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Flashing reistant to corrosion

Flashing reistant to corrosion

Flashing reistant to corrosion

(OP)
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?

RE: Flashing reistant to corrosion

Why not stainless?

RE: Flashing reistant to corrosion

I'd call Hohmann and Barnard (http://www.h-b.com/). I had a question on brick ties the other day and got to talk with one of the Hohmanns. They have about a dozen different flashing materials, like copper, membranes, etc.

RE: Flashing reistant to corrosion

copper would be better than galvanized

RE: Flashing reistant to corrosion

Stainless would be my choice.

RE: Flashing reistant to corrosion

(OP)
Would stainless blend in with the colour of the brick or would its appearance clash>

Can I be sure that itwiukd not be excessively expensive?

RE: Flashing reistant to corrosion

No matter how expensive it is, it's cheaper to do it right once than replacing it.

RE: Flashing reistant to corrosion

(OP)
Agreed

RE: Flashing reistant to corrosion

Nothing is going to look like brick, but stainless looks like you are serious about flashing. A disadvantage is that it is not as easy to form on site, as compared to a softer flashing material like copper or lead. The material is not that expensive...most of our flashings and rainwater goods in commercial buildings in Australia are fabricated from stainless.

RE: Flashing reistant to corrosion

Stainless that's fed a steady diet of salt, guaranteed in the US Rust Belt, is going to corrode, but probably not to a nice uniform brown like Cor-Ten (and salt wouldn't do the Cor-Ten any good, either).



Mike Halloran
Pembroke Pines, FL, USA

RE: Flashing reistant to corrosion

(OP)
The stainless is also vulnerable to salt (something I expect that you don't use much as winter a road deicer in Australia)..the Nickel Institute told me this about 10 years ago when I was researching things out...but it is still better than most other metals. Somone has recommended to me that we specify the following...any comment?

.1 Prefinished sheet metal flashing: Galvanized steel, 0.71 mm [24 ga.] core nominal thickness, Z275 zinc coating to ASTM A525M. Finish to Stelco's 8,000 series or an approved equivalent, applied both sides. Colour to match existing and be approved by Owner from the 12 standard colours listed in CSSBI's General Colour Card.

RE: Flashing reistant to corrosion

Put heated sidewalks in so you dont have to salt them.

RE: Flashing reistant to corrosion

Galv isn't a bad idea, but this directly exposed to deicing salts it will fail...

Stainless, particularly 316 with a specified maintenance routine of semiannual washing, may be a much better performer in this situation.

See if you can find a comparative report for materials in your exposure conditions; A good report I've got in my reference materials is "Deicing Salts - Recognising the corrossion threat".

RE: Flashing reistant to corrosion

(OP)
I'll soundout our client about whether they are willing to pay for the cost of s/s. I expect it is at least double the cost of galvanized steel and harder to work with...maybe that is why it is seldom used? The original flashing which is most likely galvanized steel is 40 years old...I will double check its condition before reaching a conclusion. Heated sidewalks are expensive and hard to justify from an energy use point of view ...particularly since this is not the main enrance to the building. As far as copper goes, I have seen copper skylight flashing totally corroded away, not exposed to salt, but it was 80 years old and in contact with steel rafters so it may have created a galvanic corrosion cell. I am dubious that copper will do well against salt, but if anyone has some specific experience with that, it would be interesting to hear about it. Thnaks for al the advice and commens to-date.

RE: Flashing reistant to corrosion

(OP)
Ron - yes that looks very interesting for thru-wall flashing. In my case the flashing is all exposed (it starts about 4 brick courses above the sidewalk and extends down the exterior face of the brick and ends at the bottom with a short turn-out away from the brick) so I am not sure if the exposed polyethylene based flashing will resist bumps and impacts against it over the years. I don't see that they are promoting it for exposed wall flashing. But it is what I had in mind for something really corrosion resistant.

RE: Flashing reistant to corrosion

I was at Lowe's the other day and walked by the flashing which was mostly aluminum, stopped to look and thought of this post. Aluminum not an option because of contact with steel?

RE: Flashing reistant to corrosion

It appears you are trying to solve multiply conflicting issues with a single magical material. Could a 2-piece metal flashing similar to a roof curb detail be utilized with the difference being it is fastened at its top and bottom? Install PVC flashing which will provide the chemical resistance workability needed. Over the PVC flashing install a colored metal flashing which will protect the PVC from physical damaged and UV deterioration. The metal flashing can be removed and replaced as needed.

RE: Flashing reistant to corrosion

a2mfk - I don't think there is contact with steel (except perhaps at the door frame), but I wonder how aluminum would do in resisting corrosion from de-icing chemicals.

cvg - I am not sure what material the existing flashing is. I will try to look at it again on the weekend. Thanks for the information in the links. Very interesting indeed.

RE: Flashing reistant to corrosion

smb4050 - interesting.

RE: Flashing reistant to corrosion

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_uses/moly_grade_st...

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.

RE: Flashing reistant to corrosion

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.

RE: Flashing reistant to corrosion

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...

RE: Flashing reistant to corrosion

Quote:

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

RE: Flashing reistant to corrosion

(OP)
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.

RE: Flashing reistant to corrosion

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.

RE: Flashing reistant to corrosion

(OP)
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.

RE: Flashing reistant to corrosion

(OP)

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.

RE: Flashing reistant to corrosion

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.

RE: Flashing reistant to corrosion

(OP)
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.

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