copper vs pvc under patio slab

jeffrowDecember 7, 2010

I am in the process of landscaping our backyard pretty much with a clean sheet of paper. I have the opportunity to run the main feed from the house to the irrigation system & several hose bibs under a as yet unpoured concrete patio slab. In SoCal so freezing not an issue. My options would be 3/4 copper sleeved in plastic or schd 40 pvc. Which would be more durable over time? I've had many issues over the years with pvc systems and while repairs are usually simple this run will be inaccessible after the slab is poured.

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Ron Natalie

How about PEX?

    Bookmark   December 8, 2010 at 8:23AM
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I like your idea to use sleeved copper rather than going cheap. That should give you piece of mind if the added cost isn't an issue. Concrete eats copper so as long as it's sleeved and better yet buried before the slab is poured, that wouldn't be an issue. I'm still a bit on the old school ways so I would be interested in what others have to say regarding the use of PEX for long term reliability. What do the local municipal Engineers recommend? I ask only because of the area being prone to earth movement in addition to the settlement of earth after construction.

Since you are working from scratch, couldn't you route the supply so it doesn't have to go under the slab? You may never have any problems but if you do, repair would be easier. The odds of not having any problems are in your favor but you'll thank yourself later if you should develop one.

    Bookmark   December 8, 2010 at 11:38AM
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I can bury it under the pour in the dirt for sure. It's not possible to route around the slab, at least not without a massive amount of digging. I would however end up burying a soldered on elbow and one connector. I know this is not recommended but not sure I'm up to brazing.

Pex is not all that common here, I think all the PB problems in the 80's scared most back to copper.

    Bookmark   December 8, 2010 at 3:08PM
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I would use the stuff we call poly pipe. It's the black stuff that comes in big rolls.

    Bookmark   December 9, 2010 at 8:37AM
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If you are referring to that stuff similar to what is used for well systems, I personally think that's a good idea. It's thick and flexible and seems to hold up forever.I think I'd be prone to use that,making sure the initial joint is good and secure.

    Bookmark   December 9, 2010 at 6:46PM
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Thanks, I'll check it out.

    Bookmark   December 9, 2010 at 8:07PM
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First off, let us clarify a couple points.
1. When running pipe under a slab there is to be NO direct contact between the pipe & concrete. The pipe must be buried in the subsoil under the slab with a minimum of 12" burial.
2. Any pipe passing through the concrete MUST BE sleeved.

All copper pipe joints under a slab MUST BE brazed.

Jeffrow stated that he is not sure that he is up to brazing. Actually brazing is no more difficult than soldering, providing of course that you have a torch that can provide the proper heat range. Personally I prefer brazing and I have brazed nearly all the concealed joints throughout my house, but then I also do Air Conditioning & Refrigeration work where all joints must be brazed so I have an Oxy/Acetelene tote torch.

In the post Jeffrow mentioned that he would have an elbow and joint that would require brazing. This leads me to believe that he is planning to use rigid copper. The preferred method would be to use continuous roll copper and make the whole run jointless. The only caveate here is when you buy the role copper make sure you get type K,L or M roll copper pipe and not copper tubing. The copper pipe is measured by its ID and has the same dimension as the rigid copper whereas copper tubing is measured by its ID and is slightly smaller. By example 1/2" copper pipe is the same size as 5/8 copper tubing.

The downside here is that copper is currently very expensive.

I would prefer to use PE (Polyethylene pipe) which is fully code compliant,readily available in 100ft continuous rolls and is only a fraction of the cost of copper. In this manner you should be able to make the whole run without any buried joints.

PEX is another option, but it is a bit more expensive than PE pipe and in the end I doubt that it would offer any better service life than the poly.

    Bookmark   December 10, 2010 at 3:02AM
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If you are referring to that stuff similar to what is used for well systems, I personally think that's a good idea. It's thick and flexible and seems to hold up forever.I think I'd be prone to use that,making sure the initial joint is good and secure.

That's the stuff. I always use the metal connectors and all stainless hose clamps not the cheap ones with the screw that rusts out.
Also has the added benefit of no joints except one at each end.

    Bookmark   December 10, 2010 at 8:34AM
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Thanks for the reply, on 1&2 I'm ok with that, I have probably a lifetime supply of sleeve from a previous job. You are correct, I was going to use rigid copper, I have used the soft copper in the past and while it worked fine it was always hidden from view so the fact that I couldn't roll it out straight didn't matter. I am connecting a 3/4" pvb at the house to an irrigation manifold. The run is only 14' or so, the cost of copper is not significant.

I have a Map torch, is that hot enough to braze with silver solder?

    Bookmark   December 10, 2010 at 10:13AM
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A turbo torch (the average DIYer can get anywhere) with a curved shield that wraps the heat around the joint on the end and using MAPP is more than hot enough to braze copper. Since you are not used to brazing, practice on a few pieces first. I say that because if you leave the torch on too long, you will melt the entire joint and it will drop as a blob to the ground. Also, with the turbo torch, you need to know the right distance to keep the flame away from the joint to make it a quick operation. Lazypup is right, brazing is no harder than soldering once you get the hang getting the rod to flow and covering the entire circumference of the joint and then backing off right away. It makes for a stronger joint also. When soldering, you don't let the flame hit the solder, you get the joint hot enough then take the flame away and let the joint melt the solder. When brazing, you keep the heat on the rod and joint and chase the melting rod around the joint with the torch. I too prefer brazing copper pipe for a number of reasons one of them being you can do a good joint even with those nuisance drops of water that always seem to show up in there. I think once you do it, you'll prefer the method also.

However, which ever way you go, is there some way you can make the joint at the house, inside the house? If that is the area that has you concerned, at least you can have the peace of mind knowing you can get to it. I doubt you'll have any trouble anyhow with the information everyone has given you and the obvious know how you already have.

    Bookmark   December 10, 2010 at 11:02AM
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Oh how well I know the frustration that some people endure while unrolling copper or roll poly pipe, if they only knew the trick, it is really quite simple.

Far too often the novice opens the copper roll in the same manner as they would a roll of electrical wire, pull the loose end out of the center of the roll then attempt to hand straighten the pipe as they pull it out of the roll.

The proper method is to remove the entire roll from the box, start with the loose end on the outside of the roll. Have a helper hold that end steady then stand the roll vertical and roll it in the direction of the run with the pipe peeling off the outside bottom of the roll on the ground as you go. When done in this manner it is easy to lay roll copper just as straight as you would rigid copper.

I have a Bernz-o-matic TS4000 torch that will burn either propane or Mapp gas although I seldom ever use Mapp. If you check the manufacturers specs on their web page you will see that Mapp burns considerably hotter when used with pressurized oxygen, but when used in a naturally aspirated air/fuel torch Mapp produces a flame that is only about 50degF hotter than what it produces with propane and both flames are well above the required temp for soldering or light brazing. When you consider that Mapp gas is about $10 a tank while propane is 1/3 of that price it is easy to see why I prefer to use propane most of the time. If I need the hotter flame I use my oxy/acetylene torch.

Silver Solder is a solder material and will not meet code for brazing the copper joints.

For brazing the copper you need to use silver braze rods which are rigid sticks of brazing material about 1/4"wide 1/8" thick and about 20" long.

Silver brazing rods are generally sold in a one pound container and the price varies by the amount of silver content and the current price of silver. When I first started doing HVAC work in the early 80's 15% silver brazing rod was selling for over $60/lb and 6% was going for about $42/lb. Needless to say, at that time we started using 0% Silphoz rod which was only $13/lb. With the price of precious metals today I would be afraid to ask the price of a pound of 15% but not to worry. If you go to an HVAC supply house or even ask a local HVAC tech you should be able to buy a single stick of 15% for a buck or two. In fact, an HVAC man may just give you a stub of 15%. I doubt that you would need more than about 2 to 3 inches for you project.

I would strongly recommend that you get a full stick and three or four copper couplings. You could then use a bit of copper to make a couple practice welds before making the connections on your project.

A word of caution here. The absolute key to successfully soldering or brazing is properly cleaning the pipe and fittings and using the proper flux.

Begin with a wire ID fitting brush and thoroughly clean the inside of the fitting. (you can get a cheap wire handle fitting brush at any hardware, home supply, plumbing supply or HVAC supply for a couple bucks. I buy them by the dozen and when I have a lot of fittings to clean I cut the handle off, then chuck the brush in a cordless drill.)

To clean the outside of the pipe use emery paper. I prefer to use the pre cut rolls of open weave emery cloth which is often called a "plumbers Roll". The open weave emery is a bit more expensive, but the debris falls through as you use it so the grit does not load up nearly as fast as common emery.

Do not be fooled into thinking you are using new copper so it don't need cleaning. Copper oxydizes very rapidly and just that little layer of oxide will make soldering or brazing difficult. Even when I clean fittings in advance, if it has been more than 4 hours since I cleaned the pipe and fitting, I take a moment to clean it again before attempting to solder or braze.

Having said all of that, if your total run is only 14' or so, I would be inclined to figure out the exact length and allow a bit of extra, then go to your local homesupply and get a length of PEX and use their tools to attach the fittings before leaving the store.

    Bookmark   December 10, 2010 at 12:26PM
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Wow..... thank you. I never noticed PEX at our local HD, I'll check it out. If I can do that it should solve the problem nicely. Is there any problem with 15"' or so of PEX sticking out of the slab in the sun durability wise?

    Bookmark   December 10, 2010 at 7:34PM
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PEX may not be exposed to direct sunlight or any source of UV light.

In this case you are going to bury the pipe under the slab. You could then continue to run it underground until slightly outside the slab and make a transition to another type of pipe before stubbing up to grade.

Rather than go to the big box home supply center I would strongly encourage you to go to a local "True Value" or "Ace" type hardware store.

The difference is that in the big box store, even though they advertise that they hire trade professionals, that does not always insure the person who is assisting you, assuming you can even get assistance, has any real knowledge of the task. In my experience they hire a plumber and have him stacking lumber while the electrician is working a register and the lord only knows where they get the monkeys stocking shelves in the plumbing department. But then, when you pay peanuts you have to expect to hire a few monkeys.

In many cases the big box stores have a huge showroom of fixtures but when it gets down to the basic nuts and bolts they are often sorely lacking. On the other hand most of the smaller hardware stores are franchised as a local Mom & Pop operation where the person waiting on you has an actual ownership interest in the store and they will go way out of their way to make sure you are happy. Generally they have a huge inventory of the basic nuts and bolts parts and if their is anything they don't have, they will get it for you immediately, sometimes within the hour but at most overnight.

    Bookmark   December 11, 2010 at 2:37AM
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