The protection and decoration of a façade or external wall requires a deeply knowledge of the problem, an extensive proficiency of the different types of preparation and reparation of the surface and the correct selection of the product according to the specific necessities.
For the diagnosis of any pathology, it is necessary to know the origin of the problem in advance in order to find the optimal solution and to avoid future unnecessary works and actions. Analyzing the problem at each of the defects observed is indispensable for the discovery of the pathology and the start point of the diagnosis. The most common pathologies are:
• Superficial contamination by dirt or filth
• Superficial contamination by microorganisms (mold, mildew)
• Cracks, fissures and micro-holes
• Efflorescence, saltpeter and solvable salts
• Loss of superficial consistency
• Damages by carbonation
Superficial contamination by dirt or filth consists in the accumulation of dust, grease, etc. mixed with other organic contaminants, which are deposited on the surface conforming ground-in stains.
Generally speaking, all façades, new or repainted, must be previously prepared to remove any kind of dirt or contaminants.
Superficial contamination by microorganisms (mold, mildew), depending on location or weathering conditions, may result in black, grey or brown stains, due to the growth of mold on the surface, or green, yellowish or ochre stains, due to the presence of lichens, moss or algae.
The presence of microorganisms reveals an elevated rate of humidity on the surface, which may derive from environmental factors (rain, condensation, dew, relative humidity, etc.), from an external surface with a high capacity of absorption, from humidity by capillarity or from critical points of thermal break.
Before any treatment may be started, the origin and causes of the elevated humidity must be analyzed, and, if feasible, to carry out corrective actions to remove it or to reduce its presence.
Cracks, fissures and micro-holes are all those openings present in the external surface. Cracks are uncontrolled openings which affect the whole thickness of the surface. This problem must be immediately solved to avoid irreversible damages or elevated costs of reparation.
The presence of cracks, fissures and micro-holes are usually due to defects of construction, ground movements, building settlement, atmospheric agents as frost-thaw, abundance of solvable salts or premature wear of any of the base materials. Prior to their reparation, you must examine the surface on which they have appeared, their depth and their exact location on the façade or the wall.
Efflorescence, saltpeter and solvable salts can manifest as whitish stains on the coating paint, on concrete or on brick. They are composed of tiny solvent salt crystals which lay in the interior of the materials, and then get dissolved and dragged through pores or cracks till the surface, where they make appearance after the evaporation of water.
The loss of superficial consistency consists on the uncontrolled detachment of the coating paint from the surface of application. This separation can manifest as cracks, flaking or blisters.
Supports get distressed with time due to the action of external agents, as industrial contaminants, weather or alkalinity of the support. The factors which most hasten the loss of resistance are:
• Alkalinity: due to the nature of the support and the presence of humidity, alkalis crystallize as solvent salts, which progressively affect the internal structure of the wall or surface; hygroscopic pressure will increase the support volume, and will cause internal tensions and expansions.
• Humidity: it consists on the filtration of water towards the interior of the support through unsealed, distressed or worn-out joints or cracks, or through leaks on decks or walls. Continued exposition of the support to humidity and water in its different states, can hasten the loss of general resistance, especially if the previous preparation of the surface has not been carried out properly.
Damages by carbonation occur when structural concrete suffer a physicochemical process from outside, by which it loses the natural alkalinity protecting the whole structure. During the hydration of the concrete, reaction with mixing water triggers off the formation of other components -considerable quantities of calcium hydroxide- which provide concrete a nature prominently alkaline preventing rusting of the steel structure.
Over the years, carbon dioxide in the atmosphere, combined with water in the form of carbonic acid, spread through the pores of concrete and reacts with the chemical compounds found there, as calcium hydroxide. As a result of their neutralization, calcium carbonates will appear.
Progressive transformation of calcium hydroxides into calcium carbonates will provoke the decrease of the original nature of concrete. Rusting will take place along the whole surface of the steel structure with the imminent increase of its volume and later, the appearance of cracks. In order to detect this pathology, it will be necessary to look for rust stains and longitudinal cracks along the whole frame.
The most common inorganic supports found in a façade or external wall are: concrete, mortar, fiber cement, precast slabs, clinker bricks, natural stone and porous surfaces.
The support must be firm, compact, clean and free of dust, dirt, laitance, free particles, rest of release agents or residues from other works.
The preparation of the support may be carried out by mechanical means (pressurized water, sandblasting, abrasive water jet, pneumatic needle scaler, water vapor at 120°) or manual (wire scrubbing brush).
Once the cleaning and preparation process has been finished, it is recommended to perform tests and other analysis to ensure good final painting results.
-Check with your hand or with a black synthetic cloth for the presence of dust and other residual particles.
-Hit the surface with a hammer to detect any hollow.
-Examine with a pin the cohesiveness of the concrete and find any inconsistent area due to external chemical or mechanical aggression.
-Damp the surface with water to detect the presence of release agents, silicones, stearates and other products of grease or water-repellent characteristics, which may cause repellence problems.
As soon as the pathology has been identified and the corrective actions performed, you should take the following steps carefully:
The first step consists in selecting the most suitable primer or sealer according to the nature, problem or kind of support. Dilutions will be adjusted to the characteristics of the support and the conditions of application.
The second step involves determining the methodology to follow according to the nature and state of the surface.
On new, well-kept surfaces, clean, leave to dry and apply the recommended painting methodology.
On distressed surfaces, if paint is not in good conditions, remove it completely by mechanical or manual means, level irregularities with cement plaster for outdoors, leave to dry and eliminate slag by sanding. If the surface is deeply contaminated by mold or mildew, clean with a fungicide or sodium hypochlorite (bleach) to destroy microorganisms, leave to dry 30 minutes and clean with a wire scrubbing brush or a sponge. If the surface is dusty but consistent, seal with a hardening sealer, adjusting the dilution to the absorption and conditions of the support.
On surfaces with a paint coaching in good conditions, do as with new surfaces.
Once the primer and the finish have been decided according to the kind of work to perform and the necessities to cover, the third step comprises the application of 3 coaches (1 of primer and 2 of finish) by roller, in cross direction and in different colors by preference.