Penetrating vs Topical Concrete Sealer

A penetrating sealer works inside the concrete and a topical sealer works on top of it. That one difference decides traction, breathability, how long it lasts and what you can put on later.

Which is better, penetrating or topical concrete sealer?

Penetrating, for almost every outdoor slab. It keeps water and salt out without a film that can wear, peel or get slick. A topical sealer is better only on smooth interior floors where you want oil and stain hold-out or some sheen.

The research leans the same way. Iowa State University’s review of concrete sealers says barrier coatings may not be the best choice for pavements because of potential influences on skid resistance (opens in a new tab), and calls penetrating sealers an effective means of treating concrete pavements and bridge decks.

Iowa State University CP Tech Center review of penetrating sealers, Concrete Sealers USA FAQ, PS-series and TS210 data sheets

What does a penetrating concrete sealer do?

It soaks into the top of the slab and coats the walls of the pores with a water repellent. Water and the salt dissolved in it can’t get in, but water vapor can still get out. That’s why the NRMCA recommends a silane or siloxane based breathable concrete sealer (opens in a new tab) against freeze-thaw scaling.

Iowa State’s review describes these sealers as pore liners (opens in a new tab) that make the pore walls water repellent while letting gases and vapors through. The common chemistries are silanes, siloxanes and siliconates. One study it cites measured silane penetrating 0.008 to 0.08 inch and siloxane less than 0.02 inch.

They don’t last forever. The same review says their effect fades over time from ultraviolet light, abrasion, weathering and the alkalinity of the concrete, though one study still found a protective effect from silane 20 years after it was applied.

The penetrating sealers on this site, by chemistry:

• Silane: PS109, solvent based, for dense concrete and heavy salt exposure.
• Siloxane: PS110, water based, for porous concrete, broom finishes, block and brick.
• Siliconate: PS101 for smooth concrete and PS102 for rough or broom-finished concrete.
• Fluorinated repellent: PS100, which also repels oil and salt, for dense interior floors such as a garage.
• Densifier with repellent: PS104, a lithium silicate that hardens the top layer of garage and basement floors.

What does a topical concrete sealer do?

It forms a film on the surface. Iowa State’s review describes barrier coatings as too viscous to penetrate (opens in a new tab) the pores, so they block them from above instead. The film is what gives a topical sealer its sheen and stain resistance.

The film is also its weak spot. The review says barrier coatings are vulnerable to premature failure from abrasion under traffic, and cites research where coated concrete took more damage in freeze-thaw because of internal pressure. That’s why breathability matters on slabs that freeze.

TS210 is a thin topical made for one job: keeping oil and stains out of a smooth interior floor. Its data sheet calls it a two-part, water based, acrylic modified polyurethane for interior smooth-troweled concrete, not for areas with standing water. It goes on at 60°F to 90°F and takes vehicles in 24 to 48 hours.

Which sealer should you use on your slab?

Penetrating outside, and either type on a garage floor depending on whether you want a film. The cases people ask about most:

• Driveway with de-icing salt. Penetrating. PS110 siloxane for broom-finished or porous concrete, PS109 silane for dense, smooth concrete.
• Pool deck. Penetrating. PS110, PS102 and PS101 all list pool decks, and a film can make a wet deck slick.
• Garage floor with oil. PS100 if you want a penetrating oil repellent that keeps traction, or TS210 if you want a thin film with stain hold-out. The garage floor sealer guide compares them.
• Bare basement floor. PS104 to cut dusting, or nothing if it’s going under flooring.
• Foundation wall. Neither. These sealers aren’t intended for below grade waterproofing, so fix drainage or the crack instead.

Can you put a penetrating sealer over a topical sealer?

No. The sealer maker’s FAQ says a penetrating sealer can’t go over a topical one, because the film blocks the pores it needs to soak into. The topical has to be removed first by grinding, blasting or stripping.

Going the other way often works, according to the same FAQ. That makes penetrating the safer first choice if you’re not sure: you can add a film later, but you can’t easily take one away.

To find out what’s on your slab now, put a few drops of water on it. If they soak in within 3 to 5 minutes, the surface can take a penetrating sealer, and if they bead, something is already sealing it.

The sealer removal guide covers stripping an old coating.

Do topical sealers make concrete slippery?

They can. The TS210 data sheet warns that the surface’s friction may decline with each coat and suggests adding an anti-skid compound while the first coat is still wet. Penetrating sealers barely change traction.

The TS210 data sheet gives numbers: a wet slip resistance of 0.65 for the matte finish and 0.45 for semi-gloss, measured under ANSI/NFSI B101.3, where above 0.42 is considered desirable. The matte finish leaves more margin on a floor that gets wet from tires and boots.

For pool decks, steps and walkways that get wet, the PS101 and PS102 data sheets list minimal impact on traction, and PS100’s says it maintains it.

Can you use either sealer over a crack repair?

Yes, once the filler has cured and the slab is dry. Fill the cracks first, because sealers stop crack filler from bonding, and neither type of sealer fills cracks. The TS210 data sheet specifically says cracks, voids and joints must be filled before it goes on.

The sealing after crack repair guide covers the order and the wait. For whether your slab needs sealing at all, see do you need to seal concrete, and the sealing guides cover the rest.

Questions

Is a penetrating sealer waterproof?

No. It makes the surface repel liquid water, but Iowa State's review of penetrating sealers notes that gases and vapors still pass through. The PS-series data sheets say the products are not intended for below grade waterproofing.

Will a penetrating sealer change how my concrete looks?

Very little. The PS101, PS109 and PS110 data sheets all say the concrete will have little or no noticeable change in appearance once dry. PS110 goes on milky white and dries clear.

Is a densifier a penetrating sealer?

It's a close relative. Lithium silicates are traditionally used to densify and harden concrete surfaces, according to Iowa State's review. PS104 combines a lithium silicate densifier with a siliconate water repellent, so it hardens the top layer and repels water.

Can I put a topical sealer over a penetrating one later?

Often yes, according to the sealer maker's FAQ, but check both products' instructions first. Most topical sealers need a clean, porous surface to bond, so test a small area before doing the whole floor.