Home>Discussions>EXTERIORS>Scoring the Mortar in the Chimney to tuck the flashing in, for waterproofing?????
6 posts / 0 new
Last post
Scoring the Mortar in the Chimney to tuck the flashing in, for waterproofing?????

Thank-you in advance for any help with my question..

We have a leaky chimney/flashing. My husband has caulked/repaired several times only for it to start leaking again.. I looked through your suggestions on re-flashing the a chimney, and it does not mention the scoring of the mortar????

We have called in the experts, and they are recommending that they score, with a grinder,???? the masonry/mortar in the chimney to tuck the flashing into this groove and then, do the caulking over that???

I am concerned about the scoring messing with the integrity of the chimney???? Possibly cracking the rest of the mortar in the bricks and causing a huge mess or additional cost to us, down the road, for a brick mason.

The home is a one story ranch built in the 1960's with a double flew chimney. Only one side is actually used (double stacks for balance/looks I guess) it is a Wood burning fireplace.

We paid $1500.00 to have a stainless steel insert put in a few years back, and some masonry work done in the garage to the concrete block that had cracked, the mortar, from a chimney fire which we never knew we had????

We live in Indiana, and usually have winters that can get to -30 below or more with wind chills, with lots of freezing and thawing....We are not protected from the winter winds in our location. Wooded lot but our house sits on the front, of the woods.

Thank-you so much for any assistance with my concern...

Re: Scoring the Mortar in the Chimney to tuck the flashing in, for waterproofing?????

Tuck flashing is the way to go. It's not cut deep enough to be a structural issue and it gets repointed which will help restore the bond and seal the joint. It's been done this way for centuries so if there was a problem we'd know about it.


Re: Scoring the Mortar in the Chimney to tuck the flashing in, for waterproofing?????

You wedge the flashing lip into the joint with small rolls of the flashing material (copper or even better, sheet lead) then point in with mortar. THAT'S how it's been done for centuries, not "glued" with caulk.

Re: Scoring the Mortar in the Chimney to tuck the flashing in, for waterproofing?????

to be extra sure =

The roof flashing comes from the roof up along the side of the chimney

The counter flashing comes from a mortar line down over the roof flashing

Its this counter flashing that - A should be lead or copper if at all possible, and B- let into the mortar, C- Stepped / shingled if needed

Re: Scoring the Mortar in the Chimney to tuck the flashing in, for waterproofing?????


Ditto, what the others said.

The initial flashing, is originally installed first on the decking surrounding the chimney & the shingles are laid over the flashing; the COUNTER flashing, that is cemented into the cut-back lower course of the brick masonry both work on the obvious rule of nature that water always flows DOWNWARD by gravity; the counter-flashing can be easily installed by cutting back/into approx an inch or two of mortar from the lowest courses of masonry with a circular saw fitted with a masonry saw blade---removing this small amount of masonry from the joints is not going to compromise the integrity of the mortared bricks; besides, the removed mortar is replaced when the counter-flashing is installed with new mortar; if you already have flashing & counter-flashing, first try to work with what you have now & try to discover & seal the leak(s).

Counter-flashing has to be used due to the fraction-of-an-inch expansion & contraction of the roof vis-a-vis the chimney as the outside climate changes with the seasons---many people don't realize this & try to seal the chimney base without using counter-flashing.

Safety first! if you attempt this work yourself, make sure you use a strong safety line that you tie around the chimney & then around yourself, so you or your husband doesn't fall.

Consult the video below to see how flashing & counter-flashing is installed, plus other areas of the chimney that have to be checked out to make sure that you are getting the accurate location of the offending leak----this can mean bringing up a garden hose up to the roof & spraying your repair efforts after you're done to make sure you have found & repaired the offending chimney leak.

You will need to have the free Adobe Flash Player to view the video, or you can contact Adobe to get the free download.


Re: Scoring the Mortar in the Chimney to tuck the flashing in, for waterproofing?????

Caulk vs. mortar is another debate, as some roofers prefer mortar and others will swear by high strength sealants designed for the application that will probably maintain their integrity through any movement longer than mortar that will eventually crumble and fall out of the joint.

But in general what the roofers are proposing about scoring the mortar joint and clipping the flashing into it is the correct way to do it. If it is not already installed that way, and some other hack just slapped the counter against the side of the chimney then nailed or caulked it, that is probably why you are having a problem. When it is slipped into the mortar joints it is sealed in to prevent wind driven rain from finding its way in there but the mechanical attachment of the counter flashing to the chimney is what actually holds it in place and keeps the majority of the water out. When caulk is the primary defense against water intrusion it inevitably fails, and when it does water inevitably gets in.

The only thing I would suggest is if the bricks look old and withered it is probably worth taking the time to hand chisel the mortar out rather than attack it with a grinder.

Sponsored Stories

TV Listings

Find TV listings for This Old House and Ask This Old House in your area.