The History and Evolution of Stone Impregnators
By Frederick M. Hueston
What Is an Impregnator?
In the stone and tile industry, an impregnator is a penetrating, breathable treatment that soaks into the pore network of concrete, stone, or masonry, then reacts or deposits a hydrophobic or oleophobic phase inside those pores. It is not a film. The goal is simple: keep liquid water and stains out, let vapor move, and avoid darkening or gloss.
Early Attempts at Water Repellency
Before modern chemistry, builders tried to keep water out of masonry with natural products. Historic records point to bitumen, resins, fats, and waxes as water barriers on structures and ships. These were mostly coatings, not true pore-liners, but they show the instinct to repel water is ancient.
The Rise of Soaps and Stearates
By the late 19th and early 20th centuries, conservation and building practice added water-repellent “soaps” and stearates. Sodium oleate and calcium stearate show up in conservation literature as commercial water repellents for stone and mortar. They reduced wetting but could alter appearance and salt behavior, and they were not very durable.
Mid-20th Century Bridge Deck Protection
In the 1950s and 1960s, highway departments used boiled linseed oil, sometimes cut with kerosene, as a deck sealer for concrete bridge decks. Reports from that period document the practice and its limits, especially shallow penetration and reactivity in alkaline concrete.
The Turning Point: Silanes in 1969
The real turning point came around 1969 when Dynamit Nobel in West Germany proposed alkyl-alkoxysilanes as concrete impregnates. Small, solvent-borne molecules could travel deep into capillaries, then react to forming a durable hydrophobic network. Patents in the following decades refined solvent systems and silane structures, bridging the gap between “seal the surface” and “line the pores.”
Transportation and Conservation Applications
Transportation agencies quickly adopted silanes and silicone chemistries for bridge preservation, while conservation fields tested silicones and alkoxysilanes on historic stone. Getty Conservation Institute research emphasized balancing breathability, reversibility, and salt transport in treatment choices.
The 1990s and Beyond
By the 1990s, silicone chemistry was firmly established in construction. Companies like WACKER advanced silicone resins, silanes, and siloxanes that supported both coatings and hydrophobic impregnation markets.
Key Ingredients
- Silanes: Small molecules (e.g., isobutyl-triethoxysilane) penetrate deeply and bond inside cement or stone, leaving hydrophobic pores. Excellent for dense substrates.
- Siloxanes and silicone resins: Larger, less volatile, and suited for porous substrates like sandstone or concrete masonry. Blends balance penetration with durability.
- Siliconates: Water-reducible salts, affordable and easy to apply, but less durable and more appearance-sensitive.
- Silicates and silica sols: Densifiers for cementitious substrates, not repellents for stone.
- Fluorinated polymers: Later additions designed for oil and dye resistance, popular for kitchen applications.
Environmental and Performance Shifts
Early silanes were almost always solvent-borne, creating VOC and flammability issues. Later developments included aqueous emulsions and microemulsions, which lowered VOCs while maintaining performance.
Europe’s EN 1504-2 standard, published in 2004, defined hydrophobic impregnation versus coatings and set clear performance requirements for concrete protection. These standards influenced building conservation and stone practice worldwide.
Lessons Learned for Stone Professionals
- Match chemistry to stone and goal:
- Silane blends for dense stones and facades
- Siloxane-rich for porous stones
- Fluorinated add-ons for kitchens
- Test for darkening and sheen changes before application.
- Respect breathability: avoid coatings unless moisture risks are acceptable.
- Apply lessons from bridges: surface prep and application rates determine penetration depth and durability.
Know the rulebook: EN 1504-2 provides terminology and test methods to help explain impregnators to clients.
Quick Timeline
- Pre-modern: Bitumen, waxes, oils on masonry (film coatings)
- Early 1900s: Stearates and “soaps” marketed as repellents.
- 1950s–60s: Linseed oil applied to bridge decks
- 1969: Dynamit Nobel proposes alkyl-alkoxysilanes
- 1970s–90s: Broad adoption of silanes and siloxanes
- 1990s–2000s: Water-based emulsions lower VOCs
- 2004: EN 1504-2 defines standards for hydrophobic impregnation
2000s–Today: Fluorinated additives improve oil resistance
Final Takeaway
From waxes on ships to advanced silanes and fluoropolymers, the evolution of stone impregnators reflects centuries of trial, error, and innovation. For today’s stone professionals, choosing the right chemistry requires balancing penetration, breathability, durability, and client expectations.
