View Full Version : Chimney cap advice needed.

11-29-2010, 08:30 PM
At the top of the chimney there's a slab of sandstone acting as a chimney cap, supported in each corner by a stack of four mortared half bricks. The mortar is the portland cement type, rather than ancient lime mortar. I've got a 6" flexible stainless chimney liner to install within the 11" x 11" tile flue, and top entry seemed best. But I need to pop that top off. I was thinking of grinding out a bit of mortar with an angle grinder so that I could get a flat bar in, then gently trying to break it loose. Later I'll set it back in place with a dab of high temp caulk on each corner, rather than trying to mortar it back.

Any comments on the plan?


11-29-2010, 08:45 PM
Where are you going to be standing while you are doing this?
Assuming that the chimney is on a pitched roof have you considered building a substantial scaffold on which you and all of your materials can stand while the job is in progress?
I speak from experience.

Oh, the procedure you were asking about sounds as if it should work, but I doubt that you'll need an angle grinder--a cold chisel and a hammer should work okay.

11-29-2010, 08:59 PM
I don't know if high-temp caulk is the way to go for replacement. Unless you have a chimney fire I doubt it will be that high-temp, out in the air. You need something that is going to withstand hurricane-force lift, or else your chimney cap will be coming down through your skylight, if you know what I mean.

11-29-2010, 09:03 PM
It's going to depend on the quality of the mortar, how well it bonded and the strength of the sandstone. It might just pop off like nothing, or you may try to lift one corner and break the stone. I would cut out as much of the mortar as possibe with the abrasive masonry wheel first to be safe, just as you suggested.

Peter Kalshoven
11-29-2010, 09:36 PM
I'm more curious about the liner. If you are installing a 6" SS liner, there is a reason. I'm guessing a woodburning insert or stove. So rather than worrying about restoring the stone cap, make sure that you have a cap that works with the liner you are putting in and with the appliance you are installing. What do the installation instructions recommend? That's what you should install.

11-29-2010, 11:19 PM
I like your plan and would use us PL masonary adhesive/caulk.


Paul Girouard
11-29-2010, 11:37 PM
Bust the whole stone cap off, install the liner and have a metal cap made to cover the top with the right sized hole for the new pipe to pass thru with a storm collar above the hole.

Painted , powder coated , or plain Galv. metal.

11-30-2010, 12:02 AM
Bust the whole stone cap off, install the liner and have a metal cap made to cover the top with the right sized hole for the new pipe to pass thru with a storm collar above the hole.

Right-o. You don't want to leave the tile flue open to the sky. So you need a cap to seal the flue around the new pipe, and also a top cap for the pipe that suits your climate (rainfall, wind, etc.) You can find another use for the sandstone slab.

11-30-2010, 07:01 AM
Alls I know from experience is, if you have a substantial length of straight chimmeny, putting in a flexible SS liner is asking for trouble. If it is for a stove, the sooting you will experience due to conensation will be excesive, and sweeping a long piece of flexi can be a disaster. Insulated stove pipe after where the chimeny passes into outside air temperature masonry is the only way to go, your fire will also draw a whole lot better

11-30-2010, 07:30 AM
Right. You all want a better story.

My plan is to get out my biggest extension ladder and run it up on the back side of the roof. I'll have to check, but I think that it will go from ground to peak, laying on the roof deck as it does so at the 11:12 roof pitch. I'll build a small (4' x 4') platform on the peak. I'll wear my safety belt and tie off to the chimney as well. If the ladder won't reach (Edit: damn, not even close.) then the plan is a ladder to the top of the ell, another to the top of the kitchen, sectional cat walk along the ridge, a short ladder (6') to the top of the main roof, and sectional catwalk to the chimney. I hope the big ladder reaches.

I have no worries about the cap going through a skylight, as it's downwind of the skylights in a northeaster. But the masonry adhesive sounds like a good idea. Of course what I have on hand now is 3M FB 136 high temp sealant, Henry 900 flashing sealant, and SeamerMate gutter sealant, plus some painters' caulk and other gunk.

I think the mortar is good quality, so I'll grind a bit, as Gib says.

The stove insert is a Vermont Castings Montpelier, which takes a 6" stove pipe, and can accept any flue up to 3x that cross sectional area. The chimney is 11" x 11" interior dimension clay tile in good condition, which means it's too big to let this insert draw at an efficient rate.

I like the look of the stone cap. It's functional and matches the one on the other chimney. My plan is to let the insert stand 2" proud of the chimney top. There will be a blocker plate around the insert at the level of the attic floor, and I'll throw down a vermiculite/mortar mix to seal it there, fill almost to the top with dry vermiculite, and then mortar to seal between the brick and the insert at the very top, sloping for rain drainage away from the liner. I might bury a little wire in the mortar for good luck. Yes, the kit comes with a cap. No, I'm not going to use it.

It's the chimney to the left.



11-30-2010, 07:33 AM
Double wall insulated SS pipe inside our old chimney when we hooked up our woodstove with a "T" on the bottom. What would be the long leg of the T hooks up to the stove, top of the crosspiece goes up the chimney and the bottom of the crosspiece has a removable cap. Very easy sweep - pop off the cap, tape a bag to the opening and run the brush down, no crud in the house. If you like the look of the sandstone cap, drill the corners and set SS allthread into the pillars and screw the cap down - you want it removable for sweeping ease. Wire top in the flue pipe is good - it keeps the wood ducks from trying (unsuccessfully) to nest in your flue. Just imagine the chaos of a sooty, irritated wood duck flapping around your house... (ask me how I know)

11-30-2010, 08:33 AM
This is a job best done in July... By someone else! :D

11-30-2010, 08:43 AM
Just imagine the chaos of a sooty, irritated wood duck flapping around your house... (ask me how I know)

The locals here sweep using a similar method, two chickens dropped in the top, caught at the bottom in the bag, rinsed, plucked, and then in the oven.:d

Rich Jones
11-30-2010, 08:49 AM
In addition to your platform on top, I'd use some roof brackets and 2x10's for staging on the lower side. I'd also use these stagings every few feet right from the edge of the roof. Just lean your ladder against the eave right below the chimney and climb the stagings. The brackets are inexpensive. You won't be able to reach everything from just the platform. I don't know how you are with heights or how nimble you are, but roof work can be very dangerous and just a little mis-step can lead to disaster. I've been in construction for 35 years and have seen more than one man maimed for life. Be careful! Or call an expert. Might be worth the price.

11-30-2010, 09:02 AM
Hmm. Cheap staging brackets a few feet down from the peak on the back would be an easy way to go. I don't know if I can get shingles pried up to nail them in in these temps. I've got two of those brackets. I'd need two more. Once installed, I'd leave them and just take down the planks.

I realized that going up the back is stupid. I should go by way of the sunporch roof, then up to the bigger chimney with an extension ladder. From there, staging across the back would be safest.


11-30-2010, 06:19 PM
It's in. It's lit.


11-30-2010, 06:35 PM

Phillip Allen
11-30-2010, 06:44 PM
you're doing fine...but the scaffold is the most important part...prep first and the job is easy...no prep and it is very dangerous...rent the scaffold and set it up right...tall enough that you can easily see over the top of the existing cap...get your heavy work hip-high

Rich Jones
11-30-2010, 08:46 PM
It's in. It's lit.


Job done? How'd it go?

12-01-2010, 07:49 AM
Before doing the angle grinder thing, I made some experimental taps with the hammer. The cap came right off.

My two biggest problems were that 1) I eventually managed to drop that hammer down the flue, at a point where it was blocked up enough that the hammer is essentially lost for good, and 2) while twisted over the peak, trying to nail on a scaffold bracket, I heard a distinct pop from the rib I injured four years ago and I felt it give an inch or so. It's a bit sore today.

The plate that's holding my hammer is about 10' down and I dumped a bunch of mortar on it from on high. I think I should do more of that. There are indications that I don't have the space around the chimney fully air sealed. I don't have the top centered properly yet either. I want to put in another plate about 6" down from the top, resting on the top of the top liner tile. That will center the liner pipe. I'll fill in the space around it with mortar and slope it to shed water. I need to finish the stove surround, which I'm making out of concrete board, angle iron reinforcement, high temperature caulk, and eventually tile on the face. And there's the plug for the fan unit, which I cut off in order to thread the cord through the hole I drilled in the side of the old steel hearth. I need to put on a new one.


Rich Jones
12-01-2010, 08:20 AM
Sounds like things are going well. Except for the hammer. 25 years ago, I dropped my favorite hammer into an inaccessilbe area behind a wall and wasn't able to recover it. Professional carpenters have a weird attachment to their favorite hand tools. I still mourn for that hammer.

Phillip Allen
12-01-2010, 01:24 PM
Sounds like things are going well. Except for the hammer. 25 years ago, I dropped my favorite hammer into an inaccessilbe area behind a wall and wasn't able to recover it. Professional carpenters have a weird attachment to their favorite hand tools. I still mourn for that hammer.

look at the first couple of courses on tall block buildings...especially 12" blocks. If you know what to look for you will find patches...they are where some mason has climed down and knocked a hole in the wall to retrieve a lost tool. I finally got out of the habit of laying tools on the tops of walls, others never did. (I also got really good at patches)

12-01-2010, 02:52 PM
I think that I framed SWMBO's 16oz Estwing hammer into a bathroom wall many years ago. It could not have been my ratty old cheapo with a wood handle, no.

I had to buy her a new one, and I am not allowed to touch it.

12-01-2010, 03:48 PM
This was a 22 oz Plumb, smooth face, straight claw, rubber coated fiberglass handle. About 18 years old. Good, but not an heirloom. I imagine things stink up at roof level just now.


Rich Jones
12-01-2010, 03:50 PM
In my case, the hammer was dropped down behind a customer's wall that was covered with nice wallpaper. Didn't think they'd appreciate me cutting a hole through that!

Paul Girouard
12-01-2010, 09:27 PM
String with a magnate ? Maybe you had to close it right up that day? I've fished a few things out of walls that way. Takes some planning to get all the not so common pieces to the right place.

Found lots of tools in walls and attic's as well , your hammer is just a future mystery for some one!