Mystery solved: sneaky leaks and persistence pipe noises in the wall

It started when there were strange noises after a bath or shower in the upstair bathtub.  It sounds like droplets of water falling from great height.  The frequency will diminish quickly into once per minute and much less, but will last hours after a bath.  I suspect that there is a leak in the drain pipes.  Water drips very slowly but falls from 2nd floor straight down into the ground, hitting some hollow pipes or other amplifications.  Or that something in the 20 year old pipe system held up water, and drips slowly inside the pipes, falling straight down over great height.

I never had a oscillating tool before and opening a dry wall is the last thing I would do in my house.  I never cut open a hole in a dry wall.  I don't know how to cut.  Drilling holes, cut by utility knife seems to be so primitive.  In addition, how to cover that irregular hole as if nothing happened?

Also we had a pinhole leak in the copper pipe once a couple of years back.  It was near the same tub, under the HAC blower.  So I cut open the bare floor board instead to have a look.  I replaced the leaking pipe section with a short flexible connector.  It was a hard to reach area from there so I opted for shark bite connectors and a flexible reinforced tube with screwed ends, with a seal inside.  I always think it's a bad job breaking all plumbing codes, and may have small leaks.  But we never saw water sipping into the ceiling downstairs again.

So I suspect there may be water collected somewhere between the walls or the ceilings.  And may be toxic mold or rots.  It could be scary and hopeless so I postpone looking into it unless I am fully ready no matter what.  I was never ready.

Then, instead of water sipping through the ceiling, a pool water was collected in the ceiling, enough to open a hole in the dry wall.  Luckily, there wasn't much water and it was only after a shower or bath.

This is where the mystery begins.  It's not like water will leak during the shower.  It's unpredictable.  I can even waited for weeks without water coming down all the time.

Then I summoned all the protective gears and all the courage to confront the toxic mold. I knocked off the dry wall around the ceiling hole for the 1st time in 20 years, after the house was built.

That would be called the crawling space I think, between the upstairs floor board and the downstairs ceiling.  There's nothing.  The dry wall around the hole is still pretty much dry.  The floor board looks dry and so is the studs.  The ABS drain pipes are pretty dry though with some water stains near the bottom of the under side of the tub.  And yes, the tub is directly above me.  The replaced copper pipe section looks brand new and the rest of the copper pipes seem to be in good condition and dry.

There are visible spider webs and old rat bites on some pipe insulation materials.  The rat infestation would have been dealt with when we moved in.  That's it.  No horrible stuff.

Obviously the drain pipes wasn't leaking and couldn't identify the source of the leak and noise from where I could see.

When cold water is turned on fully, nothing will happen.  All sorts of things happen only when the hot water is turned on.  So I suspect the faucet leaks at the hot water inlet.  As there is no height for water drops to make great noises, I also suspect something fishy at the copper pipe at top of the shower.

I could have knocked down the whole dry wall behind the tub immediately to get to the hot water supply.  But fortunately, behind the tub, there is a space for the HAC.  I can't get to the tub from behind because the one storey HAC blocks everything.  I can know down the dry walls, but can't put it back without moving out the huge HAC system.

I can knock down the tiles at the tub side to get to the faucet and pipes.  But then I have to use an oscillator tool to cut out the tiles, and then cut the backing board.  The pipes also go through holes in some studs.  Putting back everything is much worse.

So I did more diagnosis to make sure.  The copper pipe at top of the shower is dry.  You can hear the pipe noises as soon as the hot water is turned on, but it's hard to see water leaking.  I actually observed under the tub when everybody took showers and baths in the morning before work and school.  People come and go.  I can only conclude that there is no leaks.  Until my wife was in the tub for a while.  Then about a cup of water ran down the drain pipes, then stops.

So I did a final test.  Nothing happens unless I turn on the hot shower for over 5 minutes.  Nothing even if the hot faucet is fully on.  Water will start dripping down the drain pipes after 5 minutes of hot shower, and only hot shower.

The next phrase is to turn to the internet for solutions.  The first thing I hit is that ABS drain pipes were found to be defective in the 80's.  There was class actions.  My pipes should be slightly newer but the builder may use stocks several years old.  That seems a good explanation.   I should be replacing the drain pipes under the tub.  That's a horrible thought.  I have to make a big hole to crawl in and under the spiderwebs, not knowing if I can reach the back of the tub down there.

They say to look for repeated repair around the pipes.  Yes, the joints look shiny new but the pipe itself look beaten with water stains.  (But of course the joins look shiny and new with the protection of the ABS glue.)  There are a lot of couplings and turns under the tub so I guess that's right.

Someone argues to apply and apply ABS glue around the joints to fix the leaks.  Some suggest to use marine glues and repairs.  I concluded that ABS glue is the way to go because I know it welds the joints together into one piece, and that the whole piece contracts and expands as one, without extra stress.

I could have done that but then the water seems to come from the joints but really not.  It came from further up, just following the pipes down.

But then it dawned on me that the pipe noises are not caused by water leaks but by thermal expansion.  I found the information that they expand a lot and you have to allow for that in proper installation.  They must have hired a cowboy to do that in my house.  Not only they violation all codes for expansion (if they have that then), they did the minimum effort to allow the pipes to turn corners and down the wall.

So I realized that whenever I turn on the hot water, the thumping noises start, vigorously at first and then taper off when all the pipes are warm.  When the hot water is off, the noise will come back.  It thump once or less per minute and last for hours.

It's funny that we had been looking to move up and opened our house for showing with appointments.  It's very embarrassing when someone came in and hear a loud thump inside the wall in the middle of the living room.  I told my wife please don't take a shower less than a couple of hours before an appointment.

If I had known that, I could just run a lot of cold water down the drain after a hot shower, until the noise stops.  It's as quick as the noise starts.

I cut larger the holes in the studs where the drain pipes went through.  But I can't do anything when the pipes go into the vertical wall.  I suspect the pipe is pressed against a lot of studs along the height of the wall.  I thought of opening the wall to cure that, or to cut out the pipes to add a flexible section.  At the end, compared with doing nothing, with cutting out everything with no guarantee, I opted for the former.  But I don't understand why in the first 10 years we don't have any expansion noise.  Or did we not?

With one mystery solved, I went on to philosophies where the water came from.  I concluded that it's the overflow drain hole.  The seal or the pipes degenerates and water leak from there.  My reason?  When water drips down, it will look like coming from leaking pipe joints.  And it takes over 5 minutes during a hot shower for hot water to condense in the drain cover and enough to run down the pipes outside.

Now I can see the water coming but then how is it so unpredictable?  I'm much better than the plumber in this.  My wife is a compulsive person.  After summer vacation, she took a good bath, washed the bathtub, and used the shower head to spray and clean everything, including the overflow plate.  That explained there were enough water to make a hole in the ceiling.

And that a compulsive person particularly like to flush a lot of clean water into some perceived dark and dirty places, like the overflow drain.  That explains why nothing happened when I was observing under the tub, until my wife came along and until the end of her shower.  She cleaned the bathtub!

So I read on the internet that the overflow seal is a common part to be replaced.  I opened the cover plate and saw that it is.  My tub wall look straight and flat so I tried to get a flat gasket instead of a tapered/bevelled one.  Only the depot have the ones large enough for my grand old tub.  I got one but it turned out to be tapered.  I found only one on the internet that is flat.  I ordered but never came.  I asked online if the one at depot is flat.  I ordered one before the manufacturer answered.  All are tapered.

That wasted me a whole week when there is a big hole in my ceiling under ugly pipes.  But then it dawned on me that a flat straight wall doesn't necessarily use a flat gasket.  I tried to put in the tapered one and it seemed that it didn't fit.  I looked at the old one fallen down through the ceiling.  It was totally degenerated but it could be tapered.  I opened the overflow drain cover again.  I rotated the gasket upside down and there was a better fit.  I was silly to put in the other way around and claim unfit.  Then I rotate the gasket slightly to get the best fit.  Then I closed the cover tight.  I tested the seal with the shower head and then an overflowing tub.  It worked.  Just the overflow opening is not big enough to prevent overflow at maximum flow.  But that's immaterial.  We have children and will never fill a tub that way.

OK, everything explained, no serious damaged and everything fixed, except for the noise and hole in the ceiling.  It also explains why there is some water stain at the ceiling in the garage under the 2nd bathtub.  But I have no rush to fix that.  I just told my wife don't do that to the other overflow drain until I change the gasket.