Join 3,430 readers in helping fund MetaFilter (Hide)


Dry swimming pool?
March 7, 2012 9:54 AM   Subscribe

Will leaving a swimming pool dry damage it?

We are considering buying a house to be rented to university students. The house seems ideal, except it has an in-ground swimming pool (assume Gunnite). For various reasons, we are reluctant to leave the pool available to the renters. We can cover it satisfactorily and inexpensively with decking. However we're a bit worried that leaving the pool dry over a long period will damage it. Cracks? Filter apparatus? Anybody know? Oh...we live in Texas so we have long hot summers and only occasional freezing weather in the winter.
posted by txmon to Home & Garden (10 answers total) 1 user marked this as a favorite
 
Has it ever been dry before for an extended period of time? My concern would be that, if you ever got a lot of rain at once and the ground got saturated, the pool might want to float upward out of the ground.
posted by Danf at 9:58 AM on March 7, 2012 [3 favorites]


Assuming there's plaster on top of the concrete, plaster will crack if it's dry and the temps are above 80 degrees.
posted by TungstenChef at 10:03 AM on March 7, 2012


pools are designed to have water in them, obviously, but the weight of the water is part of the strength of the gunnite walls. That make sense? picture a flimsy paper cup vs. a flimsy paper cup full of water. Also, the surface of the pool itself will degrade. Things i learned from almost buying a house with a long empty pool.
posted by th3ph17 at 10:16 AM on March 7, 2012 [3 favorites]


How high is the water table? If the water table rises above the deepest part of the pool, the pool will act like a boat, and float up on the water table.

In Florida, if a pool is empty for just a week or so, the pool will rise out of the ground an inch or so in that time. And once the pool rises out of the ground, it is finished.
posted by Flood at 10:24 AM on March 7, 2012 [2 favorites]


Like Flood says, the pool can rise up out of the ground. Even if it's not noticeable to the naked eye, it can break the beam and cause leaking.
posted by PorcineWithMe at 10:30 AM on March 7, 2012


I used to work for a water hauling company (here in central Texas) and we would regularly fill swimming pools. When a new pool was put in we actually had to fill it while the plaster was still wet otherwise it would crack.

We filled one guy's pool twice, once because it was empty and he wanted to have a useful swimming pool and then again after he found out it was full of cracks from sitting too long empty and got the pool resurfaced. (Yes we warned him that could happen before filling it the first time but he "didn't see any cracks" so we filled it).
posted by magnetsphere at 10:37 AM on March 7, 2012


QFT: pools are designed to have water in them, obviously, but the weight of the water is part of the strength of the gunnite walls. That make sense? picture a flimsy paper cup vs. a flimsy paper cup full of water. Also, the surface of the pool itself will degrade. Things i learned from almost buying a house with a long empty pool.

The structural integrity of an in-ground pool requires that it be kept full with water all the time. Leaving it empty will damage it beyond repair.
posted by three blind mice at 12:15 PM on March 7, 2012


Nth-ing that a pool can rise/float if left empty. At the pool complex I worked at during high school, our pools were very well built and the concrete shell and interior plaster were quite strong. We would actually carry several large and heavy metal picnic tables into the pools to help weigh them down during our annual drain & powerwash cycle, which only lasted a week. For the outdoor pools during winter, we left them about 1/2 full of water (with a good amount of bacterial/algal/fungal growth inhibitors) so there was at least something keeping them from floating.

If your pool can withstand the individual pressure points of heavy objects, this plus keeping it 1/3 to 1/2 full could help prevent it from floating if the water table rises.

If you plan on leaving it unused long-term, you should also get the entire system (inlets, outlets, filter system) properly winterized and sealed before you partially refill the pool and make it inaccessible. This will protect against cracked pipes in freezing temperatures, as well as mold, mildew, and algae growth from leftover moisture.

Make sure that whatever method you use to cover the pool (decking, etc) is as tamper-proof as possible, and hopefully done in such a way that water can't seep or leak back into the pool. You wouldn't want it getting full and overflowing, and adding more water would dilute your anti-growth additives to the point they may not inhibit bacteria, algae, or fungal growth.

Finally - you should probably check local ordinances regarding dry pools to see if there are any rules or regs about how to properly secure them. Also check with your insurance company to see what they would require of you to treat the property as if it had no pool. Your simple decking idea, if easily removable, could still raise your premiums (and your liability) if the insurance decides the pool was still "accessible" to your tenants.
posted by trivia genius at 12:24 PM on March 7, 2012


Nthing everything above. Though I might disagree slightly with some of what trivia genius said simply because an average in-ground pool can easily be 30,000 gallons * 8lbs/gallon = about 120 tons. No disrespect to what you did in HS, but I'd be amazed if the tables did a whole lot beyond peace of mind.

Without water-table issues, an empty pool should be good for a few days. It generally takes a couple of days to replace a liner (for a non-gunnite pool, but usually they have a concrete tub that is lined with padding on the sides and sand on the bottom).
posted by aloiv2 at 5:59 PM on March 7, 2012


Also, I knew plenty of students in my university days who would see the decking you put over the pool as a challenge to be overcome. As in undergrads who want a party house and think how much more sweeeeeeeeeeet it would be to have a party house with a pool. On a year lease, they've got plenty of time to restore the decking before their move-out inspection.
posted by bendy at 6:56 PM on March 7, 2012 [1 favorite]


« Older So, you know how Hollywood som...   |  Engine braking with a cold eng... Newer »
This thread is closed to new comments.