Here is a crazy little Q: Is using aluminum flashing with cement board a bad thing? Logic would say there could be a problem with the chemicals in the cement board corroding the aluminum, but does anyone have any first hand experience? – done a tear off and found corroded metal in contact with cement board? Most aluminum pre-made flashing comes painted. Does that help much? What about galvanized steel flashing. I know someone is gonna say use copper, but now we are talking custom made flashing which is a lot of trouble when you don’t own a brake not to mention the copper $s. If I do have to brake some, what about the al coil sock with the plastic coating – would that suffice?
TIA,
Matt
Replies
Anyone have any thoughts?
According to James Hardie, painted alum. flashing is OK, but I still am not sure how long this will work. I have seen several vynal flashings on the market which are designed to be used with the new ACQ treated lumber I bet this would work great.
If the manafacturer says it is OK, then it is OK with me.
Re the vinyl flashings designed for ACQ - aren't most of those materials very flexable - more like poly sheating? On the other hand, there is (somewhat) rigid finyl coil stock available - maybe that would work. I'll probably just stick with painted aluminum though. Matt
I've never seen a problem with FC and AL flashing but I have not worked around a lot of older installations of this type.
What chemicals in the FC are you concerned with? I know the high CU content in the ACQ lumber is the culprit with AL flashing, but what does fiber cement contain that would be problematic?
Jon Blakemore
Wet cement is the problem for uncoated al. Dry /cured cement and painted/ coated al. will last .
I think it is the lime in cement that corrodes aluminum. If I'm not mistaken, the 2000 IRC does not allow aluminum flashing in contact with cementous material - concrete & masonry - galvanized steel is required. I'm not worried about code or passing inspections on this issue though, just thinking about building homes with longevity.Matt
I know someone is gonna say use copper, but now we are talking custom made flashing which is a lot of trouble when you don't own a brake not to mention the copper $s.
How is copper flashing used instead of aluminum more custom or more trouble? The flashing should be the same regardless of the material. I'll agree copper costs a little more than aluminum, but in most cases it'll last longer. Hopefully the cement board will last longer than the roof, so you want to use something that can possibly be re-used without disturbing the siding, when re-roof time comes.
I invented foresight.
I'd like to use store bought flashing if possible. I'm the construction super, not the one actually doing the work. My sider will use whatever I hand him, but already told me some time ago that he doesn't have a break so will not make his own flashings. I could make some, but then I'd be in a situation where I'd have to go use someone else's break (I do know someone who has one). Also, I already have the al coil stock if I have to go the make my own route.
If I were to use copper, would it hold paint with no special attention? Also, assuming it didn't hold paint, would there be green streaks down the side of the house in 15 years from the metal oxidation? I know working with copper is second nature for you, but, personally I know almost nothing about it. BTW - is it a break or a brake?Matt
I'd like to use store bought flashing if possible.
Around here they sell terne, galv, and copper pre-made steps. I can't remember ever seeing aluminum at the store although I have seen it on a few houses.
My sider will use whatever I hand him, but already told me some time ago that he doesn't have a break so will not make his own flashings.
You can hand bend steps, but what about aprons and other custom pieces. Does he have his own hammer? You ain't no real roofer or sider if you don't have a brake (it's brake) or access to one.
If I were to use copper, would it hold paint with no special attention?
Yup, but that kinda defeats the purpose.
Good luck.
I invented aluminum.
matt.. we use a lot of aluminum coil stock...
if you're going to stay in the business, think about buying your own brake, like greencu says..
you won't believe how much nicer and more professional your jobs will look with nice crisp flashings.. and the only way you can get those is with a brake..
mine is about 16 years old.. and the new ones are even better ... Mike Smith Rhode Island : Design / Build / Repair / Restore