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Sealing Above-Ground Concrete Fuel Tanks

Fuel Tank Construction

This procedure is applicable to above-ground fuel tanks. The steel tank is typically insulated with Styrofoam, covered by 30 mil polyethylene sheeting. The outer shell is concrete, typically 6” thick.

The purpose of sealing the concrete is to protect it against deterioration, mainly caused by rainwater and contaminants. The procedure is applicable to both new and older tanks.

Step 1: RadonSeal Deep-Penetrating Sealer

RadonSeal is a silicate-based sealer, which penetrates up to 4” into concrete and reacts with lime and alkalis. It seals bare, structurally sound concrete against water intrusion, prevents leaching of lime, and protects concrete against freeze-thaw damage, chemicals, and acid rain. RadonSeal also strengthens the concrete and hardens the surface, which stops concrete dusting and minimizes cracking. It prevents the growth of fungi, mold, and mildew.

The seal is not affected by UV rays or hot temperatures in direct sun and is permanent for the life of the concrete.

RadonSeal Standard is the best choice for poured concrete in good condition that is less than 10 years old. If older or already deteriorated, use RadonSeal Plus, which contains more minerals for larger pores in the concrete.

RadonSeal is waterborne, nontoxic, nonflammable, and non-hazardous. RadonSeal leaves the surface paintable  – the surface “wets.”

Step 2 (Optional): DryWay Water-Repellent Sealer

This is a more durable alternative to paints or surface sealers. Waterborne, nontoxic, nonflammable, and non-hazardous.

DryWay is a penetrating siloxane/silane sealer, which forms a water-repellent membrane below the surface. Beads and sheds rainwater. Unpaintable.

The sealer protects the surface of concrete deep-sealed with RadonSeal against water, chemicals, spills, and acid rain. Prevents the growth of fungi, mold, and mildew. Sheds water for over 10 years.

Delivery, Storage and Handling

Materials shall be delivered in their original unopened containers and stored in clean, dry areas away from direct sun at 40º to 80º F until ready for use. Protect from freezing during shipping or storage. 

Project Conditions

Weather Conditions: Do not apply the sealers in snow, rain, fog, or mist, or when such conditions are expected within 3 days. Ambient air temperatures shall be at least 35º F at application time.

Substrate Conditions: The temperature of the concrete shall be above freezing during the application and for at least 72 hours afterward.

Do not apply the sealers to hot concrete in direct sunlight. Avoid windy conditions to minimize over-spraying.

Preparation and Surface Cleaning

In the case of newly poured concrete, allow at least 28 days to cure.

RadonSeal can be applied only on bare (unpainted) concrete surfaces. The surfaces must be sufficiently clean to allow RadonSeal to penetrate into the concrete.

Water-absorption test: To make sure that the surface is ready for RadonSeal, spray on some water to confirm that the concrete is readily absorbing water.

Remove any paints, surface sealers, or mastics. Special surface preparation is normally not required, but oil slicks must be removed first.

Efflorescence (white mineral deposits) can build up and prevent the absorption of RadonSeal.

Remove any molds, mildew, or algae.

Pressure-wash the concrete (3,000 psi) to remove dirt and residues.

Mask glass and aluminum. Also mask copper, ceramic tiles, and fixtures, or just wipe off any over-spray while wet.

Cover up nearby plants, and shrubs. Move or cover nearby automobiles or protection from overspray

Spray Equipment

A low-pressure sprayer set at 40 psi with a lacquer tip and a long hose (100-150 ft.) for mobility, a battery-powered pesticide sprayer, or a back-pack sprayer. A sprayer nozzle with a fan pattern is more controllable than a conical pattern.

RadonSeal Application

Dampen the concrete to reduce surface tension and help RadonSeal penetrate deeper. Spray each section with water and let partially dry until just damp.

Spray the sealer in a thin continuous film. Do not over-apply, do not let the sealer run or puddle. Spread out any puddles with a broom.

Spray on RadonSeal in 2 successive applications about 15-30 minutes apart, while the concrete is still damp. If the 2nd application has absorbed fast (within 5 minutes), spray on a 3rd application 15-30 minutes later.

Dampen and seal a section at a time. Then, move on to the next section.

Coverage Rates

Surface coverage depends on the concrete’s porosity and composition. Concretes with more pores or alkalis consume more sealer.

RadonSeal Standard is used only on newer concrete in good shape. RadonSeal Plus is used on older concrete, concrete blocks, and when the concrete has already deteriorated and is very porous.

Spray at a rate of 300-400 sq. ft./gal. for each application. Estimated total consumption in 2 applications 150-200 sq. ft./gal., or 100-125 sq. ft./gal. in 3 applications.

Clean-up after RadonSeal

Clean spraying equipment with clean tap water.

The concrete will appear dry in a couple hours. Any surface residue from over-application would leave a whitish hard film, which cannot be painted or further sealed.

In about 10 to 12 hours after RadonSeal application, pressure-wash the surface using a lower pressure 800-1,000 psi to remove any residue.

Within the first several days, RadonSeal will purge minerals, dirt, and efflorescence from older concrete. This is in a powdery form and can be brushed or power-washed off, or it will just wear off.

If the concrete will be painted, let RadonSeal first cure for at least 10 days.

Concrete Repairs

Repair cracks with readily available epoxy sealants or caulking materials. (RadonSeal is applied first because cracks help the sealer penetrate into the concrete.)

If required, use concrete patching compounds for larger repairs. (RadonSeal would not penetrate through polymer-modifed compounds.)