Silane-impregnation water-repellent treatment (also called a penetrating silane protector or silane impregnation liquid) is a functional coating that forms no continuous surface film. Active alkoxysilanes such as isobutyltriethoxysilane and octyltriethoxysilane are drawn by capillary suction into the pore system of concrete, mortar, brick and natural stone, where they hydrolyse and condense on the pore walls, anchoring through –Si–O–Si– bonds with their non-polar alkyl chains oriented towards the pore centre. The pore wall changes from hydrophilic to hydrophobic. Two effects appear together: liquid water carrying dissolved chlorides and de-icing salts is rejected, while the open pore cross-section still lets internal moisture leave as water vapour. This combination of breathable waterproofing is why the treatment is specified for splash-zone marine structures, bridges, de-icing-salt environments and stone facades rather than as a substitute for tanking or paint systems.
TL;DR — Performance of a silane layer is governed by penetration depth and water repellency, not film thickness. Publicly stated acceptance criteria are penetration ≥3 mm by the dye method, water-absorption reduction ≥90%, chloride-uptake reduction ≥80% and silane active content no less than 98% (JTS/T 236-2019). Typical consumption is 250–350 g/m² for liquids and 350–450 g/m² for pastes, applied in two passes at a 3–6 h interval, protected from rain for 24 h, with the hydrolysis–condensation reaction complete after about 7 days. The treatment does not resist positive-side water pressure, does not bridge cracks, and any recoating or bonding on it must be qualified by a site first-article test.
1. Key figures at a glance
- Active content: silane active content ≥98% (detection practice under JTS/T 236-2019); manufacturer data for isobutyltriethoxysilane monomer state active silane ≥98.9%, siloxane ≤0.3%, chloride ≤0.01%.
- Penetration depth: ≥3 mm measured by the dye method; graded by substrate strength as ≥3–4 mm for concrete up to C45 and ≥2–3 mm for high-strength concrete above C45.
- Water and salt rejection: water-absorption reduction ≥90%; chloride-uptake reduction ≥80% (some published product sheets state ≥90%).
- Consumption: 250–350 g/m² liquid, 350–450 g/m² paste, split into two consecutive passes with 3–6 h between them.
- Reaction and early protection: no rain or washing for 24 h after application; about 7 days for the hydrolysis–condensation reaction to finish.
- Environmental qualification: 21 days in saturated Ca(OH)₂ with no abnormality, 50 freeze–thaw cycles between −15 °C and 20 °C without cracking, 300 h salt spray in 5% NaCl.
- Stone protectors (JC/T 973-2005): surface-grade water resistance ≥85% premium, 70–85% first grade, 50–70% qualified; water-based VOC ≤200 g/L; solvent-borne benzene ≤0.5% and toluene plus xylene ≤10%; bond-strength loss for the bottom-face type ≤5.0%.
- Length scale: an alkoxysilane molecule is sub-nanometre to about 1 nm and reaches pores larger than 10 nm; acrylic emulsion particles are typically 50–500 nm and stay on the surface as a film — the physical origin of the difference between the two families.
- Wetting criterion: a static water contact angle above 90° counts as hydrophobic, above 150° as superhydrophobic; silane-treated surfaces usually settle at 100°–120°, which rejects water without building micro-nano roughness.
2. Mechanism: pore-wall chemistry and capillary pressure reversal
2.1 Hydrolysis first, then condensation
Alkoxysilanes are written R–Si(OR′)₃, where R is a methyl, isobutyl or octyl group and OR′ is a hydrolysable ethoxy or methoxy group. After the liquid is sucked into the pore, adsorbed water hydrolyses the ethoxy groups to silanols (Si–OH) and releases ethanol. Silanols then condense with each other and with surface hydroxyls of the substrate — the Si–OH of C-S-H gel and quartz in concrete, M–OH on silicate minerals in stone — building a –Si–O–Si– network bonded to the wall. Non-polar alkyl chains then line the pore, lowering surface energy from the 500–1000 mJ/m² of an inorganic surface to roughly 20–30 mJ/m², and the contact angle rises above 100°. Ethanol and water produced during reaction are small molecules and diffuse back out, so pores are modified rather than plugged.
2.2 Liquid water blocked, water vapour passing
Capillary uptake follows Young–Laplace. In a hydrophilic pore (θ < 90°) the meniscus is concave towards the water and the pressure difference is negative, pulling water in. Once the wall is hydrophobic (θ > 90°) the sign reverses: water must be pressurised to enter, and the effect grows as the pore radius shrinks. Vapour transport, by contrast, is molecular diffusion driven by a humidity gradient and forms no meniscus, so it is not impeded. One modification therefore blocks liquid-borne chlorides, de-icing salts and dissolved CO₂ while the structure keeps drying out — the premise behind breathable waterproofing and the avoidance of water staining and frost damage.
2.3 Where film-forming products take over
Film-formers — elastic acrylic coatings, polyurethane and bituminous membranes, epoxy sealers — stop water by continuity and thickness, so they resist positive-side pressure and bridge hairline cracks, but they also restrict vapour and can blister when the substrate is damp. Penetrating silane contributes no film thickness, no crack bridging and no positive-pressure rating; it is chosen where appearance must not change, where peeling film is unacceptable and where the assembly must breathe. A robust specification layers structural waterproofing, penetrating repellency and a decorative top system rather than asking one product to do all three.
3. Four material routes compared
| Route | Representative chemistry | Scale | Penetration and bonding | Behaviour in service | Main risk |
|---|---|---|---|---|---|
| Silane monomer (current mainstream) | Isobutyl- and octyltriethoxysilane | Sub-nm to 1 nm | Deep into the pore; Si–O–Si anchoring; ethanol and water as by-products | 3–4 mm achievable, active content ≥98%, appearance unchanged | High substrate moisture reacts the material early; flash point and odour need ventilation |
| Siloxane oligomer | Partially hydrolysed methyl siloxane | A few nm to tens of nm | Concentrated in the top 0–2 mm; blocks water at the pore mouth | Fast visible beading, mild suppression of surface dusting | Big molecules are strained off at the surface; vapour permeability and depth fall |
| Alkali-metal silicate | Sodium or potassium methyl silicate | Ionic solution | Precipitates insoluble methyl siliconate with Ca²⁺ | Low cost, simple application | Fails quickly in alkaline service, may bloom white, raises near-surface moisture |
| Nano and fluoro-silane hybrid | Nano SiO₂, fluorosilane, silica sol | Particles 10–100 nm | Wall chemistry plus micro-nano topography | Higher contact and slide-off angle, approaches superhydrophobic | The delicate structure is wear-sensitive; durability becomes the limit |
Note the distinction: a superhydrophobic coating reaches above 150° by building roughness, whereas a silane treatment changes surface chemistry only. The silane layer has no film to peel and ages with the substrate, but its water rejection is milder and it does not self-clean.
4. How performance is measured
4.1 Water-repellency rate and absorption reduction
Water repellency is computed from the mass of water taken up before and after treatment: repellency = (1 − W_treated / W_untreated) × 100%, where W is the water absorption per unit area (kg/m² or g/m²) under a defined immersion cycle. The same idea exists for insulation materials under GB/T 10299-2011. Concrete protection tends to quote water-absorption reduction, with ≥90% as the published acceptance value. Three test details decide comparability: conditioning of specimens at 60 °C ± 2 °C as JC/T 973-2005 prescribes, a completed 7-day reaction before testing, and paired specimens from the same rock type or mix design.
4.2 Penetration depth by the dye method
On a drilled core or a fresh fracture, a dye is sprayed: treated zones stay colourless, untreated zones stain, and the colourless thickness is read as penetration depth, judged against ≥3 mm. Porosity profiling and chloride section analysis support the laboratory view. Depth is controlled by three variables — substrate strength and pore structure (3–4 mm up to C45, 2–3 mm above), moisture content of the base, and uptake per square metre, since an insufficient dose leaves the modification discontinuous. This is an absorbed product: consumption and pore structure decide the result, and a wet-film gauge reading means nothing here.
4.3 Chloride reduction and environmental ageing
Chloride-uptake reduction ≥80% is the public benchmark for salt resistance, and marine or de-icing projects normally add the alkaline immersion (saturated Ca(OH)₂, 21 days), freeze–thaw (−15 °C to 20 °C, 50 cycles) and salt-spray (5% NaCl, 300 h) blocks to the material qualification. Design references are JTS 153-2015 for marine concrete durability and TB/T 3228-2010 for railway structures.
5. Standards and requirement values
| Standard | Title | Scope | Values relevant to this topic |
|---|---|---|---|
| JT/T 991-2015 | Silane paste materials for surface protection of bridge concrete | Product specification for bridge silane pastes | Penetration depth, absorption reduction, chloride-uptake reduction and their test methods |
| JTS 153-2015 | Durability design standard for water transport engineering structures | Marine concrete design and surface protection | Selection logic for splash zones and chloride exposure |
| JTS/T 236-2019 | Technical code for testing of hydraulic engineering concrete | Incoming material testing | Silane effective content not less than 98%; residual alcohol controlled |
| JC/T 2273-2014 | Determination of effective content and hazardous substances in silane/siloxane building protectors | Chemical analysis method | Quantification by GC-MS and hazardous substance limits |
| TB/T 3228-2010 | Durability repair and protection of railway concrete structures | Railway concrete protection | Service conditions and the associated system requirements for impregnation products |
| JC/T 973-2005 | Protector for natural facing stone of building decoration | Stone protector grading | Water resistance ≥85% / 70–85% / 50–70% by grade; water-based VOC ≤200 g/L; benzene ≤0.5%, toluene plus xylene ≤10%; bond loss ≤5.0%; oven 60 °C ± 2 °C, ageing box with 500 W mercury lamp |
| GB/T 10299-2011 | Test method for water repellency of thermal insulation products | Repellency test method | General reference for the repellency calculation |
These entries are compiled from publicly available standard and test-house summaries. Standards are revised over time, so procurement and acceptance must follow the current valid text, the project specification and the factory inspection report.
6. Application window and workmanship
6.1 Base conditions: dry and open
The substrate must be thoroughly dry, free of standing water, oil, release agent and dusting, with cracks and honeycombing repaired beforehand, because penetrating protection seals no defects. Old concrete needs carbonation, grime and any legacy coating removed to expose an open pore structure; surfaces already painted or tanked simply cannot be impregnated, and work there is wasted.
6.2 Two passes, wet-on-wet
A typical application is two passes in the same area reaching the total consumption of 250–350 g/m² (liquid) or 350–450 g/m² (paste), the second pass laid 3–6 h after the first while the first is surface-dry but still reacting. On vertical faces the gun travels from the bottom upwards to limit run-off losses; floors and slabs take low-pressure flooding. Air temperature between 5 °C and 35 °C, substrate at least 3 °C above dew point, and work stops 24 h before rain or in strong wind and blowing dust.
6.3 Early protection and cure
For 24 h the surface must be kept from rain, ponding and traffic, while the product still migrates inwards and hydrolyses; the condensation reaction finishes after roughly 7 days, and performance then stabilises. Acceptance testing, recoating, tiling and jointing should all be scheduled after that period and qualified by a first article.
6.4 Quantity take-off and commercial terms
Budget as design consumption × area × loss factor. Rough, high-porosity substrates commonly absorb 20%–50% more than dense smooth ones, so the loss factor should come from a measured trial panel. For export cooperation we quote on EXW/FOB terms only; packaging, flash point and transport conditions differ between solvent-borne and water-based systems and must be checked against the SDS and the agreed clause.
7. Boundaries: what this treatment cannot do
7.1 No positive pressure, no crack bridging
Rejection here rests on capillary pressure reversal, which is modest in magnitude. Sustained water head on the positive-pressure side — basement slabs, tank interiors, ponded roofs — drives water through, and those cases need membranes or structural waterproofing. The layer is not mechanically continuous, so it spans no existing crack; cracks must be sealed or made flexible first.
7.2 Recoating and bonding risk
Once reacted, the pore wall carries low surface energy, which harms the wetting of waterborne paints and the key of tile adhesives and cementitious mortars; unreacted paste residue interferes as well. Where a subsequent coat, bond or joint is planned, run a site adhesion first article (cross-cut or pull-off) after the reaction period, and if it fails, restore the interface by abrasion, by leaving porous zones untreated, or with a compatible tie coat.
7.3 High-strength, fresh and precast concrete
Above C45 the pore network refines and the achievable depth falls to 2–3 mm; compensate with higher uptake or a lower-viscosity product and allow longer drying. Fresh concrete needs its hydration, alkalinity and moisture to stabilise before treatment, otherwise pore water quenches the reaction. On precast elements, residual mould oil is a frequent hidden cause of failure and wettability should be checked before application.
7.4 Efflorescence and water staining: correct order
Efflorescence and water marks come from water moving salts outward, or from vapour being trapped inside. Treating only the exposed face while the back and joints stay open prolongs internal dampness; bottom-face protectors for stone are graded in JC/T 973-2005 with bond-strength loss ≤5.0% and no water stain under the permeability test, precisely to keep the vapor path alive. Sequence the works as cut off the water first, then manage the salt, then apply repellency — the reverse order usually fails.
8. Where it fits: scenario and selection logic
| Scenario | Main attack | Recommended approach | When repellency alone is not enough |
|---|---|---|---|
| Marine and bridge splash zone | Chloride ingress, freeze–thaw, carbonation | Silane impregnation at 250–350 g/m² in two passes plus crack repair, checked against JTS 153-2015 | — (this is its strong ground) |
| Bridge decks and de-icing salt | Salt solution ingress, rebar rust jacking | Repellency with joints sealed first | Unsealed expansion joints pour water straight in |
| Fair-faced concrete and historic facades | Rain, staining, water marks | Low-viscosity silane or siloxane, keeping appearance and vapour flow | Film products change gloss and trap vapour |
| Polished stone thresholds and cladding | Oil, colour change, alkaline bloom | Surface-grade protector chosen as water or oil type, bottom-face grade behind | Treating the face only traps water inside the panel |
| Below-ground negative side | Positive-pressure water | Crystalline or polymer-modified rigid waterproofing | Capillary reversal is insufficient under head |
| Substrates to be painted or tiled | Follow-on trades | Decide sequence from an adhesion first article; restrict repellency to areas with no coating | Low surface energy makes direct recoating risky |
9. Sources and further reading
- JT/T 991-2015, JTS 153-2015, JTS/T 236-2019, JC/T 2273-2014 and TB/T 3228-2010 for silane impregnation materials, testing and design in bridge, marine and railway concrete.
- JC/T 973-2005 for natural stone protectors (classes SJ/RJ, FS/FY, SM/DM; drying oven 60 °C ± 2 °C; ageing box with a 500 W straight-tube high-pressure mercury lamp) and GB/T 10299-2011 for the water-repellency test method.
- Manufacturer published data for silane monomers (isobutyltriethoxysilane type) and Chinese third-party test-house summaries of silane impregnation indicators.
- Related articles on this site: contact angle and wetting theory, nano SiO₂ hydrophobic modification, mechanical durability of superhydrophobic coatings, nano protection of building facades, stone anti-oil protectors, and alkali-resistant primer systems for concrete.
10. Frequently asked questions
Is a silane treatment the same as a clear exterior waterproofing coating?
No. A clear coating is film-forming: it stops water by a continuous polymer layer, reduces vapour flow and can bridge fine cracks. Silane penetrates, leaves no visible film, resists water by pore-wall chemistry and keeps the wall breathing.
How do we check that the work was actually done properly?
Use two measurements: dye-method penetration depth (≥3 mm) and absorption reduction against an untreated control (≥90%). Beading water on the surface is not a valid judgement — unreacted product on the surface beads too, and often signals that the pore interior was never reached.
Can the surface still be painted or tiled afterwards?
Only after qualification. Reacted pore walls have low surface energy, which weakens wetting by waterborne paint and the key of cementitious adhesives. Run a cross-cut or pull-off first article about seven days after treatment; if it fails, abrade the surface, apply a compatible tie coat, or omit the repellent where the coating must go.
Which is better, water-based or solvent-borne?
They differ in molecular scale and handling. Solvent-borne silane monomer is low in viscosity, penetrates deep, carries ≥98% active content, but has a flash point and odour. Water-based systems are usually micro-emulsions or oligomers: friendlier to apply and to the environment, slightly weaker in depth and vapour flow. JC/T 973-2005 also caps water-based VOC at 200 g/L and solvent-borne benzene at 0.5%, toluene plus xylene at 10%.
Why is the required depth lower for high-strength concrete?
Because the pore network is finer and less connected, so the product physically cannot travel as far. The graded requirement of 3–4 mm up to C45 and 2–3 mm above C45 reflects achievability, not a weaker result — dense concrete already resists chloride uptake on its own.
Is the treatment a replacement for an anticorrosion coating system?
No. It addresses transport of water, chlorides and dissolved CO₂ through pores. Where rust jacking has started, cover is insufficient or cracks are active, repair and cathodic protection come first; exposed reinforcement and steel belong to the coating system, not to impregnation.
How long does it last, and when should it be renewed?
Since the modification lives inside the substrate there is no film to peel; it fades as carbonation, abrasion and new cracks reopen paths. Renewal should be triggered by measured repellency on site rather than by a calendar date. Published industry material claims more than ten years for organosilicon protectors, subject to exposure and retest results.
Last updated: 2026-10-08 | Basis and public sources: penetration ≥3 mm, water-absorption reduction ≥90%, chloride-uptake reduction ≥80%, 21 days in saturated Ca(OH)₂, 50 freeze–thaw cycles at −15 °C to 20 °C and 300 h salt spray in 5% NaCl come from published test-house scopes linked to JTS 153-2015, JT/T 991-2015, JC/T 2273-2014, TB/T 3228-2010 and JTS/T 236-2019; consumption of 250–350 g/m² liquid and 350–450 g/m² paste, 3–6 h between passes, 24 h rain protection, roughly 7 days reaction and the strength-graded 3–4 mm / 2–3 mm depths come from manufacturer product and application sheets; stone protector grades follow JC/T 973-2005. Values shift with pore structure, moisture content, temperature and formulation, so verify against the current standard text, the project specification and a site trial panel. Author: technical team of Kexin New Materials (Guangdong) Co., Ltd. Export cooperation is quoted on EXW/FOB terms only.