Why Acid Washing Is Bad For Your Pool
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Right away you might be confused about this article and the message I am giving you. Acid washing concrete pools is one of the most common service items that you can have done to your pool. They drain your pool, wash with a mildly diluted acid mixture and then refill the pool. The acid process strips away all of the off-colors and staining that are stuck in the plaster surface by etching the top layer of the pool surface. What I will say for sure is that this process works. The pool surface will absolutely look cleaner, fresher, newer and whiter than before. The only problem is that while the plaster looks good for this moment, the acid washing process actually worsens the situation which arrived you at needing acid washing in the first place.
Concrete swimming pool interior surfaces are intended to be smooth to the touch. When a skilled plaster finisher completes a pool finish it should be slick and smooth enough to wipe a tissue on without the tissue ripping apart. While this is how a concrete pool finish should be, not every pool plaster is finished this well. Some are rough they day they are installed. Others become rough with age while others age and fail prematurely from chemical damage. In any case if the plaster in your pool is not smooth then you are highly likely to develop problems with staining and algae as there are simply too many cracks and crevices for bacteria and plant matter to hide. even brushing the pool will fail to remove all of the growth on a rough surface. At this point many pool owners turn to acid washing services to clean the pool and make it look good again. The problem here is that acid washing makes pool surfaces rougher. So no matter how bad it is now, it will be worse after you acid wash it. This all but guarantees the algae and staining problems to return...likely worse next time.
Acid burns cement - When you apply acid to concrete (or mortar) the acid burns away some of the cement component on the surface. This then washes away leaving only the aggregate component left which leaves a rough, sandy feeling and texture to the surface. Acid washing mimics the natural erosion process of concrete where the cement layer washes away with passing water over time except the acid works immediately to erode years of life from the surface. Yes, you are reading that correctly. Acid washing concrete erodes years of life from the (should be) smooth surface finish.
Acid wash is commonly too concentrated - An acid wash process should be 90% elbow grease and 10% acid washing action. The inclination from service workers is to make acid washing solutions which are very strong. This will give the most bold stain lifting and surface whitening results, but it will also do so with minimum to zero scrubbing effort. As a concrete contractor everyone in the pool would be getting an earful from me in regards to ruining the concrete surface with aggressive acid treatments, to be sure. I hate acid washing because you have to (are supposed to) use a very diluted acid mix such that is essentially does not foam up at all. Or perhaps 1% foaming at most. The rest is all in the constant, heavy brushing with nylon acid brushes. You should be sweating and your arms feel like they are going to fall off after an acid wash of a pool surface. Rarely if ever will you see this. Usually you will see yellow acid-water pouring from a plastic watering jug, steaming and hissing as it streaks down the wall. This alone will strip any potential service life you had left from your pool plaster surface.
I love concrete pools and I can say a lot of good things about them. When it comes to rough pool surfaces and staining the actual answer here is that most likely your interior surface needs to be refinished. Many concrete pool owners go too long before refinishing the plaster simply because there is no obvious sign that the time is now due. The surface gets rougher slowly over time such that it is hard to notice for someone who uses the pool regularly. By the time the pool surface feels rough to the touch, 100 to 400 grit sandpaper commonly, this is when it is time to refinish your pool interior surface. They only last 7 to 10 years at most, and this presumes correct chemical maintenance throughout, which if I am honest, the majority of pool owners fail to do. So when your pool feels rough and starts to look faded, yellowed, or otherwise stained, save the money you would spend on an acid wash and instead get some estimates for a replaster or refinishing of your pool interior surface.
A note on color plaster finishes - If you have a color plaster finish which requires an acid wash to expose the colored aggregates then essentially you are accelerating the life of the plaster by a few years. Ignoring everything else, if you have brand new concrete (or mortar) and you pour acid on it, then you have ruined the finish of that concrete. The reason why it is done in pools is complicates, but simplified the problem is colored aggregates in plaster cost a lot of money, so people who pay for them want to see a beautiful, bold colored pool once the water fills up. However, new plaster will haze over and subdue the coloration to the tune of 80% or so, resulting in a blurry, blotchy white/grey finish with some hinting of colored aggregates underneath. If you left the pool like this the color would slowly reveal over two years or so, however that is a tough sell to a pool owner who paid big bucks for a colored finish. If it were my pool I would leave the haze and not acid wash to reveal the color, rather letting it happen naturally over time. When you acid wash, even a colored plaster reveal, you are stealing years of service life (and ultimately smoothness) from the plaster finish.
I hope this information leaves you more informed about acid washing and pool plaster interior surfaces so that you can make a more informed decision about what is right for your swimming pool. If you found this helpful you might also like this article: Common problems with concrete pools.
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Swimming Pool Steve is an award winning, second generation swimming pool and spa specialist from Ontario Canada. With over 10,000,000 views on the Swimming Pool Steve YouTube Channel, winner of the 2018 Pool & Spa Industry Leadership award and author of hundreds of pool and spa articles both online and in print Steve is committed to helping pool and spa owners as well as pool and spa industry workers learn more about the technical side of building, renovating, repairing and maintaining all types of swimming pools and spas. Follow Swimming Pool Steve on Facebook, Twitter and YouTube.
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