Is it acceptable to have a patio built on limestone screening only ?

[MiniMe4Eng]

Hi guys

I am having problems with a wet all.
Here is a high level view of the layout:

In this picture you can see the problems that I am having

And now the story, as much as I can undestand it.
The house is a bungalow built between 1955 and 1962.
The soil is pretty close to clay (let' say 80% clay, 20% sand)
The patio was incorrectly sloped and the water was accumulating next to the corner with problems.
The basement is a finished basement and I do not have access to the foundation walls.
I think that they are made of concrete up to the soil level and for there the builder used cinder blocks up to the level of the main floor.
The basement has a slight wet smell and I think that that gets to us because the ceiling is open in the furnance room.
I checked the basement at floor level, just below the corner showed in the picture and there is no smell there. It does not smell wet if you remove the power plug plate and you sniff the air trapped behind the vapour barrier, drywall and insulation.
When the weather is dry or during a winter with low temperatures the smell disappears completely. This wouldn't be the case if the source of water would be underground.

I decided to fix the slope of the patio by removing the bricks and by adding more limestone screening
We also wanted to see if there is moisture at the base of the wall so we dug there along the house wall to see how the patio was built
To our surprise we learned that there is no gravel sub base, just a weed barrier laid over the subgrade excavation and around 6" of limestone screening with some 1/4" gravel traces mixed in.

We added more limestone screening, we compacted, we added more limestone screening again and we sloped the bedding using a screening board.
As we were preparing the bricks to put them back we noticed that the newly laid limestone screening started to get wet.
We had to stop and we hopped to resume next day
Next day it rained and the bedding got wet so bad that it became almost solid (I guess the water accumulation made it look like that)
I decided that it is not safe to put the bricks back and I am now waiting for the limestone screening bedding/subbase to get dry or at least with a decent percentage of moisture

A couple of questions if I may:
1) is it normal to build a patio the way my patio was built? That is with a 6" of limestone screening and bedding in an all in one layer?
2) is there anything that I can do to improve the drainage of this patio?
3) let's assume that I put the bricks back with the subbase still wet. Is that a good idea/ Will that water ever drain? (remeber there is clay below it)
4) Do I need to remove the massive stones used as edges?
5) My assumption is that the wall got wet because there was excessive moisture in that corner AND because it was in permanent contact with the adjacent subbase which is wet limestone screening. Is this correct assumption?
6) I am now planning to build a buffer or to break the capillarity effect between the wall and the subbase by digging a trench next to the wall and by adding there some insulation. The trench will be filled with gravel or will be left empty ( I am thinking about some cement blocks like these

which I can cover with concrete slabs, then sand and pavers. Would this work ?
7) what other options do I have to fix this mess ?

 

[oldestguy]

First off I think the managers of this forum don't like us helping home owners with their projects. However, an engineer home owner
I suppose gets away with it. I am trying to keep this text within my screen. Your text is difficult to follow.

An engineer or landscaper would first do a topographic survey to see what the grades are. That is missing here. Then a surface
drainage plan can be developed.

My experience with limestone (dolomite) screenings is that they can be somewhat porous and thus allow drainage within them.
I've used them as backfill to subdrainage systems at times when ASTM C-33 concrete sand was not available.

Is there a perimeter drain system at the footings? That may be needed here.

Lacking more info, I will state that I have fixed seepage into basement backfill problems with a waterproofing of the soil below any
sod or porous zone, such as your patio. If you do a search on this forum you may find my recommendations on how do that with
powdered bentonite thoroughly blended into a layer of soil below those features. However surface slopes are also needed.

 

[oldestguy]

Here are a few links with that search for you.

http://www.eng-tips.com/search.cfm?...h=oldestguy&searchSite=1&searchArea=1&d=1&s=1

 

[MiniMe4Eng]

Hi the oldestguy

Thanks for the reply.
Actually the grading of the lot is suggested in the initial diagram (yellow lines), I just did not make any comment on it.
The lot is oriented North South, with North being the garage.
The patio is a warped surface, as far as I can tell, it was sloped as described below.

Taking as reference the horizontal plan of the first floor, (remember this is a raised bungalow) I measured the quotes of a couple of points on the patio. Here are the results:

The patio surface represented in the above picture is the ideal representation with the bricks at grade level, in a perfectly horizontal plan.
The schematic representation is what it was actually measured. The top of the picture is the North side.
The line with the two 3' 3 1/4 quotes is aligned with the wet corner showed in the picture above.
The patio settled in a couple of areas next to the wet corner

After fixing the slope of the patio I have the South East corner as the lowest point (the slopes are now along the red and blue lines represented in the initial picture)

There is no perimeter drain at the footing level. Why would I need that? The problem is localized just in that corner. The patio was incorrectly sloped and all the water was draining toward that corner.

Now that this is clear could you please give me some clues regarding my questions in the initial post? I am trying to understand what is going on here, am I looking at a patio where the contractor cut corners by not using a sub-base? Would the current limestone screening layer pose a problem in regards to draining ?

 

[oldestguy]

Good morning Mini:

I bring up the perimeter drain thing since many of them have been known to fail and cause this dampness.

Drainage and infiltration problems are not always "localized" as you imply. I recall one long apartment
building where the known source of surface water infiltration was 150 feet from where it eventually entered the building.

Your source may be a large area away from the "swale" in part.

In your patio, the slope appears to be so gentle that infiltration into any porous zone below those pavers
at any part of that area is a possibility. So fixing the immediate area of apparent infiltration may not do it.

Crushed rock screenings can be sufficiently porous that you may well need to "fix" the whole patio area. This is where
a little work here and a little there will drive you nuts.

I will briefly tell about the house I am now in for 5 years. The landscapers 10 years back surrounded the foundation with a
trench 8 inches deep and 2 feet wide, filled with clear stone to keep grass from growing there. It was an obvious
collection area for water that went down to the perimeter drain. Not trusting the drain I decided to fix it. I removed
everything on the surface (sod and all those stones) out to the edge of the backfill (10 ft plus out from all walls) all the way around.
The grade was re-shaped, removing some earth and adding some as necessary. That surface was then waterproofed with the bentonite
treatment. Stones were replaced to a 1" thick layer, plastic stone area delineator replaced, stones underlaid with plastic sheet, sod
relaid, etc. A big job for an old 85yr old guy then,with two young guys and two tractors. Since then the sump pump very rarely runs.

So you see, as I look at your situation, it likely is much smaller a job to do the same treatment in the full patio and nearby grassy
area. That would be my advice to the job right. You may want to place a few inches of the screenings on top of a treated surface
to make it easier to get the pavers in place. Otherwise the treated surface may be a little sticky. Pavers don't need a significant support
such as base course and such, since no cars park there. A tamped treated area will be needed first.

You probably will not find a landscaper than has ever done earth waterproofing. I've had to train many of them in the past.

.

 

[MiniMe4Eng]

Hmm ..If I uderstand you well your advice is to remove all the limestone screening, to make sure that the subgrade is sloped away from the house and then to use bentonite to seal the sub-base. After that I guess I should put back the limestone and the bricks. Is that correct?

Question: When I started researching this I read some advice according with it is not a good idea to seal the layers below the bricks because the water might accumulate underneath and disrupt the layers above. Someone asked if it would be a good idea to use plastic foil. That was ruled out

 

[oldestguy]

OG back.

You may find that you can water proof the existing screenings and not remove them all. I'd test three typical screening samples and
mix in 10, 15 and 20 percent bentonite to see what percentage is needed for 3 " of treatment depth. Too much and you have a mess. If you had a soils lab you could run a falling head permeability
test on each sample. Lacking that
I'd look to devise some similar test, recognizing it may take a while for the bentonite to swell sufficiently to fill the voids.

Had anyone considered a concrete slab instead, maybe with joints at 10 ft. spacing, sealed. But remember, the infiltration can be from a
variety of places.

Unless you have severe frost action in your area, I'd not get too worried about some water saturating the zone under the pavers, as long
as it can't get any farther down. However, that zone will carry water laterally.

 

[MiniMe4Eng]

The lateral infiltration, at least for the limestone screening layer is highly diminished by the fact that I have those big concrete blocks used for edging. They are very solid and they do their job to keep the limestone screening within the perimeter. However there is a problem with them: they do not allow the water to run off the patio surface, I will need to build a drain channel and to drain the water along the east edge of the patio toward the lowest point of it which is the south east corner

So I don't thing that the infiltration is a problem here

 

[oldestguy]

OG back from lunch.

Maybe you are right. However. I have found that many factors or events forever come up that were not thought
of in the beginning for many of these kinds of problems. For instance, what do you know about the orientation
of the backfill (layers) surrounding the basement?
Frequently they are sloped towards the wall, due to he way it was placed. The easier way for seepage water to go is following those
layers. How wide is that backfill zone? Are there shrinkage cracks in that material? What is it made up from? Any trash buried?
Corner cutting may not hurt, but it would appear to me this is a situation that you have not seen before and resolved.
From my situation here not knowing a lot about the job, I tend to be cautious. Keep an open mind as it goes.