Acid Wash

The acid wash process is a part of the complete Pebble-Tec installation process, but it occurs on the day after the Pebble-Tec is applied to allow the Pebble-Tec to dry and cure.  The Pebble-Tec is not fully cured at this stage (it will naturally cure under water after the pool is filled), but it doesn't have to be for the acid washing to take place.

The purpose of the acid washing is to remove the "haze" or the cement film and grit that has dried on top of the pebble aggregate from the day before.  While the pressure washing from the water wands has removed much of the surface cement, there is still a fine layer that is left behind.  It must be removed before you can see the natural color of the pebble show through.  Washing the entire surface of the pool in acid is the easiest and best way to achieve that.

February 3, 2002 - 11:42am
For the washing, standard Muriatic Acid is used to create the washing "brew."  I was told that it was not full strength Muriatic Acid in the orange bottles.  About 6 gallons of this diluted acid was used for the pool then an additional gallon for the spa.  Other than the acid, a submersible sump pump is used to apply the bath and some other simple tools (i.e. stiff nylon brush and flat hand trowel) will be used to clean the surface of loose pebbles and to brush away stubborn cement stains on the pebble.

Pre-soaking
The pool and spa are pre-soaked with water to loosen the cement haze on the surface.  Also, a small pool of water will be used at the bottom of the pool to create a diluted acid brew from which the sump pump will draw from to bathe the rest of the pool.

Creating the Acid Bath
Here you see the bottles of diluted Muriatic Acid being dumped into the small puddle of water that has collected on the bottom of the pool.  As soon as the acid hits the pool, thick acid fumes visibly rise into the air. 

SSSSsssss
Its hard to see from these pictures (even in the enlargements), but as soon as the acid touches the walls of the pool, I begin to hear loud hissing shrieks from the wall as heavy acid vapors start ascending from the pool.  Man, I heard Muriatic Acid was killer stuff, but now I've _seen_ it and _heard_ it for myself.  The interesting thing is that the guy doing the acid washing is not even using gloves.  He does this for a living, so I'm wondering one of two things must be true: 1) either people are lying about the effects of Muriatic Acid on humans or 2) this guy will be dead in a few weeks.  One or the other.

The vapors that are created as the acid washes from the walls is amazing.  I try my best to keep away from the smell of it, but even from where I'm standing at the far end of the pool taking pictures, I can definitely smell the acid in the air.  I looked down at the bottom of the pool and noticed that the acid solution has now turned a dark color - almost completely black.

After the acid washes from the Pebble-Tec, I distinctly notice that the Pebble-Tec colors are now much more darker, saturated, and vibrant.  It looks like the acid is really doing a number on the slurry.

This isn't normally included in the acid washing, but I talked the sub into acid washing my waterfalls for me.  He was very gracious in offering to do that at no extra charge.  You can see him making a pass through the waterfall, then on to the rolled beam, then back over to the bench area under the waterfall.  After acid washing the waterfall, I noticed that the Pebble-Tec near the waterfall was stained with a dark color.  It turned out that the pigment/dye that the waterfall sub used on the waterfall rocks started running a little and washed down onto the Pebble-Tec.  It wasn't a problem.  The dye could be rinsed away.

Final Rinse
After coating the entire surface of the pool in the acid brew, another pass was made using water to wash off the remnants of the acid on the walls.

After a good rinsing, each area of the pool is then scraped using a flat trowel tool.  This removes any loose pebbles from the walls.  This is necessary so that sand filter and filter pump baskets don't fill up with pebbles after starting up the pool.  Also, a stiff nylon brush is used to go over "hazy" areas that the acid either missed or didn't have much of an effect on.

The next set of pictures show the effects of the acid on the Pebble-Tec.  In the first picture below, I captured a picture near the spa where some acid accidentally spilled onto.  You can see the contrast between the area of the spa wall where the acid came into contact with.  The natural colors of the pebbles have been exposed once the cement film/haze has been burned away.  In contrast, the area of Pebble-Tec next to it that hasn't been acid washed yet, still has a grayish haze covering it up, giving it a very white chalky color.  The next couple of pictures show what the surface of the Pebble-Tec looks like after being acid washed, rinsed, scraped, and brushed.

Spa
After finishing with the pool, the sub moves over to the spa to do the same thing.  He pre-soaks the spa, then creates the acid brew at the bottom of the spa.  With the excess acid that he has, he starts to wash down the walls of the spa.  After thoroughly bathing it in acid, he rinses off the excess acid, then trowels and brushes the surface clean.

Here are some shots of the final pool surface after completing the acid wash.  You can see that a lot more of the natural brown/beige/tan colors of the pebbles have now been exposed.

Drain Covers and Lights
The last remaining activity is to put the drain covers on the main drains in both the pool and spa and the covers for the Therapy Jet and Waterfall suction pipes.

Also, the pool and spa lights that were taken out of the wells yesterday during the Pebble-Tec application phase are now returned and secured in place.

Also, the water from the Slurry Pit is now released as the cement has had ample time to settle and collect at the bottom of the pit.  You can see the solid cement collected at the bottom which is close to being rock hard.  The sub will wait a few more days for the slurry to completely harden before return to dismantle the box and dispose of the slurry.

Starting the fill water
Typically what happens right after the acid wash portion of a Pebble-Tec application has been completed is that the sub will start to fill the water in the pool immediately.  Pebble-Tec is designed to cure under water, so the pool fill is started usually before the interior sub leaves.  When I looked at the bottom of the pool, I noticed that there must have been several hundred gallons of water at the bottom.  It was pretty filthy.  I was hoping to accurately measure the amount of water going into the pool when I filled it so that I could keep it for future reference (when adding chemicals to the pool).  But with an appreciable amount of water already in there, I knew that the measurement would be somewhat skewed.  I asked the sub if I could stop the water for now and restart it in a few hours.  This would give me time to run to Home Depot to get a submersible sump pump, pump out the dirty water first, then restart from an empty state, allowing me to accurately measure what the gallonage of the pool and spa were.  He hesitated and said that if the pool is not filled evenly, that I would have to accept the risk and responsibility of having water rings develop on the sides of the Pebble-Tec.  I told him I would accept that risk and quickly made an exit to head over to Home Depot ...

Problems with the Pebble Interior Phase / Things I would have done differently:

• This was not an issue with the Interior phase, but I wished that I knew that the Pebble-Tec application more or less follows the existing contours of the Shotcrete.  I didn't realize this when the Shotcrete guys were shooting the pool shell.  I had really liked the exaggerated rounded "hump" on the rolled beams on other pools I had seen, but for some reason Fisher Shotcrete creates their rolled beams more flat looking.  I had asked the Interior guys if they could compensate for that by building up the middle of the rolled beam up a little more to give it a more rounded/circular shape.  They didn't want to do that because Pebble-Tec is not a structural material to begin with.  When it is applied on thicker than what the manufacturer recommends, it could lead to cracking issues.  I had thought about calling back the Shotcrete people to build up the hump a little, but they said that putting new concrete on top of dry existing concrete will create a stress point at the joint/seam between old and new and would also create a cracking issue.