I’ll admit it; today’s post is a little dry and somewhat technical. But, if you're going to have a cement tile product installed, it is required reading. Today’s post is about a physical phenomenon called efflorescence and how it relates to cement tile. Hopefully, by the time we’re done you’ll understand what is it, where it comes from, how to remove it or stop it.
Efflorescence on Pavers
Photo via The Brick Paver Dr.
What is Efflorescence?
Efflorescence is a powdery substance or incrustation the sometimes forms on cement tiles. It’s important to remember that efflorescence is a normal physical phenomenon. It can occur in any material containing Portland cement including clay, terracotta, and concrete. It commonly looks like a white powder or salt on cement tile. The word, efflorescence, has French origins and means to flower.
Efflorescence does not damage the tile or cause structural problems. But, it's pretty darn ugly to look at.
Where does Efflorescence come from?
Efflorescence occurs when when soluble salts and materials come to the surface of concrete and mortars. Ever boiled a pot dry or rinsed your car with a hose in full sun? Notice how there is salt ring or residue left? As the water leaves and evaporates, it leaves the salt behind. Efflorescence is a similar phenomenon. As cement or cement tiles dry, the lime in the cement rises to the surface with the water and reacts with carbon dioxide in the air to form calcium carbonate. In this case, a white powder or film forms on the tile's face. It's induced by low temperatures, moist conditions, condensation, rain and water. It can occur very soon after exposure to moist or cool conditions or more gradually in sub-grade concrete installations (like a subterranean parking garage).
Cement tiles are hydraulically pressed and then placed in racks. The tiles are soaked in water baths in order to achieve water saturation and guarantees proper cement hydration. Then tiles are left to dry for 10 days and cure before shipping.
Racked Cement Tiles Await a Water Bath to Cure the Cement
Water Bath for Curing Cement Tiles
Because of how they are made and shipped, efflorescence may be present when cement tiles are taken out of the boxes. More commonly, it may occur right after installation especially when installed on cement subfloors.
Efflorescence like I described above is sometimes referred to as 'powdery' efflorescence and is the most common. However, there are two types of efflorescence. The other type is called 'crystalline' efflorescence. When powdery efflorescence goes through cycles of being deposited on the surface it can form larger crystals that strongly bond to the surface. It is important to note since different cleaning treatments are designed to work on a specific type of efflorescence.
If there is no water source, to create capillary water flow through the tile, efflorescence can't occur. An ounce of prevention...
How do I Prevent or Stop Efflorescence?
In laying cement floor tiles, be sure to install over a stable cured cement subfloor. It is critical that the cement base be completely cured before laying floor tiles. If the concrete subfloor is not, moisture may seep up into the tiles and cause efflorescence to appear on the tile surface. If there is no water source, to create capillary water flow through the tile, efflorescence can't occur. An ounce of prevention is always better than a pound of cure.
How do I Remove Efflorescence?
Efflorescence that appears on the tile before installation will generally come off during the installation process. You may be able to sand small localized areas. Use a piece of wet sandpaper (200 grit), wet the tile, and sand the area.
When efflorescence occurs after installation, first try to remove the efflorescence by cleaning the tiles thoroughly. Use a floor polisher with green pad, a neutral soap and plentiful water. Remember, you'll need to let the tiles thoroughly dry to confirm the efflorescence has been removed and stopped.
We are told that penetrating sealer in fact stops efflorescence from resurfacing. So if you are still having a problem area, this is the next step. I would suggest you do a small test portion of the tiles in the least noticeable area and make sure to use a high quality penetrating sealer. Read our post about Sealing Cement Tile.
Additionally, efflorescence cleaners are available. I have no experience with the products so make sure to test them on a loose tile or hidden area to ensure the results. Carefully follow the directions provided by the manufacturer and avoid any acid-based products that will damage the concrete tile.
Other Good Resources on Efflorescence
To find out more about this topic, I recommend these articles. Remember, these posts discuss efflorescence with respect to masonry or ceramic tile and may not directly apply to cement tile.
- For a more technically detailed explanation, see the Portland Cement Associations FAQ, What causes efflorescence and how can it be avoided?
- John Bridge forum on tile explains How to Remove Efflorescence.
- Wikipedia defines Efflorescence.