Gunite pool leaking......? best repair for Gunite cracks

[etbrown4]

I have a large 10 yr old gunite pool which has been leaking for some time, however with the moderate earthquake in Va last year, it has been leaking more. About 2-3" overnight. Leaking stops about 6" below the normal water level.
All of the skimmer and return lines have been pressure tested. No leaks found at main drain, pool light, or in or around skimmer boxes. There is no equalizing valve.

At this point we're down to 6-7 vertical hairline cracks in the sidewalls at various places. They are so fine you can't get a fingernail to catch. The cracks start about 4" from the normal water height and are 12-20" in length.

If we have covered all usual potential leaks, we're just left to wonder about those cracks, and can imagine that at least in theory, they could be leaking that much.

No doubt the gunite is covered by some kind of plaster. Nominally this is a black pool. Actually it's a dark grey. Close inspection of the covering shows lots of small gray granules packed tightly but smoothly together. Some may call this a 'quartz' finish.

If others think that amount of leaking from these cracks is possible, what's the best repair process to follow which will not be unsightly?

Thanks for any tips!

 

[Bones]

first you need to identify the leaks,
pool-school/leak_detection
http://www.youtube.com/watch?v=2-ULevdy ... redirect=1

Then go from there

 

[etbrown4]

It's a fine video. Thankfully we're up to speed on dye testing. :-D

In this case the water level is down 30" for the winter.

I'm going to repair the cracks as if they are all leakers and then in a few weeks, we'll add water and do the dye test then!

I've read that some pros like Vulkem 116. ? any good for this repair? how about silicone?

Any tips on the best sealant would be great!

 

[swimcmp]

Get a light cord plug also not likely but possible that the light is your leak as you say it is down about 30" this winter

 

[257WbyMag]

When a gunite pool leaks, it is rarely the shell itself. It is almost always a light niche or plumbing connection.

 

[etbrown4]

That's a great suggestion and certainly worth trying. Last summer we did dye test the light, but things can change.

If all else fails we may try a gray masonry calk. Just something to seal, that won't look too bad while we are seeing what else it might be.

Any other ideas on the temp patching of the hairline cracks is appreciated. For now, they are so thin, I hate to cut them out.

 

[duraleigh]

Emphasizing what 257 just posted, it is pretty unusual for the shell to leak....especially if the cracks are hairline. Cracked skimmers, light niches, or other penetrations of the shell are the normal causes.

 

[etbrown4]

OP here, I appreciate the suggestions!

I put a similar post on another pool forum and I have two well meaning pool 'pros' jumping all over me saying that since all the piping pressure and skimmer tests so far are negative - then they say it just has to be bad foundation walls, and potentially a $40,000 job! They've painted all kinds of pictures of potentially exposed rebar - you name it!

With them, the pool is practically condemned, even though these are true hairline cracks from 12-20" long, that you can't even catch a fingernail on! Yet they've said call in the geotech and structural engineers now!

I told these over anxious guys that once I temporarily calk the cracks and refill the pool in a few weeks, I'll dye test all cracks and see if any of them represents a leak. Right now, I figure they could all leak, or maybe none leak.....so we shall see!

My experience with many pools is you need to look everywhere, and never assume you've found your only leak until you prove it's reliably holding water. I don't know if it's a minor problem or serious one, but for sure I won't call in the engineers till all else fails.

 

[duraleigh]

Leaking stops about 6" below the normal water level.

If that stays consistent, that is a major clue as to the source. Let us know what you find....Good Luck!

 

[et]

Thanks for the comment Dave.

I'd agree that it means the leak is very likely to be, at or above the 6" mark.

My focus now will be:
1. dye testing the skimmers again, and especially the flange at the front opening to the pool
2. dye testing the tile around the full perimeter (that will take forever as it's 116' around)
3. dye testing the sidewall cracks after carefully calking them
4. double checking the light even though its down at about 15" below the surface (and unlikely)

Any other ideas?

 

[swimcmp]

If the conduit going to the light is leaking the water will go to that level. I had a new commercial pool that the deck guys cut the conduit didn't tell anyone poured the deck after "fixing" it then I caught h*** for the pool not holding water. Took me several trips to find it since there wasn"t any penetrations at the water line. Finally bought cord plugs and that stopped the loss.

 

[BigSwede52]

Since the cracks start about 4" below the normal water line and then run for a foot or so downward, am I correct in assuming that the cracks do not extend through the waterline tile band and into the coping? Being as small as they are, it may be difficult to see in the mortar joints near the top of the pool. If they DO do to the top of the pool, the earthquake could have opened a small series of cracks. Are there any corresponding cracks in the deck at or near the pool cracks? If you are losing 2-3" overnight that is certainly enough that you should be able to find the exit with a leak test. The other possibility is that the ground shake cracked a piece of PVC pipe ... but you have pressure tested ALL the circulation (not just outlet) pipes , right? If the vertical cracks turn out to be the culprit, you can epoxy inject them with a crack repair material - use the low viscosity epoxy. As a last resort, you could rent a small auger and bore holes at a few spots around the pool deck perimeter to see if the ground is unusually wet at one area outside the pool. That might give you a clue where the leak(s) is located. How deep are your return inlets? Or anything else that is about the depth were your water level stops dropping?