away your concrete’s top layer, removing stains. This may lighten the look but risks weakening the slab over time.
Grinding prepares for applying stains, sealers, or other protective treatments. It needs repeating as discoloration re-emerges.
Apply an Overlay or New Coating
Covering discolored areas with fresh concrete, polymer, epoxy, or other protective coating conceals the issue. Coatings like stains need less preparation work.
For heavy staining overlays, place a thin new concrete layer on top after grinding. It is more costly but provides long-term discoloration coverage.
Consider Full Concrete Replacement
In severe cases, where discoloration is widespread, resurfacing and coating options may prove unsuccessful or too costly. Full concrete breaking and replacement may be the best permanent solution.
Preventing Concrete Discoloration
Taking steps to avoid discoloration from the start is more efficient than fixing it later. Here are some best practices:
- Check raw ingredients like cement and aggregates are certified and high-quality.
- Have your ready-mix supplier regularly verify slump, air content, unit weight, and other metrics.
- Keep detailed pour records to identify causes if problems occur.
- Limit admixtures known to affect color, like calcium chloride.
- Maintain proper water content — don’t overwater or let the mix dry out.
- Make sure conditions allow for adequate three to seven day concrete curing times.
- Precisely follow mix designs — consistently use proper material proportions.
So, Is Concrete Discoloration Avoidable?
While perfectly uniform colored concrete for every pour is difficult, following industry best practices goes a long way. Careful mixture design, quality testing, proper curing, and weather protection prevent most discoloration issues.
Minor shade variation is often unavoidable in large pours. Thankfully, remedies like stains, coatings, and grinding improve problem areas. For critical aesthetic projects, experienced concrete contractors also reduce risks.
FAQs About Concrete Discoloration
What is the most common cause of concrete discoloration?
Inconsistent concrete mixtures and improper water content during pouring are two of the most common causes. Variations in ingredients or water ratios lead to poor cement hydration and strength gain, affecting curing and color.
Does sealed concrete still discolor?
Sealers help protect against staining but do not prevent inherent discoloration from the issues covered above. For example, sealed concrete may still turn gray or develop regional shade differences if your pour consistency varies.
Can you add color to already cured concrete?
Yes, tinted stains and opaque coatings can be applied to your cured concrete to mask existing discoloration. The surface may need cleaning or grinding first to improve absorption and adhesion.
Read more: How To Change the Color of Concrete
Is consistent colored concrete possible?
Paying attention to mixture design, materials, quality, pour technique, and curing achieves high color consistency. Experienced contractors also improve results for critical aesthetic projects.
How much does it cost to fix discolored concrete?
Costs vary widely depending on the fix. Acid washing may cost around $200 for a basic cleaning. Stains could be $300 to $600. Grinding costs $2 to $6 per square foot. Overlays or replacements exceed $6 per square foot.
