The Science Behind Nanoxeal

What is a water-repellent coating, and how is the "beading effect" measured?

A surface is classified as hydrophobic when the static water contact angle reaches 90 degrees or more, and superhydrophobic at 150 degrees or more, with water rolling off as near-spheres (Brighton Science). ASTM D7334-08(2022) confirms this classification by advancing contact angle: hydrophilic below 45 degrees, intermediate from 45 to 90 degrees, hydrophobic above 90 degrees. Beading is therefore a measurable quantity, not a visual impression.

Wetting obeys Young’s equation:

$${\gamma }_{\text{lv}}\cos \theta ={\gamma }_{\text{sv}}-{\gamma }_{\text{sl}}$$

The lower the solid’s surface free energy, the higher the water contact angle. This is the fundamental physics underlying every repellent in this class.

The biological benchmark is the "lotus effect": the Nelumbo leaf shows a contact angle of roughly 162 degrees, not from chemistry alone, but from hierarchical micro/nano roughness combined with a low-surface-energy epicuticular wax (Barthlott and Neinhuis, Planta, 1997; angle value from Neinhuis and Barthlott, Annals of Botany, 1997). That dual contribution (low-energy chemistry plus nano texture) is exactly the logic of a polysiloxane/fluoropolymer/nano-silica system.

How does a silane/siloxane water repellent work, and why does it stay "breathable"?

Penetrating silane and siloxane repellents do not form a film: they penetrate the pores and undergo hydrolysis then condensation to bond a hydrophobic resin onto the pore walls (lining, not filling). Effective surface energy drops, water beads, but the pores stay open to vapor diffusion (Euclid Chemical). Siloxane is pH-independent and reacts with moisture; silane, being smaller, penetrates deeper. In both cases the substrate "breathes."

The peer-reviewed literature quantifies the effect. A 2024 review in the Journal of Materials Science reports that silane/siloxane surface treatments consistently attain 70 to 95% reductions in the water absorption of cementitious materials. In practice, repellents of this class sharply cut capillary uptake of porous mineral substrates while leaving the pores open to vapor, which is what separates a breathable water repellent from a sealing film.

Application by surface type (masonry, concrete, wood): see the Nanoxeal product.

How long does water-repellent protection last?

A landmark field study (Christodoulou et al., Construction and Building Materials, 2013) took cores from reinforced-concrete bridge cross-beams treated with silane about 20 years earlier: water absorption remained significantly reduced, demonstrating a residual protective effect after two decades. Silane impregnation therefore retains a large fraction of its water-repellent effect over one to two decades, while gradually declining over time.

The durability of a coating in this class is verified in the lab by accelerated weathering under fluorescent UV and condensation per ASTM G154: UVA-340 lamps simulating summer sunlight, alternating UV and moisture cycles.

Why does polysiloxane resist UV so well?

The UV resistance of polysiloxane comes from its silicon-oxygen (Si-O) backbone bond, about 444 kJ/mol, stronger than the carbon-carbon (C-C) bond (about 348 kJ/mol). A 300 nm sunlight photon carries about 398 kJ/mol: enough to cleave a C-C bond, but not an Si-O bond (figures from reference tables; qualitative conclusion confirmed by Silicones Europe). That is the fundamental reason silicones resist UV-induced chain scission.

Moreover, because the Si-O bond is already highly oxidized, the polysiloxane backbone cannot be oxidized further the way a C-C chain can. Silicone coatings thus offer UV, oxidative, and thermal resistance superior to organic binders (acrylics, urethanes) while keeping a flexible Si-O-Si chain. This is what allows the formation of a membrane that is both durable and flexible.

Why add a fluoropolymer?

Fluoropolymers have among the lowest known solid surface energies (about 18 to 20 mN/m for PTFE), giving smooth-surface water contact angles of about 105 to 115 degrees (Scientific Reports, 2019). Their exceptional UV durability comes from the carbon-fluorine (C-F) bond, about 486 kJ/mol, exceeding the energy of a 300 nm UV photon (about 399 kJ/mol): sunlight therefore cannot photolyze it (PCI Magazine / AGC Chemicals LUMIFLON; American Coatings Association). PVDF and FEVE architectural coatings retain color and gloss for 30 years or more.

Combined with the polysiloxane, the fluoropolymer adds a second chemical barrier with very low surface energy and very high UV stability.

The surfaces most exposed to solar radiation (roofing and metal): see the Nanoxeal product.

What does the nano-silica do?

Nano-silica provides the dual-scale roughness that turns low-energy chemistry into a strongly repellent surface. Wetting follows the Wenzel and Cassie-Baxter models: smooth low-energy chemistry gives about 90 to 110 degrees, and nano-silica roughness (Cassie-Baxter regime, trapped air) drives the contact angle toward 150 degrees and beyond (Shirtcliffe et al., Advances in Colloid and Interface Science, 2010).

The effect is documented quantitatively. Adding silica to a low-energy polymer (PVDF) raises the water contact angle from 95 to 168 degrees as silica loading increases (Materials Letters, 2016). In a silicone matrix, PDMS-silica nanocomposites reach a static contact angle of about 152.6 degrees while remaining measurably hard and wear-resistant by nanoindentation (Nanomaterials, 2025), and a PDMS/SiO2 coating retains hydrophobic performance under standardized sandpaper and Taber abrasion testing (Coatings, 2018). A PDMS/silica nanocomposite at 156.4 degrees even retained its superhydrophobicity after UV exposure, sand abrasion, water impact, tape peeling, and strong acid/base exposure (ACS Omega, 2020). Nano-silica is therefore not just a contact-angle additive: it contributes to the mechanical robustness of the coating.

Why is "breathability" (vapor permeability) so important?

Vapor permeability is essential for exterior masonry and wood coatings: a non-breathable film traps moisture and causes blistering, peeling, freeze-thaw spalling, efflorescence, and decay (building-science principle confirmed by Euclid Chemical). A good water repellent must therefore repel liquid water while letting vapor escape.

These two properties are independent and standardized separately. The EN 1062-1 framework grades liquid-water permeability on one side (w-value, w below 0.5 = water-repellent) and water-vapor permeability on the other (Sd-value, classes V1 high / V2 medium / V3 low via EN ISO 7783): a coating can therefore be both low in liquid-water permeability AND high in vapor permeability. Under EN 1504-2, breathability is classified by Sd value: Class I, Sd below 5 m (permeable); Class II, 5 to 50 m; Class III, Sd above 50 m (not permeable).

Breathability is measurable: water-vapor transmission is quantified by ASTM E96 (and ASTM D1653 for coating films), yielding a "perm" rating (a material above 10 perms is considered vapor-permeable). As a verifiable commercial example, the Sikagard-670 W coating is documented at 17.9 US perms (ASTM E96) with an Sd of about 0.4 m: proof that breathability is a testable, standardized criterion, not a marketing argument.

What does the coating actually do against UV, by surface?

UV radiation degrades each material differently, and that is precisely what a high-UV-stability coating slows down.

• Asphalt (asphalt shingles): UV photo-oxidation volatilizes light oils and oxidizes maltenes toward asphaltenes, embrittling the binder and reducing flexibility, ductility, and self-healing (Construction and Building Materials, 2026). On shingles, mineral granules shield the underlying asphalt; loss of volatiles weakens the asphalt-granule bond, granules shed, and the bared asphalt then degrades faster (InterNACHI).
• Wood: UV mainly photo-oxidizes lignin (the UV chromophore), depolymerizing it into water-soluble products and leaving a cellulose-rich surface that grays, erodes, and lets coatings delaminate (Wood and Fiber Science, 2005). This photodegradation stays confined to a thin surface zone: UV penetrates about 75 micrometers and visible light about 200 micrometers, which is why surface coatings and UV screens are effective (Evans et al., 2007; depths established in the literature).
• Organic polymers and coatings: UV photo-oxidation causes chalking, gloss loss, yellowing, cracking, embrittlement, and tensile-strength loss; UV absorbers and inorganic screens extend service life (Polymers, MDPI, 2022).

See the Nanoxeal product.

How is all of this verified in practice?

The effectiveness and durability of a water-repellent treatment are field-verified by water-absorption tests: the RILEM tube measures low-pressure uptake before and after treatment (a marked decrease indicates correct application), and bulk absorption and void volume are measured by ASTM C642 (Brick Industry Association; ASTM C642). UV durability is confirmed in the lab by ASTM G154. In other words, every major claim on this page (beading, absorption reduction, breathability, UV resistance) maps to a standardized test method.

FAQ

References

1. 1. Brighton Science, "What is a Contact Angle?" https://www.brighton-science.com/what-is-contact-angle
2. 2. ASTM D7334-08(2022), Surface Wettability by Advancing Contact Angle Measurement. https://store.astm.org/d7334-08r22.html
3. 3. Barthlott & Neinhuis (1997), "Purity of the sacred lotus," Planta 202:1-8; angle from Neinhuis & Barthlott (1997), Annals of Botany 79:667-677. https://doi.org/10.1007/s004250050096
4. 4. Euclid Chemical, "Silane and Siloxane Water Repellents for Concrete and Masonry." https://www.euclidchemical.com/company/blog/archive/silane-and-siloxane-water-repellents-for-concrete-and-masonry/
5. 5. "A review on silane and siloxane materials," Journal of Materials Science (2024). https://link.springer.com/article/10.1007/s10853-024-09771-6
6. 6. Christodoulou et al. (2013), "Long-term performance of surface impregnation of reinforced concrete with silane," Construction and Building Materials 48:708-716. https://doi.org/10.1016/j.conbuildmat.2013.07.038
7. 7. Scientific Reports 9:8675 (2019), "Water Repellent Superhydrophobic PTFE Surface." https://pmc.ncbi.nlm.nih.gov/articles/PMC6572853/
8. 8. American Coatings Association, "Fluoropolymer Coatings for Architectural Applications" (2020). https://www.paint.org/coatingstech-magazine/articles/fluoropolymer-coatings-for-architectural-applications/
9. 9. PCI Magazine / AGC Chemicals (LUMIFLON), "FEVE Powder Technology" (2020). https://www.pcimag.com/articles/107819-feve-powder-technology-for-weather--and-corrosion-resistant-coatings
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17. 17. EN 1504-2:2004, Surface protection systems for concrete (Sd classes via EN ISO 7783). https://standards.iteh.ai/catalog/standards/cen/ac5d306d-e443-4023-9888-5ff3dbdf5dfc/en-1504-2-2004
18. 18. ASTM E96/E96M, Water Vapor Transmission of Materials (and ASTM D1653 for coating films). https://www.astm.org/e0096_e0096m-16.html
19. 19. Sika USA, Sikagard-670 W technical data (17.9 perms ASTM E96, Sd 0.4 m). https://usa.sika.com/en/construction/repair-protection/coatings-water-repellents/building-facade-coatings/sikagard-670-w.html
20. 20. ASTM G154 (Q-Lab), accelerated fluorescent-UV / condensation weathering. https://www.q-lab.com/weathering/weathering-test-standards/ASTM-G154
21. 21. "Performance of UV aged asphalt mixture," Construction and Building Materials (2026). https://www.sciencedirect.com/science/article/abs/pii/S0950061826001728
22. 22. InterNACHI, "Mastering Roof Inspections: Asphalt Composition Shingles, Part 30." https://www.nachi.org/asphalt-comp-shingles-part30-84.htm
23. 23. "Photodegradation and Photoprotection of Wood Surfaces," Wood and Fiber Science (2005). https://wfs.swst.org/index.php/wfs/article/download/1520/1520/0
24. 24. Evans, Urban, Chowdhury (2007), "Violet light photodegradation of wood," US Forest Service FPL. https://research.fs.usda.gov/treesearch/29235
25. 25. "UV Absorbers in Polymers," Polymers (MDPI), PMC8747282 (2022). https://pmc.ncbi.nlm.nih.gov/articles/PMC8747282/
26. 26. Frontiers in Materials (2025), "Silane-cement permeable crystalline composite coating." https://doi.org/10.3389/fmats.2025.1627957
27. 27. Li, Fan, Lv, Fan (2020), "Hydrophobic Treatments and Salt Frost Resistance," Materials 13(23):5361. https://doi.org/10.3390/ma13235361
28. 28. Brick Industry Association, "RILEM Tube Testing and Brick Masonry"; ASTM C642. https://www.gobrick.com/media/file/bb-rilem-tube-testing_final.pdf