Thread: Access to Leak in Mono Slab

I need opinions on what method is better to access a leaking pipe in a monolithic slab. The locals in this area tend to jackhammer the slab versus cutting it with a diamond blade wet saw. The slab has some cracks which the homeowner does not wish to make worse, hence the apprehension to the jackhammering method. However if the consensus is this is the preferable method I might be able to convince to give it a try.

I would not hesitate to try the saw first. Maybe take out a small patch and see what's up with the slab, thickness and so on. The jackhammer is for big reno jobs, not a surgical repair.

Depends on how big the jackhammer/chipping hammer is - a monstrous one like road crews use or a small 20-30 pounder?

I've done surgical repairs in chipping out slabs with a small one, works good, and in no way does it 'cause or make' cracks in a slab any bigger. If the work is a large area to be removed, then start with the saw as to make the perimeter cuts, then break out the center part with the chipping hammer.

The amount of dust will be more dependent on whether the work is done wet or dry, depending on the saw as to whether or not it can be used wet or dry. The chipping hammer can be used either way. Even with water, that is not a 'nice and clean job with little to no dust', be prepared for cleanup.

Originally Posted by O Frame

I need opinions on what method is better to access a leaking pipe in a monolithic slab. The locals in this area tend to jackhammer the slab versus cutting it with a diamond blade wet saw. The slab has some cracks which the homeowner does not wish to make worse, hence the apprehension to the jackhammering method. However if the consensus is this is the preferable method I might be able to convince to give it a try.

Last year I did a job where I had to make 16 holes about 6" by 6" in a slab. There were several large cracks in the slab and significant voids below the slab. I used a 60 pound electric jackhammer. Cut through the slab like butter and did not cause much vibration or affect the cracks. Also did not create much dust.

Patches in concrete also key into holes with irregular edges better.

Many times it is about making the customer happy an not the typical or easiest method. The home owner is concerned about the existing cracks. So why not just do what will make rhew owner most comfortable. Often you get contractors that have an attitude of it is my way, the way I always do it, or nothing. Get someone that does not have a problem doing it the way that makes the owner most comfortable. Owner will be paying for the extra effort involved.

Wet saw or dry saw are a toss up depending on what you are willing to clean up. A wet saw where you build a dam around the area to be cut (rolled up towles and some duct tape with plastic works well and use a shop wet vack while you cut will keep the mess minimal.

Should not be a big deal. If it is a problem then you are talking with the wrong contractor...

In reality breaking up the area with medium size jack hammer would not cause any problems, but that will stress the owner. So why bother.....

Thanks for all the input guys!

Cut the slab or Jack hammer or a combination, it is your choice. The more important issue is to locate the cables first if it is a post tension cable system. The contractor needs to avoid cutting the cables. Also, depending on the location, tunneling is another viable alternative to totally avoid cutting or jack hammering the slab. Get a foundation repair company to do the tunneling and/or concrete work. In my experience they are cheaper, faster, and better than paying a plumber to step outside of his expertise in order to get to his pipes. Plumbers can be dangerous with saws that cut anything beside pipe!

Originally Posted by Garry Sorrells

Many times it is about making the customer happy an not the typical or easiest method. The home owner is concerned about the existing cracks. So why not just do what will make rhew owner most comfortable. Often you get contractors that have an attitude of it is my way, the way I always do it, or nothing. Get someone that does not have a problem doing it the way that makes the owner most comfortable. Owner will be paying for the extra effort involved.

Wet saw or dry saw are a toss up depending on what you are willing to clean up. A wet saw where you build a dam around the area to be cut (rolled up towles and some duct tape with plastic works well and use a shop wet vack while you cut will keep the mess minimal.

Should not be a big deal. If it is a problem then you are talking with the wrong contractor...

In reality breaking up the area with medium size jack hammer would not cause any problems, but that will stress the owner. So why bother.....

That is one way to look at it. However, if the contractor is experienced it can be better to educate the homeowner as to what is the most cost-effective solution that will not cause damage. If they still have concerns, then it is up to them to decide what they want.

Regarding dry sawing concrete, that would probably make any client unhappy. Containing dust inside a house from concrete sawing is difficult. Another consideration with sawing is the choice of saw. Gas is not practical inside and electric limits the choices-I'm not sure if there are water cooled electric concrete saws. Hydraulic saws are an option, but cost goes up.

Great point Jim. Typical plumber seems to not care about damage since they figure another trade will just have to deal with what ever the plumber destroyed.

As someone who has had to repair pipes, wire and heating ducts all on mono slabs, the issues are usually closer to the surface ( within 6 inches) that you think or within 18 inches of an exterior wall. Most of the repairs i have made I just used a cold chisel to make enough of a hole to do the repair. I would use less is more before I cut or got our the major equipment.

IMHO breaking a slab for a water pipe repair is a waste of time. If it is leaking in one place, it is likely leaking in others or soon will. It's an endless and expensive proposition. Just bite the bullet and repipe. Been there and done that.

Originally Posted by Dana Bostick

IMHO breaking a slab for a water pipe repair is a waste of time. If it is leaking in one place, it is likely leaking in others or soon will. It's an endless and expensive proposition. Just bite the bullet and repipe. Been there and done that.

Hasn't anyone heard about tunneling. I have repairs damage pipes by digging and shoring under a mono slab years ago.

Originally Posted by Richard Burkard

Hasn't anyone heard about tunneling.

Yes, we, or at least I, have heard of tunneling ... and all thebad tthings left behind - such as the inability to properly and thoroughly compact the soil when the repair work has been completed and the worker backs out of the tunnel.

Not good long term results from tunneling.

Cut the concrete in a square around the area of the leaking pipe using a skill saw and diamond blade, that way there is a smooth surface for the new concrete to form to. Then use a roto hammer with a chisel bit to remove the concrete and get to the pipe. Repair the pipe. Pour new concrete .

Originally Posted by Sean Prior

Cut the concrete in a square around the area of the leaking pipe using a skill saw and diamond blade, that way there is a smooth surface for the new concrete to form to.

You don't want, or need, a smooth surface for the new concrete to form to, if you have a smooth surface you will definitely need to install some dowels into the sides of the existing slab, about 6" into the existing slab and then across the open hole, then the new concrete will stay where it was put.

Even with chipping out the opening out you would want the dowels across the opening, but at least the chipped edges would provide some keys for the new concrete to grab onto, whereas as smooth sides does not provide any keys.

Sometimes ... smooth is overrated ...

Originally Posted by Jerry Peck

You don't want, or need, a smooth surface for the new concrete to form to, if you have a smooth surface you will definitely need to install some dowels into the sides of the existing slab, about 6" into the existing slab and then across the open hole, then the new concrete will stay where it was put.

Even with chipping out the opening out you would want the dowels across the opening, but at least the chipped edges would provide some keys for the new concrete to grab onto, whereas as smooth sides does not provide any keys.

Sometimes ... smooth is overrated ...

You are right about not wanting a smooth surface. Also, cutting concrete with a saw is very dusty. Assuming the concrete is placed on well compacted fill dowels are typically not needed. I am assuming we are talking about a small hole. If a large opening was made then dowels may be desireable, especially if the flooring is tile or similar. With tile you should still use an isolation membrane or lath.

Unless the hole is quite small or the cut/chipped out slot is quite narrow, dowels are needed even with well compacted soil.

The cut is only 1" deep, I was assuming the concrete is the finish surface. when you chip it out that creates a rough surface below the cut line. I have done this many times. Creating a little dust is part of construction. I would be done with the project and you guys would still be talking about it.

Originally Posted by Sean Prior

I would be done with the project and you guys would still be talking about it.

Haste makes waste ... apparently you have not thoroughly digested and understood all the concepts discussed and asked about ...

You are correct, though, if you wanted to do it your way without considering the clients wishes and concerns - you would indeed "be done" ... before you even started.

Saw vs Jackhammer?

Check to see which walls the underslab pipe comes up into.

Just abandon the offending section under the slab, and run it overhead.

It would be less expensive, messy, and disruptive to the customer.

Originally Posted by Jerry Peck

Unless the hole is quite small or the cut/chipped out slot is quite narrow, dowels are needed even with well compacted soil.

Based on what?

Originally Posted by Mark Reinmiller

Based on what?

Good construction practices, ACI 318, the fact that the concrete is part of "reinforced" concrete slab on grade (reinforced with either WWM or fiber-reinforced) and then one intentionally cuts out the reinforcement and patches the concrete without adding the reinforcement back in.

The only people I have seen who do not use dowels for repairs in concrete slabs are non-contractors who do not know, DIY'ers who do not know, and people who cut corners without considering the consequences.

I could go on if you need me to.

O Frame, typically concrete is reinforced with rebar, remove the concrete and leave the rebar intact. If you have to cut the rebar, cut it in the middle of the hole and bend it out of the way. When you are done with the repair bend the rebar back into place cut a new piece of rebar that is long enough for a 12" overlap on each side then tie it together using bailing wire. I live in a climate where pipes can freeze in the winter, so we don't run plumbing in the attic space, it also adds length to the supply lines which means it takes longer to get hot water to the fixtures. Hope this helps.

Originally Posted by Jerry Peck

Good construction practices, ACI 318, the fact that the concrete is part of "reinforced" concrete slab on grade (reinforced with either WWM or fiber-reinforced) and then one intentionally cuts out the reinforcement and patches the concrete without adding the reinforcement back in.

The only people I have seen who do not use dowels for repairs in concrete slabs are non-contractors who do not know, DIY'ers who do not know, and people who cut corners without considering the consequences.

I could go on if you need me to.

ACI318 is for reinforced concrete. Concrete with reinforcement for shrinkage control is not part of ACI318. Maybe in your area slabs are commonly reinforced. Around here rebar or WWM is not that common. I see patched slabs quite a bit (about every other house has a retrofitted perimeter drainage system) and none of them are doweled. Concrete keys is quite well to irregular surfaces.

Originally Posted by Mark Reinmiller

ACI318 is for reinforced concrete. Concrete with reinforcement for shrinkage control is not part of ACI318. Maybe in your area slabs are commonly reinforced. Around here rebar or WWM is not that common. I see patched slabs quite a bit (about every other house has a retrofitted perimeter drainage system) and none of them are doweled. Concrete keys is quite well to irregular surfaces.

ACI 318 is for reinforced concrete, and concrete is reinforced for many reason and by different means - reinforcement of concrete slabs on grade is not for shrinkage control, that is why control grooves should be let into the concrete.

If WWM is not used, is the concrete fiber-reinforced concrete? If not, what reinforcement is used in your area, surely no one uses unreinforced concrete for slabs anymore (other than driveways, sidewalks, etc.).

Originally Posted by Jerry Peck

ACI 318 is for reinforced concrete, and concrete is reinforced for many reason and by different means - reinforcement of concrete slabs on grade is not for shrinkage control, that is why control grooves should be let into the concrete.

If WWM is not used, is the concrete fiber-reinforced concrete? If not, what reinforcement is used in your area, surely no one uses unreinforced concrete for slabs anymore (other than driveways, sidewalks, etc.).

Jerry, I am not trying to turn this into an argument, but just making clear what is required or necessary. The IRC requirements for slab on grade construction do not require reinforcement. Neither does the ACI332 standard for slab on grade.

Section R7.12.1 specifies the requirements for shrinkage and temperature reinforcement for slabs. It also states that these provisions are intended for structural slabs only, they are not intended for soil supported slabs on grade.

There is a section in ACI318 for structural plain concrete (Chapter 22). In 22.1.1.2 it states that design of soil supported slabs such as sidewalks and slabs on grade shall not be governed by the code unless they transfer vertical or lateral forces from other parts of the structure to the soil.

Most newer construction I see around here is track construction and they seldom exceed code (actually they seldom even meet code).

Personally, when it comes to patching an opening in a slab on grade I don't think anything up to a couple feet in length of a side would need to be doweled, unless I had concerns with the sub-grade or sawcut edges. There is just not that much vertical force involved to worry about. Not that it would be a bad practice, clients and contractors don't like to spend extra money or do extra work.

If I am tying a new slab into an old slab or on any new slab in general I specify reinforcement. I try to get them to use rebar. I have never seen WWM installed properly. Every contractor thinks you can pour concrete on top of it and then pull it up to the top half of the slab (while standing on it).

I may be jumping in over my head, but it seems to me that all monolithic slab foundations are, by definition, structural. Anyone building without reinforcing steel or post tension cables would be laughed out of town. Heck, we don't build ANYTHING including walks, driveways, etc. without some sort of steel, fiber, or cable. Soil is to active here, even perfectly good reinforced concrete gets stressed to the point of failure.
Anyone repairing a patch more than a foot or so would be foolish not to dowel.

Originally Posted by Jim Luttrall

I may be jumping in over my head, but it seems to me that all monolithic slab foundations are, by definition, structural. Anyone building without reinforcing steel or post tension cables would be laughed out of town. Heck, we don't build ANYTHING including walks, driveways, etc. without some sort of steel, fiber, or cable. Soil is to active here, even perfectly good reinforced concrete gets stressed to the point of failure.
Anyone repairing a patch more than a foot or so would be foolish not to dowel.

Construction practices are often very regional. We have no shrink/swell clays in my area. A residential contractor would not even know what a post tensioned slab is. Monolithic slabs are not that common either because they are not as practical to construct when they need to extend 3 feet below grade. With the slabs you are probably used to dealing with I agree that dowels below much more important (as well as not cutting tensioning cables).