Sealer manufacturers offer you little assistance as you try to find your way through the maze of products available, reported to be as many as 500 individual systems.
Even though there is a finite number of families of sealers, as outlined in the following sections, within each family manufacturers will try to differentiate themselves from all others, even though most are very similar systems.
There are numerous chemical formulations created using the basic silicon molecule that forms the basis for most of the penetrating sealers. These formulations result in the basic family groups of: Silicones, Silicates, Silanes, and Siloxanes. There is often confusion as to the basic families of sealers; for example, some will classify Siliconates as a family even though it begins as a derivative of a Silane. From these basic groups, manufacturers formulate numerous minor changes that offer little if any improvements and only tend to con- fuse the purchaser into thinking they are buying something totally unique.
Derivatives include Alkylalkoxysiloxane (siloxane), Isobutyltrialkoxysilane (silane), Alkylalkoxysilane (silane), methylsiloxanes, and many blends of the family groups such as a silane/siloxane combination. These formulations or chemical combinations should not confuse a prospective purchaser. With a few basic guidelines, the best selection for each individual installation can be made easily.
First, any water repellent used should have the basic characteristics necessary for all types of installations: sufficient water repellency, and long life-cycling under alkaline conditions. The latter, performance in alkaline conditions, usually controls how well the product will perform as a repellent over extended life cycling. For the penetrating sealers listed above, no matter how well the product repels water during laboratory testing, the product will virtually become useless after installation if it cannot withstand the normal alkaline conditions of concrete or masonry substrates. Concrete in particular has very high alkaline conditions that can alter the chemical stability of penetrating sealers, resulting in a complete loss of repellency capability.
Therefore when reviewing manufacturer’s guide specifications, the high initial repellency rates should not be depended upon solely; rather emphasize the test results of accelerated weathering, especially when application is used on concrete or precast concrete substrates. Verify that the accelerated weathering is tested on a similar substrate, as masonry or most natural stones will not have alkaline conditions as high as concrete.
In addition, when the proposed application is over concrete substrates with substantial reinforcing steel embedded, the resistance of the repellent to chloride ion infiltration should be highlighted. Chlorides attack the reinforcing steel and can cause structural dam- age after extended weathering. Many sealers have very poor chloride resistance.
Since water penetration begins on the surface, depth of penetration is not a particularly important consideration. While all penetrating sealers must penetrate sufficiently to react chemically with the substrate, many penetration depth claims are made on the solvent carrier rather than the chemical solids that form the repellency. The effective repellency must be at the surface of the substrate to repel water. Water should only penetrate the surface if there is cracking in the substrate, and if this is the case, no repellent can bridge cracking or penetrate sufficiently to repel water in the crack crevice (see Fig. 3.5).
 |
| FIGURE 3.5 Clear repellents cannot repel water entering through substrate cracks. |
Penetrating capability is a better guide for a sealer’s protection against UV degradation.
Having the active compounds deeper into the substrate surface protects the molecules from the sun’s ultraviolet rays that can destroy a sealers repellency capability.
When comparing the capability of sealers to penetrate into a substrate be sure to review what is referred to as the uniform gradient permeation (UPG), which measures the penetration of the active ingredient rather than the solvent carrier. Most alcohol carriers will penetrate with the active ingredient deeper than those using a petroleum-based carrier will.
Some manufacturers will make claims as to the size of their active molecules being so small that they penetrate better than other compounds using larger molecules. While this may be the case, compounds with larger molecules usually repel water better than those using smaller molecules.
The amount of solids or active ingredient is always a much-trumpeted point of comparison. Certainly, there is a minimum amount of solids or active agent to produce the required repellency, but once this amount is exceeded there is no logic as to what a greater concen- tration will do. For the majority of penetrating sealers, 10 percent active compounds seems to be the minimum to provide sufficient water repellency, with 20 percent moving towards the maximum return for the amount of active agent necessary. While manufacturers will often exceed this to increase a product’s sales potential, the value of its in-place service capability is often no more than those with a smaller percentage of active compounds.
When considering film-forming repellents, a greater percentage of solids is important since these solids are deposited directly on the surface of the substrate and left to repel water directly and without the assistance of the substrate environment. With film-forming repellents, the closer to 100 percent solids, the more likely the repellent will be capable of repelling water.
When trying to compare products through the maze of contradictory and confusing information available, it is best to review the results of completed standard and uniform tests that are most appropriate for the substrate and service requirements required. The next section expands on the most frequently used testing to compare products, a much better guide than reading sales literature about percent solids, size of molecule, and chemical formulations. In most cases it is not appropriate to make comparison without the use of standard testing, and no product should be considered without this critical information being provided. Recognize however, that these tests are conducted in the pristine conditions of a laboratory that are never duplicated under actual field conditions. This requires that a sufficient margin of error or safety factor be used for actual expectations of performance results in actual installations.
Sealer testing
Several specific tests should be considered in choosing clear sealers. Testing most often referred to is the National Cooperative Highway Research Program (NCHRP). This is the most appropriate test for concrete substrates including bridges and other civil construction projects. Although often used for testing horizontal applications, it remains an effective test for vertical sealers as well. NCHRP test 244, Series II, measures the weight gain of a substrate by measuring water absorption into a test cube submerged after treatment with a selected water repellent. To be useful, a sealer should limit weight gain to less than 15 percent of original weight and preferably less than 10 percent. Test results are also referred to as “a reduction in water absorption from the control [untreated] cube.” These limits should be an 85–100 percent reduction, preferably above 90 percent.
Testing by ASTM includes ASTM D-514,Water Permeability of Masonry, ASTM C-67, Water Repellents Test, and ASTM C-642, Water Absorption Test. Also, federal testing by test SS-W-110C includes water absorption testing.
Any material chosen for use as a clear sealer should be tested by one of these methods to determine water absorption or repellency. Effective water repellency should be above 85 percent, and water absorption should be less than 20 percent, preferably 15–10 percent.
Weathering characteristics are important measures of any repellent, due to the alkaline conditions of most masonry and concrete substrates that will deter or destroy the water repellency capabilities of penetrating sealers. In addition, UV degradation affects the life-cycle repellency capabilities for both film-forming and penetrating sealers. Accelerated weathering testing, ASTM 793-75, is an appropriate test to determine the capabilities of a sealer to perform over an extended period. Be sure that the testing is used on a similar substrate, however, as the alkaline conditions of concrete are more severe that masonry products.
Of course, it is always appropriate to test for the compatibility of the sealer with other envelope components and on the exact substrate on which it will be applied. This testing will ensure that there will be no staining of the substrate, that the sealer can penetrate sufficiently, and that the sealer does not damage adjacent envelope components such as glass or aluminum curtain wall etching and sealants, as well as surrounding landscaping.
Acrylics
Acrylics and their derivatives, including methyl methacrylates, are film-forming repellents.
Acrylics are formulated from copolymers of acrylic or methocrylic acids. Their penetration into substrates is minimal, and they are therefore considered film-forming sealers. Acrylic derivatives differ by manufacturer, each having its own proprietary formulations.
Acrylics are available in both water- and solvent-based derivatives. They are frequently used when penetrating sealers are not acceptable for substrates such as exposed aggregate panels, wood, and dense tile. They are also specified for extremely porous surfaces where a film buildup is desirable for water repellency.
Acrylics do not react chemically with a substrate, and form a barrier by filming over surfaces as does paint. Solids content of acrylics varies from 5 to 48 percent. The higher a solid’s content, the greater the amount of sheen imparted to a substrate. High-solids materials are sometimes used or specified to add a high gloss or glazed appearance to cementitious finish materials such as plaster. Methyl methacrylates are available in 5–25 percent solids content.
Most manufacturers require two-coat applications of acrylic materials for proper coverage and uniformity. Coverage rates vary depending on the substrate and its porosity, with first coats applied at 100–250 ft^2/gal. Second coats are applied 150–350 ft^2/gal. Acrylics should not be applied over wet substrates, as solvent-based materials may turn white if applied under these conditions. They also cannot be applied in freezing temperatures or over a frozen substrate.
Higher-solids-content acrylics have the capability of being applied in sufficient millage to fill minor cracks or fissures in a substrate. However, no acrylic is capable of withstanding movement from thermal or structural conditions. Acrylic sealers have excellent adhesion when applied to properly prepared and cleaned substrates. Their application resists the formation of mildew, dirt buildup, and salt and atmospheric pollutants.
Acrylics are available in transparent and opaque stains. This coloring enables hiding or blending of repairs to substrates with compatible products such as acrylic sealants and patching compounds. Stain products maintain existing substrate textures and do not oxi- dize or peel as paint might.
Acrylics are compatible with all masonry substrates including limestone, wood, aggregate panels, and stucco that has not previously been sealed or painted. Acrylic sealers are not effective on very porous surfaces such as lightweight concrete block. The surface of this block contains thousands of tiny gaps or holes filled with trapped air. The acrylic coatings cannot displace this trapped air and are ineffective sealers over such substrates. (See Table 3.5.)
Silicones
Silicone-based water repellents are manufactured by mixing silicone solids (resins) into a solvent carrier. Most manufacturers base their formulations on a 5 percent solids mixture, in conformance with the requirements of federal specification SS-W-110C.
Although most silicone water repellents are advertised as penetrating, they function as film-forming sealers. Being a solvent base allows the solid resin silicone to penetrate the surface of a substrate, but not to depths that siloxanes or quartz carbide sealers penetrate.
The silicone solids are deposited onto the capillary pores of a substrate, effectively forming a film of solids that repels water.
All silicone water repellents are produced from the same basic raw material, silane.
Manufacturers are able to produce a wide range of repellents by combining or reacting different compounds with this base silane material. These combinations result in a host of silicone-based repellents, including generic types of siliconates, silicone resins, silicones, and siloxanes. The major difference in each of these derivatives is its molecular size.
Regardless of derivative type, molecular size, or compound structure, all silicone-based repellents repel water in the same way. By penetrating substrates, they react chemically with atmospheric moisture, by evaporation of solvents, or by reaction with atmospheric carbon dioxide to form silicone resins that repel water.
Only molecular sizes of the final silicone resin are different. Silicone-based products require that silica be present in a substrate for the proper chemical actions to take place.
Therefore, these products do not work on substrates such as wood, metal, or natural stone.
A major disadvantage of silicone water repellents is their poor weathering resistance.
Ultraviolet-intense climates can quickly deteriorate these materials and cause a loss of their water repellency. Silicone repellents are not designed for horizontal applications, as they do not resist abrasive wearing.
Silicone repellents are inappropriate for marble or limestone substrates, which discolor if these sealer materials are applied. Discoloring can also occur on other substrates such as precast concrete panels. Therefore, any substrate should be checked for staining by a test application with the proposed silicone repellent.
Lower-solid-concentration materials of 1–3 percent solids are available to treat substrates subject to staining with silicone. These formulations should be used on dense surface materials such as granite to allow proper silicone penetration. Special mixes are manufactured for use on limestone but also should be tested before actual application. Silicones can yellow after application, aging, or weathering.
As with most sealers, substrates will turn white or discolor if applied during wet conditions. Silicones do not have the capabilities to span or bridge cracking in a substrate.
Very porous materials, such as lightweight or split-face concrete blocks, are not acceptable substrates for silicone sealer application. Adjacent surfaces such as windows and vegetation should be protected from overspray during application. (See Table 3.6.)
Urethanes
Urethane repellents, aliphatic or aromatic, are derivatives of carbonic acid, a colorless crystalline compound. Clear urethane sealers are typically used for horizontal applications but are also used on vertical surfaces. With a high solids content averaging 40 percent, they have some ability to fill and span nonmoving cracks and fissures up to 1 16 in wide. High-solids materials such as urethane sealers have low perm ratings and cause coating blistering if any moisture or vapor drive occurs in the substrate.
Urethane sealers are film-forming materials that impart a high gloss to substrates, and they are nonyellowing materials. They are applicable to most substrates including wood and metal, but adhesive tests should be made before each application. Concrete curing agents can create adhesion failures if the surface is not prepared by sandblasting or acid etching.
Urethane sealers can also be applied over other compatible coatings, such as ure- thane paints, for additional weather protection. They are resistant to many chemicals, acids, and solvents and are used on stadium structures for both horizontal and vertical seating sections. The cost of urethane materials has limited their use as sealers. (SeeTable 3.7.)
Silanes
Silanes contain the smallest molecular structures of all silicone-based materials. The small molecular structure of the silane allows the deepest penetration into substrates. Silanes, like siloxanes, must have silica present in substrates for the chemical action to take place that provides water repellency. These materials cannot be used on substrates such as wood, metal, or limestone that have no silica present for chemical reaction.
Of all the silicone-based materials, silanes require the most difficult application procedures. Substrates must have sufficient alkalinity in addition to the presence of moisture to produce the required chemical reaction to form silicone resins. Silanes have high volatility that causes much of the silane material to evaporate before the chemical reaction forms the silicon resins. This evaporation causes a high silane concentration, as much as 40 percent, to be lost through evaporation.
Should a substrate become wet too quickly after application, the silane is washed out from the substrate-prohibiting proper water-repellency capabilities. If used during extremely dry weather, after application substrates are wetted to promote the chemical reaction necessary. The wetting must be done before all the silane evaporates.
As with other silicone-based products, silanes applied properly form a chemical bond with a substrate. Silanes have a high repellency rating when tested in accordance with
ASTM C-67, with some products achieving repellency over 99 percent. As with urethane sealers, their high cost limits their usage. (See Table 3.8.)
Siloxanes
Siloxanes are produced from the CL-silane material, as are other silicone masonry water repellents. Siloxanes are used more frequently than other clear silicones, especially for horizontal applications. Siloxanes are manufactured in two types, oligomerous (short chain of molecular structure) and polymeric (longer chain of molecular structure) alky-lalkoxysiloxanes.
Most siloxanes produced now are oligomerous. Polymeric products tend to remain wet or tacky on the surface, attracting dirt and pollutants. Also, polymeric siloxanes have poor alkali resistance, and alkalis are common in masonry products for which they are intended.
Oligomerous siloxanes are highly resistant to alkaline attack, and therefore can be used
successfully on high alkaline substrates such as cement-rich mortar.
Siloxanes react with moisture, as do silanes, to form the silicone resin that acts as the water-repellent substance. Upon penetration of a siloxane into a substrate it forms a chemical bond with the substrate. The advantage of siloxanes over silanes is that their chemical structure does not promote a high evaporation rate.
The percentage of siloxane solids used is substantially less (usually less than 10 percent for vertical applications), thereby reducing costs. Chemical reaction time is achieved faster with siloxanes, which eliminates a need for wetting after installation. Repellency is usually achieved within 5 hours with a siloxane.
Siloxane formulations are now available that form silicone resins without the catalyst— alkalinity—required. Chemical reactions with siloxanes take place even with a neutral sub- strate as long as moisture, in the form of humidity, is present.
These materials are suitable for application to damp masonry surfaces without the masonry turning white, which might occur with other materials. Testing of all substrates should be completed before full application, to ensure compatibility and effectiveness of the sealer.
Siloxanes do not change the porosity or permeability characteristics of a substrate. This allows moisture to escape without damaging building materials or the repellent. Since siloxanes are not subject to high evaporation rates, they can be applied successfully by high-pressure sprays for increased labor productivity.
Siloxanes, as other silicone-based products, may not be used with certain natural stones such as limestone. They also are not applicable to gypsum products or plaster. Siloxanes should not be applied over painted surfaces, and if surfaces are to be painted after treatment they should first be tested for compatibility. (See Table 3.9.)
Silicone rubber
These systems are a hybrid of the basic silicone film-forming and the silicone derivatives penetrating sealers. The product is basically a silicone solid dissolved in a solvent carrier that penetrates into the substrate, carrying the solids to form a solid film that is integral with the substrate. Unlike the penetrating derivatives, silicone rubbers do not react with the substrate to form the repellency capability.
The percentage solids, as high as 100 percent, carried into the substrate supposedly create a thickness of product millage internally in the substrate to a film thick enough to bridge minute hairline cracking in the substrate. This elongation factor, expressed as high as 400 percent by some manufacturers, does not produce substantial capacity to bridge cracks, since the millage of the film that creates movement capability is minimal with clear repellents. Only existing cracks less than 1/ 32 in are within the capability of these materials to seal, and new cracks that develop will not be bridged since the material is integral with the substrate and cannot move as film-forming membranes are allowed to do.
Through chemical formulations and the fact that they penetrate into the substrate, the silicone rubber products have been UV-retardant, unlike basic silicone film-forming sealers. At the same time they retain sufficient permeability ratings to permit applications to typical clear repellent substrates. These systems are also applicable to wood, canvas, and terra cotta substrates that other penetrating sealers are not applicable, since the rubber systems do not have to react with the substrate to form their repellency.
Silicone rubber systems are applicable in both horizontal and vertical installations and make excellent sealers for civil project sealing including bridges, overpasses, and parking garages. Like the generic silicone compounds, silicone rubber does not permit any other material to bond to it directly. Therefore, projects sealed with these materials can not be painted over in the future without having to remove the sealer with caustic chemicals such as solvent paint removers. This can create problems on projects where some applications are required over the substrate once sealed, such as parking-stall painted stripes in a parking garage. Manufacturers of the silicone rubber sealers should be contacted directly for recommendations in such cases.
These materials generally have excellent repellency rates in addition to acceptable permeability rates. Overspray precautions should be taken whenever using the product near glass or aluminum envelope components, since the material is difficult if not almost impossible to remove from such substrates. (See Table 3.10).
Sodium silicates
Sodium silicate materials should not be confused with water repellents. They are concrete densifiers or hardeners. Sodium silicates react with the free salts in concrete such as calcium or free lime, making the concrete surface more dense. Usually these materials are sold as floor hardeners, which when compared to a true, clear deck coating have repellency insufficient to be considered with materials of this section.
No comments:
Post a Comment