Use a silane on dense, alkaline concrete — driveways, garage aprons, sidewalks, anything that sees road salt. Use a siloxane on porous, more neutral masonry — brick, concrete block, many natural stones. And if you are sealing a mix of surfaces or are not sure, a silane/siloxane blend is the safe default, which is why most consumer penetrating sealers on the shelf are exactly that.
The reason comes down to molecule size and chemistry. Silanes are tiny, so they travel deep into the fine pores of dense concrete, but they need the alkalinity of fresh cement paste to react and they are volatile enough that some evaporate before they bond. Siloxanes are larger, partly pre-reacted molecules that stay closer to the surface, react faster and are far less fussy about the substrate — ideal for the bigger pores of brick and block. Both leave the surface looking unsealed, both let the masonry breathe, and both are a different product category from the acrylic sealers that make concrete look wet.
How Penetrating Repellents Work
Silanes and siloxanes are both organosilicon compounds. Each molecule has two ends that matter: a silicon-based end with reactive groups (usually methoxy or ethoxy) that can bond chemically to the silica and hydroxyl groups in concrete, brick and stone, and an organic "tail" — typically an alkyl chain such as isobutyl or octyl — that is hydrophobic.
Applied as a liquid, the product soaks into the pores. Moisture in the substrate hydrolyses the reactive groups into silanols, which then condense with the mineral surfaces and with each other. The result is a thin, chemically bonded polysiloxane (silicone) layer lining the walls of every pore it reached, with the water-hating tails pointing outward. Nothing sits on top. The pores are still open; they are just lined with something liquid water will not wet.
That distinction is the whole value of the category. Liquid water is held out because it can no longer be drawn into the pores by capillary action — it beads and runs off. But water vapour, which is a gas and is not affected by surface tension the same way, still passes freely in both directions. The masonry can dry out from the inside. This is what people mean by a "breathable" sealer, and it is why penetrating repellents are the default recommendation for anything exposed to freeze-thaw cycles or rising moisture.
Because the protection lives inside the material rather than on it, foot and tyre traffic do not wear it off the way they wear a film, and sunlight does very little to it. The surface layer does erode slowly — the top fraction of a millimetre is exposed to abrasion and UV — which is why water beading on the surface fades over the years even while the treated zone a few millimetres down is still doing its job.
Silanes: Small, Deep, Slow
A silane in this context is a single monomer molecule — an alkyltrialkoxysilane. Isobutyltrimethoxysilane and octyltriethoxysilane are the workhorses. They are the smallest molecules in the category, small enough to follow the very fine capillary pores in dense, well-cured concrete.
Penetration. On concrete, silanes commonly reach a few millimetres deep — manufacturers typically quote around 1/8 to 3/8 inch depending on the product's solids content, the concrete's density and how much is applied. Depth matters because it is what lets the treatment survive surface wear and keep salt water away from the steel reinforcement. A treatment that is 5 mm deep still works after the top millimetre has been ground off by tyres.
Alkaline substrate. The hydrolysis and condensation reactions that bond a silane in place are catalysed by alkalinity. Concrete is ideal: the cement paste in sound, uncarbonated concrete sits around pH 12–13. On neutral substrates — fired clay brick, many natural stones, and old concrete whose surface has carbonated — silanes react more slowly and less completely, and more of the product evaporates before it bonds.
Volatility and solids. Small molecules are volatile. Apply a silane in hot sun or wind and a meaningful fraction can flash off before it reacts. Manufacturers compensate by selling silanes at high solids, typically 20% to 40%, with 100% silane products available for highway and bridge work. A 40% silane is the long-standing specification for many state transportation departments sealing bridge decks against chloride, which tells you where the chemistry is strongest. Low-solids silanes (under about 10%) exist but give up much of the depth that justifies choosing a silane.
Carrier. Silanes were traditionally carried in solvents — alcohol or mineral spirits — and solvent-based versions still penetrate well and tolerate cooler weather. Water-based silane emulsions are now common and perform well; in states with strict VOC rules (California and much of the Northeast), they may be the only high-solids silanes you can buy locally. Water-based products need the surface to be reasonably dry and temperatures above freezing during cure.
Speed. Silanes take longer to develop full repellency than siloxanes — it can be days before beading is at its best. That is not a defect, just the price of a molecule that is still travelling and reacting.
Siloxanes: Bigger, Shallower, Faster
A siloxane in sealer terms is an oligomer — a short chain of silane units that has already been partly reacted together, still carrying reactive groups and alkyl tails. Being several times larger, a siloxane molecule cannot follow the finest pores in dense concrete, but it fits comfortably into the larger, more open pore structure of brick, block, stucco and porous stone.
Penetration. Shallower than silane — generally a couple of millimetres or less in dense concrete, more in porous masonry because the pores are bigger. On a soft brick or cinder block that is enough: those materials drink water through large capillaries near the surface, and that is exactly where the siloxane ends up.
Reactivity. Because they are already part-condensed, siloxanes need fewer reaction steps to form the final water-repellent network, so they cure and bead faster — often within hours — and they depend much less on substrate alkalinity. That makes them the better chemistry for neutral materials like fired clay brick and many stones.
Volatility and solids. Larger molecules are far less volatile, so siloxanes do not need high solids to make up for evaporation losses. Consumer siloxane sealers are commonly sold at well under 15% solids, many around 5–10%, in water-based form. That is not a sign of a weaker product; the active ingredient is simply more efficient at staying where it is put.
Polymeric siloxanes and silicone resins. At the larger end, silicone resins are fully polymerised and behave more like a very thin, highly vapour-permeable surface treatment than a deep impregnant. Older "silicone" masonry sealers were often of this type. They bead well initially but sit close to the surface and wear faster on trafficked areas, so they are better suited to vertical walls than driveways.
Side-by-Side Comparison
| Property | Silane | Siloxane | Silane/siloxane blend | Siliconate |
|---|---|---|---|---|
| Molecule | Small monomer | Larger oligomer | Mix of both | Water-soluble salt |
| Typical penetration (concrete) | Deep — ~1/8 to 3/8 in | Shallow | Moderate to deep | Shallow |
| Needs alkaline substrate | Yes, works best on it | Much less | Partly | Cures with CO₂ in air |
| Speed to bead | Slow (days) | Fast (hours) | Fast surface, slow depth | Moderate |
| Typical solids | 20–100% | ~5–15% | ~7–40% | Low, diluted |
| Best substrates | Dense concrete, driveways, bridge decks | Brick, block, stucco, porous stone | Mixed jobs, pavers, general use | Budget brick and stucco walls |
| Salt / chloride protection | Best | Fair | Good to very good | Poor |
| Realistic life | 5–10+ years | 3–7 years | 4–8 years | 2–5 years |
| Changes appearance | No | No | No | Can leave white residue |
Life ranges assume correct application on clean, sound substrate. Coverage rate and solids drive the result more than brand.
Blends and Siliconates
Silane/Siloxane Blends
Blends exist because each chemistry covers the other's weakness. The silane fraction travels deep and gives long-term protection on concrete; the siloxane fraction stays near the surface, cures quickly and gives visible beading within hours, which also protects the slower-reacting silane from being washed out by an early rain. On neutral substrates the siloxane does most of the work; on alkaline concrete, both contribute.
Most water-based penetrating sealers sold for general masonry — driveways, patios, brick, pavers — are blends, and for a homeowner treating several surfaces with one product that is sensible. Read the label for the solids percentage and the recommended substrates. A blend sold at 7% solids for brick and block is not equivalent to a 40% silane for a salted driveway, even if both say "concrete" on the front.
Siliconates
Potassium and sodium methyl siliconates are water-soluble salts that react with carbon dioxide in the air to form a water-repellent silicone resin in the surface pores. They are inexpensive, water-based and easy to apply, and they work on brick, stucco and block walls.
The trade-offs are real. Siliconate solutions are strongly alkaline, so they must be kept off glass, aluminium frames and painted trim, which they can etch or stain. They can leave a white haze on dark brick or coloured concrete. Penetration is shallow and durability is modest — a few years in exposed positions — and they offer little resistance to chloride. They make sense as a budget treatment on vertical walls; they are not the answer for a driveway.
Repellents vs Film-Formers vs Densifiers
Most confusion in this category comes from three different product types all being sold as "concrete sealer". They do different jobs.
| Type | Examples | How it works | Look | Breathable |
|---|---|---|---|---|
| Penetrating water repellent | Silane, siloxane, blends, siliconates | Lines pores with a hydrophobic layer | Unchanged, matte | Yes |
| Film-forming sealer | Acrylic, polyurethane, epoxy | Builds a coating on the surface | Satin to wet-look gloss | Limited (acrylic) to none (epoxy) |
| Densifier / hardener | Sodium, potassium, lithium silicate | Reacts with free lime to form extra binder (C-S-H) | Unchanged; can polish | Yes |
Film-formers — acrylics most commonly outdoors — sit on the surface. They enhance colour, give a satin or wet look, and resist oil and staining better than a pure repellent, but they wear in traffic lanes, can turn white or peel when moisture is trapped beneath them, become slippery when wet, and need recoating every one to three years. They also reduce vapour permeability, which matters on masonry that needs to dry. If you want the wet look on pavers or stamped concrete, you need a film-former, and our concrete sealer guide covers both types side by side.
Densifiers are silicates, not silanes, despite the similar names. They react with the calcium hydroxide in concrete to form additional calcium silicate hydrate, hardening and tightening the surface. That reduces dusting and makes concrete more abrasion resistant, which is why they are used on warehouse and polished floors. On their own they are not strong water repellents. Some products combine a densifier with a silane or siloxane to get both effects, and on an older, dusty driveway that combination can be worthwhile.
One practical consequence: a silane or siloxane makes the surface water-repellent, which can stop a later acrylic or paint from bonding properly. If there is any chance you will want a film or coating later, check that the repellent is labelled as compatible with topcoating, or choose the film first.
Which to Use on Each Surface
| Surface | Best chemistry | Typical coverage | Notes |
|---|---|---|---|
| Concrete driveway / sidewalk | Silane, 20–40%+ solids, or silane-rich blend | 100–200 sq ft/gal | Best for de-icing salt and freeze-thaw |
| Garage apron / exposed slab | Silane or blend | 100–200 sq ft/gal | Add a fluoro-modified product if oil stains matter |
| Clay brick walls | Siloxane or water-based blend | 75–150 sq ft/gal | Fix leaks and efflorescence first |
| Concrete / cinder block | Siloxane or blend, two coats | 50–100 sq ft/gal | Very porous; above-grade only |
| Concrete pavers | Blend | 100–200 sq ft/gal | Natural look; does not lock joint sand |
| Sandstone, granite, bluestone | Silane or blend | Varies widely | Test a patch first |
| Limestone, marble, travertine | Impregnator labelled for calcareous stone | Varies widely | Often siloxane or fluoro-based |
| Stucco | Siloxane, blend or siliconate | 100–200 sq ft/gal | Mask glass if using siliconate |
Coverage figures are typical label ranges for a full saturating application; always follow the specific product's rate, because it is set to deliver the depth the manufacturer designed for.
Driveway Concrete
This is silane territory. A driveway is dense, alkaline, horizontal, takes tyre abrasion, sits under standing water and slush, and in cold climates gets salted. Every one of those favours deep penetration over fast beading. Look for 20% solids at minimum and ideally 40%, either straight silane or a blend whose label makes clear the silane fraction is high. Our concrete driveway sealer roundup sorts products by exactly this distinction. New concrete generally needs to cure about 28 days first unless the label says otherwise.
Brick
Fired clay brick is closer to neutral than concrete and has larger pores, so siloxanes and water-based blends are the better fit. Before sealing brick, deal with whatever is letting water in from behind — failed mortar joints, missing flashing, a cracked chimney crown, gutters overflowing down the wall. A repellent on the face of a wall that is getting wet from inside slows drying at the face and can push salts to crystallise just beneath the surface, which spalls brick. Clean off efflorescence, repoint where needed, and then seal. The brick sealer guide covers breathable options specifically. Glazed or very hard-fired brick may absorb so little that a repellent is pointless; if water beads on it already, leave it alone.
Concrete and Cinder Block
Block is the most absorbent common masonry, and siloxanes or blends at generous coverage are the right approach on above-grade walls. Plan on two coats applied wet-on-wet, and expect to use considerably more product per square foot than on brick. What a penetrating repellent cannot do is stop water under hydrostatic pressure on a below-grade basement wall — that needs drainage and a waterproofing system, not a water repellent. The cinder block sealer reviews separate the two jobs.
Pavers
Concrete pavers are dense and alkaline like a slab, so a blend works well and keeps the natural, unsealed look while cutting down on staining, moss and freeze-thaw damage. The limitation is the joints: a penetrating repellent does nothing to bind the sand between pavers. If joint sand washing out or weeds are your problem, you want a joint-stabilising film-former or polymeric sand. See our water-based paver sealer guide for products that do one, the other, or both.
Natural Stone
Siliceous stones — sandstone, granite, quartzite, bluestone — have plenty of silica for silanes and siloxanes to bond to, and either works, chosen by porosity: silane or blend for denser stone, siloxane for soft sandstone. Calcareous stones — limestone, marble, travertine — are calcium carbonate, which offers fewer reactive sites, so products formulated specifically for them (often siloxane or fluoro-modified impregnators) perform more reliably. Natural stone varies enormously even within one quarry, so test a hidden patch and wait a week before committing.
Salt, Freeze-Thaw and Driveways
Concrete driveways in cold climates fail in two connected ways, and silanes address both.
Freeze-thaw scaling. Water absorbed into the surface freezes, expands by about 9%, and fractures the top layer of paste. Repeated through a winter, this produces the flaking, pitted surface called scaling. De-icing salts make it worse: salty water stays wet longer, raises the number of freeze-thaw cycles at the surface, and builds osmotic pressure in the pores. A deep silane treatment dramatically reduces how much water and brine the surface absorbs in the first place.
Chloride-induced corrosion. Where a slab contains rebar or mesh, chlorides from road salt that reach the steel break down its protective oxide layer, and the expanding rust cracks the concrete from inside. This is the problem transportation departments seal bridge decks against, and high-solids silanes are the standard treatment because their depth keeps working after traffic has worn the surface. A driveway is a lower-stakes version of the same problem.
Two caveats. First, repellents do not bridge cracks — anything wider than a hairline (a few tenths of a millimetre) will still let water in, so fill cracks before sealing. Second, silanes and siloxanes repel water, not oil. A pure silane will not stop motor oil from soaking in. If oil drips matter, look for a product with a fluoropolymer additive, which adds oil repellency while keeping the penetrating, breathable character. Our step-by-step driveway sealing guide covers crack repair and cleaning before application.
Applying Them Properly
Penetrating repellents are forgiving compared with film sealers — there are no lap marks to fight and no film thickness to manage — but the details still decide how deep the product gets and how long it lasts.
Clean and dry. The surface must be free of dirt, efflorescence, old film sealers and oil, because anything in the pores blocks penetration. Pressure-wash if needed, then let it dry: typically 24–48 hours after washing or rain, longer for thick masonry. A wet surface has its pores already full of water, and the repellent cannot get in.
Temperature and weather. Most products want surface temperatures roughly between 40°F and 90°F and no rain for 12–24 hours. For silanes especially, avoid direct midday sun and wind, which flash off the volatile fraction. Early morning or late afternoon on a calm day is ideal.
Saturate, do not paint. Apply with a low-pressure pump sprayer from the bottom of a wall upward (so runs land on untreated material) or in a steady pass across flat work, flooding the surface until it stops absorbing. On porous materials, a second coat goes on wet-on-wet — while the first is still damp — not after it has cured, because a cured repellent will reject the second coat. Brush or roll out puddles on flat surfaces so they do not leave a darkened or glossy patch.
Protect what you do not want treated. Overspray on glass and painted trim is easy to clean from silanes and siloxanes when fresh but much harder once cured; with siliconates it can etch. Mask windows and keep it off plants.
Test a patch. On anything decorative — stone, coloured concrete, old brick — treat a small inconspicuous area first. Most repellents are invisible once dry, but some darken certain materials slightly, and you want to know before you have done the whole wall.
Testing and Reapplication
The Water-Beading Test
The simplest check is to splash or spray water on the surface. Well-protected masonry beads the water into rounded drops that sit on top or run off, and the surface underneath stays its dry colour. If the water spreads out flat, darkens the surface and disappears into it within a minute or two, protection there is gone or was never adequate.
Do not treat beading as the whole story, though. Beading measures the outermost surface, which is the part that wears away first. A silane-treated driveway can stop beading after a few years while the treated zone a few millimetres down still sharply limits absorption. The more useful sign is darkening: if water sits flat but the concrete does not darken or absorb, the deeper protection is still working.
Professionals use a RILEM (Karsten) tube — a small graduated glass tube sealed against the surface — to measure how much water the masonry absorbs over a fixed time. Comparing a treated area with an untreated patch gives a real number rather than a judgement call, and it is worth asking for if you are hiring someone to treat a large brick facade.
How Often to Reapply
Realistic intervals depend on solids, exposure and traffic:
- High-solids silane (20–40%+) on a driveway: 5–10 years; some manufacturers claim longer for 100% silanes.
- Silane/siloxane blend on driveways and pavers: 4–8 years.
- Siloxane or blend on brick and block walls: 5–10 years on sheltered walls, 3–7 on exposed ones, since vertical surfaces see no traffic wear.
- Siliconate on walls: 2–5 years.
Reapplication is simple: clean, let dry, and apply again at the label rate. Unlike a failed acrylic, there is nothing to strip, and the old treatment does not need removing. The usual sign it is time is that the surface darkens in rain on areas that used to stay dry — often on the most exposed side of a wall or in the tyre tracks of a driveway first.
Common Mistakes
Using a low-solids product on a salted driveway. A 7% water-based siloxane will bead impressively for a season and then fade, because it never got deep enough. Salt exposure calls for depth, and depth comes from silane at real solids content.
Sealing over a moisture problem. On brick and block, a repellent is the last step, not the fix. If water is entering from the top or the back of the wall, seal the leak first, otherwise salts can collect just beneath the face and spall it.
Applying to a wet or freshly washed surface. Water-filled pores cannot take in the product. Wait the full drying time even if the surface looks dry on top.
Under-applying. Penetration depth is mostly a function of how much product goes into the surface. Stretching a gallon over twice the labelled area roughly halves the protection.
Expecting it to stop oil or a wet look. Silanes and siloxanes repel water, leave the surface looking natural, and do not stop oil. If you want gloss or colour enhancement, that is a film-former's job; if you want oil resistance, look for a fluoro-modified penetrating sealer.
Applying a second coat after the first has cured. A cured repellent repels the next coat too. Go wet-on-wet within the window the label gives.
The Short Version
Driveways, sidewalks and anything that gets salted: silane, 20–40% solids or more, or a silane-dominant blend. It goes deepest and lasts longest on dense alkaline concrete, and it is what bridge engineers use for the same reason.
Brick, block, stucco and porous stone: siloxane or a water-based silane/siloxane blend. It cures fast, works on neutral substrates and fills the larger pores where these materials take on water.
Pavers and mixed jobs: a blend, chosen with an eye on the solids percentage for whichever surface matters most.
Want gloss, colour enhancement or joint stabilisation? That is not this category — you need a film-forming sealer, and you accept the shorter recoat cycle that comes with it.
Whatever you choose, the job is mostly preparation: clean, dry, cracks filled, moisture sources fixed, then a saturating coat at the label rate. Do that and either chemistry will outlast most acrylics several times over.
Frequently Asked Questions
Both are penetrating water repellents that bond inside the pores of masonry and leave no surface film. Silanes are small single molecules that penetrate deeply — often 1/8 to 3/8 inch into concrete — but react slowly, need an alkaline substrate like concrete to bond well, and are volatile, so they are sold at high solids (20–100%). Siloxanes are larger, partly pre-reacted oligomers that penetrate less deeply but cure faster, depend less on alkalinity and work well at low solids (typically around 5–15%). The practical upshot: silane for dense concrete and driveways, siloxane for porous brick, block and stone, and a blend when you need some of both.
Silane, or a blend with a high silane content. Driveway concrete is dense and alkaline, which is exactly what silanes need to penetrate deeply and bond, and depth is what lets the treatment survive tyre wear and keep de-icing salt brine out of the concrete. Look for at least 20% solids and ideally 40%. A low-solids siloxane will bead well at first but sits close to the surface and fades sooner on a trafficked, salted slab. Fill cracks before sealing, since no penetrating repellent bridges cracks wider than a hairline, and wait about 28 days on new concrete unless the label allows sooner.
Siloxane or a water-based silane/siloxane blend in most cases. Fired clay brick is closer to neutral than concrete, so silanes react more slowly and less completely on it, while siloxanes cure quickly and fill the larger pores through which brick absorbs rain. Before sealing, fix any route by which water gets in behind the face — failed mortar joints, missing flashing, a cracked chimney crown — and clean off efflorescence. Sealing a wall that is wet from behind can trap salts just under the surface and cause spalling. Very hard or glazed brick that already beads water usually does not need sealing at all.
Yes, and that is their main advantage over film-forming sealers. They line the pores with a water-repellent layer rather than blocking them, so liquid water is kept out by surface tension while water vapour still passes through in both directions. The concrete or masonry can dry out from within, which reduces freeze-thaw damage and avoids the whitening, blistering and peeling that happen when moisture is trapped under an acrylic or epoxy. Vapour permeability is reduced only slightly in properly applied products, which is why they are the standard choice for exterior masonry in cold climates.
A high-solids silane (20–40% or more) on a driveway typically lasts 5–10 years. Silane/siloxane blends on driveways and pavers run about 4–8 years, and siloxanes or blends on brick and block walls 5–10 years on sheltered walls and 3–7 on exposed ones. Siliconates are the shortest-lived at around 2–5 years. Because the protection sits inside the material, UV and traffic affect it far less than they affect acrylic films, which usually need recoating every one to three years. Surface beading often fades before the deeper protection does, so watch for the surface darkening in rain as the real sign to reapply.
Splash water on the surface. If it beads up and the surface stays its dry colour, the treatment is working. If the water spreads flat, darkens the surface and soaks in within a minute or two, it is time to reapply. Check the most exposed areas first — tyre tracks on a driveway, the weather side of a wall — since they wear soonest. Note that loss of beading alone is not conclusive with silanes: the top layer wears off first while deeper protection remains, so water that sits flat without darkening the concrete still indicates useful protection. Reapplying is simple, with no stripping required: clean, dry and apply at the label rate.
Often not, at least not reliably. A cured silane or siloxane makes the surface water-repellent, which can prevent water-based acrylics, paints and stains from wetting and bonding to it, leading to poor adhesion or peeling. Some repellents are formulated and labelled as compatible with topcoating, and some film sealers are designed to go over them — check both data sheets before combining. If you think you may want a wet-look or coloured finish later, it is usually easier to choose the film-forming sealer from the start, or wait until the repellent has largely worn out and test adhesion on a small patch first.
No, despite the similar names. Densifiers are silicates — sodium, potassium or lithium — that react with the free calcium hydroxide in concrete to form extra calcium silicate hydrate, hardening the surface and reducing dusting. They are not strong water repellents on their own. Silanes and siloxanes are organosilicon compounds that line the pores with a hydrophobic layer, which is what keeps water and salt out. The two do different jobs and can complement each other; some products combine a densifier with a silane or siloxane, which suits older, dusty or weathered concrete that needs both hardening and water repellency.