Folks – I had posted a few days ago regarding seepage and leaking around a basement slab that was poured directly on uncompacted mud. (Link to thread: http://forums.taunton.com/tp-breaktime/messages?msg=59265.1) The quick version is that I’m getting water seeping in around the edges of the slab, mostly where the slab meets the existing house. I’d guess there’s less seepage around the three new walls because there’s a new footing drain running outside those three walls. But without any sand or gravel under the slab, I’m guessing that water farther in can’t move out to the footing drain, so it’s coming in at the weak link – the slab/old foundation junction.
It took a couple days to get ahold of the GC, but I did today. He told me that he’d intended the concrete guy to put down a poly barrier before pouring the concrete; when I told him that didn’t happen, he called the concrete guy who admits not having put the barrier down.
Meanwhile, I’ve still got the leaking slab. So the GC tells me what he’d like to do is put down the poly barrier sheet on top of the current slab, then pour another slab on top of that.
Given the track record here, I’d like to check if folks think this is a reasonable solution. I don’t think I’m going to be able to get the guy to remove the existing slab and do it over the right way, so I’m looking for a 2nd-best type solution.
Many thanks for all the good info and assistance –
Ken
North Granby, CT
Replies
I don't think that a vapor barrier would have done anything to prevent the problem. The leak is around the edge of the slab and that is where the vapor barrier would stop anyway. The vapor barrier would help in the middle of the slab when the inevitable cracks develop.
I also don't think that the fact that there was no sand or stone under the slab is the cause of these leaks. Water that is under the slab would not flow to the footing drains unless there was a pipe that connected the interior to the footing drain. Though it is poor practice to pour a slab on mud, I don't think that this would cause water leaks, especially at this early stage.
If these leaks persist, I think that you need to lower the water table. One way to do this is to install a sump. It would be a lot more effective if you had stone or sand under the slab, but it is still probably your best shot. It is also cheaper than pouring a new slab atop the old. I am not sure what that, by itself, would do.
I think losing 4" of headroom would be a problem for me. The concretes
still green so it should break up real easy. Thats what I would do.
Sometimes the contractors got to bite the bullet.
Its a costly mistake but I think if hes willing to pour over it it shouldnt be that hard to talk him into ripping it out. He has already
admitted the mistake, court cases are a hassle.
I have been sued twice,both times I won the case but lost alot of money
because of the time in court. I didnt use a lawyer or would have really lost my a--.
He is blowing smoke up your butt and hoping you will just sit there acting like a chimney and not do anything.
without any gravel and adequate drainlines to give that water someplace to go, the vaporbar under the first slab would have done absolutely nothing. The water would still be getting forced up around the edges of the crete and plastic.
So doing that now would still be a waste of money. he can poutr five such slabs and the only way it will prevent water ingress is when he eventually gets above the ground water table
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Many thanks all. I spoke with the GC today, told him I didn't think another slab would really fix the problem, and now he's considering a curtain drain to a sump. It'd be nice if he'd just give up and do the whole thing over, but I doubt that's going to happen.
Ken
That might help somewhat, but supposing that you are conmvinced of how it needs to be done. Ask him how much he thinks it will cost him to do it his way. Then get bids on having him do it right. Offer to split the difference with him
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I was with you right up till the split the cost part.
Very generous.
Probably the way it will end up, but I don't think I would offer it up on the front end.
carpenter in transition
I don't like the cost splitting either, but sometimes incentive is needed to come to a solution. Instead of kicking and whipping a mule that hase stubbornly sat down, it's time to tease him with a carrot.
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Putting sand under a slab isn't normal practice - or at least as far as I know. The vapor barrier needs to be there, but doesn't have anything to do with the leaks. It is to prevent water vapor from permeating up through the slab and into the house. In my area, under slab inspections are required and gravel, perimeter insulation and a vapor barrier have to be in place.
My advice is this: check whatever building code is in effect in your area. Call the local building inspections dept and ask some specific questions about what is required. I'll bet you a beer that at least a vapor barrier is required. Armed with this info, call the GC and tell him to have the slab jacked out, have unsuitable substrate removed, a drainage system installed that is either drains to daylight or to a sump, proper substrate installed, vapor barrier installed and a new slab installed. Then tell him to have a nice day.
It is likely not his fault that there is a water problem, but it is his fault that it wasn't dealt with, so be a nice guy and offer to pay for the sump pump - if needed.
sand may not be normal in your location, but providing a means for water to escape is - right? Whewther by sand, gravel, pipes, or some combination of the above, it is always done in any place I have worked. It depends on local soil conditions, but I have never heard of pouring on mud being acceptable.
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Agreed.
Matt
"Then tell him to have a nice day."
I always did think that phrase meant FU.
Seriously though, I don't think that the cost of this should be completely met by the contractor. We don't normally install a sub slab drainage system unless there is an apparent reason why we should or if it is called for in the contract(one or two times in 25 years). If the hole is muddy we drop in stone as needed so that the hole does not become an unworkable mess and we add coarse sand as needed to grade evenly under the slab.
Over the years we have had two cases of the water table rising up inside a basement. The first was a flat site but with a completely dry hole during construction and well drained soil. Unbeknownst to us, every spring the water table creeps up to a level just above the slab. Two years after construction there was an inch of water on the floor. We installed a sump on each end of the basement which run intermittently for a month every other year. There is no problem now.
The second house was on a sloped site with adequate drainage to daylight installed around the foundation. This should have eliminated any water table problem. Everything was fine until one of the subs drilled a hole in the basement floor. They were hit in the face by a 3 ft geyser of water. Apparently there was bedrock under the slab which we had covered with 6" of stone. There was a fissure in this rock that, under high spring water tables was bringing a spring directly under the slab. The water table was higher inside the footings than outside. Once again a simple sump took care of the problem.
In both these cases we were able to work out an amicable financial arrangement with the owners involving cost sharing. I am sure that this was because we were forthright in dealing with the problem and that we had established a basis for trust through our work with them. This gave us a chance to deal with these problems in what turned out to be an inexpensive (relative to tearing out the slab) yet effective solution.
two sub slab drainage systems in 25 years.
that's amazing to me. around here, PA, high water tables are the norm and crushed stone and perf pipe are an inexpensive standard.
really inexpensive.
i look at so many leaking basements a year that were built pre 1980's without drains that it makes me sick to hear that contractors aren't doing this as cheap insurance in 2005.
our repairs usually start at about $4000. how much would the perf pipe and stone have cost ?
carpenter in transition
Water problems can pop up on sites you leat expect. I had a customer who wanted a deck added. Wanted me to check a foundation water prob first. House was stemwall/slab on grade construction. The house sat on the top of a small hill - almost a perfect topology for a building site. The thing was that the ground was completely saturated around 3 sides of the house and the slab (inside the house) was showing signs of settling - there was a 1/4" gap between the shoe molding and the hard floor surfaces around the outside of the house. I recommended a foundation drain system be installed with a daylighted tail on 3 sides of the house. The front of the house wasn't wet, and to install a drain tile there would have required tearing up the driveway and front walk concrete. Once the Homeowner saw my price, he elected to DIY under my direction. In addition, extensions were added to the downspouts to get all the gutter water away from the house. I believe the problem was fully resolved as I checked the ground several months later during a rainy spell - no subsurface water that I could find with my probe rod. Matt
there may be some times when some things are unnessesary, but this is more clear. He was told by the inspector to do this and ignored the 'advice' - to his own risk. he is at fault.
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You could cut the concrete around all 4 sides, dig a trench, put in "french drains", all running to a sump, and then re-pour over the tops of those.
Are we there yet ?
I'm sticking with my post in the previous thread.
Do you owe him money ?
Consider what Piff recommended, getting quotes to have the floor hammered and put in properly. Give them to the builder and tell him it will be deducted from his final unless he wants to do it himself.
If you can live with the sump pump, then I would pay for it, but not the tank.
carpenter in transition
It is an unfortunate fact that virtually all home in north america and possibly the world that are built on impervious soil have incorrectly
constructed footing and drainage.A controversial statement? you bet.
Is it true?Once it is pointed out to you why it is so it is totally
obvious-like all great ideas.Do you have to believe me,no because
it unfortunately isn't my idea.Go to http://www.fastfoot.com and follow the
product fastfoot-rising damp path for a picture of how a footing/drainage should be constructed.
Nice sales pitch WIP, you on commission or salary?
Can't necessarily say I agree with you or the web site and would say that those methods shown are appropriate for building sites with granular soils... but... the fact that cementous materials that are in contact with the earth are inherently damp is undeniable - or at least in the damp south east US. We (here at BT) have discussed lining footings with a vapor barrier, but I've never really heard of anyone who actually does it - up until now...
I remember a while back when I explained here that concrete "conducts" moisture from the ground up into the structure via a wicking effect. One guy, emphatically told me that I was wrong - I guess he had to though since he builds underground houses... Really though, from what I gathered, his strategy was to protect the structure via various moisture barriers so I guess he kinda missed the point. Matt
Not really talking about the fastfoot product itself more the technique
of installing drain rock under the footing and putting the drain tile
lower than the bottom of the footing.Is there any way that water could
pool anywhere under the slab or footings?Don't see how.The whole water
table is lowered to the level of the top holes in the drain tile which
is below the bottom of the footings.This may obviate the need to use
a vapour barrier since the footing should be sitting on pretty dry
drain rock.The vapour barrier whether fastfoot or anything else would
be a bonus.No association with the company allthough I did speak with
a builder who uses it regularly.He told that it was particularly good
going over irregular rock shelves-saves all that lumber forming-and
that one time they did not use it under those circumstances they regreted it.
I remember a while back when I explained here that concrete "conducts" moisture from the ground up into the structure via a wicking effect. One guy, emphatically told me that I was wrong - I guess he had to though since he builds underground houses... Really though, from what I gathered, his strategy was to protect the structure via various moisture barriers so I guess he kinda missed the point.
Matt, that was me? Don't remember the thread and I certainly don't remember saying that concrete could never conduct moisture. Clearly it can. Has to? That's another matter, largely determined by your concrete. Let me quote an old HUD brochure, only thing I have readily available:
"Very little water vapor will pass through a high-strength, dense concrete, but concrete of low strength that is poorly consolidated is quite permeable. Therefore, the first line of defense against water problems is well-controlled concrete construction."
All we do is shed ground water away from the house, think umbrella. Concrete here's been dry these last 12 yrs, 15' underground. No drainage system necessary. Damp/water-proofing also unnecessary. Quite certain I understood your point and was inviting you to take a peek outside the box. I once successfully installed an umbrella around a traditional house where I poured the basement. Worked the same as here regarding moisture. Dry.
Grew up in a slab-on-grade, then concrete block walls, house. No barrier, no crushed stone, just concrete on dirt. No wicked moisture. But that was central Arizona, dry dirt again. And probably crappy concrete. Certainly the block was highly permeable.
We're being pro-active here in wet Virginia, providing an environment where our concrete works like a charm, stays dry. I'm also picky about my concrete. Dry dirt's a byproduct of building our passive cooling/heating system. You wouldn't be the first person to tell me that it can't work. That's fine. Consider a visit? Concept was first tested, far as I know, in the early 80's.
the fact that cementous materials that are in contact with the earth are inherently damp is undeniable - or at least in the damp south east US.
Sorry, that's wrong. You really ought to visit.
Getting back to this thread, and the hydraulic one, the only interior, non drainage, solution I could see working would be to use bentonite waterstop between the new slab and the walls. Trying to turn the house into a boat. Not something I'd try, but it might very well work, long as the house didn't float. Those bentonite ropes work well in cold joints to keep water in a pool. It's the hydraulic action of the bentonite at play. PAHS Designer/Builder- Bury it!
Tom:
You quoted above: "Very little water vapor will pass through a high-strength, dense concrete, but concrete of low strength that is poorly consolidated is quite permeable. Therefore, the first line of defense against water problems is well-controlled concrete construction."
Care to expand on that a bit? I have read that 5000PSI concrete is waterproof. Is that what is being referred to? Do you order your high quality concrete from a ready mix company? What special methods do you use when placing it, etc. The concrete we normally use is either 3000 or 3500 PSI. Is what is considered low strength? Also, how does air entrainment fit into this equation? Just trying to learn something here. Thanks,
Matt
Edited 6/19/2005 2:04 pm ET by DIRISHINME
Matt, that was simply a quote from a HUD booklet. But it goes along with my understanding of concrete. Air-entrained is absolutely critical for water tightness. A major problem locally is with watering down of the concrete to make it flow easier. I was actually told by a readymix salesman that adding water didn't weaken the mix. Yikes! I'm sure you know better than that. My understanding of 5000# is as yours. Don't know if you could then do without air-entrained. I wouldn't.
As for my concrete, I start at 3500# minimum and go from there. Slump is specified at 4" max. I was skeptical about what I was getting, without testing, until I met a previous employee of an independent testing co. She assurred me that their testing of both of our major readymix suppliers never came out less than 500# over specification. That helps to explain our abnormally high concrete cost, compared to Richmond, for example. Perhaps it also partially explains your and my apparently differing experiences. I also don't trust anyone but me for vibration, but that's another subject. Pumping is a sore point with me, always get inferior concrete.
Concrete isn't anything I claim great expertise with having only poured several hundred yds. Before our house I'd never done any. What I did do was read everything I could get my hands on, especially from the American Concrete Institute and the Portland Cement Association. Neither group has any goal but to ensure a good experience with use. I've been a very happy user.
For the small cost difference to get an extra 500# concrete, 1 bag/yd, I've found it easy to justify the cost. Obviously I don't work in your market.
Here's a pic of a wall, buried +8' just around the corner, 6' here. It has no umbrella, no damp/water-proofing, no drainage system, and is dry on the inside. I expected a leak at the cold joint at the footing, necessitating an umbrella. Didn't happen, but I don't know why, other than decent surface drainage. The concrete, as I expected, had no moisture apparent through it. Same for the funky-looking retaining wall, an afterthought.
Thank you for a civil response.
Edit: Forgot to mention that our head building inspector, no dummy, shared your position- until he came here a couple yrs after we'd finished. He's had a change of mind. Now occasionally suggests someone call for info. We've become friendly and he does all my inspections as his people understandably get nervous with construction they don't understand. Not that he's very concerned with my structures. Success builds confidence.
PAHS Designer/Builder- Bury it!
Edited 6/19/2005 10:21 pm ET by VaTom
If you don't mind, briefly describe this "umbrella" technique you refer to.
You said: >> A major problem locally is with watering down of the concrete to make it flow easier. << I think that is probably more like an international problem!!! Same as terrorism!! :-) Especially with footers. The flatwork guy I'm using now likes to place his concrete nice and think. Sometimes I get pi$$ed at him for other reasons, like leaving 'elephant turds' on my job site, but I'll probably keep him around...
Also, do you know the name of that product that is sprayed on concrete foundations to make them more water impervious? It is a clear liquid - not a heavy coating - and supposedly changes the chemical makeup of the surface of the concrete. I'm having a brain block here.
Matt
Edited 6/20/2005 7:30 am ET by DIRISHINME
Your liquid is news to me. When it comes back to you, please post. Back before I understood my needs, I used bentonite rolls for water-proofing. Worked fine, just was over-kill.
The umbrellas are (usually) 3 layers of 6 mil poly. For heated spaces, they encapsulate XPS starting with 4" and thinning toward the perimeter. They extend, ideally, 20' from the perimeter. The whole idea, from a Passive Annual Heat Storage (PAHS) viewpoint, is to get enough mass under the insulation umbrella to provide annual storage. This requires 20'. If there's ground water moving through the mass it'll wash away a large part of that stored heat. So we use cheap poly to keep the mass dry. A dry foundation is a side benefit. Obviously there will be some small water migration under the umbrella, but it hasn't been a problem. I also have yet to see a bug or critter issue.
This time of year that mass is our cooling system, storing the heat until next winter. We're currently at 73º and have diurnal changes of 2º maximum, usually not more than 1º. 20k cu ft, .5 ACH.
The basement under that traditional house got an umbrella slightly smaller, due to nearby trees. I attached the poly sheets with termination bar and made sure there was positive drainage away from the house. The HO, a friend, couldn't see burying expensive insulation in the yard. LOL So he got no heat storage, other than what any bermed house gets. But the basement's had no water problems. Don't know if the umbrella was necessary, but it was cheaper than most water-proofings and his lot was the opposite of the great drainage I enjoy.
This was more than you asked for, sorry, but I'll throw out one more item. How much do you spend annually for your creature comforts (heating/cooling)? Normally it'll be 1 month's income. I'd rather have the time. PAHS Designer/Builder- Bury it!
Tom:
Thanks for the explanations. Yea, I'd estimate that our yearly utility bills are about 1 month of my pay. Luckily, my wife works too..
Matt
You thinking of XYPEX?
>Pumping is a sore point with me, always get inferior concrete.????????
Yeah, that one kind of puzzled me, too, because my experience with pumps has been really good unless the mix was bad.
But, from what I've read here, we're kind of spoiled in my area, because our pump guys do all the pump and hose work and work with the drivers to get the right slump.
They're also mindful of the forms and, on a couple of highwall pours where the forms had some flaws, worked carefully to avoid bulges or blowouts.
On jobs where we've tested, it's always been well above spec., good consolidation and a lot easier on the back.
The only real problems we've encountered, was last year when there was a cement shortage and some of the batch plants were experimenting with a variety of fillers, some that didn't work so well. We pumped one little 5 yd. job for some deck footings and a sidewalk and spent a majority of the time unplugging hoses....a real PITA.
Are you dropping the mud very far? I have no complaint about the readymix companies or the pump operators (except one), only the result. I haven't pumped for quite awhile and hope never to again. But you sure are right about being easier on the back.
This isn't the first time at BT this has come up. Certainly no expert here, I've only poured 6-800 yds. PAHS Designer/Builder- Bury it!
Rarely use a boom pump; partly because of local availability, and then only on high-wall pours, but usually use a line pump on them, too (just have to plan walkway layouts with a hose in mind).
Whether boom or line pump, on walls, we always pour in 3' to 4' lifts, starting in corners and moving toward center of walls, but building up to the blockouts as we go. It's a little easier to control consolidation at the blockouts that way. Rarely get voids.
I most always grout CBU walls with a pea gravel mix; it costs a bit more, but we get better consolidation in the cores and bond courses.
On residential, we always use a pencil gun for vibration (start at the bottom and pull up about a foot per second), in part because of the heavy rebar schedule spec'd in the area due to seismic requirements (get one of those 2" tips hung up in the rebar and the fun begins!).
I started getting better results on high walls when I started practicing the methods used in pouring ICF walls.
"Sir Francis Drake circumcized the world with a 100' Clipper." -unknown
Edited 6/21/2005 10:06 am ET by Wormdrive
Whether boom or line pump, on walls, we always pour in 3' to 4' lifts, starting in corners and moving toward center of walls, but building up to the blockouts as we go. It's a little easier to control consolidation at the blockouts that way. Rarely get voids.
Thanks for the advice. The above is what I was taught, and practice. And so long as I stay away from boom pumps I get great concrete. On tall walls I'll pour 8', often out of a loader bucket, and then reset the forms for the top pour a few days later. This is the old plywood/snap tie system. Slow, but works great for me.
First time I pumped, with only 4' wide blockouts, I was horrified when I stripped. Thought it was me. Later changed my mind when it happened 100% of the time, no matter what I did. My vibrator head is 1 1/2", which is plenty for my rebar-filled walls. Backup vibrator has a 2" head, which I can get in there (and out) if I have to.
I'm dealing with roof systems 300 psf and up, 300 tons or so, placing 3 tons/lineal ft on the walls, plus typically 15' of dirt against the back wall. Got some serious engineering to accomodate.
The last supervised pump, which looked like all the rest when I stripped, convinced me that while others may do fine, I'd do better to stick with another method. PAHS Designer/Builder- Bury it!
I know, makes no sense to lots of people. Far as I can tell it's due to the over-sized boom pumps that are the sole pump around here. Last time, with a very large co., I got the guy in charge of Va to come out and supervise. He assurred me we'd get/gotten great concrete.
Wrong. As usual, it didn't flow well below the blockouts, leaving large voids. I've only pumped 5 times, 5 different operators, 3 companies, and every time I get voids that I never get when chuting. I'm the only guy vibrating. Average cost $700+ per and I get inferior concrete. What a deal.
My theory is that the booms are too large for my treed sites, necessitating raising the mud too high and letting it fall too far, separating the mix. Every pump co. tells me that's not the problem, but I don't know what else it can be. I'm paying for plasticizer and pay special attention to vibrating the problem areas. With chuting, or a concrete bucket, I don't get the voids, even without plasticizer.
Solution for me was to buy a crane as I had at least 3 times to pump on my own next house. Crane (just slightly younger than me) was also cheaper, for that one job. Unfortunately my last client insisted on pumping. With limited access, the crane was too small to reach across the minimum 50' span we had. I wanted to leave a corner out of the house and park the crane inside, leaving the open corner for last. At the end of the job, after looking at a chuted wall, the client apologized. Anybody could tell what was chuted and what was pumped, even where there weren't large void patches.
This, after supervision by a very knowledgeable guy who'd been in the business 25 yrs. He was up there 16' on the forms with us, also checking out my vibration. I know that structurally the voids aren't a problem, but it riles me to pay that much and get an inferior product. Fortunately the retaining walls, which remain uncovered, were chuted. Everything else not buried got either copper or plaster over it.
PAHS Designer/Builder- Bury it!
As long as you qualify it that the boom pump may be the problem, and not pumped concrete, I'll take away the ??????????. Never used a boom. Always regular hose. Never had a problem stemming from the pump, except if it blows a cylinder or hydraulic hose, of course. Had some of the best mud I've ever seen flowing through a nozzle. Last time we ordered, and got, a 1 slump. Pumped just perfectly. But then, I'm partial to our local company, Southern Concrete. The plant here has been awesome.
Sorry for the confusion. I equate booms and pumping as that's the way it is here. And everybody tells me here that there's no reason I shouldn't get as good concrete as from a chute or bucket. But it just doesn't happen. I believe that a much shorter boom might be the solution. Or parking the pump truck much farther away, if I could.
You pumped a 1" slump? Wow. Low slump concrete, and not that low, is a constant battle to get here. The readymix companies here think I'm strange. They're probably right.... If you asked for 1", particularly to pump, I'm pretty sure they'd call for the guys with the white jackets. <G> PAHS Designer/Builder- Bury it!
Tom,
Re: voids under blockouts; The liquification effect of a vibrator is only 12"-18" at best. The way the crews I have been on have done blockouts is to have a four man crew.
1 nozzle man, 1 vibrator and two guys on the ground looking for blowouts and other problems. They also are equipped with bladeless recip saws to vibrate the sides of the form.
When doing the blocked out area, the vibrator is dropped right next to it. This would be the only time the vibrator is dropped slowly. Keep it moving about 1'/sec up and down from the bottom of the form to the bottom of the blockout.
The concrete is pumped down on the vibrator on one side only until it flows out the other side flush with the bottom of the blockout.
The two ground guys help to push the mud along under the blockout by sweeping the sides of the form with the recip saws.
If you got an extra guy and an extra Donkey D----, you can drop it on the exit side once the mud gets up about halfway between the footing and the blockout. That one should be kept just buried in the mud untill you move the hose over and get some back pressure on the blockout, then run it up and down to the bottom as usual.
Using the recips sweeping upwards with the vibrator as you pour also helps keep pinholes from happening.
SamT
Thanks Sam, included a little something extra BTW. Hope you like it.
I have no problem with 8' wide blockouts as long as I don't boom pump (is that better Cloud?). Longest I've done was 16' (with a chute) and it had very little void. The professional trade groups make it very clear that moving concrete with a vibrator is a bad idea. Of course they also say to never drop mud more than 5'. But we would never do that, right?
Uh, is it ok to 'fess up here? I don't own (and have never owned) a recip saw. Never found much use. I always figured that if I was ever forced to use ICF's I'd buy one.
The pump companies never suggested a recip. I've got an abnormally long vibrator and have been known to insert it under a blockout. Haven't gotten it terminally stuck yet...PAHS Designer/Builder- Bury it!
"I've got an abnormally long vibrator ..."
Oh the jokes that come to mind...
It would seem you haven't spent much time with concrete pours... Much more than normal construction site humor. They go on and on. You did notice SamT's description I hope. Well, mine's longer. <G>
Size does matter.PAHS Designer/Builder- Bury it!