Film-forming treatment

A film-forming treatment is a continuous protective layer (resin, paint, varnish, hard wax, liquid membrane, etc.) applied to a building substrate—concrete, steel, wood, sometimes zinc or plaster—to act as a barrier against water, salts, CO₂, UV radiation, and chemical/mechanical damage. Unlike non-film-forming treatments (penetrating water repellents, silanes/siloxanes) that permeate the material, a film-forming treatment covers the surface and creates a measurable barrier (dry thickness, Sd). When properly selected and applied, it slows carbonation, protects steel, limits soiling, and stabilizes the appearance of structures.

Film-forming treatment: operational definition and uses

A film-forming system combines a primer (adhesion/anti-corrosion), one or more base layers (thickness, waterproofing) and a finishing layer (UV, cleaning).

Common families:

- Acrylics/polyurethanes : UV stable finishes for facades/exposed concrete, parking lots.

- Epoxies : hard and chemically resistant films (technical rooms, interior tanking), often UV protected by a polyurethane.

- Film-forming waxes/varnishes for wood : surface protection (interior terraces, exterior joinery depending on the range).

- Reinforced liquid membranes (PU/PMMA): bridging of microcracks, watertight upstands.

Typical applications : concrete facades (anti-carbonation), soffits and parking slabs (de-icing salts), beams/columns in chlorinated environments, HVAC rooms (civil engineering protection), steel structures (anti-corrosion systems).

Advantages, limitations and points to consider

Interests

• Barrier against aggressions: water, chlorides, CO₂ → slowed carbonation, preserved steels.
• Durability & maintenance: less porous surface → reduced soiling and dust, easier cleaning.
• Appearance & readability: controlled color, more homogeneous works (useful in visible parts).
• Specific functions: anti-slip parking, bridging micro-cracks, marking technical areas.

Boundaries

• Vapor permeability: film too tight = risk of blistering/deadherence if residual moisture remains.
• UV aging (depending on resin) → periodic restarts (maintenance cycle).
• Demanding preparation: dry, clean, sanded/hydro-stripped surfaces; defects → unpredictable adhesion.
• Shocks & punctures: thin, sensitive films (provide thickness and reinforcement if needed).

Points to consider

• System selection: aim for a compromise Sd (vapor barrier vs breathability) adapted to the climate and the support; anti-carbonation if exposed concrete.
• Compatibility: check old paint, concrete pH, moisture (CM%), salts; anti-corrosion primers on steels.
• Thicknesses: check DFT (dry film thickness) per pass; respect consumption and recoating time.
• Details: take care of edges, repairs, upstands, joints (compatible sealant) — frequent areas of detachment.
• Safety/air quality: VOCs, fire classification, anti-slip (parking lots, traffic areas).
• Maintenance: plan re-inspection (cross-cut adhesion, micro-cracks, wear) and refurbishment cycles.

Anecdote — “A parking lot that withstood the tide in La Rochelle”

In La Rochelle, the concrete slabs of a semi-open parking lot were turning white, and the rebar was protruding from the sea spray. The site received an anti-carbonation film-forming system: a suitable primer, an epoxy bonding agent, and then UV-stable aliphatic polyurethane, reinforced at the cracks. Two winters later: efflorescence stopped, chlorides contained, washing simplified, and no blistering—proof that with the right Sd value, the right primer, and meticulous application, the film acts as a barrier without suffocating the structure.