If I was you,( and I wish the column was here instead of your house)I would take a sander and course sandpaper and sand it down, then make a mixture of thinset thick but paintable and paint a coat on. Thinset will then work just fine on this. GEII will also work, but thinset is cheaper.

Ditto what flag said. I have also roughened the surface, sprayed it with plastic primer and worked directly over that; HOWEVER (big exception here) my climate may be different fron yours. I am in north central TX where we rarely get subfreezing temps, snow or ice.

HTH,
Pat

I haven't gotten into mosaics, but am thinking about trying it. Where can I find thinset?

Thinset is in every home improvement store...Home Depot ..
Lowe's..True Value...etc!

I use old cement sewer drain tiles and mortar them together, and using a cement stepping stone at the bottom and top for a base and top. I have also filled my wiremesh mushrooms with gravel so they are sturdy when I placed them...

Here is a link that might be useful: {{gwi:156551}}

In a magazine a couple years ago, I saw some very large pvcs done for a lady's garden. I'd do as FLAG suggested, being sure to really sand it well. Then just use thinset. If it has enough "tooth" to grab the mortar, it'll be just fine w/o the thin coat first, IMO.

I do appreciate all the very good advice.The angel came in the mail and is much too delicate to put on the pvc column.New plans.....I have a metal clothes dryer drum that will make a perfect base, and a stepping stone will cover the hole. At least part of it will be mosaiced, maybe the rest will be faux stone spray.

Don't forget about those cardboard tubes at Lowes, used to make columns. They work beautifully. I used them to make my first garden column.