Should mod bit be coated?
Have an addition on the house with a very small pitch, not quite flat, anyway had the roof on it replaced a couple of months ago with modified bitumen. Should it be coated with anything?
Typcially we only coat non granulated modbit. The exception is the GAF Energy cap, we coat all the seams with the matching paint. If its a small flat, we just coat the whole thing.
Question 1: What type of modified Bitumen is it Atactic Polypropylene (APP, plastic modified), or Styrene Butadiene Styrene (SBS Rubber Modified)
Question 2: Why didnt the roofer add slope to get the water off the roof? No Mod bit does well if ponded.
Question 3: Is it a two ply mod bit? Mod bit should ALWAYS BE MUTI-PLY
Recommendation 1: Do not coat it until it goes through a snow melt or two, so it is under hydraulic pressure. You may have voids that wont show up till then, and it is easier to patch without coating. APP produces what is called tobacco juicing, and this will delaminate coating. It is really plasticizer oil loss, but that's what they call it.
2. There is a slight slope, maybe I didn't describe it well, but it's enough to shed water well, I can see this roof from upstairs window and no ponding
3. Again, not sure. I do know that I helped him carry some rolls up and they were very heavy and they were torched down, if that helps
Thanks for the advice! I guess I will wait for spring/summer for any coating
Mod Bit Coating
OK heres the short version.
Both APP and SBS come in a torch grade.
SBS has a much lower application temperature so it can be mopped in special steep ASTM D312 Type IV asphalt, or torched.
APP Must be torch applied because it has a much higher application temperature than can be acheived by heating asphalt and mopping. Basically the asphalt would reach its flash point before it got hot enough to properly fuze APP.
APP is more resistant to UV light, and does not need to be coated, but it is good to do so, as it extends its life. Wait to coat it though, as described in my previous post, for the reasons stated.
SBS must be protected from UV because it is much more susceptible to damage from UV light. You did not say whether your roof was granular surfaced or smooth. The top ply of all SBS roof systems is usually granulated. APP can be either.
If I were you, and my roof was APP, I would coat it with two coats of aluminum roof coating. Re-apply as needed. Usually about every 7 years, depending on the product.
If my roof was a granular surfaced SBS, and it was a two ply roof, I would not coat it. If it was installed as a single ply I would coat it with an elastomeric white coating as recommended by the roof system manufacturer.
The fact that you have good drainage is of paramount importance with the use of mod bit. It does not tolerate ponding well.
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