Around 10:00 last night I checked on my chalkboard and found that although the paint had dried and the grout was roughing it up, it still had a high-gloss sheen to it that made for a poor chalkboard. the paint wasn't fully hardened yet though, so I took an all or nothing approach and did a third coat of paint in a small bastardization of the typical chalkboard paint recipe.
Using the leftover paint I had mixed from the previous coat, I added about 2 tablespoons of grout, then added about 2 tablespoons of paint thinner. Now the paint was almost nail polish consistency, with little lumps in it. I brushed it on using a cheap basting brush. Then using an old roller, I made a quick pass to remove any brush strokes and rough up the surface a little.
This morning I went down to check on my results, Things actually looked really good, so I impregnated the board with chalk and ...
We have a chalkboard!