Sure, your inground swimming pool is a resort-like escape where you work on bronzing your skin poolside while children splash about on giant, inflatable alligators, and immature friends tirelessly scream, “CANNONBALL!”
It’s also one giant chemistry beaker perpetually on the brink of bubbling over with green algae blooms or suddenly breaking out with colorful stains as your friends slowly back away from water and ask “Eeew, what is that stain? You must be doing something wrong with your pool.”
If you own a concrete or plaster swimming pool, or are about to become the proud owner of a plaster-surfaced pool, we have some pointers to help you keep it looking like paradise and not like a 20,000 gallon petri dish.
Plaster pool finishes are traditionally the most popular swimming pools dating all the way back to the very first backyard pools. Typically a mixture of cement and fine, crushed marble sand, otherwise known as marcite, it’s a durable, impact resistant surface.
Perhaps best of all, they can be sculpted into almost any shape your budget can afford. Additionally, gunite pools are very sturdy and strong because of the steel framework.
However, the plaster finish on a gunite pool needs to be replaced about every 15 years and that can get quite pricey (over $5,000) for a surface that is a bit rough on the skin due to it’s natural, porous nature. Oh, yeah, about that porous surface…
Smoother surfaces, like vinyl or fiberglass, are less prone to stains because they do not lend themselves as easily to cozy little nooks and crannies for metals, oils, or organic debris to eventually coagulate into an unsightly, rash-like stain on your pool plaster.
Plaster pool surfaces create their own vicious cycle – because plaster is so porous, more cleaning is required to prevent algae growth, and the high alkalinity and pH of plaster requires frequent adding of acid to counteract the effect which in turn, of course, slowly deteriorates the plaster surfaces that you are trying so hard to keep clean – making them even more porous which makes them more susceptible to stains…You can see where this is going.
Let’s get on with it – how to remove stains in a plaster pool, and the best methods to prevent plaster pool staining.
Heavy metal is the enemy, and I am not referring to Iron Maiden or Slayer. I’m talking about the invisible metals dissolved in your pool water from sources like rain run-off, pool equipment, salt water pool systems or even your concrete pool deck surface. Bits of metal like screws or hair pins can make a nasty rust stain.
A great product for removing metal from your pool is Metal-Free by Natural Chemistry. It is one of the strongest products available for sequestering metals. It works especially well on well water, is not affected by pH or temperature, and is All Natural.
The Sapphire Stuff by Jack’s Magic is another fantastic sequestering agent. It not only removes metals but also oils, soaps, cosmetics and other organic matter from your pool water.
For oily stains at the waterline, or a bathtub ring from winterization water levels, use an enzyme product like Pool Perfect to consume oils, fats and other greasy pollutants that enter the water.
What’s that Stain?
It’s important to know what kinds of metals are creating the stains in your pool. Here’s a pool stain chart as a guide for metal stain identification in pools.
Metals are certainly not the only cause of stains in a plaster-surfaced swimming pool. Leaves, berries, bugs, sun tan oil, or even your water-loving dog can all contribute to staining. These types of stains can be cleaned with good old fashion elbow grease using a combination of a PoolStone and pool shock. Pouring a bit of pool shock directly onto a stain works similar to bleach and is ideal for plaster surfaces but a bit harsh for vinyl liners.
The Stain Eraser is another great stain removal product that does not require the use of chemicals and is great for smaller stains and stains in tough corners. It’s designed to be mildly abrasive so it’s tough but not destructive to the plaster.
For extreme staining or serious algae blooms, plaster pools can be cleaned with an acid wash with muriatic acid, or the safer to use Acid Magic. Acid washing removes a thin layer of plaster, exposing bright white and unstained plaster underneath. Having your pool acid washed will remove most surface stains.
Finally, keep your pool water balanced, with good pH, alkalinity and calcium hardness levels. A pool that is out of balance can stain more easily, and makes stain removal difficult as well.
Removing Stains from a Plaster Pool
- Granular pool shock for organic stains
- Sequestering agents for metal stains
- Stain Eraser or Pool Stone for mineral stains
- Enzymes for oily, dirty stains
- Acid Washing for all stains
- Keep pool water balanced
InTheSwim Staff Blogger