Concrete surfaces around your home—driveways, patios, sidewalks, and garage floors—take a beating from weather, foot traffic, oil spills, algae growth, and more. Over time, these elements can leave your concrete looking dirty, stained, and worn out. That’s where pressure washing comes in as a fast and effective way to restore the look of your concrete. But before you fire up the pressure washer, there’s one important step you shouldn’t skip: pre-treating the surface with the right spray solution.
Knowing what to spray on concrete before pressure washing can make all the difference between an average clean and a spotless, like-new finish. The right cleaner helps break down tough stains, loosens embedded dirt, and ensures your pressure washing efforts deliver maximum results with less effort.
In this guide, we’ll cover the importance of pre-treatment, the best cleaners to use depending on the type of stain, how to apply them safely, and when it’s time to call in a professional. Whether you’re a DIY homeowner or someone looking to up your cleaning game, this article will give you the complete lowdown on preparing your concrete the smart way.
Why Pre-Treating Concrete Matters
Before pressure washing concrete, applying the right spray solution helps tackle the tough grime that water alone may not remove. Pre-treatment breaks down the dirt, grease, algae, and mildew at a chemical level—making it easier to lift off during pressure washing. When you skip this step, especially on older or deeply stained surfaces, you risk spending more time and water trying to clean the concrete. Worse, you may not even get the results you’re aiming for.
By using the proper cleaning spray, you not only improve the effectiveness of your cleaning but also protect your concrete from overuse of high-pressure water, which can sometimes lead to surface damage. In simple terms, spraying the surface before pressure washing saves time, reduces effort, and enhances results. It’s the key to a cleaner, longer-lasting finish.
Types of Stains and Residue Found on Concrete Surfaces
Not all concrete grime is the same. Understanding what you’re trying to clean will help you choose the most effective spray solution before pressure washing.
Oil and grease stains are the most common on driveways or garage floors and typically come from vehicles, lawn equipment, or tools. These stains are stubborn and require powerful degreasers for proper breakdown. Mold, mildew, and algae often appear in shaded or damp areas and not only make concrete look dirty but can also become slippery and unsafe. For these types of stains, you’ll need a mildew or mold-killing solution, often bleach-based or a safer biodegradable option.
Rust stains, which result from metal furniture, tools, or water runoff, leave behind unsightly orange-brown marks and usually require a rust remover formulated for concrete. Paint or sealant residue left over from previous home improvement projects may need a specially formulated paint stripper before pressure washing. Finally, if your surface is simply dusty or slightly dirty, a basic concrete detergent should be enough to prep the surface before pressure washing.
Best Sprays and Solutions to Use Before Pressure Washing Concrete
Let’s dive into some of the most effective products and solutions used to pre-treat concrete surfaces before pressure washing.
Concrete degreasers are ideal for tackling oil, grease, and automotive fluid stains. These heavy-duty cleaners break down petroleum-based residues and are available in both commercial-grade and homeowner-friendly formulas. A popular choice is Simple Green Concrete & Driveway Cleaner, which is applied generously and allowed to dwell for 10 to 15 minutes before washing.
For organic stains like algae, mildew, and moss, mold and mildew cleaners work best. These solutions, like Wet & Forget Outdoor Cleaner, are often sodium hypochlorite-based or made from biodegradable ingredients. They’re left to sit on the surface for several minutes, or longer for heavier growth, and then rinsed off thoroughly after pressure washing.
If you’re dealing with general dirt, grime, and surface stains, concrete detergents are a great option. These can be added to your pressure washer’s detergent tank or applied manually using a pump sprayer. Many options, such as Zep Driveway and Concrete Cleaner, are designed to be eco-friendly, making them safe for lawns and gardens.
When it comes to rust, it’s best to use acid-free rust removers to avoid etching the surface. Products like Singerman Laboratories Rust Remover are highly effective at removing deep-seated rust stains on patios and sidewalks.
If safety and sustainability are top priorities, there are eco-friendly and biodegradable cleaners available. These are often made from plant-based or non-toxic ingredients and are safe for runoff into storm drains and nearby soil. ACT Concrete Cleaner, for example, is a microbial formula that works effectively without harming the environment.
For small DIY jobs, homemade cleaners are a budget-friendly alternative. A mixture of vinegar and baking soda works well for general grime and light mold, while a bleach and water solution in a 1:10 ratio can disinfect and kill mildew—though it should be used with caution. Dish soap and hot water are also effective for cleaning mildly dirty concrete. Regardless of the homemade mix, it’s always important to test the solution on a small area first to avoid unexpected results.
How to Apply These Sprays Safely and Effectively
Proper application of the cleaner is just as important as the solution itself. Start by gathering the necessary tools: a pump sprayer or garden sprayer for applying the cleaner, rubber gloves and safety glasses for personal protection, a stiff-bristle brush for scrubbing tough spots, and a garden hose for rinsing.
To begin, clear the area of debris, leaves, and loose dirt. Spray the cleaning solution generously over the stained concrete and allow it to sit, or “dwell,” for 5 to 15 minutes depending on the severity of the stain. For particularly stubborn areas, use a brush to scrub the surface gently. After the dwell time, rinse the area lightly with a hose or pressure washer set on a low setting before applying full pressure.
Always follow basic safety precautions. Never mix incompatible cleaners such as bleach and vinegar, as they can create toxic fumes. Wear protective gear, especially when handling chemical-based sprays. Avoid spraying on windy days to reduce the risk of airborne chemicals affecting other surfaces or areas.
Mistakes to Avoid When Spraying Before Pressure Washing
A few common mistakes can undermine your entire cleaning effort or even damage your concrete. One of the biggest issues is using the wrong type of cleaner. For example, bleach won’t help much with oil stains, and degreasers won’t kill mold.
Skipping dwell time is another mistake. Cleaners need time to penetrate and break down the grime—rushing to rinse too early often leads to underwhelming results. Over-spraying wastes product and might damage nearby plants or lawn, while under-spraying won’t be effective enough to loosen the stains.
Another concern is ignoring safety precautions. Not wearing gloves, inhaling fumes, or mixing chemicals improperly can lead to serious health issues. Lastly, failing to test a small area first could result in discoloration or damage, especially on older or previously treated concrete surfaces.
When You Should Call a Professional
While most homeowners can handle basic concrete cleaning, there are situations where it’s best to call a professional. If your concrete is heavily stained, very large in size, or hasn’t been cleaned in years, the job may be too time-consuming or risky to do yourself.
Some signs that you need help include deep oil stains that won’t budge, large mold infestations that return quickly, or rust that has set in over several years. Slippery algae around pool decks or walkways can also pose safety hazards.
Professional pressure washers have access to commercial-grade cleaners and equipment that go far beyond what you can get at your local hardware store. More importantly, they know how to treat different stains without causing damage—saving you time and delivering results that last longer.
If you want the best results from pressure washing your concrete, don’t skip the pre-treatment step. Knowing what to spray on concrete before pressure washing helps you break down stubborn stains, save time, and avoid damage. From degreasers for oil stains to mildew removers for green gunk, and even eco-friendly solutions for environmentally conscious homeowners, choosing the right cleaner is the first step in getting that fresh, clean look your concrete once had.
Before you start spraying, make sure you’ve identified the type of stain you’re working with, selected the right cleaner, and followed the proper safety and application methods. A little prep work goes a long way—your driveway, patio, or sidewalk will look better, last longer, and be safer to use.