A question about lead flashing on a roof?

Blagadan · May 13, 2008

I recently built a small slate roofed canopy. I used lead to cap the slates. It looked really nice for a few days but recently I've noticed a white substance seems to be leaching from the lead? I noticed white streaks running down along the slates and it seems to have originated on the edges of the lead. The lead has a white powder accumulated in a few spots and when it rains, the white powder runs down along the slate in the rain drops.
Anyone know why the lead is oxidising? Can I simply scrub it off? Will it reoccur if I do scrub it? Is there a way to neutralise the lead to prevent it from leeching?

thanks,

b

I'll post a few photos tomorrow.

Reg · May 13, 2008

Blagadan said:
I recently built a small slate roofed canopy. I used lead to cap the slates. It looked really nice for a few days but recently I've noticed a white substance seems to be leaching from the lead? I noticed white streaks running down along the slates and it seems to have originated on the edges of the lead. The lead has a white powder accumulated in a few spots and when it rains, the white powder runs down along the slate in the rain drops.
Anyone know why the lead is oxidising? Can I simply scrub it off? Will it reoccur if I do scrub it? Is there a way to neutralise the lead to prevent it from leeching?

thanks,

b

I'll post a few photos tomorrow.

A couple of possibilities;
a) Acid rain.
b) You paid for lead, but got something other than lead, e.g. a cheaper alloy, perhaps containing Tin ?
c) I think lead (the REAL stuff) just darkens as it oxidizes, then self protects from further oxidation with that oxide coating.

European churches, cathedrals and country estates seem to need new roofs about every 150 years IIRC.

Charlesaf3 · May 13, 2008

odd, I can't remember ever seeing that. All the things Reg said make sense.

I'd love to see a picture

Charlesaf3 · May 13, 2008

Read up on it as I'm interested - I've used a lot of lead flashing. Evidently the patina can be washed off and stain. Especially with basic substances? Odd that, I'd guess your rain would be acid.

It could be alkalis from Mortar if you used mortar near or above the slate?

Best thing to do with it might be to leave it be, call it character. If it is an oxidation patina on the lead, you may simply have to let it build up - scrubbing at it will just expose fresh lead to oxidize.

Where in Europe are you?

bigshovel · May 13, 2008

It will continue to whiten. We use alot of sheet lead for x-ray rooms under the drywall and in steel door jambs. It chalks just like aluminum siding, even out of the weather.

Brad

Blagadan · May 14, 2008

I hope these come out. Please excuse the mess behind. I havent finished this project yet, walls to be plastered, light to be fitted, shrubs to be planted, mulch to be spread out, etc, etc, etc

The biggest white run that you see in the pic is a result of a bird dropping this morning! The rest are the real deal, leeching coming from the lead... One other thing might be worth noting, I used silicone adhesive in a few spots along the ridge cap to hold the lead in place. I wonder is the silicone reacting with the lead?
You can see the white material seems to be forming along the edges of the lead.

The white marks rub off really easy, I was thinking about trying a test area, scrub the lead with a coarse scrubbing sponge to bring the lead back to shiney silver, maybe put some wax floor polish on it then to see if it seals? I wonder is there a chemical that will neutralise it?

I used lead as for ridge capplng on my cupola a few years ago and it did leach for a little while but no way as bad as it has done on this canopy...

BTW, this is the original concept drawing I had in mind for the canopy. It will eventually look like this.