How can I tell if I'm looking at APP or SBS Modbit?

I have a residential flat modbit roof in Brooklyn where I am going to install a solar array. I am using Chemcurbs to waterproof my stanchions, and their literature says not to apply them to an APP modbit roof (SBS isn’t mentioned, and is presumably fine). How can I tell if that’s what it is? Thanks very much for any advice,


Modified Bit is still Modified Bit whether its app or sbs. Some products eat other products, be careful.

FYI both are asphalt based products so if one isn’t “ok” don’t assume the other is. When in doubt call the manufacturer and talk to tech support.

There are people out there that think SBS modified is rubber.


Hey guys, thanks for the info. Since the client has no idea who did the roof or what it is, I’m on to plan B: Chemlink says that in order to safely install Chemcurbs on an APP roof, I need to first “melt an overlay of granulated APP before installation.” That sounds to me like I just need to get a sheet of granulated APP and cement a square of it onto the existing membrane as a kind of underlayment before I pour my curb… am I way out of my depth here? Thanks again.

It’s a subtle difference but APP is harder (more like hard plastic) than SBS.

You are correct. Chem Curbs should not go to smooth APP or SBS. Needs the Granular surface, Brite, if DerbiGum, etc.

Just keep in mind that the Chem Curb is only bonding to the Granular surface installed, if you install it poorly, it can leak. Use a nice modified mastic and maybe 3 course the edges.

Ya, i agree w/ Ricky. Make some pitchpockets, strip em in w/torchdown, & fillem w/ pourable.

Thank you guys for the advice. It’s kind of seeming like a lot of steps though…

[Grrr. Filter doesn’t like URLs]

EternaBond’s EternaPocket product seems to fill a similar function, but the lit indicates that it will be fine on smooth modbit. If I use this, with the counterflash detail, would that be pretty well in line with a high standard of work? Or is this kind of thing viewed as short-cutty or pipe-dreamy?

Thanks again :slight_smile:


There are people out there that think SBS modified is rubber.



In order to create roofing grade asphalt, asphalt flux is air-blown at elevated temperatures which converts the flux to roofing grade asphalt. In the early 1970’s, the Italians, lacking the blowing equipment, were looking for a product that would convert asphalt flux into a usable roofing product. They discovered that if Atactic Polypropylene (APP) - a by-product of propylene polymerization - was added to asphalt then it gave the asphalt some plastic properties. They found that by adding about 30% of APP modifier, they could stretch the modified asphalt up to fifty percent of its original length before it would break.

Next came the need to make it into a usable roll product. Some type of reinforcement would be needed. They looked into various reinforcement materials and decided on a polyester mat because polyester would accommodate the APP modified asphalt’s elongation properties whereas the more commonly used woven glass mats would not. The reinforcement material is dipped into the hot modified bitumen mix, then goes through a rolling cylinder, cooled, and then wound into a roll.

APP membranes are applied using a torch. The back of the sheet has extra asphalt on it which, when heated, bonds to the substrate. This was especially convenient for the smaller, more cut up roofs because less room and equipment is needed on site to torch-apply a membrane than is necessary for application using hot bitumen.


While APP was being looked into in southern Europe, northern Europe was experimenting with a different type of modifier called Styrene Butadiene Styrene (SBS). The French and Germans found that if they added 10%-15% of SBS rubber to asphalt, the asphalt’s characteristics changed to those of the rubber additive. They learned that they could stretch the SBS modified asphalt up to six times its original length and that, unlike the APP, it would return to its original size when allowed to relax.

There are a wide range of reinforcements used in SBS roofing materials. These include fiberglass or polyester mats and scrims, or combinations of both. The fiberglass mats range in weight from 1.0 to 2.5 pounds per 100 square feet or around 50 to 125 grams per square meter. Polyester reinforcements range in weight from 3.5 to 5.0 pounds per 100 square feet or 170 to 250 grams per square meter. The type of reinforcement used depends on the material’s performance requirements.

SBS membranes can be hot asphalt applied, torch applied, or cold process applied.