Category: Stone

Why Pool Decks Turn Green and Black

What is that green and black stuff growing on my pool deck? This is a question pool owners often ask. This article will help you identify and remove pool deck discoloration, as well as minimize the likelihood of future discoloration.

Biological Growth Types

The majority of unsightly green and black spots on pool decks are the result of biological growths in the form of algae, molds, lichens and mosses, and plants such as ivy and grasses. Let’s take a look at each:

• Algae is commonly green in color but can also be black, orange, red or yellow. It is easy to identify since it grows in mats, films, and patches on the surface of stone, brick and concrete. Algae is a single-cell plant but lacks roots, leaves, stems and vascular tissue. Most algae, especially the green type, needs moisture and sunlight to grow. However, there are species that will grow in damp, low-light areas.
• Moss is most commonly green but can also be red. Like algae, it requires sunlight and moisture to grow. It also needs a mineral source often found in soils. Unlike algae, moss has a root structure and a very small leaf structure. It will often grow in grout between stone and masonry.
• Mold is a fungus, not a plant. It does not require sunlight but does require moisture and an organic food source. Mold is generally black in color but can also be red, orange, brown, or yellow. Limestone is especially susceptible to mold growth, since it contains organic matter that can feed mold.
• Lichens are comprised of a fungus living in a symbiotic relationship with an algae or a relative of bacteria called cyanobacterium (or both in some instances). They can be red, yellow, red, green, or white. Lichens are identified by crusts or leaf-like structures with defined borders growing away from the surface of the stone or masonry.
• Ivy, grasses, and higher plants are easily identified by their root systems and large leaf structures. They are often green in color.

Removal of Biological Growth

Regardless of the type of biological growth, removal requires the use of biocide cleaning chemicals, such as peroxide, bleach, or other biocides. Here is a basic cleaning procedure that is recommended to remove these growths. Be sure to carefully read the directions on chemicals and take all necessary precautions. Wear gloves and protective clothing. A mask is recommended, since some mold and algae can emit spores that can be harmful to your respiratory system.

Algae is best removed when it is dry since the spores are more likely to become airborne when wet. Allow the surface to fully dry, or expedite the drying process with a fan. Remove as much algae as possible by scraping or scrubbing with a stiff broom or brush.

A pressure washer can be used to remove the remaining biological growth, but there are a few additional precautions and recommendations:

1. Do not use high pressure. Test the pressure in a non-conspicuous area to make sure you are not damaging the stone or masonry.
2. Use hot water, if possible. Hot water will kill some of the biological growth and sanitize the surface.
3. Use a wide nozzle tip to minimize damage. Keep the tip of the wand at least 12 inches away from the surface.
4. Bleach or vinegar can be used to clean stubborn growth. Mix the bleach or vinegar. Use one cup of bleach or vinegar with one gallon of water. Test this mixture in a non-conspicuous area to see if it will cause discoloration. Some stone and masonry types can lighten, discolor, or etch with bleach or vinegar.
5. Apply the bleach or vinegar mixture on the deck and allow it to sit for 15-20 minutes. Do not let it dry. (If it accidentally dries, apply more of this mixture.)
6. Scrub the area with a nylon brush. Rinse with plenty of clean water. Be careful to avoid nearby plants, since this mixture can kill landscaping plants and grasses.

In lieu of bleach or vinegar, you can use many of the commercial cleaners appropriate for your pool deck surface type. You can find them at most home centers. If your pool deck is natural stone, be sure to use a pH-neutral, stone-safe cleaner. Read the directions carefully.

Spot Removal

If you have just a few spots, you can use 3% hydrogen peroxide. Simply spray the growth with the peroxide, allow it to sit for several minutes, and then rinse with water.

Prevention

Your best defense to keep biological growth at bay is to clean the deck on a regular basis. We can professionally clean your pool deck for the best results. We can also apply sealers and preventive biocides to inhibit new growth.

We can provide specific recommendations regarding cleaners for green and black growth on your pool deck.

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This article is one of a series of articles written and published on behalf of Surface Care PROS Partners.

It’s kind of funny what people who should know better will say about common stone failures or issues. Over the past several years, we have heard many stories about the reasons stone will fail, turn color, fade, and so on. Many are comical and most are just plain false. Here’s a sampling you may enjoy…

A Warped Sense of Humor

Many seasoned installers who have tried to install green marble tiles with ordinary thin set or other water-based setting materials have experienced warping problems. Here are two ways we’ve heard them explained.

1. Myth: “Green Marble will warp because it contains living plant material. As water is added to the marble, the plants start to grow and this makes the marble warp.” We nearly fell over laughing, but he wasn’t kidding. He really thought this was the reason.

2. Myth: “Green Marble will curl on the edges because the installer did not put enough setting mortar on the edges. The green marble will have a tendency to lift off the floor where there is no mortar and hence will curl.” While not quite as outrageous as the first explanation, it is still just as wrong.
Truth: The real reason green marble warps is a condition known as hysterisis. Green marble is very sensitive to moisture. When water enters the stone, it causes the marble to release any internal stress, thus causing it to warp.

Home Sweet What?

3. Myth: “Your stone floor needs to be homed!”
Truth: No, this is not a spelling mistake – the word used was “homed.” We have run into several sales people who have called the honing process “homing.” Maybe they also worked with pigeons, but we’ve never heard of homing a floor. The proper term, of course, is “HONE,” which means to abrade a stone.

“Plop, Plop, Fizz, Fizz…”

4. Myth: “Your stone floor has an effervescence problem.”
Truth: The key word here is “effervescence.” Let’s clear this up right now. Efflorescence is the deposit of soluble salts on the surface of the stone that is caused by water that carries the salts from the setting bed of the stone to the surface; it is often deposited as a white powder-like residue on the surface of the stone. Effervescence is what happens when something fizzes. A good example is when you drop a tablet of Alka-Seltzer into a glass of water. The fizzing is referred to as “effervescence.” We’ve never seen a stone effervesce unless someone was pouring acid on it!

5. Myth: “Sealing your stone will help with your efflorescence problem.” Truth: We’ve heard so-called experts instruct people with an efflorescence problem to seal the stone as a remedy. This is wrong. Sealing will only block or reduce the pore size of the stone, which will not only cause more efflorescence, but it could also cause spalling, which is when the stone flakes at the surface.

Are You Cracked?

6. Myth: “That’s not a crack, it’s a fissure!”
Truth: Many fabricators will try to blame cracks that occur in stone installations on natural fissures that occur in the stone. Sometimes they are right and sometimes they are wrong. If you look up the word “fissure” in the dictionary, guess what? A fissure is a crack. The distinction they are trying to make is between fissures, which are naturally occurring as part of the formation of the stone and cracks (more appropriately called “breaks”) caused by external forces on the stone. Of course, the most likely place for a break to occur is on a natural fissure. Consequently, definitions need to be clarified and the stone needs to be examined carefully to determine if natural fissures are at risk of becoming breaks during normal usage.

Would You Like Some Salad With That?

7. Myth: “To remove oil from stone, saturating it with water will force the oil out.” Truth: Since it is true that oil floats on water, you would think this makes sense. But trust us, it doesn’t work. The oil is trapped in the pores of the stone and no amount of water is going to force it out. The best way to remove oil from stone is with a poultice and a degreasing chemical. For specifics and poulticing instructions, see https://surfacecarepros.com/stain-management-app/ .

8. Myth: “Just use some vinegar and water to clean your marble or limestone.” Truth: Generally folks in the stone business know better, however this is often recommended by tile installers. Don’t do it! Vinegar is an acid and will etch calcium-based stone. Marble and limestone are generally the most susceptible, but some types of granite will also be damaged by vinegar.

Stones Can Be So Vein!

9. Myth: “If it’s got veins, it’s marble.” Truth: This is a fib we hear all the time. Many people in the industry believe that if a stone has veins, it must be marble. This is totally false. Veins can also be found in granite and limestone.

You Make Me Sick!

10. Myth: “Granite countertops harbor bacteria and emit harmful radon gas.” Truth: This is absolutely FALSE! NIOSH and the CDC have no reports of granite or any other stone used as a countertop being unsafe. If stone were unsafe or unsanitary, why would it be used in food laboratories or sold as cutting boards? There has been no known proof of any illness caused by using stone as a countertop. And as for the rumors that granite contains harmful radon gas — there is so little radon in granite that you would have to live to be 10,000 years old for it to have an ill effect on you. There is likely more radon coming from the ground and the concrete that your house is built on.