1) What is the best adhesive to glue 1/2" XPS to poured concrete walls. Is there a preffered method for this---lines of adhesive, dots, put on thick, thin etc?

2) I have a new cultured marble top for a bath cabinet. The old top was formica and screwed in place. Directions for the cultured marble say to apply adhesive to the cabintet top and marble top's backsplash. It does NOT say what kind to use but reccomends something light in color so it does not 'show thru' the marble. What should I use here?

Adhesive is only used to fix it in place till it's mechanically adhered. It comes in caulking tubes and is clearly labelled for attaching foam, such as DAP Panelling & Foam adhesive. I found adhesive wasn't much use on an irregular poured wall. I just propped the foam up with a two by four, drilled a pilot mark through the foam. Once one concrete screw was in, I did the rest through the foam.

2) Use a quality clear silicone adhesive. If it's a large or awkward counter you might put down dowels across the bead first so you can located the counter without disturbing the bead. When you've got it into position, pull out the dowels.

Is there anything I can glue directly to the XPS for on the closet. I do NOT want to frame around pipes, I want then left open for clean puts,leaks etc. I CAN fit some xps in back of them. I can fit furring strips on top and then drywall. Is there anything up to code that I can glue over the xps for the closet OR is there a mold issue with having something directly adhered to the XPS? Is there perhaps and XPS product that already has a fireproof (u to code) barrier already in place?

I try not to be! I just kind of like it down here in the basement!

There's no mould issue with attaching anything directly to the XPS. But I'm not sure if it would hold a thermal barrier such as the 1/2" drywall.