A cloud rises from a drained pool. Inside, a solo pool technician washes down the walls of the pool with his mixture of muriatic acid and water. As the cloud condenses and hangs over the pool, the tech, who isn’t wearing a respirator, breathes in the poison.
In a backyard a few houses down, Eric Nielson sees the cloud and looks over. He watches as his fellow service technician takes in a large breath in the acid cloud and passes out. Nielson runs over, dialing the paramedics as he moves.
The tech woke up and was just fine, but there could have been a less happy ending. His mistake was in not watching out for the hanging cloud of acid, which wasn’t dispersing. “He was a guy who was old enough and should have known better,” says Nielson, owner of Willow Creek Pools in West Hills, Calif.
That’s the way it works with acid washes. “It’s that dangerous if you’re not paying attention,” Nielson says.
In general, this procedure is something of a last resort. Sometimes a pool needs a wash to address cosmetic stains, or remove algae that’s been left to grow too long.
While this may be a rare job in some parts, proper care should be taken to make sure the job is done safely, with the correct precautions in place. Not only that, it also should be performed correctly and in a manner that leaves behind a pristine, clean and clear pool.
Here, PSN takes a look at what goes into acid washing — when to do it, what methods service technicians can use to keep safe, and what goes into a proper job.
Why take a bath?
Acid washes are performed most often to remove staining. If it refuses come out through normal chemical treatments, then it’s time to consider the possibility of an acid wash.
The causes can be regional. South Florida, for instance, seems to have a preponderance of metal staining in its pools.
“I get a combination of iron and copper,” says Mark Goodwin, the owner of Pool Water Medic in Palm Beach Gardens, Fla. “We have a lot of houses ... that are on wells and they’re very shallow wells. Iron is a huge problem in those wells.”
Additionally, after the recession, a number of houses in his area went into foreclosure, so he regularly gets called out to homes with pools left stagnant for a few years and whose surfaces have been stained by sludge and slime.
In California and Arizona, the problems generally revolve around algae and calcium. If neglected, for instance, calcium may even build up and create “stalactites” on the side of the pool, Nielson says. Algae tends to result from chemical imbalances.
A more universal problem is copper staining, often from old heaters or another result of imbalanced water.
The time of day can affect the job.
Nielson prefers to start early in the morning when it’s still a bit cool out. “A misty, cooler morning or overcast days are the best,” he says. “A drizzly day is ideal. It’s not going to effect the concentration of the acid. [You] don’t have to worry about the sun, and it keeps the pool moist.”
The equipment needed for an acid wash is fairly standard and should be easy for most service technicians to find. You will need a hose, sump pump, bottle of muriatic acid, a bicarbonate such as soda ash, and a bucket for mixing the muriatic acid to create the solution.
Those are the basics. Options include a pressure washer, spray pump, chemical or acid sprayer, a brush and a watering can such as those used in a garden.
There are reasons for including or not including the optional equipment, which will be explained further below.
Protection is one of the most important aspects of preparing for an acid wash. Rubber boots, protective eye wear, and a respirator are necessities.
“I never go without some type of eyewear on,” Goodwin says. “I did in the beginning but I only made that mistake once. Just a little splash was all it took.”
Nielson wears coveralls similar to those worn by painters. “Some of them breath a little bit, and you can toss them when you’re done,” he says.
Inspecting the pool
Acid washing a pool requires that the vessel in question be drained. When the pool is mostly empty, professionals should check the walls and floor. “The surface of the pool determines how strong a mixture you want to put on the plaster,” says Luke Stoten, president of Down Under Pool Care in Chandler, Ariz.
Look for any flaws on the surface. These can range from cracks to the plaster being too thin to even take an acid wash.
Pros most often will find bulges or bubbles in the plaster, indicating that it’s separated from the shotcrete. When tapped, these bulges produce a hollow sound.
It’s best to avoid acid washing in the presence of any cracks, Nielson says.
If the customer insists, have them sign a disclosure agreement to protect against potential litigation. (Although he suggests having customers sign one for any acid wash in general.)
If any of these surface problems exist, it’s important to repair them or refer the customer to someone who can.
But there may be cases when an acid wash simply isn’t appropriate — specifically if the surface material is too thin. Goodwin prefers the plaster to be at least 3/8- or 1/2 inch thick. Otherwise a weaker solution should be used, if anything.
“You can lighten [the stain] but you can’t remove it,” he says. “If you try, you’ll eat so far into it that you’ll produce a weak spot in the surface.”
Attend to light fixtures if the pool has any. Goodwin recommends removing the fixtures and cleaning out the niches. He sprays them out with a hose or pressure washer, as it’s mostly loose dirt or algae.
“Algae and dirt get behind the niche,” Goodwin says. “If you don’t take [the light] out and clean behind it really good, once you fill it up, all that [dirt] will leak out of the light niche and you’ll have a streak down the bottom of the light.”
There may be minor differences in how service technicians perform acid washes but, as a whole, a standard and similar process plays out each time.
First, the pool is mostly drained, leaving about a foot or so of water in the deep end.
Next, technicians mix the solution — generally 50 percent acid and 50 percent water. When Goodwin is washing a pebble surface, he might cut the acid content down to 30 percent, since these surfaces may not withstand the substance as well as plaster. Because of the expense to replace this material, he tries to be very careful with it.
At this stage, technicians also have the option of adding products meant to whiten the plaster.
With that step finished, place the sump pump in the remaining pool water. During the acid-washing process, it should always be on and pumping out the water.
A pre-wash and scrub are recommended before starting with the acid, in order to remove as much gunk and material off the walls as possible, especially from algae-stained pools. Stoten sprays the walls with a hose, then scrubs with a pool brush.
“If you haven’t washed it down, you’re going to have to do two acid washes,” he says.
Before starting the wash, it’s a good idea to plug up any return lines so the acid doesn’t get caught in them and cycle back into the pool once it’s refilled.
When it’s time to do the actual acid wash, it’s best to start at the shallow end so the strong solution will run down to the water in the deep end.
Stairs require special attention, so Goodwin prefers to start there. “Steps or insets, seats... you’ve got to be careful, you’ve got a horizontal surface there,” he says. “You have to wash those off really quick, otherwise you’ve got acid eating into the steps and the turn.”
Technicians have options when it comes to the application method for the acid mix. It’s basically a matter of watering can versus sprayer.
Nielson swears by the sprayer. He likes the level of control it affords. “It [coats] evenly and you don’t have the concentrated acid flowing down in one area,” he says.
On the other hand, Goodwin uses a watering can to hold the solution and pour it on the walls. He believes that sprayers don’t hold up well in the long run, while the can does.
Stoten uses a watering can, as well. But to ensure consistency, he doesn’t let the acid rest. Instead, he uses a brush to scrub down the area that he just doused with the acid.
With the can, Goodwin usually washes one 5-foot section at a time. The sprayer allows for more coverage, so Nielson works in 8-foot sections.
Regardless of how the solution is applied, it’s important to thoroughly spray down the wall when finished, paying special attention to rinse the cove leading into the floor. Using the hose, direct the acid mix towards the bowl in the deep end. Goodwin recommends leaving the acid on the wall between 30 seconds and 1 minute. A second or third pass always can be done if the stain is too severe to vanish in a minute.
Throughout the process, it’s important to keep the plaster wet so it doesn’t crack or dry out. Nielson generally wets down the pool after he acid washes a section and repeats it for each new section.
As the process goes on, the water will build up with the acid concentrate. Some let this sit longer than others. Goodwin lets the deep end of pool sit with the incoming acid for about an hour so it can dissolve any stains.
Nielson moves directly to the next step — adding bicarbonate to dilute the acid and ensure that it doesn’t eat away the plaster. For most techs, adding in the bicarbonate is an eyeball test but Goodwin estimates that he uses between 2 and 3 pounds. Nielson admits that it depends on the size of the pool and how much acid is being used.
Once the shallow end is done and the walls of the deep end have been attended to, it’s time to bail the water out.
“Get all of the water out so that the color is even everywhere,” Nielson says.
Use a sump pump rather than a standard pool pump to send the water out. Goodwin recommends dumping the water in the clean-out at the front of the house.
If enough bicarbonate is used, the acid water should be diluted enough to enter the sewer system safely, he says. But be sure to follow local codes when it comes to disposing of the water.
At this stage, it is a good time to change out the main drain, if necessary. Goodwin also likes to bring in a wet vac to remove any dirt and sand in the drain.
“It’s like preparing a surface,” he says. “If you’re prepping a surface to paint and you don’t get all the dirt off, the end result will be poor.”
For an extra smooth finish, techs can sand the walls down after the wash. Nielsen allows the plaster to dry just enough so wet material doesn’t come off onto the sanding discs and clog them. He uses a power sander with 60- to 80 grit paper.
“It smooths everything out and seals the pores of the plaster,” he says. “It makes servicing the pool afterwards like night and day.”
This can actually help prevent stains in the future, he adds. Once the pores in the plaster get sealed, dirt and bacteria have a harder time settling into the walls.
“It ends up being better than new plaster because of how it seals up,” he says.