Painting - Anyone ever had BIN fail?

So, customer has leaky flashing on chimney, which allowed water to run down through attic, and damaged drywall in upstairs hallway. All damaged surfaces were those covering the chimney which runs down through the hall. I came in to fix it. Scraped away all loose drywall/mud/debree from brickwork. Per recommendation of Ben Moore staff here in town, I scrubbed brick with bleech solution to remove any potential 'life forms' and allowed to dry for about 3-4 days.

Applied Zinnser BIN to seal subsurface, waited for a day. Came back, looked fine. Applied drywall mud. Came back next day, and the mud was now bone dry, but had huge brown stains all over it, which actually appeared to be slightly raised bumps. Sanded mud, stains remained (not surprising). Applied one coat of BIN and left. (Customers not in town for winter in case you're wondering why I'm coming and going as I please.)

Called Zinnser support line to ask if they've ever seen this before. They said I was doing everything right, but shouldn't have (didn't need to) applied first coat, as BIN is a primer and should have just been applied to finished drywall mud. I explained that I was trying to seal the surface to ensure no future potential problems. They said it was overkill. Said to call back if had further problems.

Went back to house. Brown stains bleeding through again, but not as much. Three coats of BIN later, I was satisfied that the stains were sealed up enough to apply latex paint.

Two coats of latex later, things looked great. So, to make a long story short, BIN worked in the end but I've never ever had to put more than one coat of BIN on ANYTHING to make it go away forever.

Sorry for the lengthy story, but I'd rather include as many details of process as possible to ensure everything was explained correctly.

Any ideas as to what might have happened here? Perhaps the stains weren't water stains, but some other type? Creosote or something?

I don't know that I've ever had any failures with zinnser's BIN but I've used a lot of other brands pigmented shellac [years ago] and would occasionly run into stains that would require a 2nd coat of pigmented shellac. I do remember a steel post in a YWCA back in the early 70's that had an ink stain that bled thru multiple coats of pigmented shellac - we finally had to strip it down to raw steel and start over. It seemed liked we spent more time on that 1 steel post than the rest of the job:wall:

Was the Bin you were using mixed well? ever been thinned?

Thanks for responding Marksr. Yup, it was fresh off the shaker, paid for and applied. No thinner whatsoever. Stirred prior to each subsequent coat with no solids present.

I just went back over there today (customer comes back on the weekend) to take a last look. Some tiny hairline lines of stain coming through. Couldn't believe it. That's after 4 coats of BIN on top of the mud. The customer is a friend of mine who is a retired handyman.

All I can hope for at this point is that he'll get a kick out of the story I can tell him about what I went through.

Interestingly, I went to the Zinsser website and looked at the 'application guide' or something, and it even indicates that it'll cover grease stains, creosote stains, etc.

I guess we'll never really know what I've imprisoned in this wall.