Surface Treatments for Roof & Walls
Surface treatments include any material applied to either horizontal or vertical surfaces of concrete to provide protection. The objective is to limit corrosion by reducing the existing moisture level in the concrete and preventing further ingress of moisture and chlorides. All the materials in contact with each other must be compatible to avoid bond failures of the surface treatment materials with the underlying substrate. Appropriate surface preparation is a must for success of surface treatments.’
The surface treatments must be applied to a clean, dry, and sound substrate at moderate temperature and humidity conditions in a well-ventilated space. A relatively smooth surface is needed for liquid-applied membranes. All concrete repairs are completed and allowed to cure before applying most of the surface treatments. The curing time is usually 28 days but varies with the repair material.
Details of expansion and control joints, door and window openings, drains, and curbs must be reviewed and installed properly.
Surface treatment classification: The surface treatment can be by using penetrating sealers, surface applied corrosion inhibitors, surface sealers, high-build coating, membranes, overlays, and joint sealants.
1. Penetrating sealers
Penetrating sealers are materials that are generally absorbed within the repaired concrete and the depth of penetration varies by the product, the size of the sealer molecule and the size of the pore structure in the concrete. Deep penetration of sealers is usually not an important factor although it may be desirable for abrasion resistance of surfaces. These sealers are effective for protection in two ways; as water repellents and as surface hardeners. Penetrants do not have crack-bridging capabilities, but the hydrophobic properties imparted by some of these products may reduce the intrusion of moisture into narrow cracks. The appearance of concrete surface is usually not affected by applying these sealers, only slight change in color may take place. Such sealers include boiled linseed oil, silanes, siloxanes, certain epoxies, magnesium and zinc fluorosilicates, and high molecular-weight methacrylates. The sealants do not usually hide the surface flaws.
These products may be applied by roller, squeegee, or spray to the concrete substrate and proper surface preparation is important for successful application. UV, wear, and abrasion resistance are generally good when compared with coatings or membrane systems. Penetrating sealers do not bridge new or existing cracks. Some of these products are solvent-based (that can cause air-pollution) and others are water-based.
2. Surface-applied corrosion inhibitors
Surface-applied corrosion inhibitors are designed to reduce the rate of corrosion. The effectiveness and life expectancy of these materials varies with the properties of the concrete, site conditions and type of inhibitor material.
3. Surface sealers
Sealers and paints are applied on the surface of concrete where it adheres. The finished thickness may be 0.03 to 0.25 mm. Pigmented or naturally colored paints are used according to the requirements, while transparent paints result in a wet or glossy appearance. Surface sealers do not have significant crack-bridging capabilities. The hydrophobic nature of some of these products may reduce the movement of moisture into narrow cracks and some of these products may fill dormant cracks, reducing the penetration of moisture through those cracks.
Epoxies, polyurethanes, HMWM (high molecular weight methacrylate), siloxanes, silanes, moisture-cured urethanes, and acrylic resins are included in this category. Certain paints, whether oil-based or latex-based (such as styrenebutadiene, polyvinyl acetate, acrylic or blends of these with other polymers dispersed in water), can also be included if the resulting thickness of layer is less than 0.25 mm.
These materials have the capability to reduce the intrusion of water, chlorides, and mild chemicals. They also may or may not permit the transmission of water vapor. The materials may be applied with brush, roller, sponge, or spray. Surface sealers reduce skid resistance and they do not bridge moving cracks. However, these are effective in filling (not bridging) small, nonmoving cracks. These products are affected by UV exposure and wear under surface abrasion. Some of these products depend on solvents to work and may have problems with environmental quality.
4. High-build coatings
High-build coatings are materials with a dry thickness between 0.25 mm and 0.75 mm applied to the surface of the concrete. High-build coatings alter the appearance of the surface and may be pigmented. The base polymers of such products include acrylics, alkyds, styrene butadiene copolymers, vinyl esters, chlorinated rubbers, urethanes, silicones, polyesters, polyurethanes, polyurea, and epoxies. These products are generally used for decorative or protective barrier systems but some products may be suitable for use against rain, salts, and mild chemicals.
These products may be applied with brush, roller, sponge, or spray. For exterior environments, the coating must be resistant to oxidation and UV and infrared radiation exposure. On floors, resistance to abrasion and punctures and resistance to mild chemicals (salts, grease and oil, and detergents) are also important. The coating material must be durable and the bond between the coating and concrete substrate must be strong. Epoxy resins are commonly used repair materials that generally have good bonding and durability characteristics and can be mixed with fine aggregates to improve abrasion and skid resistance. Some high-build coatings result in a very slippery surface when wet and may not be suitable for pedestrian or vehicular traffic. Non-elastomeric high-build coatings generally do not bridge moving cracks, but are usually effective in filling small, nonmoving cracks. These products have better wear characteristics than thinner systems. A coating intended to reduce reinforcement corrosion in repair work may also be required to waterproof the structure, protect against chemical attack, or improve the appearance. Breathability is often an important factor when selecting a protection material on exterior walls and slabs-on-ground. Some of these products are solvent-based and can have pollution problems.
Membrane systems are treatments with thicknesses between 0.7 mm and 6 mm applied to the surface of the concrete, significantly changing the appearance of the concrete surface. They may be bonded, partially bonded, or unbonded to the concrete surface. Elastomeric membrane systems generally have sufficient thickness and flexibility to bridge narrow, nonmoving cracks of various widths.
Some systems require that cracks wider than 0.25 to 0.375 mm should be located and sealed before application of the membrane. Elastomeric membranes are usually gray or black, but some manufacturers offer several other colors.
Chemically these materials consist of urethanes, acrylics, epoxies, neoprenes, cement, polymer concrete, and asphaltic products. The membranes are generally used as protective, waterproofing, wearing course for traffic and damp-proofing systems.
Liquid forms of these products may be applied by brush, sponge, roller, trowel, or spray. Preformed sheets are sealed at the edges to form a continuous waterproofing membrane. Most of these membranes are resistant to water absorption. These bridge small (less than 0.25 mm) moving or nonmoving cracks. Membranes with a rigid urethane mortar or epoxy-mortar top coat offer reasonable skid and abrasion resistance under traffic. Standardized tests must be conducted for permeability, elongation, tensile strength, tear strength, adhesion, modulus of elasticity, abrasion resistance, low temperature flexibility, and water vapor transmission.
Overlays are depositions of 6 mm or greater in thickness that can be bonded, partially bonded, or unbonded to the surface of the concrete. The details of the overlay materials and the placing methods are given earlier. The materials for the overlays may be Portland cement concrete, latex modified concrete, polymer concrete and silica-fume concrete, as described earlier.