Danger to underlayment using light torch on flashing?

fixizinJanuary 28, 2010

This is a So-Fla HVHZ concrete tile roof, but I'm sure the principles apply elsewhere. The galvanized edge flashing was too new, and not properly etched, before an expensive primer (designed/labeled for just this application) was applied.

All LOOKED well for 21 mos. until Hurricane Wilma came through, and gave it a good sandblasting. It's looked very "poxy" ever since. FINALLY getting around to addressing this... (hey, gimme a break, it's cosmetic, and it's not visible from the street. ;')

I supervised this roofing job back in 2003, so the details have faded a bit. IIRC, the L-section flashing was nailed down after the felt, but before the hot-mop asphalt layer. Per newer codes, there's a 1x2 strip that spaces it out from the rafter ends/sheathing edge.

Anyway, I want to strip the old primer, rub the bare flashing with white vinegar to micro-etch the surface, and have another go at the primer... maybe even follow up with paint this time, LOL.

Was contemplating messy chemical stripper, when someone suggested ye olde propane torch. Sure enough, a few seconds of even the cooler tip of the flame, and the primer scraps off "like buttah". Did a tiny test section, didn't smell anything like burning tar... so, is it a roof-safe method?

Also, I remember that roofers use propane to melt the hot-mop tar (570degF, IIRC); add to that the not-great heat transfer of thin sheet metal, and the dissipation offered by the adjacent cool sections, and I think I've got "margin" to play with.

BUT... wanted to bounce it off the RKIs/experienced DIYers here to see if any yellow/red flags went up!

Thanks in advance.

Thank you for reporting this comment. Undo
brickeyee

Use a wire wheel in a drill.

    Bookmark   January 29, 2010 at 11:48AM
Thank you for reporting this comment. Undo
macv

Galvanized metal must be specially treated and painted in the factory immediately after application before it can oxidize. The longer you wait to paint it, the less likely the paint will adhere contrary to popular lore. Removing the oxidation later is difficult and rarely worth it but not impossible. Google it to find some procedures.

Removal of paint can be done with a hot air device made for that purpose. An open flame in the hands of an amateur is never a good idea.

    Bookmark   January 30, 2010 at 5:57PM
Thank you for reporting this comment. Undo
brickeyee

"Removal of paint can be done with a hot air device made for that purpose."

Hot air guns are powerful enough to melt solder. Around 700 F.

There use on metal that may be against wood is not a great idea.

Paper and cellulose products begin to char as low as 451 F.

It is not that hard to etch galvanized in situ for painting.

    Bookmark   January 31, 2010 at 9:59AM
Thank you for reporting this comment. Undo
fixizin

Didn't mention it in my OP, but I already tried Ye Olde Wire Wheel--it just stains the white primer--the stains being the exact color of the wire wheel, lol. That's some serious primer!

But I agree with everything Brick said in his 2nd post.
So will vinegar (5% acidity) do the etching job, or is there something better? Muriatic acid just seems WAY too strong.

The part of the flame I'm using will not even melt lead-free solder with a melting temp. of 425degF, let alone the roofing tar at 570F... I'm gonna go for it... carefully.

PS: I'm no rank amateur with ye olde open flame... I'm an ADVANCED amateur, lol... let you know how it goes. ;')

    Bookmark   February 2, 2010 at 11:34PM
Thank you for reporting this comment. Undo
brickeyee

"Didn't mention it in my OP, but I already tried Ye Olde Wire Wheel--it just stains the white primer--the stains being the exact color of the wire wheel, lol. That's some serious primer!"

Any primer that tight is fine as it is.

    Bookmark   February 3, 2010 at 9:43AM
Thank you for reporting this comment. Undo
fixizin

Well a light and judicious application of the torch did work, but it was causing some warpage of the flashing, which mostly "relaxed" when it cooled... but not entirely. Was especially noticeable at the overlaps.

And of course the torch just loosens the primer, does not burn it off--still gotta scrape, albeit lightly. That's when it hit me, that my Red Devil scraper edges had become almost uselessly DULL over the eons. Took said scraper to my local True Value guru (age 74 going on 61), who restored some wickedly square-sharp edges to that puppy.

No torch req'd--that Red Devil now scrapes on both the push stroke AND the pull, and that old primer is tough, but brittle--catch one edge and it breaks up like an ice sheet.

Now I'll let the bare flashing "weather" for a few weeks, then hit it w/ vinegar, followed by quality primer and paint from Acrylux... worry about it again in 2021.

Thanks for all the inputs. There's just no textbooks for some stuff. ;')

    Bookmark   May 4, 2010 at 8:13PM
Sign Up to comment
More Discussions
Where to purchase Spanish roof tiles? I just need 2 pieces.
One handyman came to my house to evaluate the price...
janesylvia
Need advice for gap under door frame
Hi, We had a contractor install pre-hung interior doors,...
pam27d2001
Cellulose Insulation - Do we really need the blower?
We have 8 to 10 packages of cellulose insulation that...
kendog2
Can you clear my doubt about home security system?
I have a home security system installed recently. Do...
jeckjiem
How to fix 1" gaps in drywall seams?
We recently bought our home (build in 1938). One of...
Bongo
Sponsored Products
Sunpan Bachelor Driftwood Modern Side Table
Overstock.com
Bruck | Bling II 120V Down Pendant Light
$142.50 | YLighting
Tolomeo Mega Wall Light by Artemide
$730.00 | Lumens
Elba Collection Twelve Light Chandelier
Lamps Plus
Type 75 with Wall Bracket - White - Anglepoise
$215.00 | HORNE
Outdoor Lighting. Brielle Collection Wall mount 2-Light Outdoor Lamp
$77.40 | Home Depot
People viewed this after searching for:
© 2015 Houzz Inc. Houzz® The new way to design your home™