Conundrum regarding rust stain in 3yr old plaster pool

[MattM]

Hello,

Our pool was built ~3yrs ago and the builders comprehensive warranty for any issues is about to run out. Over the last six months we noticed a rust stain developing on a deep end wall nearest to a backyard hill. We've worried for awhile that there might be a water seepage issue with this wall, as after construction it took well over a year for the tile grout to completely dry and the grout had to be applied 3 times. There was also a leak in the deep end plaster that required significant patching.

We had the pool builder come out to look at the stain and they confirmed that it was a rust stain extending all the way from the initial foundation rebar. They are hoping that it is a just a small issue. But, I'm worried that we may just be seeing the tip of the iceberg with regard to water near the hill wall causing more stains in the future. I've asked the pool builder to inspect the status of rebar when they open up the wall to fix and replaster that section.

Unfortunately, the pool builder states that they need to completely drain the pool in order to patch the stain. We do have a hydrostatic valve in the pool, but it has never been tested to my knowledge and I'm wondering what the risk of the pool popping up is...The builder has stated they will not be responsible if the pool pops up during work. That doesn't make sense to me as they are the original builder and are fixing an original construction defect.

The pool is 34'x16' and takes up most of the space in the backyard. The builder provided only 2ft of clearance from the retaining hill wall. Standard code in our area is 3ft but they said that was not necessary...was this a big mistake?

What would you all advise? Any suggests are much appreciated.

 

[Swampwoman]

I can't speak to the specifics of your build, but I have a vinyl pool in a small footprint with a terraced hill and pump below the deep end. On ours, there is a drainage around the perimeter that connects with the French drains from the property, covered with larger stone at the edge of our cement. I don't know if a perimeter drain is an option for you, but I suspect it might help you ultimately manage storm runoff. You should also consider using the pump whenever you have more than six inches of rain over a few days...that helps relieve any hydrostatic pressure building up.

So if they go to repair it and it looks like a more extensive problem, you might want to ask him about building a drainage perimeter. Hopefully, you won't have to go that route...but I'm glad the original builder of ours did

 

[Divin Dave]

Hi,
The rust stain is an all too common problem. What probably happen is the rebar in that area is too near or at the surface of the gunite and not covered sufficiently to preven corrosion.

Draining the pool and chipping into the shell as you described is the right way to fix it.

About the hydrostatic valve.
If its a manual plug type, it should be opened before more than about 1/2 of all the water is drained. If there is ground water under under the pool, it will flow into the pool and you'll be able to see it.

Some valves are just a plug type, where you physically remove a plug. Some are springloaded and will automatically open when the pressure under the pool is greater than the pressure in the pool.

Either way, the likelihood of it not working is rather small I think.

Of course for consideration of the risk is the level of your water table. If you dont have a high ground water to begin with, then the risk is much lower. If it has been raining a lot, then the the ground water may be higher.

 

[JamesW]

All hydrostatic relief valves (hydrostats) open automatically.

Hydrostats can only let in a limited amount of water per minute. If the pool is pumped out faster than the hydrostat can allow ground water in, the pool can still be at risk if the ground water ends up higher than the water in the pool.

I would be concerned that the builder doesn't want to take responsibility for the stability of the pool during the time that the pool will be drained.

If I remember correctly, ground water has been an issue from the beginning. I think that it's important to actively manage the water table to help ensure the safety of the pool.

 

[TreeFiter]

One question that comes to my mind is did they install a Brodie Valve? A brodie valve is basically a check valve that gets installed underneath the pool, and is connected to a pipe that goes to the surface. The purpose of this line is to allow you to pump out the water underneath the pool if necessary. Usually they are not connected to anything. Just a pipe that daylights and is usually capped off. When the time comes, you can hook it up to a pump and suck out the water.

 

[Swampwoman]

^actally, on mine, its connected to the pump itself, where you just reverse it to pump off any built up water in the sump.

If you PB knew water table was an issue, I'd think that would be the way he built yours. Can you confirm if yours works that way?

 

[MattM]

I can't speak to the specifics of your build, but I have a vinyl pool in a small footprint with a terraced hill and pump below the deep end. On ours, there is a drainage around the perimeter that connects with the French drains from the property

We have a basin for water removed from the pool cover, and various drains drilled in the deck floor to keep the pool from overflowing when there is rain..but as far as I know nothing for groundwater or any associated pump. Thanks for the idea..I hadn't heard about that before.

I'm forwarding questions to the pool company and contacting the home insurance today to see what their take is...I'm not sure what/if anything of the pool would be covered if it popped during repair. The pool is included as an additional structure in our insurance.

 

[MattM]

I sent an inquiry to our pool company regarding whether they installed a brodie valve and if the hydrostatic valve was automatic or if there was a way to test it before completely draining the pool.

 

[JamesW]

The hydrostat is an extra safety measure. I don't think that it should be relied upon to keep the pool from floating. All hydrostats are basically check valves that open when the water pressure under the pool is greater than the water pressure at the bottom of the deep end. This allows ground water to flow into the pool. It's the same idea as putting a hole in a boat to make it sink or to prevent it from floating.

From what I can remember, the build did not include a well point for pumping out ground water. That is part of the reason for some of the early issues related the ground water causing defects in the plaster.

I would ask the builder what needs to be done to make sure that the pool does not float.

I think that a well-point could be worthwhile and would give you a good idea about how much ground water there is.

I wouldn't feel comfortable with someone draining the pool who won't take responsibility for making sure that it won't float.

The only real way to check the hydrostat is to have someone dive and check to see if it's opening and allowing water in. A diver could see if the valve opens easily which would indicate that the pressure under the pool is getting close to equal with the pressure in the pool.

The diver would have to check multiple times as the water in the pool gets lower and lower.