Slab surface moisture issue in existing building 6

[Arizona3106]

Moisture buildup between tile and concrete floor slab (Photo attached). Shallow water conditions are known to exist in the area. Perimeter french drain was installed over 4 feet deep, however, issue now noted in central portion of building. I believe it's due to head pressure after removal of a portion of the ridge for construction of the building. Raising or removal of the floor slab for an underfloor drain is not viable. Any solutions or seal methods you're aware of that actually work well? Not too excited about about surface seals I've seen before, but maybe I just didn't see good ones...Thought I read about possibly waterproofing the underside with polyurethane, but don't recall.

 

[r13]

Subsurface soils are typically medium dense to dense Clayey Sand with PI of 25-30

I don't think it is the case, but if this the soil under the slab, wouldn't be it cause problem?

 

[Arizona3106]

Foundation Plan may be useful (attached).

I should mention, the subsurface water here is not your typical groundwater table. It's more of a thin, perched aquifer that may be for example, located in a porous bed 6 feet below grade, prior to excavation of 0 to 10 feet.

As shown, top of concrete stems terminated at top of slab. Masonry walls above. That masonry/concrete interface is located at the problem elevation.

@Ron - That gradient testing of internal humidity is a great idea! How would you suggest the area be prepped to ensure results provide the desired info, i.e., is the issue from the bottom or the top?

 

[r13]

I wonder is there a standard detail for preparation of the construction joint shown on foundation type 1 to 3. If untreated, it could be where the water gets in. I suggest to walk the building, and mapping the findings. Then you maybe able to connect the dots.

 

[r13]

Below is a checklist of tasks that I would perform for troubleshooting.

1) Visual building inspection on building interior and exterior, and mapping damaged areas/spots.
2) Perform RH study on the slab per ASTM F2170.
3) Engage geotechnical engineer to categorize the backfill and determine water content.
4) Identify the source of ground water, through piping leakage testing, and groundwater/perched water probing.

Notes on RH probing:

Notes on water probing:

 

[oldestguy]

Water diviner here at an engineering site??? I've seen a few at work. Even I could find one, but when he is 30 feet wrong?? No need for mistakes here. We need a new rule here "you pay for space used". Only one post will come up. Ron's one sentence.

 

[r13]

OG,

Please provide/impart pertinent methods of geotechnical subsoil exploration to help. I do enjoy you and Ron's ideas most of the time. The diviner thing was highlighted by the author, I left it there just for fun. Maybe I would try one day to verify the accuracy. Isn't that an engineer way (hands on) other than sitting on theories and calculations only?!

 

[oldestguy]

I for one know better than to advise a geotech on this site with how to do it. He seems well qualified. Mater of fact he now only needs a suitable answer on how to run the moisture test. I'd refer to what ever Ron says, since he has done these before. I've done some, but do not consider myself to be an expert. Once that comes in the post can be deleted. You don't see me advising structural guys even though my minor at Cornell grad school was structures.

 

[r13]

You don't see me advising structural guys

I've read quite a few of your responses/comments. Why not, if you know the topic, and the tricks sometimes.

 

[oldestguy]

Simple answer. Seeing my responses hopefully don't rile folks and result in them generally then not respecting my knowledge. It only takes one "goof" to develop a reputation that follows on all other posts..

 

[Arizona3106]

@oldestguy - Thank you for your insights!

@retired13 - Really appreciate the summary info on RH testing, visual survey, & damage mapping

@Ron - Would appreciate any suggestions you have on RH testing, based on the previous ones you've done, and that we only have a 4in slab. Never used it before, but is sounds like what I need to get done.
Will get a copy of F2170. I'm guessing one would remove areas of flooring & adhesive first in test zones. Would this likely require surface grinding/chipping to allow slab to reach equilibrium?. Wait at least 24hrs before drilling test hole & testing?

 

[r13]

Arizona,

Suggest to explore a few articles on this webpage to get the basic on RH testing, Link.