Pinhole leaks in sheet metal shed roof


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Old 09-02-22, 02:22 PM
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Pinhole leaks in sheet metal shed roof

Can I use asphalt driveway sealer to cover an old flat galvanized sheet metal shed roof that has pinhole leaks?

More than 30 years ago a previous owner built a 126 square foot shed on my property. It's a welded steel frame with tarps for three sides and three long pieces of thin galvanized steel sheeting for the flat roof. Last winter I had to start keeping some machinery in the shed. In spring the dirt floor was a muddy mess. The machinery was OK because I had it tarped and on skids, but getting it out through the muck in spring was a pain. I've solved the muck problem by covering the floor with old concrete patio slabs that I got for free. I'd now like to fix the pinhole leaks, but need a solution that's very cheap and easy to apply. I tried rolling on a small can of Flex Seal liquid rubber sealant, but the liquid is very thin/fluid and spreading enough to fill in the pinholes would cost several hundred dollars. A $40 can of driveway sealer would cover the roof with 3 or 4 coats. The roof is sheltered by tall cedar trees but snow can pile up over a winter.

Plan B is to work from the inside and use caulk to fill in most or all of the pinholes one by one. They show up very well on a sunny day now that I've cleaned about a half-inch of dirt and cedar needles off the roof. The underside of the roof is clean and easy to access on a step ladder.

Thanks for any help.
 
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Old 09-02-22, 02:29 PM
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I've never heard of anyone using asphalt sealer on a metal roof. I'd be inclined to use something like this [assuming I didn't mind a black roof] https://www.lowes.com/pd/APOC/5013298735

How many holes are there? Caulking is a good idea.
 
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Old 09-06-22, 03:20 AM
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I've repaired pinhole leaks on a metal shed using an adhesive metal foil tape made by Nashua. I don't see a descriptive name on it, just Nashua Tape (on the inside of the roll). It's a thin metal tape, 2 inches wide, with a strong adhesive covered by a removable backing. I've also used it to patch a plastic tarp. You just cut a small piece to cover the hole, peel off the backing, press it down on the cleaned metal, and roll something over it to make sure it's adhering well.

I think it's called foil duct tape, the outside is shiny like tin foil. I bought it at Home Depot.
 
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Old 09-06-22, 12:50 PM
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Lowes has a elastomeric sealer coating for $30 for 3.6 quart/ 3.4 L can. Not sure how far that would go to cover your roof. I would think you could put a masking tape on the underside to hold the stuff in the pinholes until it dries.
This stuff is flexible and says it works well on metal roofs.
 
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Old 09-06-22, 02:17 PM
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The elastomeric roof coating works well but it needs to be applied over rust free metal, if there is rust you should apply a solvent based primer first. Rust will come thru elastomeric unless it is stopped first.
 
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Old 09-12-22, 07:48 AM
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Thanks for all the advice. I decided to take the easiest cheapest route for this winter and just caulked the pinholes and seams. We got a heavy rain overnight (finally!) and I see no wet spots. Will again tarp all machinery parked in the shed for the winter. Will most likely paint/roll a better coating next spring when I have time to look at everything available in the local stores. Caulk may be OK now but will get me into a game of whack-a-mole as more pinholes appear -- the shed is very old. I made a big mistake in using clear caulk I already had. Sunlight shines through so there's no way to spot new holes. Flex-Seal liquid rubber has adhered very well to the small area where I applied it. Per marksr's comment, there is rust on the roof.
 
 

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