Can you take another photo from a different angle? How many planks have this issue? Is it ONLY on the stairs? This looks like it might have something to do with a chemical reaction. Like something is/was eating at the surface. If this is ONLY on the stairs, then the question about the adhesive used and the CLEANER used to wipe of the adhesive. The single (odd angle) photo you show has a "drip" pattern...which is an indication of some sort of corrosive liquid either dripping or been applied to the surface. On a stair installation, the most common liquid is adhesive. The second most common is the "cleaner" used to remove the extra adhesive that hits the surface of the plank. Keep going with your concern. Keep contacting the retailer. The manufacturer USFloors should be supporting the retailer. Which means the retailer has to get in touch with USFloors. Please post more photos and tell us how many planks are affected and are they only on the stairs.

6 mil. I’ve decided to go with COREtec Pro Plus with the higher wear layer. We should be installing in about 2 weeks.

Here is the color we are contemplating. Very difficult to visualize with such a small sample.

@SJ McCarthy My CoreTec Luxury Vinyl Plank was installed throughout my "new" 1989 house Q1 2018. About 4 months ago, something that looked like "glue" (to me) was coming from the seams of the planks. THe original Contractor stopped by today to give it a look and he advised that CoreTec does not use glue, so I'll just call it "gook & moisture." It's awful and I have to SCRAPE the gook to try and get it clean but it's getting worse and I cannot keep up with it. The Contractor advised that CoreTec does not use an underlayment and, from what I interpreted from your reply to another, that an underlayment is NOT the same as a vapor or moisture barrier. My 1-1/2 store house is on a slab, stucco, built in 1989. This issue began about 4 months ago and is increasingly getting worse. The worst areas are far from the walls that are against the exterior of the house (hope I described that properly.) For example, the worst seepage of moisture and gook is in the hallway which has a bedroom between the exterior wall and the hallway. Meanwhile, the seepage of moisture and gook is growing worse as time goes on and spreading slowly throughout the house. While I have several dogs, they are not in the area of the foyer and hallway because I have baby gates so they are restricted to the living room that goes into the sunroom that has a doggie door to the fenced back yard. They have lots of room and no need for the rest of the house and that helps me keep it clean. Would appreciate your thoughts. I know the company will try to find an issue that would not be their liability. I really just want what is fair. I'm going to have to have the entire main level re-floored. It's a 1-1/2 story on a slab, as I described above. Thank you! Denna Neff Independent Senior Lady, 76 years old. :)