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Penetrating Sealer for Impermeable Concrete Surface

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 counter-top 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 damp-proofing to improve durability against destructive corrosion of embedded reinforcement and damage from freezing and thawing. Exposed concrete building exteriors, parking struc-tures, 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. Seal-ers 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 chlo-rides, 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 vary-ing degrees of protection to concrete. Each particular sealer

Sonjoy Deb, B.Tech, Civil Associate Editor

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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 prod-ucts with alcohol or mineral spirits as carriers have the lon-gest 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. Qual-ity concrete is highly alkaline. Siloxane, and some silane, products contain catalysts and can react with lower alkalin-ity. 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 sub-stances. 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 min-imize disturbance to occupants. Use of solvents indoors also presents a potential fire hazard. Even VOC compliant prod-ucts can be flammable.

The Ideal Sealer for Concrete Countertops Must Satisfy these Basic Criteria

- 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 1: Penetrating Sealer Application

Figure 2: Penetrating Sealer Application

Figure 3: Sealer Applications

Figure 4: Water Should Bead up on Surface of Sealed Concrete

has application, performance, maintenance and other char-acteristics 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.

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 appear-ance of dry, bare concrete. Some leave it looking dry, while a few provide a darker, wet (but not very shiny) look. Pene-

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- 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 prod-

ucts - 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 penetra-tion. 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

Figure 6: Concrete Surface Preparation before Sealer ApplicationProducts often are available in 500ml to 5 litre contain-

ers, 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 prod-uct may gel at low temperatures or separate at high tem-peratures. 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 tem-peratures are between 10° and 37.5° C. Manufacturers may recommend special procedures outside this range or suggest warming or cooling the material to intermediate tempera-tures before application. Windy conditions complicate ap-plication 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

For successful application and performance of sealers, surfaces should be “clean, sound, and dry.” These criteria are subject to interpretation, and their implementation is proj-ect-specific. The extent of effort required to achieve these criteria depends on the nature, age, and exposure of the con-crete surface. New concrete may not require much prepa-ration, 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 appli-cation. 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 re-moved from new concrete surfaces. Some specifications do not allow the use of curing compounds on new concrete sur-faces where sealers will be applied. Removal of curing com-pounds 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 clean-ing is sometimes used for bridge decks.

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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 surfac-es 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 compat-ibility is verified by pretesting. Etching of windows can be caused by the solvent carrier or compounds used as a repel-lent; 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 vege-tation, 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 adhe-sion. 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 con-ditions. Typical quoted rates of coverage for horizontal sur-faces are 100 to 250 square feet per gallon, and for vertical surfaces, 150 to 300 square feet. Some manufacturers rec-ommend 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 ex-perienced workers. Consult specific manufacturer recom-mendations and Material Safety Data Sheets (MSDS) before beginning any project. Because solvent-based and VOC com-pliant 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 gog-gles and gloves should be worn. Indoors, provide adequate ventilation using explosion-proof equipment. Wash off over-spray of solvent-based materials on cars as soon as possi-ble. 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 addition-al 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

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 7: Application of Penetration Sealers

Figure 8 : Sealed vs Not Sealed Concrete Surface

Sealers can be applied by brush or roller for very small areas, by squeegees or low-pressure (15 to 30 psi) spray-ers 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

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after the solvent or water carrier has evaporated. There are ways to check whether the material has actually been ap-plied. 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 color-ing 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 complexi-ty. 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 usual-ly is satisfactory; however, project requirements may require deeper penetration.

Conclusion

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 weather-ing. Most penetrating water repellent sealers are formulat-ed 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 penetrat-ing sealer, the silane or siloxane is still bonded within the concrete surface, repelling water and salt. When the bead-ing agent is no longer active, water will “sheet” off the con-crete 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

- http://www.chemquest.com/PDF-files/Polyurethanes_in_Home_Construction.pdf

- http://www.stolaf.edu/people/jackson/08-124/gbreport/Concrete-Seal_J04.pdf

- http://www.cement.org/docs/default-source/fc_mat-app_pdfs/arch-deccon/concrete-countertop-sealers.pdf?sfvrsn=2

- http://www.euclidchemical.com/fileshare/elit/cure_seal_comp_guide.pdf

- http://www.concreteconstruction.net/images/Applying%20Pene-trating%20Sealers%20to%20Concrete_tcm45-342481.pdf

- Edward McGettigan, “Silicon-based Weatherproofing Materials,” Concrete International, June 1992.

- Paul D. Carter, “Preventive Maintenance of Concrete Bridge Decks,” Concrete International, November 1989. w

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