My roof has a few ponding issues, and I want to put Henry 287 Solar-flex on it.
Solar-flex specifies that it won't handle standing water and that you should fix that with Henry 176 Pond Patch.
Home Depot doesn't carry pond patch because they specify to use 208 Rubberized Wet Patch, which can be built up by laying it down and applying a fiberglass weave saturated with asphalt and laying more on top.
It seems like 208 isn't intended for this, but rather for simply sealing a leaking roof. On the other hand, 176 specifies that it will continue to release moisture and thus isn't useful for elastomeric roof coatings like 287--which specifies 176 to build up ponding areas to eliminate standing water.
What the hell?
Why did I go to Home Depot again?
If you can't explain why, then you don't know what you're talking about. I'll keep asking until I find someone who does.
176 can be used under roof coatings, but they indicate you need some way to allow water vapour to move out of it. Personally, this sounds like a CYA (cover your ass) statement in case people don't allow the patch to cure/dry. I don't see the asphalt emulsion being any less vapour permeable than the coating would be. If you allow it to cure well there shouldn't be a problem.
I did have to laugh at this instruction in the 176 data sheet though: "When starting to mix, it may feel like the batch needs more water; but after a few minutes of mixing, it feels right"