RadonSeal Application Instructions and Tips

RadonSeal Standard or RadonSeal Plus?

RadonSeal Standard is the best choice for poured concrete that is less than 15 to 20 years old and in good condition. Use it also on concrete floors with a very smooth machine-troweled finish or on high-strength structural concrete.

RadonSeal Plus contains more minerals, in order to seal larger pores in concrete. A must for concrete blocks or cinder blocks. Also use on poured concrete that is already porous or older - previous water seepage, high water vapor infiltration, significant efflorescence, indoor concrete over 20 years old or outdoor concrete over one year old.

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Number of applications

Two spray-on applications are standard for poured concrete, three for concrete blocks, and four for very porous cinder blocks.

• Poured concrete normally needs two successive applications, three if extremely porous.
• Concrete blocks usually need three successive applications or four if extremely porous. (If a toothpick will stick in a pore, the block is extremely porous.)

The sprayed on film should absorb within 10 minutes (it still looks damp but there is no more gloss). If the concrete is unusually porous or alkaline, it will absorb very fast, letting you know that it badly needs more sealer – spray on another application.

Coverage

Surface coverage depends on the concrete's porosity and composition. Concretes with more pores or alkalis consume more sealer. Concrete blocks are more porous and have the lowest coverage.

As a "rule of thumb," one 5-gallon pail seals 1,000 sq. ft. of poured concrete in two applications. An average basement (floor 800-1,200 sq. ft.) usually needs 2 pails of RadonSeal for the floor and walls, or 3 pails if it has block walls.

Example:
	Basement. 10-year old poured concrete in good condition.
	Dimensions:	20 x 40 ft, height of walls 7.5 ft
	Wall circumference:	(20 + 40) x 2 = 120 ft
	Wall area:	120 x 7.5 = 900 sq. ft.
	Floor area:	20 x 40 = 800 sq. ft.
	Total area:	800 + 900 = 1,700 sq. ft.
	Pails for 2 applications:	1,700 / 1,000 = 1.7 pails
	Order:	2 pails

Preparation of concrete surfaces

RadonSeal requires bare (unpainted) concrete surfaces. Special surface preparation is normally not required - just mop up or vacuum excessive dust. But the concrete must be structurally sound and free of paint, sealers, adhesives, oil, grease, wax, oil, form releases, efflorescence, and similar.

Dirty concrete or minor oil slicks can be cleaned with laundry soap in hot water or solvents. Grease can be steam-cleaned with a strong degreaser such as "green" tri-sodium phosphate. For easy degreasing, cleaning oil spots and more, use Novion Universal Cleaner (see Concrete Cleaners).

Check out FAQ's or paint stripper for tips on removing paints, surface sealers, or adhesives. However, if it is latex paint, you can avoid this chore by using our Ion-Bond Armor (seals also against negative side water pressure like in basements) or Concrete Armor Plus (see Products and Prices), which penetrate, seal and waterproof even through a single layer of latex paint. First, wash off the painted surface with a detergent solution and scrub with a stiff brush to clean dirt from the pores in the latex paint. Then, rinse off the surface and let thoroughly dry for a few days before sealing. Although the seal is not quite as tight as with RadonSeal, it saves lots of work and permanently repels water.

Is it latex- or oil-based paint? Scrub a small area with a solution of warm water and household detergent or dishwashing liquid. Rinse well and towel-dry. Soak a Q-Tip, cotton ball or soft rag in rubbing alcohol and rub it back and forth over the clean area. If the paint comes off, it is latex. Or take a chip of the paint and take it to a paint store.

Very old basement floors may have a build-up of soap from doing laundry decades ago and the floor has to be pressure-washed.

Remove any efflorescence ("white powder") on the walls or floor. More info on FAQs

RadonSeal application

The Basic Application Instructions are on each pail. Also check the detailed instructions and tips below for your specific situation. Basic steps:

1. Dampen the concrete
2. Apply RadonSeal
3. Hose and scrub off the surface

Dampening the concrete before application reduces surface tension and helps the sealer penetrate faster and deeper, particularly on a tight surface.

To apply RadonSeal, use a low-pressure sprayer like a garden hand-pump sprayer (about $20 in stores) or, for large projects, a backpack or a battery-powered pesticide sprayer. Use a spray nozzle with fan pattern, which is more controllable than conical pattern. Or you can use a paint sprayer, provided the pressure can be turned down to 30–40 psi.

Do not spray on glass, porcelain or ceramic tile, glazed surfaces, aluminum, zinc or galvanized steel, plants or leather. Mask glass, protect your glasses and your watch. RadonSeal bonds to glass and smooth surfaces. Wipe off any over-spray with a wet cloth immediately.

Spray on enough RadonSeal to just create a thin, glistening wet film on the surface (10-15 mil thick). Do not over-apply! Do not let it puddle or run (actually, a 2-3 inches rundown on vertical surfaces is optimal.) Over-application would leave a hard glassy or whitish film on the surface, which is unpaintable and difficult to remove. When spraying walls, mask the floor with papers or rags.

The sealer is not chemically aggressive - it is comparable to a mild soap solution. You can walk in it during application, but it is slippery. You can seal one half of the basement first and finish the other half later.

Basic Application Instructions on pail labels (in PDF)

      

Cleanup after RadonSeal application

If properly applied, RadonSeal does not form a film on the surface and leaves it suitable for painting, tile adhesives, thinset, levelers or patching compounds.

However, if RadonSeal has been over-applied or allowed to puddle, it will leave a hard glassy or whitish film to which paints or adhesives do not adhere. Acids or chemicals will not budge it. Once allowed to harden, it can be removed only by shot-blasting or with a floor sander using a very rough (16 grit) sandpaper.

Hose off and scrub the surface with a stiff bristle brush or use a wet scrubber 6–10 hours after RadonSeal application, in order to remove any residue from the surface, particularly if you plan to paint it or install floor tiles.

RadonSeal does not damage the sprayer, just rinse it out and spray some water through the nozzle.

As RadonSeal cures and expands inside the pores, it purges dirt, minerals or efflorescence, particularly from older concrete. Several days after the application, you may notice loose white powder or brown crystals on the surface - just brush it off.

Thin concrete floors

Concrete caps less than 3 or 2 inches thick are often found in old basements and crawlspaces. Or, highly reactive soils in some regions "eat away" concrete (unless previously sealed with RadonSeal) and in several years can reduce a 4-inch slab to 2 inches.

There is less concrete to seal and some RadonSeal would penetrate right through into the soil. Use Ion-Bond Armor, which does not penetrate as deep, but creates a tight water-repellent membrane below the surface.

Fibercrete

As cement paste cures and shrinks, it tends to create microscopic cavities next to the fibers, which may later cause vigorous moisture migration by capillary action. Sometimes, it draws in water by capillary action so vigorously that there is a layer on the surface. It badly needs sealing.

However, fibercrete often contains various additives, which hinder the penetration and reaction of RadonSeal. Use LastiSeal Concrete & Brick Sealer, which does not depend on a chemical reaction for sealing.

Highly absorbent concretes

It is normal to find faster-absorbing areas in concrete, where deterioration and increased porosity has already started. Just spray more RadonSeal on such areas.

In some regions, particularly in the North West, cement kilns produce high-lime Portland cement by adding fly ash from kilns to the cement. The resulting concrete tends to be weaker, easily absorbs moisture, expels free lime, and is prone to dusting and chalking. It badly needs RadonSeal to bind the lime and strengthen the concrete but it seems to "drink" it. Spray on additional applications, as long as the concrete is readily absorbing the sealer. If there is lots of efflorescence on the concrete, first use our Efflorescence Cleaner to neutralize the lime on and below the surface.

Concrete blocks

Concrete blocks are more difficult to seal because of larger pores and the thin walls (about 1 1/4-inch) outside the hollow cores. They provide only a weak barrier against water or radon and usually start leaking as soon as the exterior waterproofing coating deteriorates.

Dampen the surface and spray on RadonSeal Plus in 3 successive applications half an hour apart. If the 3rd application still absorbs fast or there are large pores that can hold a toothpick, apply a 4th application. About 6 to 10 hours later, hose and scrub off the surface to remove any residue from the surface.

Do not apply RadonSeal on actively leaking blocks or when a rainstorm is expected within three days. It would push out the sealer from the pores before it had a chance to react and start curing. Damp concrete is acceptable but void applying RadonSeal on wet, water-saturated concrete, because water dilutes the sealer and prevents it from reacting.

Good ventilation, a fan, a dehumidifier or a heater will help, particularly in damp areas, evaporate water from the sealer, so that it can react and cure before the next big rain.

If the hollow cores are not filled, a water column builds up inside the blocks and the hydrostatic pressure easily pushes water through the thin wall of the lower blocks. Drain the accumulated water by drilling weeping holes in the bottom blocks (3/8-inch masonry drill) and let dry out for a couple of days. After RadonSeal cures, fill the holes with caulk. Some contractors also use the holes to inject expandable foam into the cores, in order to prevent the build-up of water.

Prevention is always better than cure – it is much easier to seal concrete and particularly, blocks before they start leaking. Long-term water seepage carries away lime, which shows up as efflorescence ("white powder"), enlarges the pores in concrete and speeds up the seepage, leaving hard-to-seal leached out blocks. For leached out concrete blocks, blocks with pores large enough for a toothpick, or minor cracks and defects, or blocks that still leak after applying RadonSeal, use the "filing the pores" method below.

If the top blocks are hollow (a potential termite problem), water vapor and radon from the ground will be drawn through the cores into the house - seal the openings with expandable closed-cell foam.

Cinder blocks

Cinder blocks are more porous and contain less cement which is partially replaced by fly ash from power stations or cement kilns. (Studies show that they may release mercury and other heavy metal contaminants into the indoor air – another good reason for sealing cinder blocks.)

The same methods apply as for concrete blocks but 4 back-top-back application of RadonSeal are usually needed.

If the cinder blocks have already been leached out, have cracks or defects, or still leak after applying RadonSeal, or if you want to guarantee the result to your customers, use the "filing the pores" method below.

"Unsealable" blocks

There are many different types of concrete blocks that vary widely among regions and manufacturers. Although RadonSeal can seal almost all concrete blocks, the result cannot be guaranteed across the board. RadonSeal is not a caulk, cannot seal holes or cracks in blocks, or blocks with little or no Portland cement:

• lightweight blocks or CMU's (much lighter than the 38 lbs. of standard concrete blocks), dry-pressed blocks, hadite blocks, and decorative splitface blocks made with little or no Portland cement.
• "popcorn blocks" made with a very course aggregate which often have large straw-size holes.

You may be able to seal these "unsealable" blocks with RadonSeal Plus and the "filing the pores" method below.

Filling the pores in concrete blocks

In some cases, RadonSeal alone is not sufficient. Very porous blocks or cinder blocks and leached out blocks need an additional step to seal the pores. This method has so far proved foolproof in very difficult situations. (Although lightweight CMU's cannot be sealed 100%, this method will greatly reduce water seepage.)

Make sure to hose and scrub off the block walls about 6 hours after the 3 (or 4) applications of RadonSeal Plus, so that there is no sealer residue on the surface.

Get Mapei "Keraset Professional Grade Dry-Set Mortar", which is available in the tile section of home improvement centers, is inexpensive (about $20 for a 50-lb. bag), spreads easily, adheres very well, and does not shrink.

Wet the surface. Apply the mortar on the blocks with a 3/16-inch notched trowel just like tile adhesive. Then, using the smooth edge of the trowel and going at a 45° angle, push the mortar very hard into the surface. The purpose is to push the thinset mortar into the pores. You will end up with basically no layer on the blocks and lots of droppings on the ground. You can finish it off neatly by going over the mortar joints with a round tucking tool. The result will look like a brand new block wall. But if you prefer the look of poured concrete, you can leave a layer (say 1/8") on the surface.

Mortar is porous and would soon leak but RadonSeal would not react with it because of additives. Let it dry out for 4 days and then, seal it with our Ion-Bond Armor in two successive applications about 20 minutes apart. Ion-Bond penetrates through the mortar, bonds with RadonSeal inside the blocks, and seals both the blocks and the mortar.

Stone foundations

Stone foundations usually do not leak through stones but through the mortar. Scrape out and brush off any loose or soft mortar with a stainless steel brush (no rusting specs). Spray on RadonSeal Plus in 3 applications about half an hour apart. If the stone is decorative, you can apply RadonSeal only on the mortar with a sponge and wipe off the stones with a rag after about 15 minutes.

Let dry out and cure for at least 3 days before re-pointing (tuck-pointing). RadonSeal will seal the old mortar, improve the bond to the new mortar, and prevent water or efflorescence from separating the new mortar.

If there is not enough mortar left between the stones, sealing the mortar will not be enough. You may have to parge the surface, let cure, and seal with Ion-Bond Armor.

RadonSeal also seals porous limestone, because it penetrates and reacts with alkali.

Sandstone foundations: Usually the problem are the mortar joints, but some sandstone is so porous that water seeps through it, too. And there is not enough loose lime in sandstone for RadonSeal to react. First, remove any cracked or loose mortar. Re-point. Let cure for at least 2 weeks. Wait for suitable weather until everything is thoroughly dry and seal the walls with LastiSeal Concrete & Brick Sealer.

When RadonSeal cannot seal well

RadonSeal can properly seal only sound concretes with normal content of Portland cement and of sufficient thickness. It cannot properly seal concretes with low content of Portland cement, lightweight concrete, fibercrete with additives, concrete with a calcium chloride additive, concrete thinner than 3 inches, or structurally unsound, cracked or crumbled concrete.

Low-grade concretes may contain lots of sand and gravel but little Portland cement. They consume a lot of RadonSeal but allow only sub-par sealing. Supplement RadonSeal with two application of Ion-Bond Armor or use LastiSeal Concrete & Brick Sealer.

Calcium chloride additive used to be popular for accelerating the hydration of concrete, particularly in cold climates. But in the long run, chloride ions gradually break down concrete and corrode embedded steel, just like road salt "eats up" a driveway. This additive may appear as hard, wet-looking spots in the concrete, which hinder proper penetration of RadonSeal.

New concrete - curing and sealing

RadonSeal is also used as a curing compound on freshly poured concrete slabs. It retards water evaporation, maintains ideal moist condition inside the concrete for hydration, and eliminates/reduces surface shrinkage cracking. It forms an integral, colloidal gel membrane, which slows down evaporation, conserves generated heat in cold weather or reduces heat absorption in higher temperatures, hinders the development of large capillaries, and results in a less porous and significantly stronger concrete.

Spray on RadonSeal as soon as the concrete can be walked on without leaving shoe marks, right after finishing, usually in 3 to 5 hours after the pour. Spray on just one application of RadonSeal in a thin continuous film at a rate of 2,500 sq. ft. per pail.

In cold weather, thermal blankets are still needed to protect outdoor concrete. Freezing the water in concrete is just like rapid evaporation.

Other curing methods: Moist curing (misting for at least 7 days or burlap covering) is labor-intensive and may leach out lime and alkali, causing laitance in lower spots on the surface. Plastic or paper sheets tend to leave marks, discoloration and laitance. Chemical compounds expose workers to high levels of VOCs. Temporary wax or chemical sealers leave a surface film unsuitable for painting or tile adhesives and have to be removed first. Flooring manufacturers prohibit the use of curing compounds that form a surface membrane due to the incompatibility with their new, VOC-compliant adhesives.

Why is my new concrete slab all white? Probably a result of "watery" concrete covered by sheets or blankets that trap all moisture. The excessive water in the surface leaches out lime and minerals, causing the white color and blotchy areas where it puddled - laitance. This can happen regardless of RadonSeal or other curing compounds and does not mean the concrete is "bad." For appearance sake, laitance can be removed with a floor sander. Acid etching can also remove a thin surface layer.

This RadonSeal application also serves as a floor hardener - the surface layer will become much harder (like a flint), resistant to abrasion and dusting. Compared to other floor hardeners used on industrial or warehouse floors, RadonSeal has a much higher solids content and works much deeper.

Curing is a completely separate application from deep-sealing the concrete with RadonSeal. As the concrete slowly cures, it will still develop capillaries although much smaller. Allow new concrete to cure for at least 28 days and then, seal the walls and slab with RadonSeal Standard in 2 applications. This bonds and strengthens the concrete, neutralizes alkali, and seals it against water, vapor, and even radon gas. In case of concrete block walls, let the mortar cure for at least 21 days before applying RadonSeal Plus.

The permanent vapor retardant for new construction

RadonSeal can be used in addition to or instead of the vapor retardant sheets under the slab. It seals concrete slabs against vapor and does not deteriorate. Contractors sometimes forget to install the "vapor barrier" (properly - vapor retardant) required by local codes and some counties have approved RadonSeal as a substitute. Allow new concrete to cure and develop capillaries for 28 (min. 21) days before applying RadonSeal.

Plastic barriers get punctured during construction and gradually disintegrate due to the lime in concrete. In fact, pouring the slab directly on a plastic sheet is detrimental to its quality. While free water evaporates easily from its top layer, the bottom remains saturated with water. The American Concrete Institute says: "Slab-curl, surface map cracking, soft friable surfaces, reduced strengths, permeability, and excessive drying shrinkage are some typical results when plastic sheets are used." The ACI does recommend spreading a 3-inch pervious sand bed on top of the plastic sheet to reduce cracking, but this is usually not cost-effective and the sand holds water right under the slab.

New construction - sealing foundation walls

Exterior waterproofing gradually peels and disintegrates similarly to paint, as it is attacked by lime and alkalis from the concrete. Elastomeric spray-on membranes last longer than tar coating, which is brittle and cracks as the house settles and concrete expands and shrinks. Elastomeric ("rubberized") membrane sheets depend on a primer for adhesion and on a tape holding them together, but because of the alkali attack, will eventually separate and let in water.

Although RadonSeal provides a tighter and permanent seal in good-quality concrete, it is normally used in conjunction with the traditional waterproofing coatings. Visible exterior coating is required in most counties and it spans holes, tie-rods and joints.

RadonSeal can be applied only after the poured concrete has cured for 28 (min. 21) days, or 14 days for mortar in block walls. Then, the concrete has to dry out for at least 5 days before applying exterior waterproofing coating. This is fine for existing walls, but new construction usually requires no delays in backfilling.

Most contractors use the usual waterproofing coating on the exterior and later, apply RadonSeal on the interior of the walls and on the slab. It seals, waterproofs, and strengthens the concrete and by neutralizing lime and alkalis, extends the life of the exterior waterproofing.

Complementary moisture or radon reduction steps

Sealing a basement against moisture or radon is like sealing a boat with leaking planks and a few holes. If you seal only the planks, more water will gush in through the holes, and vice versa. It has to be sealed all at once.

Seal and caulk all openings, gaps or cracks. More info on FAQs

Cover the sump pit with a purchased sump pit cover or make a cover of a rigid airtight material like plexiglas or wood. Transparent plastic lets you see the pump. Fasten the cover with silicone or other non-permanent caulk for its easy removal when servicing the pump. Caulk around all penetrations for water ejection pipes and electrical wiring.

Drains without U-traps let in a flow of radon-rich, moist soil gas. If not needed, cover and caulk floor drains or install floor drain check valves. Seal the tops of open drain pipes or service pipes coming in from the ground.

Take common sense measures to keep water away from the foundation like cleaning gutters, adding downspout extensions, proper grading, a trench, drainage of window wells, no bushes or flower beds next to the foundation. More info on basement waterproofing

Testing the results

Similarly to concrete, RadonSeal continues to react and slowly cure. The seal is about 50% effective against gases several days after application and it reaches its full strength in 60 to 90 days.

You can order radon test kits online. In addition to the lowest prices anywhere, you will get a $10 rebate with the purchase of RadonSeal. These are the most widely used, EPA-approved radon test kits. EPA recommends placing two test kits in tandem to minimize errors. Radon levels fluctuate widely depending on factors like barometric pressure, rain, winds, and the season. For more reliable results, use a long-term radon test kit. For more information, visit Free-Radon-Test-Kits.com.

To measure water vapor transmission through the concrete, particularly before painting or installing a floor, use our pre-weighed Vapor Transmission Test Kits. Depending on the concrete porosity and application, RadonSeal typically reduces vapor transmission rate down to the range of 3 or 4 lbs. through 1,000 sq. ft. over 24 hours. For the average basement, this means less than a gallon of moisture per day and a much drier basement.

If a qualitative indication of moisture transfer is sufficient, fasten a 2x2 ft. plastic sheet or aluminum foil on the concrete with duct tape. First, insert an object in the middle to form a tent shape, which helps droplets to form and run. After 2 days, check the underside - there should be no droplets and the concrete should not be dark due to moisture.

Concrete driveways, roofs and outdoor concrete

Driveways and outdoor concrete like sidewalks, patios, decks, and parking areas are exposed to severe conditions: rainwater, groundwater, repeated melting and freezing, road salts or deicers, and the settling of gravel and soil.

Pores in concrete soak up rainwater from above and groundwater from below just like a sponge. When water freezes, it forcefully expands (by 9 percent) and cracks the concrete. The freeze-thaw cycle causes scaling, pitting and hairline cracks. Chloride ions and ice removers, particularly with ammonium, attack the concrete chemically. Concrete deterioration and subgrade settling eventually causes structural cracks.

The first step is deep-sealing the concrete with RadonSeal. It strengthens the concrete and seals it against rainwater, groundwater, and chemicals. The surface does not change and remains non-slippery. Best of all - it is permanent! Outdoor concrete becomes porous very quickly. If over 6 or 12 months old, use RadonSeal Plus and if over 2 years old, use 3 applications.

If you would like a water-repellent surface, use our Concrete Armor Plus, which create an elastomeric subsurface membrane. Since it works well below the surface, it resists UV-rays and usually lasts for 5-7 years. If applied after RadonSeal, it bonds with it inside the concrete and the combination provides the ultimate in concrete waterproofing.

Painting or covering sealed concrete

By purging minerals and foreign matter from the surface, RadonSeal improves the adhesion of paints, thinset and adhesives.

After applying RadonSeal, let the concrete thoroughly dry out for about 5 days before installing carpeting or painting the concrete with latex and other vapor-permeable ("breathable") paints. But before installing floor tiles or linoleum, or painting the concrete with impermeable paints like epoxy or urethane, wait about 10 days. You may sand the floor first to ensure that there are no glassy areas from over-application.

Crawlspaces

Open soil in the crawlspace releases large amounts of moisture, molds, soil gas, and radon. It should be covered and probably vented outdoors, depending on the climate. Cover the soil with 6 mil polyethylene sheets, overlapping 12". Insert a 3" perforated PVC pipe underneath the sheets and vent it to the outside. Fasten the sheets together and to the walls with silicone caulk (very durable) or duct tape. Seal it off from the basement with polyethylene sheets fastened with duct tape.

Application procedures for specific projects

(Printer ready. Opens in a new window.)

    How to seal and acid stain concrete floors

    How to seal factory or warehouse floors

    How to seal high-strength factory or prison floors

    How to seal parking garage floors

    Sealing above-ground fuel tanks

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