Acid washing pool surfaces that have succumbed to staining over a long winter is among the most common and lucrative services typically offered in the spring.
While it is labor intensive and time consuming, it is also a good source of profit for service professionals who don’t mind using a little elbow grease. According to our 2021 Service Industry News Survey, pool technicians charge an average price of about $625 to perform an acid wash.
The results can be astonishing, too. But while acid washing can dramatically improve the appearance of some plaster surfaces, it is a good idea to discuss customer expectations about the finished product prior to doing the job.
The hope, of course, is to return to plaster to its original state, but acid washing is not always the miracle cure that the customer might get. Furthermore, not all pools should be acid washed for a variety of reasons. It isn’t recommended for older pools, for example, because acid washing strips away some of the plaster.
If the life of the plaster is nearly up, it may be a better idea to recommend resurfacing. Technicians can examine the surface for blistering, which could be an indication that the plaster is separating and must also be refinished.
For pool plaster is more than eight years old, the plaster could chip when it dries, which should be explained to the customer. Furthermore, it’s essential to think about the water table where the pool is located because hydrostatic pressure from underground water could cause the shell to pop of the ground.
Be sure to explain a reasonable expectation of what the what the process may achieve because aside from these risks, there are discolorations and defects that acid washing can’t help. Trowel marks, water marks, or uneven surfaces won’t be improved through acid washing.
It is a good idea to arrive with the National Plasterer’s Council “Pool and Interior Finish Disclosure,” which specifies that plaster has color variation by its nature, and this should not be viewed as a defect. This is available online on their website under the “Library” tab.
Keeping all this in mind, acid washing frequently does effect some miraculous changes to the pool’s appearance and can remove stains caused by calcium deposits and algae.
Service technicians should take great care when doing the work, however, because it involves using a caustic chemical and it must be handled carefully. Use protective equipment, including rubber boots gloves, suit, goggles, and a gas mask respirator. Don’t work alone, and be sure that there is always plenty of ventilation.
These safety precautions really can’t be overstated. There are service techs who perform acid washes without goggles or a respirator, and while barefoot, but the cumulative effect of inhaling acid fumes, exposure to the skin, and effect of fumes on the eyes can’t be measured. Moreover, if the wind shifts, it could send a plume of fumes your way, leaving you choking. And – if any chlorine residual remains in the plaster — it will react with the acid to form chlorine gas, which is lethal.
Remember to always add acid to water and never the reverse or an explosion could result.
Beyond personal safety, service professionals should also consider the integrity of the pool finish and avoid using too concentrated an acid solution, which could damage the surface.
Furthermore, use plastic or wooden utensils for mixing and keep it away from metals. Whenever possible, remove all metal pool equipment, and if any metal fixtures have come into contact with the solution, they should be immediately rinsed with plenty of water.
A hose should be kept running throughout the procedure. Hose off the deck and keep it wet throughout to prevent inadvertent staining or spills. Remember to hose off your boots every time you exit, too, because they also carry acid.
After the solution has been mixed, it should be kept away from decks, coping, and landscaping, which could be damaged. Service professionals generally use muriatic acid for acid washing. This acid is usually packaged in a 20° Baume strength, or a 32% dilution of hydrochloric acid. For acid washing, experts recommend a weak to medium strength concentration of from 3 to 10%. The 10% solution may etch a bit of the plaster, however. To obtain a 4% solution, mix 1 gallon of 32% muriatic acid with 4 gallons of water. For a 10% solution, mix 2.5 gallons of 32% muriatic acid with 2.5 gallons of water. Remember to always add acid to water and never the reverse.
Wearing personal protection gear, work with a partner in sections, taking all precautions to avoid splashing. Beginning in one section, one partner should apply the solution to the surface with a plastic garden can or sprayer, while the other partner scrubs the area with a non-metal brush. The partners should work quickly together, with one scrubbing vigorously while the other follows with the hose to prevent streaking.
Soda ash, sodium carbonate, should be poured where areas of waste water accumulation to neutralize the water.
The acid should not be allowed to dry on the pool surface because it will damage the surface. Each section should be finished before moving on to the next section. Stubborn stains will sometimes require multiple applications, but take care not to over apply the acid, and be aware that not all stains can be removed.
A solution of soda ash, mixed in water, is then used to wash the entire pool shell, which will neutralize any acid remaining on the surface and raise the pH of the waste water to acceptable levels. Finally, rinse all of the surfaces with plenty of water.
A sump pump should be placed at the bottom of the deep end to remove the standing water there, which will leave marks on the pool floor if allowed to stay there.
Test the waste water left in the pool to determine its pH. If the pH is less than 2.0, the solution should be removed to plastic drums and disposed of at a hazardous waste facility. If the pH is less than 5.4, soda ash can be added to neutralize to an acceptable level of between 6 and 8. In addition to these general instructions, there are a few extra facts and tips that may help to improve the job:
• Acid additives are available that can help to improve the acid’s performance. These are thickening agents that allow hold the acid to the wall a little longer for better penetration. This can help with streaking problems as well. They also promise to cut down on fumes to make the job less unpleasant.
• Commercial quality brushes are available with curves to help get into edges and steps.
• It takes 40 pounds of soda ash to neutralize 5 gallons of muriatic acid.
• If the pool has an exceptional calcium content, experts recommend giving the pool an acid soak before the acid wash. Add one gallon of acid per 1,000 gallons of water about 10 days prior to the planned acid wash. Take care not to use the equipment during this period because the low pH involved will damage it. Also, plug skimmer and return lines if there is copper plumbing.
• Limit the amount of time that the pool is empty. Drain the pool the day before the work is to be done.
Do not allow pool to remain empty for longer than 5 days.
• After draining, review the quality of the plaster with the customer, pointing out any defects or new problems. Provide them with reasonable expectations.
• Drain pool water to a legal and appropriate location.
• Don’t work alone. It is not only unsafe, but a two-person team has much better control over the acid, brushes, and hose.
• When the wash is complete, the team should review the surface to determine if another wash or a higher concentration wash is in order.
•Any roughened areas or remaining rust stains can be smoothed or removed by sanding with wet-dry paper.
• After the acid wash procedure is finished, refill the pool as quickly as possible. As with newly plastered pools, do not stop filling until the water reaches halfway up the skimmer. Stopping water flow can cause a ring around the plaster.
• Ensure that there is a responsible party present to stop the water flow when the filling is complete. Fill water left unattended can flood homes and cause other calamities.