Was the colorant a blue or green? They are the worst for doing that (even sealed) when exposed to moisture.

I don't think there's a sandpaper coarse enough to affect it. If you could score it a bit with the corner of a putty knife or something, that might help, but I'm thinking that there isn't going to be too much that can roughen the surface enough to make much difference.

The best way may be to saturate the sphere with water, either submerging it or letting a sprinkler spray it, let the excess water drain but not dry, then mix up a slurry of cement, water AND sand. Cement by itself is very, very weak and brittle.

If you happened to use any additives (like acrylic, etc) in the original mix, I would use the same stuff in the fresh coating, and brush some onto the damp original surface.

Sue

Thanks Sue. I tried soaking overnight and it looked wet but no real penetration and the new coat of portland, fortifier, color didn't adhere. So I did the slurry thing and that was OK. So then went back to portland mix and it accepted that layer. I had some problems with a rough surface but it worked out fine. I use a tan color with my mix. The color is still uneven so I would like to add some color to smooth it out. I will upload a picture later today. Marie

Here is a picture of one of my spheres.
{{gwi:67651}}