preparing concrete for painting

Interesting question. My house, that I bought ten years ago, had the carpet on the concrete porch. I pulled it up and scraped as best I could and resorted to a blow torch to try to get rid of the glue. Now, ten years later, I still have glue showing on my porch.

I stayed with the concrete and chose not to paint. IMO, it might be better to tile the porch. I will watch with interest for any ideas.

Listening......

I guess to get rid of the old adhesive properly you should scabble the surface with a pneumatic or electric scabbling tool.
This will make the surface rough, and you may possibly have to re-screed it with cement mortar.
Then, the mortar should be sealed with a proprietary concrete sealing agent.
Then, two coats of floor paint.

Enjoy.

Does it need to have a waterproof coating?

Dont know why I posted that question as i know nothing about the subject.

That would depend on the paint used, Material Girl.

There are plenty of concrete paints, stains, and sealers available. The trick is in getting the gunk off before painting, and as McTag said, perhaps having to add a thin layer of leveling (or filling) material. I think they make something now specifically for that, though I forget what it is called.

To get the gunk off, I think one can rent a device that does that (didn't realized it was called scabbling..) What McTag is talking about is probably the same device I recently rented to get old tile up off a concrete slab recently from Home Depot - I guess in the UK you'd call it a DIY store. I didn't do the scabbling myself, my contractor did. My teeth probably would have hopped out of my mouth and I would have likely scabbled my feet. I don't remember the name of the device, sorry. It came in different sizes and had different sized attachments.

These are some scabbling tools

http://www.frueh-maschinen.de/Fraesmaschinen/Fraesmaschinen-e.htm

Ah, that looks much more useful that what I rented for the tile episode. Thanks, McTag.