Torch down repair


The business owner has a torch down roof on his building. He put tar on it to coat it. He now has some leaks in his building. I would like to know if there is something that I can do to help stop the leaks? The tar has crakes in it where the leaks are. But I do not know if tar is ok on torch down roofs or not. He is going to let me do a reroof with epdm roofing. I do epdm roofing but not torch down roofing. But I need to repair the roof until I can get to the job. It will take me 6 weeks before I can get to his job.

Thank you all


The cement in place won’t hurt the mod bit but needs to be covered before the EPDM goes on. You could cold process over the current patches or use cement and cotton fab to tide him over, if you don’t do torch on.


ive never seen anything go through the actuall
membrane of torchdown.
the leak could most likely be coming from a
head lap or granual laped area.
torching to the granuals is the hardest part of torching.
usually it doesnt get heated enough and water
works its way under the not so sealed lap.

i have fixed many many leaks of this nature.
you have to find the lap leaking , pryit up a few inches, let it dry out a bit, then retorch it.

if your just tryin to get a few weeks then go by
some cool seal and coat it.



the type of mastic used to fix a modified roof (in lieu of using a torch) is neoprene flashing cement.


There is a lot of bad advice on this forum. :frowning:


fancy bull Axiom,
and please explain,



[quote=“gweedo”]fancy bull Axiom,
and please explain,


Neoprene is a totally different formulation, the only similarities it has with common tar is color and consistency.
It costs much more.
It hardens/cures into a very tough rubbery consistency.
You can easily tell the difference by the smell.

Neoprene is not compatible with shingles and common tar is not compatible with modifieds.

You know that Gweedo, you must have temporarily forgotten. :roll:


THe neoprene I have used is a bit runny for my liking. Will it eat at the shingles like they say plastic cement will eat the modified?

I have personally never seen the plastic cement “eat” the modified, but hey… everlone says it will happen and Im scared to try it.

I dont think I have ever needed plastic cement on a mod roof anyways, but there might be some that do.


I very rarely use neoprene with mod bit either.
The last guy I worked for used it in pitch pockets and hard to get at places were the danger of starting the building on fire was high.



fancy exspensive bull.



Actually, qweedo, its a different chemical makeup completely with different physical properties.


if it wasnt for me the mod bit adhesive wouldnt excist.
it was i who stopped using primer with derbigum, along time ago,
because torchdown would break loose from primed metal.
so i started using bull, soon evryone followed suite and the industry was left with no choice but to create a bull like product so torchdown could stay stuck to things.
enter modified bitumen adhesive.

fancy bull.
like cheech and chong once said,
"looks like bull, smells like bull, taste taste"
i guess it taste like bull.
never tasted it.

and no bull does not eat through torchdown.



Thats awesome because if it wasn’t for me epdm primer wouldn’t exist either. I was mixing gas and black glue as a seam cleaner in the eighties to save on rags and it worked so good they all use it now. :roll:
Oh ya and Mod bit is torched to primed metal every day. Its the way its done on a torched roof.


fair enough.
but just remember that theres a little puddle of
primer in the top of a can of roof cement.



I would agree that the Henrys spray can of primer does not work well.
I would agree that it is better to not use primer if you are using the spray can primer. It’s what everyone seems to use around here. I liked it for a while myself. extremely conveniant.
No one liked the regular brush primer in the 1gallon/5gallon cans because we all seem to spill it everywhere before we use the can all up.

But now i am back into it. I really like the henry asphalt primer in the one gallon can. I think it does work well.

I disagree that primer is not needed on the evedrip.
I disagree that the liquid substance at the top of the cement can is acceptable.

Now for Self-adheared modified bitumen? totally different ballgame.

Torch-down does eventually pull away from your evemetal (primer or not) if it is a “endlap”.(after your workmanship warranty is over)
During the last half of its life.

Gweedo, are you saying that you have not seen torchdown shrink yet?
It does!
The results of the shrink is 1/2 an inch to 3/4 inch on each end. resulting in ripping away from your perfect endlap bleed-out that lasted for 6-7 years.
I now let my torchdown “endlaps” hang over the eve-metal by 1/2 an inch. So that way in the future when it shrinks, it shrinks even to the outer edge of the metal.

You wont be reading this on the Certainteed, GAF/ELK websites!
You wont read it anywhere else, because no one else has written it and i just now wrote it.


i beg to differ. i have only seen mop grade modified
shrink from edge like you say. alot more rubber in that product.
it also looses its granuals in ponding areas after a couple of years.
i dont do mop grade.

its not even in the same leage as torch, to me.



** The best way to repair torchdown is with more torchdown.**

Barring that, you can use neoprene mastic, and do a “tar & fab”.
Depending upon what needs to be done you may not even need the fabric.
Neoprene mastic is pretty good stuff ( it generally costs 4x - 5x as much a common tar), if applied correctly of course.


I have no personal experience with neoprene harming shingles, I do use it on shingles very sparingly sometimes.
Like you, this is what I have been told ( by people I trust & respect) So I don’t mix the 2.
I haven’t seen excessive blistering of shingles from an excessive amount of common tar either.
Just a PITA to remove…

Common tar to repair modified on the other hand…
That just ain’t right.

Common tar dries out and cracks, it won’t bond to the substrate properly.
It will work for a little bit, your repair is going to require complete removal of the hack job patch and surrounding area.