Sonjoy Deb, February 2015

Transcription

1 Penetrating Sealer for Impermeable Concrete Surface 108 Sonjoy Deb, B.Tech, Civil Associate Editor Bare concrete is porous and vulnerable to staining and chemical attack. Liquids will tend to soak into the surface, carrying stains into the concrete itself. Acidic substances like vinegar and lemon juice will dissolve the cement paste, etching the surface. For concrete to be a practical countertop material, it must be properly sealed to protect it from stains and etching and rebar corrosion. Penetrating sealers, including silanes, siloxanes, and blended products, are a cost-effective means of protecting new and existing concrete surfaces. When applied properly, penetrating sealers can serve as chloride screens and dampproofing to improve durability against destructive corrosion of embedded reinforcement and damage from freezing and thawing. Exposed concrete building exteriors, parking structures, and bridge decks are typical applications. Sealers can be applied at the time of original construction, as part of a maintenance program, or as protection for repairs. Sealers penetrate the concrete surface and react chemically to form a water- repellent layer. Water usually will bead up on a treated surface. However, water trapped in the concrete or which soaks in can escape from the treated surface as vapor. These sealers have little or no effect on the concrete surface coloring. In addition to helping repel water and chlorides, sealers also help minimize penetration of dirt, grease, and oil, making surfaces easier to clean. Refer Figure below for sealing technology of penetration sealers. Available Sealing Materials There is a wide range of sealing materials that offer varying degrees of protection to concrete. Each particular sealer

2 Figure 1: Penetrating Sealer Application Figure 2: Penetrating Sealer Application has application, performance, maintenance and other characteristics and requirements that differentiate it from other sealers. Sealers can be separated into two basic groups: penetrating sealers and topical sealers. Refer Figure Below for available sealer applications. trating sealers either work by reacting with the concrete to decrease its porosity and increase the surface density (the hardeners/densifiers) or by increasing the surface tension to cause beading (the repellants). Silane (alkyltrialkyoxysilane), siloxane (oligomeric alkylalkoxysiloxane), and combination sealers are available from many manufacturers. Solvent or water-based materials are available. Solvent based products with alcohol or mineral spirits as carriers have the longest track record. Typical solvent-based silane products have solids contents of 20% or 40%. Water-dispersed silanes frequently have solids contents of about 10%. Siloxanes are partially reacted materials and often have a solids content of 10% or less. Silanes and siloxanes require some moisture and an alkaline environment to react successfully. Quality concrete is highly alkaline. Siloxane, and some silane, products contain catalysts and can react with lower alkalinity. Regulation of emissions of volatile organic compounds (VOC) has prompted the development of alternate materials. Many of these are water-based, rather than solvent-based. Water-based products may be supplied as emulsions or as concentrates (to be mixed onsite before application or mixed and dispersed during application). However, water-based and other VOC-compliant materials can still be highly toxic substances. Use of VOC-compliant products helps lessen the inconvenience to building tenants. Some owners request the use of nonsolvent- based materials, even when they are not required by regulation. For projects where parking garages are in the building basement, or in buildings with air intakes near the work area, offensive fumes can spread through the ventilating system. This has resulted in building evacuation on some jobs. Application of solvent-based products in office building garages can be scheduled during weekends to minimize disturbance to occupants. Use of solvents indoors also presents a potential fire hazard. Even VOC compliant products can be flammable. The Ideal Sealer for Concrete Countertops Must Satisfy these Basic Criteria Figure 3: Sealer Applications Penetrating Sealers Penetrating sealers are liquids that are applied to bare concrete, soak in, and then once wiped off and dried, are usually nearly invisible. They often don t affect the appearance of dry, bare concrete. Some leave it looking dry, while a few provide a darker, wet (but not very shiny) look. Pene- - Enhance the appearance of the concrete without degrading the look or feel - Non-porous - Completely resist stains from food, oil and other common household substances - Resist any etching from acidic substances like lemon juice and vinegar Figure 4: Water Should Bead up on Surface of Sealed Concrete 109

3 - Resist heat from hot pots and pans take directly from the oven or stove top at a wide range of temperatures - Resist UV degradation and yellowing from sunlight - Scratch-proof - Food safe (non-toxic) - Easily cleaned using common household cleaning products - Provide long term protection without the need for frequent maintenance or reapplication - Not peel, flake, chip or bubble - Easy to repair Delivery, Storage, and Handling Guidelines of Penetrating Sealers evaporation before the material could penetrate and react. Now, some manufacturers maintain that conditions of low humidity create the dry substrate favorable for penetration, and that the sealer will enter the concrete before evaporating. Most manufacturers recommend against applying sealers when rain is expected within 4 hours. Rain can wash away unreacted product. Water- dispersed products may not need this much time and water-based emulsions may need longer. After rain, allow 1 or 2 days for a surface to air-dry before applying sealers. A dry substrate maximizes sealer penetration. Although a surface may be dry to the touch, the concrete may be too damp for successful application. Alcohol- and water-based products may be more moisture tolerant than other materials. The Importance of Surface Preparation Figure 5: Storage of Penetration Sealers 110 Products often are available in 500ml to 5 litre containers, so material can be furnished to meet the requirements of a particular project. The shelf life typically is 1 year for unopened containers. Avoid repeated opening and closing of containers, since moisture in the air may be sufficient to activate the product before application. Protect water-based emulsions from freezing and high temperatures. The product may gel at low temperatures or separate at high temperatures. Store containers upright, out of direct sunlight. Store and use material away from extreme heat, sparks, and open flames. Don t use drums as substitute workbenches. Water-based products can be formulated and shipped as concentrates, then mixed onsite or combined with a water source at the spray nozzle. Material costs are lower, since less material is packaged, shipped, and handled. It is necessary, however, to verify that the material is mixed correctly. Environmental Conditions to be Considered Sealers should be applied when surface and air temperatures are between 10 and 37.5 C. Manufacturers may recommend special procedures outside this range or suggest warming or cooling the material to intermediate temperatures before application. Windy conditions complicate application due to the loss of material to the atmosphere and consequences of overspray. High humidity can adversely affect depth of penetration. In the past, many believed that application in conditions of extremely low humidity led to Figure 6: Concrete Surface Preparation before Sealer Application For successful application and performance of sealers, surfaces should be clean, sound, and dry. These criteria are subject to interpretation, and their implementation is project-specific. The extent of effort required to achieve these criteria depends on the nature, age, and exposure of the concrete surface. New concrete may not require much preparation, but old concrete that is dirty, carbonated, or stained by oil or grease may require aggressive cleaning. Repairs to existing concrete should be completed before sealer application. Also remove dust and dirt, grease, oil, or residues from cleaning. New concrete surfaces need to cure then dry before surfaces are prepared further for sealer application. Typically, manufacturers recommend that sealers not be applied until concrete is at least 28 days old. Surface laitance, form release agents, and curing compounds must be removed from new concrete surfaces. Some specifications do not allow the use of curing compounds on new concrete surfaces where sealers will be applied. Removal of curing compounds requires more extensive and costly cleaning. Cleaning may range from pressure washing fairly clean surfaces to aggressive blast-cleaning. Pressure washing commonly is used to clean building exteriors. Parking structures and bridge decks frequently are prepared by shot blasting to make the surface clean and porous, removing contaminated or weak carbonated material. Pressure washing without blast cleaning is sometimes used for bridge decks.

4 Aggressive shotblasting, which leaves a profiled surface, is unnecessary. Some specifications have required that sealers be applied on the same day as shotblasting, but this usually is too strict. Supplemental sandblasting of horizontal surfaces often is required at walls or parapets, columns, and other penetrations since shotblasting machines cannot clean close to a vertical face. Vertical concrete faces also can be sandblasted. This is practical for smaller areas, such as beam sides or parapets, but may not be feasible for building facades. Other Preparations to be Considered On facade work, mask windows unless sealer compatibility is verified by pretesting. Etching of windows can be caused by the solvent carrier or compounds used as a repellent; specific window materials may react differently. Control overspray to avoid contact with other building glass, as well as nearby vehicles. Windows may not need to be covered before applying silanes. Dirty window surfaces are prone to buildup of a residue caused by reaction of the product with dust particles. Precleaning or applying a soapy solution to windows may help prevent residue buildup. Many applicators prefer simply to clean windows after sealant application. When using solvent-based products, protect trees and other vegetation, asphaltic materials, and ornamental railings or other objects. Plants should be sprayed with water before covering. Many manufacturers recommend applying and curing joint sealants or caulking before sealer application. Some sealers may act as bond breakers and prevent sealant adhesion. When in doubt, check with the product manufacturers and test the compatibility of the sealer and caulking on the job. Application Procedure surface so that sealer runs 6 to 12 inches down the face. Some manufacturers recommend bottom-up and others suggest top-down application. Coverage Details of Sealers Sealer coverage varies significantly with individual conditions. Typical quoted rates of coverage for horizontal surfaces are 100 to 250 square feet per gallon, and for vertical surfaces, 150 to 300 square feet. Some manufacturers recommend coverage rates of 125 to 150 square feet per gallon for planning purposes. In some cases, two applications of product may be required to achieve the desired penetration into the substrate. Precautions to Follow Application of penetrating sealers should be done by experienced workers. Consult specific manufacturer recommendations and Material Safety Data Sheets (MSDS) before beginning any project. Because solvent-based and VOC compliant sealers may be flammable, eliminate potential ignition sources including pilot lights and smoking materials. Sealer vapors may travel to ignition sources far from the application area. When applying solvent-based materials, workers should wear respirators, goggles, and chemical-resistant gloves. Water- based products may not require respirators, but goggles and gloves should be worn. Indoors, provide adequate ventilation using explosion-proof equipment. Wash off overspray of solvent-based materials on cars as soon as possible. Rubbing compound has been reported to be effective in removing sealer residue that has been on a car for several days. Consult manufacturer recommendations for additional cleanup procedures. Some product residue will remain in containers, so do not reuse them for other purposes. Replace container caps and follow manufacturer instructions and other regulations for disposal. Quality Assurance Guidelines 112 Figure 7: Application of Penetration Sealers Sealers can be applied by brush or roller for very small areas, by squeegees or low-pressure (15 to 30 psi) sprayers for somewhat larger areas, and by bar sprayers for very large areas. A spray wand often is used to supplement the bar sprayer for hard-to-reach areas. Airless sprayers are preferred, with spray nozzles set for a wet spray rather than a fine mist. Apply sufficient material to saturate the surface, but don t overapply, especially where surfaces are sloped and material can flow down a drain. Each pass of material should overlap the previous pass. For vertical surfaces, saturate the Water-based emulsions are milky in appearance and can be seen on the concrete surface for a time after application. However, many penetrating sealers are colorless and most do not change the appearance of the concrete significantly Figure 8 : Sealed vs Not Sealed Concrete Surface

5 after the solvent or water carrier has evaporated. There are ways to check whether the material has actually been applied. Fugitive dyes can be used to confirm the application of penetrating sealers. A coloring agent (usually red or bluish green) is mixed with the sealer before application and fades with time, mostly due to breakdown from exposure to sunlight. Coloration may persist for a long time where there is no direct sunlight, such as in a basement parking garage. Dye content can be adjusted to modify the length of time the coloring is visible. Fugitive dyes may not be suitable on structures, such as building facades, where the color is inappropriate or fading of exterior surfaces may not be uniform. Other ways to confirm application of sealers vary in cost and complexity. Simple methods include full-time observation of sealer application and later wetting down the concrete surface to verify that water beads form on the surface. Cores can be extracted from the concrete and examined to confirm the presence of sealer and depth of penetration. Core samples also can be extracted for laboratory study. When applied to quality concrete, a penetration depth of about 1/8 inch usually is satisfactory; however, project requirements may require deeper penetration. Conclusion 114 By far, the durability of a penetrating water repellent sealer surpasses that of a cure and seal. This is because penetrating sealers soak into the concrete and chemically bond within the surface, leaving no film or membrane on top of the concrete that can wear off under traffic and weathering. Most penetrating water repellent sealers are formulated with a beading agent that causes water to bead up on the concrete surface like on a freshly waxed car. Over time, the beading agent dissipates and water may no longer bead like it once did. This does not indicate failure of the penetrating sealer, the silane or siloxane is still bonded within the concrete surface, repelling water and salt. When the beading agent is no longer active, water will sheet off the concrete instead of beading. Under normal use conditions on a concrete driveway, the protection provided by a penetrating sealer will last 5-10 years before requiring reapplication. Reference - Construction.pdf arch-deccon/concrete-countertop-sealers.pdf?sfvrsn=2 guide.pdf Edward McGettigan, Silicon-based Weatherproofing Materials, Concrete International, June Paul D. Carter, Preventive Maintenance of Concrete Bridge Decks, Concrete International, November w