We earn a commission if you buy through links on this page, at no cost to you. How we choose products
Not always. Concrete doesn't fall apart without a sealer, but outdoor slabs that stay wet, freeze and get de-icing salt hold up better with a breathable penetrating sealer, and garage floors that collect oil benefit from an oil repellent. A slab going under flooring, a foundation wall below grade or concrete that already sheds water doesn't need one.
Does concrete need to be sealed?
No, concrete doesn’t need to be sealed to last. Good concrete, placed and cured well, holds up on its own, and a sealer is extra protection for slabs that face water, freezing and salt. Indoor slabs that stay dry rarely need it.
The research puts sealers in that place too. Iowa State University’s review of penetrating sealers calls surface treatment an additional measure for protection (opens in a new tab) against water and chlorides getting in. The NRMCA’s guidance on scaling starts with air-entrained, properly cured concrete and lists a sealer as one of the extra steps.
So the real question is what your slab faces. A salted driveway in Minnesota and a covered patio in Arizona get very different answers.
When does sealing concrete help?
Sealing helps most on outdoor concrete that stays wet and freezes, especially where de-icing salt is used. It also helps garage floors that get oil and bare floors that shed dust.
- Freeze-thaw with de-icing salt. The NRMCA says saturated concrete that freezes is susceptible to scaling (opens in a new tab), and de-icers make it worse by increasing saturation at the surface. For slabs that stay moist, freeze and get salted, it recommends a silane or siloxane based breathable concrete sealer (opens in a new tab).
- Driveways and walks in salt country. Research summarized by Iowa State found silane treatment had a positive effect on scaling resistance (opens in a new tab) for concrete exposed to de-icers. The same studies found it couldn’t save concrete with a poor air-void system.
- Pool decks. They’re wet most days and, in cold climates, freeze over the winter. A penetrating sealer that doesn’t change traction much is the usual pick.
- Garage floors with oil drips. A plain water repellent won’t stop oil. You need a sealer made to repel oil, or a topical stain protector.
- Dusty bare floors. A densifier hardens the top layer of a garage or basement floor and cuts dusting.
When should you not seal concrete?
Skip it when the slab is about to be covered, when it’s below grade, when it already sheds water or when it has an old coating on top. In those cases a sealer either can’t get in or doesn’t do anything useful.
- A basement floor going under flooring. Follow the flooring maker’s instructions for what can be on the slab. The before flooring guide covers crack prep.
- Foundation walls. The PS-series data sheets say the products aren’t intended for below grade waterproofing. A wet basement wall is a drainage or crack problem, covered in the foundation crack guides.
- Concrete that’s already sealed. If water beads up on it, a penetrating sealer has nowhere to go and the excess can dry white.
- A slab with a topical coating. The sealer maker’s FAQ says a penetrating sealer can’t go over a topical one. The coating has to come off first, which the sealer removal guide covers.
- Dry, covered, indoor slabs. A slab that never gets wet, salted or oiled has little to gain.
Sealing is also not a fix for a moving crack. If the slab has cracks wider than 1/4 inch, one side higher than the other, or a foundation wall is bowing, a sealer won’t help, and wall problems like those need an engineer.
What happens if you don’t seal concrete?
Usually nothing dramatic. Indoors, an unsealed floor stains and dusts more easily. Outdoors in a freezing climate, salted concrete is more likely to scale, which means the surface flakes or peels.
The NRMCA calls minor scaling a cosmetic issue (opens in a new tab) that may not need repair. Heavy, spreading scaling is harder to fix, so the cheap protection is worth it where salt is used. The spalling and scaling guide covers damage that’s already started.
You can cut the risk without a sealer too. The NRMCA says to use de-icers in moderate amounts and to hose off salt that cars drag onto driveways and garage slabs. It warns against ammonium-based and magnesium-based de-icers.
How do you tell if concrete is already sealed?
Drip a few drops of water on it. If they soak in within 3 to 5 minutes, the concrete is unsealed or the old sealer has worn off. If they bead up and sit there, it’s sealed or too dense to take a penetrating sealer.
That’s the test the PS-series application guidelines use to decide whether a surface is a candidate. Try it in a few spots, since an old sealer may have worn unevenly.
A glossy or slick surface usually means a topical coating. Flaking, peeling patches mean an old coating is failing, and it has to be removed before a penetrating sealer can go on.
Should you seal new concrete?
Yes, if it will face salt and freezing, but give it time. The sealer instructions say concrete should ideally be at least 28 days old or fully cured before sealing. The NRMCA also says to avoid de-icers on new concrete and to skip them in the first winter (opens in a new tab).
There’s one exception. The PS102 application guidelines say it can also be used to cure new broom-finished concrete, applied once the bleed water is gone and finishing is done. If you’re having a slab poured, ask the contractor what curing method they plan to use.
The NRMCA calls late summer, after a few dry days, an ideal time to seal. That lines up with getting a new slab protected before its first winter.
Which sealer does your concrete need?
A penetrating sealer for almost every outdoor slab, and an oil repellent or topical protector for a garage. The table matches the common cases. The penetrating vs topical guide explains the difference in more depth.
| Your concrete | Seal it? | What to use |
|---|---|---|
| Driveway or walk that gets salted | Yes | PS110 siloxane (broom finish) or PS109 silane (dense, smooth) |
| Patio or steps in a freezing climate | Usually | PS110, PS102 or PS101 |
| Pool deck | Usually | PS110, PS102 or PS101, which list pool decks among their uses |
| Garage floor with oil drips | Yes | PS100 oil and water repellent, or TS210 topical |
| Bare, dusty garage or basement floor | If the dust bothers you | PS104 densifier |
| Basement floor going under flooring | No | Whatever the flooring maker specifies |
| Foundation wall | No | Fix the drainage or the crack instead |
| Covered patio in a dry climate | Optional | A penetrating sealer if you want stain protection |
NRMCA CIP 2 and the PS-series and TS210 data sheets
For a garage that gets oil drips, look at PS100, which repels water, oil and salt. For a dense driveway that’s salted all winter, PS109 silane is the heavy-duty option. The driveway sealer guide and garage floor sealer guide go further.
Should you seal concrete after crack repair?
Yes, on slabs that are worth sealing anyway. Fill the cracks first, because sealer on the crack walls stops the filler from bonding, then seal once the filler has cured and the slab is dry.
A sealer won’t fill cracks, and the data sheets say so. The sealing after crack repair guide covers the order, the wait and the sealer to use, and the sealing guides cover the rest.
Questions
Is a concrete sealer the same as waterproofing?
No. A penetrating sealer makes the surface repel liquid water but still lets water vapor out, according to Iowa State University's review of penetrating sealers. The PS-series data sheets say the products are not intended for below grade waterproofing, so they won't stop a leaking basement wall.
Does sealing concrete prevent cracks?
No. The sealer data sheets say these products are not intended to seal cracks and won't fix structurally unsound surfaces. Cracks come from shrinkage and movement, and the why concrete cracks guide covers the causes.
Does sealed concrete get slippery?
Penetrating sealers barely change it. The PS101 and PS102 data sheets list minimal impact on traction, and PS100's says it maintains it. Topical coatings are different: the TS210 data sheet warns that friction may decline with each coat and suggests an anti-skid additive.
How long does concrete sealer last?
The sealer maker's FAQ says penetrating water repellents can last up to 5 to 7 years or more, densifiers 10 years or more, and topical acrylics 1 to 3 years. Research summarized by Iowa State found silane still protecting concrete bridge beams 20 years after it went on, though it weakens over time.