hydrostatic lateral foundation wall pressure

go ahead and figure out how to place, install, drain tiles around boats and when you do, lmk. We could save quite a few boats from sinking if they had drain tiles inside the perimeter and outside, right? And according to some peeps way of thinking, the drain tiles around DUH boats would magically remove, reduce hydrostatic pressure… right? Sadly, too many elevators do not go up to the first floor on this subject yet they claim to have most-all of the answers on leaky basements, foundation cracks

First of all, some soil moisture under the footing is a good thing. Soil naturally has voids and when these voids go dry the soil structure collapses causing settlement issues during a severe drought. But there is a point where too much water starts to displace the soil particles, which lowers the load carrying capacity of the soil. The Proctor test is used to determine the moisture content that produces the maximum soil density or load carrying capacity. Most people never heard of a Proctor test unless you do commercial or heavy highway work.

A curtain drain is only a tool in the toolbox. It reduces the amount of water that reaches the foundation and is not applicable in all cases. In fact, I have seen contractors use them incorrectly and capture water that could have been diverted with diversion ditches. Intercepting subsurface flow is their primary function, capturing surface flow should only be done when the topography doesn’t allow for diversion ditches, swales, etc.

My original post was to outline all the factors involved so Michael can make an informed decision. Your job is secure as long as you want to work.

okay Randy, i apologize to you for being, sounding like, a frigging crabby azz, sorry man. you’ve always provided people with good advice, far as my old azz can tell, not that i check on your posts or anyone else lol, just saying.

it’s just this stinky azz trade/subject i catch incompetent, lying crap all the time, every day, for decades and some days are, bad days for me, its frustrating as hlll trying to honestly help some peeps.

like some of you guys here, I’ve been out here a long damn time, have done all estimates for free, 40 yrs, have done 1-2-3 hour water tesrs for free, 40 yrs.

hundreds of those I’ve done water tests for did NOT need any waterproofing, that’s i did the tests. They only needed some tuckpointing or caulking or their clean out/lateral line snaked etc and it just pizzez me off to see, hear so many scamming azz, lying azz sobs cheat people, and make a boatload of $… okay man, appreciate your reply.

I get home late and it is dark which is why I said I needed to wait till the weekend. John your going to have to give me a break here and not ride me about this water test until at least Sunday! :slight_smile:

We are spending alot of time on exterior drain tiles because that is the topic for which I have remaining questions. You have thoroughly explained and answered all of my other questions and I sincerely thank you for that. You will never hear me say an interior drain tile will prevent water from entering through an external foundation wall crack! Not because I fear one of your rants (LOL!) but because I can see the logic behind why it won’t.

In my defense, the very title of my thread has the words hydrostatic foundation wall pressure. It occurred to me this pressure would seem to linger if the exterior perimeter drain tile system is not functioning even after your water proofing and proper backfill recommendations were followed. Intuitively this seemed to me to be a potential risk which is why I started asking about it. I’m just trying to get a full understanding of my situation and potential future risks assossiated with each potential course of action.

So to be concise, my remaining question is what are the ramifications of leaving high hydrostatic pressure to push against my foundation wall for long periods of time.


Because the water is entering through a crack at least 5’10" above the slab floor, one possibility is water is accumulating at least this high against my foundation wall. This hypothesis is bolstered by the fact that when the leak appears and I pull back my plastic “foundation roof” at the corner, the ground there is bone dry.

I don’t know. That is why I am asking the questions. To get opinions from experienced people like you and Randy about my potential risks to a lingering hydrostatic water situation. I can’t say it enough but am truly grateful for the knowledge that you have already dropped. I realize you guys are not getting paid for this.

I agree, but that was one of the things that intuitively bothered me. Of all of the people who came out no one cared about assessing the ACTUAL state of my exterior drain tiles. If indeed they are “fully clogged” what are the ramifications of that?

No. :slight_smile: (I know that was a rhetorical question!)

My understanding of the design of proper gravel backfill against a wall foundation that leads to a properly functioning exterior drain tile located at the footer (not above), is to provide a low resistance path for water to get out of that area. Apparently this prevents hydrostatic pressure from building up against the wall and lingering there for too long. Did I get that right?

It would seem to me that when you replace the clay soil backfill with gravel without clearing a completely clogged drain tile, the low resistance path of the gravel does not speed the draining of the backfill volume around the foundation wall. The only thing left to determine that is the infiltration rate of the native soil underneath and around the footer and drain tile. If it has a high clay content it will be slow. If it is slow enough that the hydrostatic pressure is high and lingers around the wall for long periods of time I am back to wondering what are the ramifications of that.

John I agree with your point, and appreciate your supporting links, that you do not want soil under the footer to repeatedly saturate and dry out and crack because that would cause the “differential settlement” Randy talked about and potentially lead to future wall cracks. I think Randy clarified his point in his response. I would only add that it seems to me that a properly functioning drain tile located at the footer, not below it, will not dry out the soil under the footer any faster than what the native soil underneath will do. Why? Because the low resistance drain tile path ceases to be used as the ground water falls below the bottom of the drain tile pipe.

So I am back again to wondering what are the ramifications of high lingering hydostatic pressure against my foundation wall.

Why do you hold such disdain for the poor exterior drain tiles? :slight_smile:

Seems like you replace them grudgingly! :slight_smile: Why o you replace a clogged drain tile at all?

I have 4" perforated corrugated ADS. How do you assess whether the insides are clogged? Do you cut them open and look?

This is getting way too long and I still want to respond to Randy so I will end with this:

The bottom line is I want to understand:

  1. under what conditions will a clogged drain tile and the resulting lingering hydrostatic pressure against my wall be a problem?,

  2. how bad those problems will be if they occur?

  3. what is the likelihood that my home satisfies those conditions?

Thanks Randy. Given I haven’t yet had a chance to talk about my topography, your curtain drain option seems extremely insightful. What made you suggest this option?

I suspect subsurface draining might be contributing to my high hydrostatic wall pressure. Although John still has me thinking about whether this is a problem or not. When you wrote:

I didn’t understand the relationship between the amount of hydrostatic water pressure at the wall and saturated soil under the footing. Maybe you could elaborate.

There is a large portion of my community that lives above me on a hill to the north. There is a large 5 acre wet pond 300ft to the south of me that drains into a stream. I have a walk about basement and my southern facing wall is above grade. My backyard has a decent slope down to the wet pond.

After heavy rain I suspect the water that infiltrates the ground of my neighbors to the north, starts its path underground towards the wet pond. My northern basement was is in the way and as this subsurface water hits it, the hydrostatic pressure builds up against the wall. It eventually flows around my east and west walls and then continues flowing underground until it reaches the wet pond.

If my drain tile was properly functioning do you think it would be able to redirect the subsurface water away from my northern foundation wall fast enough to keep the hydrostatic pressure from becoming a problem?

How does one determine the need for a curtain drain and how does one determine that the curtain drain is performing at the required level.

Thanks again!

John as promised here is a link to pics from the leak test you suggested I perform:

Foundation inspection + Leak Test - Google Photos

Quick summary:

Brick veneer is below grade which is not what I thought and stated previously. I didn’t realize this until I was making sure my hose test wouldn’t put water above my foundation wall. I had to dig down about a foot and still didn’t find the foundation wall. That is when google clued me in on what a foundation brick ledge was. It must be deeper.

Could only run the hose long enough to put ~2.5 gallons in the hole before water level rose to point where I thought the top of the foundation wall was. Turned hose off and < 5min the leak appeared at corner crack about 5’7" above slab floor just like after a heavy rain. It also appear at various places along the same vertical corner crack but no water at the cove joint.

I feel I did not run the test long enough to fully saturate the soil around foundation in order to see if there more leaks other than the vertical corner crack. Should I pull my foundation roof skirt back further and turn down my hose rate to try and get more water flowing into the ground for a longer period of time without it rising above where I think the top of foundation wall is? I was scared I might soak my top plate and header.

This is revealing that my grade is to close for comfort. How much distance should be between top of foundation wall and grade?

I will explain my “foundation wall hydrostatic pressure test well/manometer” science experiment in another post. :slight_smile:


ok so when you ran water from ground level down, you got water in.

I can’t tell you if that crack actually penetrates THROUGH the wall to the exterior, IF it does then my recommendation to you is to hand-dig (whatever) that area out, maybe 5-6’ in length and all the way down to the footing n drain tiles and waterproof the crack AND all bricks and joints at—and below grade in that area.

I would apply hydraulic cement in-over the crack and those bricks n joints, let it harden/dry, then apply a THICK mastic aka roofing cement (looks like tar) over the entire area of wall that is dug out, from the footing all the way up and onto bricks n joints, then backfill the trench with 90–100% gravel, add a little top soil. When we do/waterproof those small size jobs here, there is NO ‘price per foot’, cost here, depending on the exact depth from grade level TO footing, should be between $1,350 and 1,675. One day job, more like 5-6 hours to have everything done. City permit fee (if required there) may be around $100-150 so add that.

Bricks and mortar joints that will be built, exist, BELOW grade level should be waterproofed because bricks can allow water in and so can the joints. Fairly often some of the mortar joints are not ‘tooled’ so good, some thinner than others so those will deteriorate sooner n then allow water in.

Lastly, it is possible that some or all of the water is actually FIRST entering through 1+ bricks or mortar joints that are below grade and sit on top of the F- wall. So “if” the crack does NOT penetrate through to the outside, then that is where the water is first entering. That crack may indeed go through so if it were my house, I would waterproof the wall and bricks etc in that area all the way down as I explained above, just my 2 cents.

Like this Mike, first minute of video INSIDE basement, then see the crack on the outside and the open mortar joints etc below grade, they all need to be sealed correctly.

Should look like this just before backfilling with all gravel

The following two videos is what you do not have, in the way of water that is but my point here are the bricks and joints BELOW grade and blocks, none of them were protected = problems


Thanks John for the recommendations. Looking at top of F-wall from the inside relative to my hose Bibb, it appears that the brick cannot rest on the top of my F-wall but rather must sit in a “brick shelf” that was created when the F-wall was poured. In your experience how far down typically does the brick shelf extend?

Also shouldn’t the space between brick shelf in F-wall and below-grade bricks be filled with mortar?

If I only waterproof this area at the corner all the way down to the footer what are the chances water gets in through a below grade open brick mortar joint say 10ft away from the waterproofed area, travel along the brick shelf and enter the same possible hidden crack at the corner between bricks and shelf?

In general when do you recommend customers waterproof more than just the portion of the F-wall at a known existing external crack?

Sometimes there are 6–8 courses below grade, maybe 1-2 '.

Sure, i’d seal anything you soaked, that got wet when you ran the water test.

Yes you sure could seal/waterproof all bricks n joints below grade as a preventive measure.
Was it Miller beer who had the ad, ‘If you got the time, we got the beer…’ so, if you have the green to do more of the bricks n joints it won’t hurt.

Anytime 1++ mortar joints or bricks deteriorate (see videos previously posted) they can allow water in.

If a homeowner has poured walls, like you, and their basement is NOT finished then that homeowner and i can walk around the basement and eyeball all 4 walls and see if there are other existing cracks in walls. If there are, they can have those waterproofed as well, same day… if they choose.

Would also show them how to check their rod holes if they don’t know how.
Would also be looking for any water stains UP HIGH on the wall, like under basement windows or where their front-back-side doors are, because water can get in through some windows or through/under a window ledge-sill, around doors etc.

Some homeowners have 1 or 2 existing cracks in their poured walls and i’ll ask the homeowner if they have ever got water in through the crack, bottom of crack (near floor)… if they have lived in the house for years, through numerous long rains and say they’ve never had water in through other cracks then they could just have the one-leaky-crack done, they may not have the funds to do more work so, fix the one that leaks and know that, in the future the other 1-2 cracks may begin to leak and if so will need to be repaired.

Some of these hairline vertical cracks are located where the homeowners garage is or where their front–back porch is so, those areas are a little less likely to leak because the garage, floor, porch, footing ‘kind-of’ deflects some water away, a bit harder for water to get to these cracks is all I’m saying. If they are selling the house they should disclose that there are 1 or 2 other existing hairline cracks and simply be truthful… that those other 2 have never leaked… as of this point in time lol. I’ll tell buyers, to be safe, if there are 2 cracks then maybe bid around $2,000 less

Then we have some existing hairline cracks that do NOT go through the thickness of the F-wall, don’t penetrate to the outside so, they don’t… won’t leak. Quite a few poured walls have ‘corner cracks’ that don’t go all the way through, UNLIKE block foundation walls where any exterior crack or cracked parging allows water in. There are a few differences between poured walls and block, brick etc as to how-where water gets in

Thanks again for your advice.

Therein lies the problem LOL!

I would like to finish my basement but don’t want to do a insufficient waterproofing job and then have to come back and rip out my finished walls if a new crack and leak develop.

I also don’t want to go completely the other way with possible overkill and excavate around my entire wall down to footer, waterproof everything, and replace backfill with grave when only one crack is leaking. But maybe that is the only solution that will give me comfort. Hmmm what to do what to do…

I have insulation covering all of my unfinished walls so to at least see if I have anymore subgrade cracks I need to remove this insulation and examine things. That is just my time. I need to figure out how best to do this so I can put it back up with the least amount of hassle.

Any ideas?

How do I examne my “rod holes”? If you look at my pictures it seems like I some kind of thin metal strips protruding from the poured walls that look like they are some kind of reinforcement. Are these the “rod holes” you are talking about?

Been in house 7 years and never have seen water near or around the wall/slab (cove?) joint. One of interior solutions guys who did come by pointed out that previous owner or builder put some kind of sealer in the cove joint in a few places around the basement (I never noticed this) on the below grade north wall but I have never seen any moisture there. They said that was a sign of previous water entry and why I needed to relieve exterior hydrostatic pressure. I’ll take some pictures upload them.

Do you think I need to do some more aggressive water tests after I pull the wall insulation away?


rod holes in your walls, are those ‘gray things lol’ every 18" ?
some builders use/apply different things to rod holes, most just pop in a cork in all rod holes and then apply a tad of mortar over them = they begin to deteriorate and when they do, they allow water in and can allow a lot of water in behind drywall etc.

your bricks and joints below grade, if you hired someone to seal ‘em all and the very top of the foundation wall, I wouldn’t call doing-that, overkill. It shouldn’t cost too much because they’d only need to hand dig 2’ deep or maybe a tad less, ya know? Nothing like digging 6–10’ deep.

cove, I-joint sealer… some plop some mortar etc along the coves. Pretty much all it’s good for is maybe keeping radon gas etc from easily coming up into basement, it doesn’t hurt anything. Int-system companies tell people all kinds of crap… like in this video…
Listen to the homeowners, they even gave me Foundation dorks of Mich paperwork (estimate), lool it’s nonsense… $17,000

‘Pushing through the market square, so many mothers sighing, NEWS had just come over…’