Pool Concrete Deck Large Cracks Expanding

[rolodoc]

I bought a house in Bay Area, CA 1 year ago with a pool. The concrete deck had small cracks that I didn't really pay attention to at first. In the past 2 months, the cracks have expanded significantly with smaller cracks appearing weekly. The worst area is in the close-up picture, where the outer concrete sunk 1/4 inch. The pool itself has no visible crack. I am new to owning a pool but realize this is a serious issue. I would appreciate any advice on 1. Cause of this; 2. How urgent is this; 3. How to proceed on repairs; 4. Estimated cost to repair?
Thanks.

 

[duraleigh]

The substrate was not compacted properly before the concrete was poured. Now it is settling and causing the concrete to crack.

Unfortunately, there is nothing you can do except to plug the cracks with polyurethane caulk.

In some areas of the country, they "jack up" settled concrete and that might make a difference but you can never hide that crack.....perhaps get the deck back level and stop further settling.

 

[Bluegrassman]

After jacking up/leveling concrete, and filling the crack, couldn't one use a solid sealer to hide the damage? I know this would negate the intent of the aggregate, but might look better. Or maybe only seal a straight line, then stain faux bricks through just that area and do other opposite corners the same way to match?

 

[rolodoc]

Thanks for the response. This pool is probably 20 years or older so why did the cracks suddenly accelerate in severity and spreading rapidly across multiple concrete panels in the last month? I see some erosion of soil under the edge of the concrete deck but that was probably present for years. I am concerned about the structural integrity of the concrete deck and if this will affect the pool also. I want to fix this economically because we'll move in a few years but still need to level the deck and prevent future damage. How do I refill the substrate and "jack" up to level without replacing the concrete?

 

[duraleigh]

How do I refill the substrate and "jack" up to level without replacing the concrete?

Call a professional...it is not a DIY job and it may be pricier than you want to deal with.

 

[257WbyMag]

Foundation repair companies would be where to start looking. They do mud jacking and similar type repairs.

 

[rolodoc]

An update on my situation: I had contractors look at this and determined that the problem is soil erosion under the concrete deck and the backyard being downslope. The clay type expansive soil eroded down the slope over time from rain water/pool leak and created voids under the concrete, which gradually cracked and sunk. The suggested solution from several contractors is to build a retaining wall at the downslope area (next to the spa), then replace the cracked concrete. Mud jacking is not an option for me.

I hired a structural engineer to design the retaining wall. The construction drawings says to empty the pool because the soil around one end of the pool will be excavated for the retaining wall. My concern is will the pool be damaged if it is empty for 2 weeks during this construction? Or can we leave the pool filled with water if soil is excavated 6 feet deep and there is little soil supporting the pool on one end? It is a gunite pool.

 

[CraigMW]

The major concern with having an empty pool would be hydrostatic pressure from a high water table. On a slope like your pool is situated near, the chances for a high water table are quite low as any ground water would run off from the surface of the slope. I wouldn't lose any sleep over this. Incidentally, my parents had a similar problem with their pool, as it was built on the top of the slope near a ravine. They replaced the deck a couple of times and finally decided to build a series of retaining walls. After that, the problems with subsidence seemed to abate. So, I think your engineer is giving you good advice. You might want to let the retaining wall do its work for some time to see that the subsidence has stopped before doing any repair/replacement on the deck though.

 

[rolodoc]

It hasn't rained for 5 months so the water table is likely quite low. The concrete deck needs to be removed for the excavation, so it has to be replaced anyway.
What about damage to the plaster if the pool is empty for 2 weeks? Looking at the construction drawing above on where the retaining wall will be, can we keep the pool water filled without much soil around the pool supporting that weight?

 

[duraleigh]

can we keep the pool water filled without much soil around the pool supporting that weigh

The answer is "probably". Why not go ahead and partially drain it anyway?

You don't say where you live but I can't imagine your climate being harsh enough this time of year to damage the plaster. If you are subject to really drying conditions, you could even wet the surface down a couple of times daily for some insurance.

 

[rolodoc]

I am in the SF Bay Area in San Mateo county. In October temperature reach the 70s. The suggestions sound like I should empty the pool during construction and the plaster should be ok if I wet the surface down daily.

 

[duraleigh]

The suggestions sound like I should empty the pool during construction and the plaster should be ok if I wet the surface down daily.

Yeah, I am not a plaster expert but that makes sense. You probably don't evgen have to spray it down with those temps but it sure won't hurt. Perhaps "On Balance" will be able to opine.

 

[Just-a-PB]

I would get the opinion of a local plaster company.
When plaster is dry it shrinks, and cracks.