The aesthetic of building facades is important as it determines the first impression of a residence, office, industry, brand or business. In addition to bringing colors to facades, paints protect them from environmental deterioration arising out of weather, wear and age factors. With time, external stresses leave their mark and facades loose visual appeal because of staining, algae growth, cracks formation, and discoloration. Facades may require cleaning and recoating to improve building appearances. It is noteworthy that buildings with shrubs and trees around have greater exposure to algae and north facing facades remain wet for longer, all factors affecting façade condition.
Prior to the application of any façade rendering material, ensure that the strength of the substrate is at least equal or better than the strength of the rendering material. Substrates must have an open texture so the rendering material may penetrate and adhere to the surface. For good adhesion, the rendering material should not be sucked in too quickly to achieve best adhesion and not too slowly to allow for enough capillary action for good bonding. Thus, it is preferable to avoid application in direct sunlight, use clean and pure mixing water, as cool as possible, and cover works with shade nets during a curing period of 2 to 3 days to achieve best results.
It may also prove appropriate to apply fiberglass mesh into wet renders at positions of high stress, particularly at junctions and corners of windows, doors and openings. Expansion joints must be carried through the rendering surface. Once the finished rendering is applied, it is important to protect it from damage, as repairs to decorative renders often differ in color and are costly.
In refurbishment projects, remedial actions will depend on the type of damage. Prior to conducting paint works, repair products such as crack filling compounds, joint sealants for waterproofing and flexible compressed expansion joints for waterproofing can be used to repair small surface damages once carefully cleaned. Small hairline cracks can be filled with grout. Larger cracks can have a variety of causes, which need to be ascertained to identify the appropriate repair method to avoid subsequent damages.
Bonding agents for concrete repair mortars
Bonding agents may be used in façade repair works to increase the adhesion or bond of concrete repair mortars to cleaned and prepared existing concrete substrates. These materials improve the wetting of profiled surfaces, filling troughs in the surface profile of concretes. They reduce suction due to concrete porosity and lubricate the interface ensuring a fully homogenous bond and thus optimum adhesion. Two of the critical factors affecting the bonding between new and old concrete, provided sound concrete practices are followed, are (i) the strength and integrity of the old surface and (ii) the cleanliness of the old surface. Bonding Agents are classified in accordance with the type and nature of the specific concrete repair mortar being applied and the type and extent of the concrete damage being repaired. The main types of bonding agents used in the construction industry are latex emulsions and epoxies. Although good adhesion may be obtained without a bonding agent, generally a bonding layer consisting of cement and sand slurry, cement/latex slurry or epoxy increases bond strength.
Hand-applied concrete repair mortars
Hand placed concrete repair mortars are ready to use cement-based mortars possibly modified for improved strength or resistance with polymers and/or other additions such as silica fume, or special graded sands and aggregates, etc. Hand-applied concrete repair mortars are applied by gloved hands or trowels and finished by trowel, to match the original line and profile of the parent concrete. They are used for patching repairs and for repairs to concrete spalling in areas of locally corroding reinforcements.
Machine applied/sprayed concrete repair mortars
Machine applied/sprayed concrete repair mortars are usually supplied ready to use. By incorporating polymers and other additives, performance characteristics of repair mortars are improved such as better cohesion of sprayed mortars, which results in a significant reduction of rebounds and thus significantly reduced wasted material. Machine applied concrete repair mortars are primarily designed for use where large volumes of repair mortars are needed, or where a significant volume has to be applied as fast as possible to minimize downtime or closures. Traditional gunite systems for sprayed concrete repairs are normally produced on site. They are generally specified for applications requiring thicker layers of repair, where the constituent materials grading and granulometry are not as critical as for layers of sprayed concrete with a thickness not exceeding 50 mm.
Flow-applied concrete repairs (re-casting concrete repair)
Flow Applied Concrete repair materials, also referred to as poured concrete repair materials, are supplied as pre-batched mortars for consistency and quality control purposes, as they are frequently used where there is difficult access or around congested reinforcements. Their aggregate grading, granulometry, water-cement ratio (W/C), and flow properties are specified. When modified with polymers and super-plasticizers their flow properties are improved, achieving a good surface finish against formwork. Concrete repair products used for flow applications in smaller scale repair and re-casting situations are also frequently referred to as grouts and are based on modified cement grout technologies.
Leveling mortars for concrete repairs
Surface Leveling Mortars, also known as Concrete Fairing Mortars, are used after localized concrete patch repairs have been carried out, to fill and level any minor surface defects, such as blowholes in concrete surfaces, which would otherwise allow the future ingress of water and aggressive liquids or gases into the concrete.
Surface Leveling Mortars are also used to effectively add an additional concrete cover, albeit with only a thin layer of material that is equivalent to a much greater thickness of normal concrete. These products exhibit significantly better resistance to carbonation and water ingress, thus providing additional protection to embedded steel reinforcements. By pre-sealing blowholes, which allow penetration through a surface coating, they render the surface uniform, restoring its original line, level, profile, and texture, providing for an ideal substrate when another protective coating needs to be applied.
Surface leveling mortars are usually specified in one of two ways: either to fill and level any surface defects and blow holes in which case no defined thickness is specified, or applied at a nominal thickness, usually of 20 mm, to provide the defined amount of additional concrete cover required. The specification and the required thickness of the surface leveling mortar are critical parts of a technically correct concrete repair and protection job.
Protective surface coatings for concrete
Protective surface coatings are primarily used to protect new or repaired concrete surfaces from future chemical attacks such as sulfurous and nitrous pollutants and the ingress of aggressive liquids and gases such as waterborne chlorides and atmospheric carbon dioxide. The concrete surface protection can also be specified to be water-repellent through impregnation and pore blocking, elastic and crack-bridging with different degrees of elasticity at different temperatures, resistant to different chemicals, such as in containment zones, or abrasion and wear-resistant, if on horizontal concrete surfaces such as balconies and car park decks.
On reinforced concrete facades, single pack, acrylic resin-based anti-carbonation coatings are normally used as protective coatings. Alternatively, protective coatings based on elastic film-forming, styrene acrylates, or other copolymer resins based products are used when additional crack-bridging properties are required. On horizontal decks for combined chemical and wear resistance, the best protective deck coating products are usually 2 component epoxy and polyurethane resin-based solutions that are specifically designed to accommodate additional stress and exposure.
Hydrophobic impregnations for concrete protection
Hydrophobic impregnations for effective concrete protection are generally based on silanes or siloxanes, or blends of these materials. Their small molecular size and penetrating ability, together with their unique water-repelling or hydrophobic properties allow them to penetrate completely into the surface pores and capillaries of concrete and other facade surfaces, creating a water repellent hydrophobic surface, albeit without forming a surface film and therefore without changing the surface appearance, as would a protective paint coating or cement-based material.
The treated reinforced concrete façade surface is waterproof, albeit open for water vapor diffusion in each direction. This allows any residual moisture, internally generated water-vapor, or interstitial condensation within the structure to escape, protecting the structure from freeze-thaw damage, such as scaling. The amount of material that is applied and the depth to which it is able to penetrate into the concrete surface, are critical factors determining the effectiveness of the treatment, and the resulting water-repellency performance and durability.
Hydrophobic impregnation products designed to protect concrete surfaces can be supplied in many different formulations. These include solvent diluted silane and siloxane impregnations and blends thereof with the best performance in cold weather conditions and water-based silane and siloxane impregnations and blends thereof, with no associated solvent risks. Gel or cream formulations of silane and siloxane impregnations and blends thereof are a relatively new development allowing precise levels of consumption, optimum penetration depth, and longer penetration time with no run-off or evaporation, thus minimize wastes.
Particular attention should be placed on the interaction between the roof and façade, as well as windows and railings. Façade surfaces, which are wet for an extended amount of time, are affected by the growth of algae and mold, as microorganisms need moisture. To reduce algae and fungi growth, innovative paint technologies help facades retain as little water as possible and thus dry quickly. Self-cleaning paints with hydrophobic materials, for maximum resistance to soiling, ensure facades look better and for longer. The self-cleaning effects of paints, which are not statically charged, allow for rainwater to run-off, taking all the dirt particles on the surface with it, thus providing active, moisture-regulating weatherproofing. While on conventional facades, dirt particles can form a deposit on the surface that can become wet more easily, allowing dirt particles to stick to it, with special paints, the façade coating has a micro-textured surface, which significantly reduces areas of contact of dirt and particles and thus dirt stickiness.
Paints with special products can be recommended for mineral substrates and historic buildings. Façade design means in many instances color design, in which case color stability, shades, and brilliance become relevant factors that must be considered. In this context, it is important to note that lighter shades show dirt more. Holderchem’s large variety of paints, with high color stability, because their contents are highly UV stable, provides designers the freedom of choice and functionality they require. This applies to the full-color spectrum whether pure white, soft-pastel, or dark intense tints.
It is important products be applied by qualified applicators as their expertise is important in your ensuring that you will be enjoying your investment for a very long time. Authorized Applicators can provide, with the support of Holderchem technical representatives, information customers may require regarding a refurbishment project or a new build.
Special paints with patented VLC technology
In the industrialized world, increased pollution carries increasingly harmful substances. Special paints with patented VLC Technology effectively break down nitrogen oxides and ozone pollution, thereby reducing the build-up of particles. These concepts for fresher air have been confirmed by external reports as effective and sustainable.