Water in chimney cleanout - can I seal off the cleanout with concrete?

guitarguy888

I have an older brick chimney that my oil furnace vents to. The previous owner had also had a woodstove connected to the same chimney, but years ago I had that changed to a steel double wall stovepipe for the woodstove. So the chimney is jsut for the oil furnace, and the furnace venting enters the chimney about 12" above the cleanout.

Just recently, for the first time in the 28 years I've lived here, I got water dripping out of the cleanout door at the bottom of the chimney. I had about 2" of water there, in a depression in the middle of the cleanout. Vacumed the water out a week ago, kept an eye on it. We've had about an inch of snow which melted since then, and now I have even more water... about 3 cups worth. No way this is condensation. And I think I now see the problem... 2 years ago I had a contractor install a french drain that runs flush with the outside wall of the chimney. At the end of the cleanout, it's open...there's just a little dirt and I can actually see the plastic of the french drain! I'm contacting the contractor, because they should have seen there was a hole in the back of the cleanout, or maybe they made the hole accidentally. But before I do, I'd like some ideas on the best way to fix it.

The opening at the end of the cleanout up to the chimney is small, only about 3-4" deep x the width of the cleanout which is about 10". So my questions are:
-Do I really need the cleanout... can I just seal it off?
-If I don't need it, what's the best way to fix this?
-My thought is to seal that open wall of the cleanout with hydrophobic concrete, from the inside of the trap (ground is frozen, no way I'm digging down there now). And in doing so I'll probably seal the upper opening from the cleanout to the chimney flue, it's probably unavoidable given how little depth that opening has.
-Is there a better way?
Thanks for any ideas!

guitarguy888

BTW, you'd think the french drain would catch all the water, but I'm guessing that the plastic has a hole in it. When poking around the back of the cleanout there was an old piece of wire mesh about 3"x6" heavily rusted. It's also strange that the hole at the end of the trap where the dirt and plastic is exposed, doesn't look like it used to have concrete or anything. Hard to say what it was before the french drain, though. Regardless, I'm convinced that's where the water is entering... there's no mositure I can see coming down from the chimney, but there'es a lot of moisture where the dirt and plastic is.

STEVEusaPA

A few things. Is the brick chimney lined and is it the only appliance in that chimney, meaning the double wall isn't using the same chase.
Also is the water entering because of a lack of a chimney cap or because of flue gas condensation.
And what's the temperature of the flue gas, entering the chimney, and preferably exiting the chimney.

Jamie Hall

In my opinion, and I'm not a chimney sweep, the cleanout should not be sealed. Rather, assuming from the description in your post that this is at or very near ground level, the ground should be regraded to slope away from it.

Why? Because no matter how careful you are, if part of the chimney is above the roof of the house, condensation will occur within the chimney in the colder parts -- no matter how carefully it is sealed -- and you don't want that pooling in the bottom of the chimney. That would cause all kinds of unhappy mischief, even if it never froze.

Robert O'Brien

My money is on condensation

guitarguy888

Really appreciate the replies. Yes, it's tile lined. No, nothing else shares the flue or chimney in any way. The old woodstove chimney hole was lined and sealed, and that's on the inside of the house anyway. It has a flue cap, same cap has been in place for about 6 or 8 years. Temperature: I don't know that, but guess I can figure a way to measure the exit.

While it's true it could be condensation, if you saw the back wall with the dirt/plastic I think you'd see why I firstly suspect that. The dirt/plastic is wet there. Above it, it's not. So I'm pretty sure I know where it's leaking in. And I've never had a condensation problem with my chimney in 28 years, same service company.

Re: slope etc., I totally get that and have improved the slope all the way around about 5 years ago. But the slop here is not good, yet this area has no option to regrade. It's a 200+ year old house with a stone foundation, but I'm already sloped up as much as I can and yet be below the sill beam enough. Plus, there's a slight elevation rise in the lawn near, but that's now got a nice slight depression over the french drain.

But after cogitating on it a bit, I'm starting to form some ideas... fix that back wall, and extend a concrete sidewalk to divert any water near the chimney out further, and more over the center of the french drain...

1. That back wall needs to be repaired, regardless. After taking a few more looks and measuring the back end of a 2.5' hole, I think I can do a back wall repair without blocking the top hole to the flue. It also looks like the top hole is partly covered with debris/ash and can be opened up a bit in the direction away from the back wall. I think I can fit a 3/4-1" thick run of hydrophobic concrete back there without blocking the top. I'd like to do it from the outside but that's not workable... concrete covers half the area, and the french drain abuts it on the rest.
2. On slope, facing the chimney from outside, the left side is already bordered completely by a concrete sidewalk and concrete pad for a bilko door. So I'm going to extend the concrete sidewalk all around the chimney to the right side, out about 3', so that it drains well over the french drain. It's a small area and that will ensure the water from that area gets further from the house. It will make a nice little sun porch too.
3. In the meantime, I'm going to lay out some plastic tomorrow, tacking it temporarily to under the siding.
Ground is now frozen again, but I'm guessing the problem will be greatly reduced on the next thaw.

What do you think?
Thanks!

STEVEusaPA

Can't see/say anything without pictures.

guitarguy888

In case it helps someone else, here's the result. After spreading the plastic, the water mostly stopped. So I ruled out condensation for the most part, and mixed 50/50 hydraulic cement and concrete, since the hydraulic isn't very structurally strong. I then made a small flat "trowel", a piece of wood with flashing on it, attached to a swivel, like a mic stand holder, that swiveled up and down with a nut for tightening (just barely tight enough to stay in place), and put it at the end of a stick. I tilted the contraption up at a 45 angle, loaded it with the mix, pushed it to the back "wall", and as I pressed against the dirt/plastic the swivel straightened out and I was able to push and smooth. I did this several times and built up a slanted wall, thicker at the bottom. I bent a small trowel and was barely able to reach the back and smooth it out, pressing into the corners. The hardest part was getting enough at the top, but it doesn't block the opening to the top at all.

2 days now and not a drop of water! I'll of course keep an eye on it.

While condensation does certainly seem plausible, I've been here 28 years and never a problem with that. And a couple days ago my furnace guy looked at it and said that amount of water is not likely to be from condensation. And the only thing that's changed was the french drain.

I did find a couple very small cracks in the concrete surrounding the chimney, ground level, but really small, doubtful if that was the main problem. So in the spring I'll use hydraulic cement on those.

Now I can check that off my list. On to the next!
Thanks for your help!