Free & Same Day Ground Shipping  | View Details

Home » Radon FAQ

Radon FAQ

Frequently Asked Questions – RadonSeal

Can I Buy your Products in a Store?

No. We ship by courier (usually UPS) directly from the factory.

Which Concrete Sealer Is Best?

“I am confused with the different sealers. Which is the best one?”
It depends on your concrete. No single sealer is suitable for all situations.

Of all sealers, RadonSeal penetrates the deepest (up to 4 inches) and seals the tightest (also against vapor and gases). It reacts chemically inside cementitious materials like concrete, gunite, shotcrete, mortar, grout, and stucco. Not suitable for colored concrete, fibercrete, polymer patching compounds because color pigments or additives may interfere with the reaction. The seal is permanent. The surface remains suitable for paints, adhesives, thinset, and patching compounds.

LastiSeal also penetrates very deep (2–4 inches) and hardens inside the pores. It waterproofs concrete, bricks, stones, and porous materials. Unlike RadonSeal, it does not depend on the content of alkalis. The seal is also permanent. The surface remains suitable for paints (except latex and silicone) and adhesives. LastiSeal Concrete Stain offers a wide choice of attractive stains.

Subsurface water-repellent sealer Ion-Bond Armor has very small molecules and penetrates up to 1.5 inches into concrete or masonry. It waterproofs permanently, including against negative side water pressure. Does not depend on alkali content. When used on concrete already sealed with RadonSeal, it provides the tightest possible internal seal against water vapor and gases.

Concrete driveways or shop floors sealed with DryWay Water-Repellent Sealer bead water. Spills are easy to wipe off. Unpaintable. Continues to shed water for over 10 years. Can be applied to concrete deep-sealed with RadonSeal to protect the surface layer.

More information on How to select the best sealer for your project

Can I Seal Through Paint?

“I have recently painted the walls but the basement is still very damp. Can I still seal it against moisture?”
Sorry, you have to remove the paint first. However, if the paint is just a single layer of latex-based paint like Drylock, which is porous and does not stop water vapor, you can still seal and waterproof right through it with our Ion-Bond Armor. But first, wash and scrub the paint with a detergent solution to remove dirt from pores in the paint and let it thoroughly dry out for 2 or 3 days.

How Do I Remove Paints and Surface Sealers?

Before applying a penetrating sealer, paints or surface sealers have to be removed first. When fixing a localized seepage through concrete, you could just scrape off loose paint and seal only the spot but water will soon find another weak area. The proper approach is to seal the entire wall or floor.

You can hire a contractor or do it yourself. Equipment rental stores offer various options:

  • sand-blaster, including a compressor and bags of sand,
  • shot-blaster for cleaning concrete floors,
  • water-blaster for high pressure washing (3,500 – 4,000 psi) with a rotary zero tip,
  • dustless floor grinder with a carbide scraper plate or a heavy duty hand grinder with a very stiff wire wheel cup,
  • floor disk sander/polisher with a very rough oxide paper (16 or 20 grit) or a carbide scraper disk or wire brushes.

Sand blasting thoroughly cleans both walls and floors but leaves lots of sand everywhere. If there is good drainage, high pressure water-blasting is usually much easier. Floor sanding is only for floors and if the paint is soft, it can gum up the sandpaper, rendering it ineffective.

Shot-blasting is usually the best method for cleaning large floors. It does not leave all the sand mess or dust. Concrete finishing contractors provide this service. Smaller shot-blasters are now also available for rent to the public.

Paint strippers require patience and typically, emit unhealthy fumes. Ideally, they should bubble up or lift the paint for easy scraping off. If the stripper is dissolving the paint, it may fill the pores in concrete and make sealing impossible. 

How Do I Remove Embedded Oil?

Oil and grease stains are a common problem in garages, car repair shops, driveways, and parking areas. Oil can penetrate so deep into concrete that common cleaners cannot remove it. Consequently, sealers would not penetrate and paints or coatings would not adhere well.

Our Novion Universal Concrete Cleaner is an environment-friendly penetrating degreaser that cleans deep inside the concrete. Use it fully concentrated on the oil spots and diluted with water (3 parts of water to 1 part of cleaner) on surrounding areas. Then, power wash twice to remove all oil and Novion Cleaner residue, preferably, with a “hot water” power washer.

Let the surface dry out for a day or two and acid-etch. In addition to opening up the surface, the pH shock helps emulsify any remaining oil. Neutralize with ammonia or baking soda and power wash it off.

Since power washing drives lots of water into the concrete, let the concrete dry out for 3 days if outdoors or a week if indoors before sealing.

How Do I Remove Tile Adhesive?

Floor tile adhesive can be removed with chemical paint strippers or citric acid solvents (delemonene) that do not emit harmful vapors but are effective only on modern water-based adhesives. Mastic removers are also sold in stores.

But avoid filling the pores in concrete with diluted adhesive or mastic, which could make the concrete unsealable! We recommend our Lightning Strip Paint & Mastic Remover, particularly for the old, thick, black mastic. Test it on a small area first. Afterwards, wash the area with water to remove any residue.

Alternative methods include shot-blasting, sand-blasting, or grinding. But avoid using abrasion on old tiles or mastic which may contain asbestos.

How Do I Remove the White Powder (Efflorescence)?

Water carries dissolved lime, alkalis, and minerals from inside the concrete to the surface, where it evaporates and leaves behind white or brown mineral deposits. Sometimes, it “grows” from the pores like fluffy cotton fibers. Efflorescence pushes off paints, including waterproofing paints. If left unchecked, it eventually hollows out and destroys the concrete – it is also called “concrete cancer.” Efflorescence would prevent a proper penetration of RadonSeal sealer and consume some of it, leaving less for sealing.

You can remove light efflorescence with a stainless steel wire brush. Homeowners often use muriatic and other acids. But you can avoid the hazards of acids by using RadonSeal Efflorescence Cleaner. It dissolves and oxidizes efflorescence – makes it disappear! It also eliminates the steps of neutralizing the acid residue with ammonia and hosing off the surface. More information on cleaning efflorescence.

Carbonation: Over time, efflorescence reacts with carbon dioxide in the air and builds up as a rock-like layer of calcium carbonate (limestone). This is very difficult to remove – try a chisel and hammer, sandblasting, or repeated applications of the Efflorescence Cleaner and scrubbing with a stiff brush.

Laitance: A thin layer of cement particles and free lime that float to the surface of freshly poured concrete and form a pale, friable layer in low spots when the concrete sets. Caused by high water content in the concrete or by curing under a plastic sheet. If a coating is applied, it can be lifted off almost like a carpet. Before coating or sealing, the laitance must be removed by sandblasting, shot-blasting, scarifying, acid etching, or similar.

Painted Walls and Efflorescence?

“I wire brushed and acid etched the walls and painted them with a masonry sealer. The basement is mostly dry now but after a short time efflorescence is returning in areas and causing the sealer to peel. I have wire brushed, re-etched, and repainted the problem areas but the efflorescence keeps returning. Can I apply RadonSeal?”
Paints or surface sealers cannot stop efflorescence. You have to remove the surface sealer and the efflorescence. You can use our Lightning Strip and RadonSeal Efflorescence Cleaner, or remove it all at once by sand-blasting. Sealing the concrete with RadonSeal will prevent future efflorescence by neutralizing lime inside the concrete and by stopping capillary seepage of water. Then, you can paint it again.

Does RadonSeal Cause Efflorescence?

No. But as RadonSeal cures and expands inside the pores, it may purge dirt, loose minerals, and old efflorescence from the concrete for several days. It typically comes out in a soft, powdery form that can be easily brushed off. Purging is more obvious on older concrete and it confirms that RadonSeal has reacted well.

Can I Seal a Very Smooth Concrete Floor?

Power troweling provides a nice-looking, smooth finish on concrete floors. It creates a “hard cap” (crust) on the surface. But when overdone, the surface looks shiny and the crust becomes thick (say 1/8″ instead of 1/32″), which may lead to problems. (Uncured lumps pushed into the surface while still plastic will become stress points that may cause spider web cracking later. The thick hard cap may delaminate as the concrete underneath cures and shrinks. Paints will not adhere and sealers will not penetrate.)

RadonSeal seals most machine-troweled concrete like typical garage floors. However, if the surface is “over-beaten,” it is difficult to penetrate. Sealers cannot penetrate polished concrete (also called burnished, honed, or diamond ground).

Unevenly troweled floor: This may happen in some areas when the concrete has higher spots which get hit harder by paddles of the power trowel. They often become the weak areas for moisture infiltration because they trap migrating moisture similarly to a floor covering, and for condensation because they are the cold spots.

Very hard-troweled surfaces have to be opened up first either by acid-etching (like our organic EasyEtch) or mechanically with a shot-blaster or floor grinder.

Do I have to Acid-Etch the Floor?

If the machine-troweled floor surface looks very smooth, almost shiny, you should test if it is porous enough for sealing:

Eyedropper test:
Get an eyedropper in a drugstore (costs about a quarter), fill it with water, add a drop of liquid soap (which breaks surface tension), and shake. Lay about a dozen drops on the surface. If the drop just sits there for over 10 minutes or spreads out to leave a large damp spot the size of a quarter, the surface is not porous enough. But if the size of the damp spot is a nickel or dime, it is fine for sealing.
All areas will not absorb evenly but at least 70 percent of the drops should meet this test.

Or you can directly check the penetration of RadonSeal by spraying a small 4 x 4 ft. test area after dampening it first. The glistening film should absorb into the concrete within 10 minutes. If not, wipe off the sealer and rinse the area (or it would protect it against acid etching), and proceed to open up the surface.

Alternatives to Acid-Etching

Shot-blasting: For best prep of very large floors, hire a concrete finishing contractor to shot-blast (“bee-bee blast”) the floor to a 60 grit finish (CSP Standards, 330 Shot size). Small shot-blasters are now available for rent in some areas.

Or rent a diamond floor grinder or scarifier. Or you can use a disc or drum floor sander with very rough sandpaper (16 or 20 grit). Or use a sand-blaster to open up the pores but this leaves lots of sand.

Acid-Etching Concrete Floors with Muriatic or Phosphoric Acid

Follow manufacturer’s instructions. Procedure recommended by several coating manufacturers for etching floors with muriatic or phosphoric acid:

Let new concrete cure for at least 30 days. Remove paint, oil, grease, sealers, release agents, dirt, and grime from the concrete. Oils and grease stains can be easily cleaned with the use of our Novion Universal Concrete Cleaner. Remove paint by mechanical means or by use of chemical paint strippers. Curing agents and sealers can be also removed with a floor grinder or scarifier.

Using clean water, dampen the concrete just on the verge of puddling. The concrete should remain wet until acid mixture is applied.

Mix a dilute solution of acid to water in an acid resistant container. Muriatic acid is typically mixed at a ratio of one part acid to three parts water. Always dilute acid in water, not vice versa, and ventilate the area. A respirator and goggles are recommended.

Apply the acid solution in a consistent manner over the surface area with the use of a plastic garden sprinkling container. Do not dump or splash acid on floor. Scrub thoroughly with stiff bristle broom working acid into the concrete. Bubbling will indicate acid is reacting to the surface layer of concrete. Areas failing to produce bubbling action would indicate contaminates preventing proper etching. Clean and re-etching may be necessary. Acid solution should be allowed to remain on concrete as long as bubbling continues (5-10 minutes usually). Do not let dry!

Neutralize acid residue by spraying a mixed solution of one pound baking soda to five gallons water. Then flush with plenty of water while scrubbing with a stiff bristle broom. Repeated rinsing with clean water is recommended to remove residue from surface. Clean liquids with wet vac if no drains are present.

The concrete surface should have a uniformed texture of a #80-#60 grit sandpaper. If not, repeat etching process.

Check the pH level of the concrete while the concrete is wet. An ideal reading would be 7 (neutral). A range of 6-9 would be acceptable for LastiSeal Concrete Stain & Sealer. Below 6 would indicate acid residue remains on surface and concrete must be neutralized (test pH again). If pH is above 8 then repeat etching process and neutralize again.

Organic Acid for Safe Etching

Etching with muriatic (hydrochloric) acid or similar presents hazards to health and the environment. And if overdone, it can “burn” the concrete, eating away cement paste and exposing bare sand.

Our EasyEtch Concrete Etcher uses a bio-degradable organic acid, which is much safer for the user and the environment.

Can I Seal My Finished Basement?

“My basement is already finished. Can I use RadonSeal to reduce radon?”
If you can lift the floor covering and seal the slab, chances are good that it will reduce radon significantly. Many homeowners do that. Most radon gas gets in through the floor, because it is trapped underneath the slab between footings.

“Should I caulk around the bottom of the existing paneled walls?” It would be useless, because radon easily passes through drywall and paneling.

Peeling Floor Tiles?

“My floor tiles keep on peeling and the glue has turned into a white powder.”
Just like paints, tile adhesives are attacked by lime and alkalis from the concrete. Lift and discard the tiles. Then, remove the adhesive. Adhesive removers are available in hardware stores, e.g. citric acid (delemonene) or use our Lightning Strip Paint & Mastic Remover. Shot-blaster or floor grinder may also be used but older tiles may contain asbestos, which means you have to use a stripper.

Today’s adhesives on self-stick floor tiles are water-based. But moisture in the air will penetrate through the joints, condense on the concrete, activate the lime in concrete, which break down the glue.

Before installing tiles, seal the concrete with RadonSeal to neutralize alkalis and stop moisture migrating through the concrete.

I Am Busy, Can You Apply the Sealer for me?

We have professional applicators available in several areas. However, our products are designed for an easy and safe do-it-yourself installation. Best to recruit a relative or hire a handyman.

I Meet the 4 pCi/L limit, Isn’t That Enough?

The 4 pCi/L level is not a “safe” level. Radon gas is radioactive and dangerous at any level. For the sake of your family, always try to reduce radon to a minimum.

If you are selling the house, there is always a risk that it could read above 4 pCi/L during the building inspection and nix the closing. Radon levels fluctuate widely and depend on factors like barometric pressure (a low-pressure front), rain or ice (it bottles up radon in the ground), wind, and the season. Because of the fluctuations, seal the basement with RadonSeal before putting the house on the market.

Why Doesn’t EPA Recommend Sealers?

EPA (1990): “Sealing cracks and other openings in the foundation is a basic part of most approaches to radon reduction. EPA does not recommend the use of sealing alone to reduce radon because, by itself, sealing has not been shown to lower radon levels significantly or consistently.”
Absolutely correct! Sealing cracks and openings is not enough. Moreover, radon gas easily passes through basement paints or surface sealers as tested by EPA back in the late 1980s.

Since then, multiple scientific studies have showed that radon gas easily infiltrates into basements through the microscopic pores in concrete and that this can constitute the major infiltration route. Although radon kills over 20,000 Americans each year, EPA’s budgets for radon have been severely cut and there have been no updates on the infiltration route through concrete.

RadonSeal penetrating concrete sealer works very differently from the paints and surface sealers tested by EPA. It penetrates up to 4 inches into the concrete, reacts and expands, sealing the capillaries permanently. All basement walls and the entire floor have to be sealed.

Moreover, any openings, gaps, or cracks must be also sealed or caulked just like with all radon mitigation methods. The sealed concrete will stop the slow oozing of radon gas through the pores in concrete but the basement “stack effect” will try to make up for it by drawing in more soil gas through any opening. The underground soil gas has a high radon concentration typically well over 100 pCi/L. If there are large openings and the radon concentration in the soil gas is high, the radon level in the basement could actually increase!

What if I Already Have a Radon Fan System?

Over time, the gravel underneath the floor slab tends to silt up, which will make the fan system less effective. RadonSeal will reduce your radon level further by sealing both the slab and the walls. It will also lower the operating costs of the fan-based system ($150/year on average) by reducing the energy losses in heated/cooled air now pulled out through the slab. RadonSeal will also act as a backup during an equipment or power failure. Using both methods simultaneously will provide the lowest possible radon level.

The More RadonSeal I Apply, the Better?

No! Over-spraying should be avoided. RadonSeal seals deep inside the concrete and any surplus left on the surface is not effective. The hard, glassy or whitish finish is difficult to remove. It is unpaintable and would have to be sanded or scraped off first.

What if I Have Some RadonSeal Left?

It has a long shelf life – at least one year and can be used inside or outdoors. Seal your garage floor. It will purge oils and dirt from inside the concrete within several days, waterproof it against wicking water, and make spills easy to wash off. Or apply it to your concrete steps, sidewalks, or driveway for protection against spalling or pitting due to salts and “freeze-thaw” damage. 
Or you can return unopened pails for a refund of the product price less a re-stocking fee.

How to Repair Cracks and Gaps

Apply RadonSeal before sealing cracks because they help the sealer penetrate into the concrete and preserve it. And as RadonSeal strengthens the concrete, it reduces further cracking. Note that RadonSeal tends to close fine hairline cracks in slabs as it expands inside the concrete but this cannot be guaranteed.

The usual repairs with a caulk or hydraulic cement do not last. Caulk peels. Hydraulic cement does not adhere well to concrete and is very rigid. As the concrete naturally moves, hydraulic cement gets loose and allows water to seep around it.

Repair permanently hairline or wide cracks in poured concrete walls with our Foundation Crack Repair Kits. Forceful expansion of the injected polyurethane ensures that the entire depth of the crack is filled, so that water will never find the crack again. Cracks in block walls are more difficult
to repair – use our ElastiPoxy Crack Filler mixed with sand for a strong and permanent repair.

For various options on repairing cracks in concrete floor slabs and floor-to-wall joints, visit How to Repair Cracks in Concrete Slabs and Corners

Penetrations through the floor or walls: Use our PipeTite Gap Filer Kits to fill the gap around pipes through the full width of the wall. To stop water leaks through form tie rods or wire ties, use also the PipeTite Kits for a permanent repair.


Map of RadonSeal website and how-to articles.