While replacing our baseboards we noticed that there was mildew on the bottom of the wall. I opened the wall and found that there is a 3/4 inch copper hot water pipe that comes up out of the slab and joins at a T about 6 inches up. Both outlets of the T are 1/2 copper. One continues up the wall and one goes back down into the slab and continues on to the sink. The pipes were wet from the plastic wrap at the slab up to the T. The T was behind a piece of 2x4 between the studs so it was difficult to see. I had a plumber out who couldn't detect any leaks. He put a piece of paper towel in there and 3 hours later it was soaked.

I thought it might just be condensation so I put the pipes in insulation, but that didn't help much. I checked tonight and the back of the 2x4 block was wet right behind the T and there was a damp spot where the wall insulation met the sill plate next to the water pipe. It is also fairly damp down in the hole where the pipes go into the slab.

I took off all the insulation and took off the 2x4 that was in the way. The T has calcification on it and seems to get fairly wet periodically. But the pipes seem to be dry above it. There is no obvious leak that I can see.

Any idea what is going on?

Thanks.

It sounds to me like the calcified joint has a slow leak. Before doing anything else, wrap a paper towel or rag around the pipe above the tee. Make sure the ends do not flop down on the tee. If it stays dry, and the tee and below are wet, the leak is below the towel. Check to see if there is any chance it is rain leaking in from the outside.

I have not had good luck trying to fix others' careless work. I usually end up taking the fitting completely loose, cleaning up it and the pipes to bright metal, tinning, and then resoldering, adding wet rags to each joint as I solder the next. This could be difficult to do in a tight area. The 2 x 4 may be to support the pipes and could be remove to fix the leak. Maybe Tom will have a better idea.

Thanks for the reply.

I wouldn't be surprised if you are right, but I've never heard of a leak in copper pipe so slow that you couldn't actually see it. But then, I'm not a plumber!

I believe the 2x4 was there to support a gas line that is close to the water pipes. It comes down from above and then goes out the wall where it is capped off. I guess it was put in to connect a barbecue or something.

I'm actually trying to finish putting in new laminate floors and don't really want to be screwing around with plumbing. I shouldn't have to - the house was built in 1997. So I guess I'll have to call a plumber as I learned several years ago that messing with soldering copper pipes takes more practice and patience than I have for this little project.

I would take a good look at that gas line where it goes through the wall. If you have had rain, it may be coming in around the gas pipe and running down the 2 x 4.

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Originally Posted by Ralph

While replacing our baseboards we noticed that there was mildew on the bottom of the wall. I opened the wall and found that there is a 3/4 inch copper hot water pipe that comes up out of the slab and joins at a T about 6 inches up. Both outlets of the T are 1/2 copper. One continues up the wall and one goes back down into the slab and continues on to the sink. The pipes were wet from the plastic wrap at the slab up to the T. The T was behind a piece of 2x4 between the studs so it was difficult to see. I had a plumber out who couldn't detect any leaks. He put a piece of paper towel in there and 3 hours later it was soaked.

I thought it might just be condensation so I put the pipes in insulation, but that didn't help much. I checked tonight and the back of the 2x4 block was wet right behind the T and there was a damp spot where the wall insulation met the sill plate next to the water pipe. It is also fairly damp down in the hole where the pipes go into the slab.

I took off all the insulation and took off the 2x4 that was in the way. The T has calcification on it and seems to get fairly wet periodically. But the pipes seem to be dry above it. There is no obvious leak that I can see.

Any idea what is going on?

Thanks.

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Hi Ralph,

First off you have to pinpoint the leak. My money's on the tee but water's a odd actor. If the pipe's dry above the tee then we can discount water coming in along the gas line. BTW. We call leaks so small we can't spot them "weeps".
Sometimes a leak under the slab will force water up the Armo-Flex,(insulation) and out along the pipes. However you took care of that when you removed the Armo-Flex. That just leaves the tee and its solder joints. All the water in the pipes will have to be evacuated and the pipes totally dry. Then the tee can be unsoldered and a new one soldered back in. Good luck, Tom