Flashing reistant to corrosion

[ajk1]

Is there any flashing that is particularly resistant to corrosion from de-icing salts? The situation is a public library where the existing deteriorated flashing extends from ahout the 4th brick course above the sidewalk down to the sidewalk. We are removing the sidewalk, sounding the garage roof slab below to detect delaminations and repairing, re-waterproofing the garage roof slab, placing a high stength drainage board, then re-pouring the sidewalk and putting in new flashing to replace the existing deteriorated flashing. I am not sure that galvanized steel flashing would be as resistant to corrosion in the salt environment as would be wanted.

QUESTIONS

Is there a PVC flashing, or any other non-metallic flashing, that could be used?
If so, are there any disadvantages to it?
Does it come in brown colour?
Is it UV resistant?
How should it be specified (thickness, etc.)?

If a metal flashing is deemed to be corrosion resistant in a chloride environment, how should it be specified...how thick, etc?

 

[hope9010]

smb4050 - interesting.

 

[a2mfk]

cvg- That article specifically addressed the newer pressure-treated wood preservatives being harmful to aluminum, which is a different beast than deicing salts (but my corrosion chemistry knowledge is very limited). Connections, nails, bolts, etc. in the new PT wood need to be galvanized.

We all know aluminum performs well in saltwater, which is why boats use it in their propellers, and they make docks, decks, and handrails near or on saltwater out of aluminum. But I guess the same cannot be said about the exposure to deicing salts, probably because the NaCl concentration is so much higher in deicing salts?

This article says stainless steel is the way to go. But it seems to be an industry website, so take that with a grain of deicing salt.

http://www.imoa.info/molybdenum_use.../architecture/global_deicing_salt_article.php

For example, there is a common misconception among architects that aluminum’s corrosion resistance is similar to that of stainless steel. This is incorrect. In locations that are exposed to chlorides (coastal or deicing salt), the corrosion rate of aluminum is typically 10 to 100 times that of stainless steel.

 

[hope9010]

a2mfk - thank you for the info. I did not know that about aluminum in boat propellers. Your "grain of salt" comment is appropriate, in more ways than one. I will see if I can upload a picture over the weekend.

 

[hope9010]

Attached is a photo of the flashing

 

[grogannc]

I would go with copper fabric if this is flashing in a wall. I can't tell from the pic if you are doing stepped through wall flashing or more of an exterior counter flashing. If this is inside the cavity, from my experience stay away from anything pvc or self adhering. The corrosion over time is a secondary issue compared to the poor installation typical of the plastic stuff. I would rather have it leak in year 40 than year 1. Those self adhering ones don't stick due to dust and debris. There is no substitution for fabric copper in a bed of asphalt in regards to quality of installation.

something like this

http://www.advancedbuildingproducts.com/commercial/copper-fabric.cfm

 

[MikeHalloran]

We all know aluminum performs well in saltwater, which is why boats use it in their propellers, and they make docks, decks, and handrails near or on saltwater out of aluminum.

No, we don't all know that.

Landlocked boatbuilders use aluminum for handrails because it's cheap, looks good in the showroom, survives the warranty period in freshwater, and so far they haven't been forced to make their handrails OSHA-compliant.
Saltwater boats are different.





Mike Halloran
Pembroke Pines, FL, USA

 

[ajk1]

grogannc (Structural)- the flashung that I am talking about is on the exterior face of the brick wythe of a bonded brick and block wall (not a cavity wall). I believe that the flashing to which you are referring is internal flashing. But thanks for the info. always good to see what is available and what it looks like.

 

[grogannc]

Ok-now I see. So basically exterior counter-flashing is all it is. That in my opinion is a tough detail. I know they do things differently in different parts of the country but seems that not having a cavity is asking for trouble. I know a lot of older buildings were done this way but with the newer brick and mortar they tend to be more porous and designers fight tooth and nail to maintain that cavity. Mortar nets are often spec'd on bigger projects even. That being said, if I had to do this detail I would probably go with prefinished galv. steel with a kynar 500 coating. Then touch up and cut edges (I think they make touch up paint). Reason for the prefinished is they do weather testing on the coating, etc. so it has a benchmark. I would call them and tell them what you are after and I'm sure they will steer you in the right direction. I believe they offer a warranty. I wanna say 30 years but its been awhile and I can't remember.

So Kynar 500 finish for the flashing and the detail would be a step flashing with each piece having a term. bar at the top and the top of the flashing angled to accept a sealant cove. Or you could cut the mortar joints and do a recessed top with lead wedges securing the flashing. The bottom of the detail is going to be the worst. Unless I am missing something it looks like you have to stop the flashing at the stair sealant/wall joint. If this is the case, seems the best you could do is get the hem as low as possible and angle it out (which it normally is). Good luck. Hope that helps some.

 

[ajk1]

grogannc (Structural)- yes what you describe is exactly my case, including the geometry of the counterflashing. I did get a recommendation on Friday from someone with an architectural background that I know, and it was I believe very similar to what you recommend, except it was Stelco finish rather than the kynar 500, but I suspect that they are similar. I will try to retrieve his recommendation and post it here Sunday and see what you think. This building was built in 1974 and this wall is not a cavity wall. Thanks for the help. I think it is right on. Sounds like you have had a lot of experience in this. Much appreciated.

 

[ajk1]

Belwo is what an aquaintance with archotecturla background gave me for the floshing. I think this is about right and close to what groganic recommended.

Sheet Metal Flashings
.1 Prefinished sheet metal flashing: Galvanized steel, 0.71 mm (24 ga) core nominal thickness, Z275 zinc coating to ASTM A525M-80. Finish to be Stelco's 8,000 series or an approved equivalent. Finish to be applied on both sides. Colour to be approved by the Owner from the 12 standard colours listed in CSSBI's General Colour Card.
.2 Fabricate and install counter flashings in general accordance with applicable CRCA 'FL' series specifications and / or as indicated on Drawings. Fabricate counter flashings in 2400 mm maximum lengths. Provide an "S-Lock" joint at all end joints and at all horizontal joints between the vertical flashing and base counter flashing. Make allowance for movement at joints. Hem all exposed edges at least 12 mm for appearance and stiffness. Form sections square, true, and accurate to size, free from distortion, oil canning and other defects detrimental to appearance or performance.
.3 Apply isolation coating to metal surfaces to be embedded in concrete or mortar joints. Turn top edge of flashings into recessed reglets or mortar joints a minimum of 25 mm. Fasten sheet metal flashing into reglet joint at a maximum spacing of 450 mm or more often if required.

 

[grogannc]

That sounds pretty good. I like the reglet idea. Hadn't thought of that. Gives you extra adjustment to install and given the tough detail I think you may need it. Just make sure the flashing is secured in the reglet well. I've seen a lot on roofs that are half falling out.

I'm sure the finishes are similar. In my mind you just want something with some ASTM weathering requirements met. The kynar is good stuff and thus all I have ever used. But I am sure there are others out there that do just as well.

I would also check into touch up paint since you are going to have direct salt contact. I am pretty sure it comes in a spray can even. Just have to make sure the contractor doesn't make graffiti art out of the flashing. If you were really worried you could look into prefinished aluminum. I've used it for a standing seam metal roof before at the coast.

 

[ajk1]

grogannc (Structural)- ok sounds like we have a soliution. I will look into the touch-up paint. Thanks grogannc for the great assistance, as well as to everyone else. Much appreciated.