Best way to seal this flashing to the concrete stoop

Sometime in the past a contractor installed this flashing between the siding and the concrete stoop. It was sealed with tar and then concreted over, which, of course, failed and has been leaking water under the flashing. The concrete stoop is exposed to the elements, getting rain and south Mississippi morning sun. I’ve removed the concrete he used to cover the flashing and fixed all the water damage.

Any ideas on the best way to seal the flashing to the concrete, especially considering it is exposed? No problems in caulking the top part of the flashing where it meets the siding, but not sure what to use to seal the flashing to the concrete. I’ve thought about using a silicone caulk or a urethane adhesive and then covering with a strip of EPDM single adhesive roofing repair/joint tape. I don’t think flashing tape is a good choice because of the exposure. Whatever I come up with, what would be the best way to prepare the concrete for a good bond? Also, can you paint the EPDM tape?

I know this is a bad design and the best solution would be to tear out the stoop but that is not an option at this time.

Had the original contractor waterproofed the wall behind the siding and concrete, you wouldn’t have this problem. Sealants will work for a time and then will need re-doing. You might consider using a deck coating system. Use a deck to wall detail where you embed reinforcing mesh in the corner to reinforce the corner, then use a 3 coat deck system over the concrete top, bringing it up at the corner to tie in with the metal and wall. One other thought is to use the existing metal (or add wider metal) and adhere it onto the deck with Seal Bond 500 or Chem Link M1. Both of those products will permanently adhere the metal to the deck.

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Dry it down with a heat gun, load it with water cut off.


Dang. You mentioned the nastiest substance known to all roofers. You can cut a tube open on a 3 story building and by the time you get to your truck, it’ll be on the seat, your shirt…


I’ve pulled 30 year old wall flashings and it was still gooey. If it doesn’t see daylight it might last forever. The only way to tame it is a rag with membrane cleaner or paint thinner on standby.

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Thanks donl. I was taught to use a urethane product to bond to concrete. The SB500 is polyether based (not sure the difference) and the bonding specs look good. How easy is this stuff to work with; I will need to get a liberal amount under the flashing and will need to clean up the excess. How would you suggest prepping the concrete for a good bond? Going to be fun cleaning under the flashing.

As a side question, would EPDM tape stick to the flashing and concrete if I wanted to use it in addition to the SB500 to seal the edge and cover the flashing?

The polyether is one STRONG adhesive/sealant. You would need to clean the metal and concrete (Weathered Membrane Cleaner or toluene or similar), then apply a reasonable amount between the two using an 11:1 or 24:1 caulking gun. You don’t need a 2" strip or anything that wide. Do a 1" line and then push the metal down to make a good sandwich. If you can fasten the metal down or weight it down until the product dries that would be best. That product and water cut off mastic, as rooferama says, are best kept off clothes. I have to laugh at water cut off mastic… throw away your clothes if it gets on them ‘cause it ain’t comin’ off anytime soon.

I make a lot of money doing repairs on roofs of contractors that laugh at water cut-off. I really do appreciate the cash flow!

I would cut a 1 inch deep slot the width of saw blade in the concrete parallel to the wall, clean it out really well, fill full of sealant and install a z flashing into the groove and up the wall behind the siding.


Thanks Jastewart878. That’s a great idea and would definitely work. Right now I’m trying to do this without removing the outside siding. It’s obvious from the inside that it has been leaking underneath the existing flashing so I was trying to seal the existing flashing. If I end up removing the outside siding (not all of course) I will definitely consider that.

Maybe cut the siding up an inch and try to stuff in new flashing? This would have the added benefit of keeping the siding from rotting more because it is too low.

I have never seen any sealant that would be able to hold that metal down on its own, but maybe one of the specialty sealants mentioned above could work . If you go that way, I would use some hammerset concrete anchors every 6" or so to hold flashing/sealant sandwich together.

Does the water pond there, if it wasn’t running under the flashing?

It doesn’t actually pool there, but it gets alot of water coming from a roof valley just above the porch end of the stoop. In addition to sealing the flashing I’m going to either (1) install a couple of diverters or (2) a couple of uncapped gutters to move water away from the stoop.

Also what about using EPDM tape? Will it stick to the concrete?

You’re making this too hard. I’ve never seen a terpolymer or silicone coating adhere without doing the whole surface. Problem being that moisture will wick on masonry, get under partial coatings, and divorce them. Go ahead and pull the flashing, clean out the dirt, replace any rotten wood. Then make your flashing how you want it, if your going to stay with white, pvc coated coil stock would work well. Cutting a reglet will work until you hit the inside corner, unless you work it into the brick also. I’d break the flashing in an L shape, with the leg running under the wood siding. Tension fit it in there before you pump 5-10 oz of water cut-off under the joint and install it. Water will not get past a contiguous bead of butyl. It’ll look sexy and you can forget about it for 20 years or so… Un capped gutters with a good fall will be self cleaning and solve half of the problem.

Thanks Darkthirty. I’ve never done a reglet although I understand it to be a grove in the vertical wall with counter flashing that goes over the main flashing. In this case I’m trying to understand how the counter flashing would work. If it’s not too much trouble could you do a simple drawing. You have a lot more experience with this. By the way, where the siding meets the brick is under a short overhang and the gap between the siding and the brick is concreted. I’ve been leary about taking some of the siding off because if I damage it, I will have to have more milled since it is not a standard profile.

as far as the term “reglet”, wasn’t sure what else to call it. Y you want to run the flashing behind the siding above the termination. Cut the paint with a utility knife and take your time. If the siding is hung with finish nails or they won’t loosen enough to pull, just drive them all the way through the siding.

Not sure whether anyone is still monitoring this. Darkthirty, you suggested Water Cut-Off Mastic. I was wondering what brand you prefer. I find Carlisle on line but my roofing supplier only has Firestone S-20 Water Block.

Water cut off mastic is all pretty much the same across brands.

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They’re pretty much the same.

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I can find some pvc coated coil stock as Darkthirty suggested but it only comes in 24" x 50’ for about $100 at Home Depot or Lowes. Roofing suppliers don’t carry it here. I hate to spend $100 when I need less that 10’ of the stuff. I can find some 14" x 30’ vinly flashing that might work. Any suggestions.