Project S-Crete

Lately I have not been very happy with my countertop concrete produced using prebagged 5000psi dry concrete mixtures. I have used a number of different brands and they are highly variable on aggregate gradation, coarse aggregate size, and fine aggregate angularity. For someone used to batching concrete in a laboratory, the variable is driving me crazy. I end up usually adding more water than I would like because the aggregate is dirty and one of the last pours had really large aggregate that had to be pulled out by hand. More water results in lower strength, more shrinkage, and inconsistent color. Luckily all of the last countertops have been black which is a little more forgiving. The big size aggregate (I'm talking one bag with a 3/8" top size and the next from the same brand with 1 1/2") and variable workability makes it difficult to get a really nice surface texture. I have spent too much time doing slurry fills and grinding recently.
Last weekend I got a new grill and had to modify our built-in brick grill to fit it. In the process I ended up relaying a bunch of deteriorating brick. That gave me an idea. My best concrete countertops have been placed using mortar. Buying sand and cement and weighing it out in the garage is a pain. Brick mortar comes prebagged, why not develop a countertop mix using as simple as possible products from Lowes, Home Depot, etc. Here goes Project S-Crete.
The rules are simple, create a forgiving countertop mix using Type S masonry mortar mix. Type S mortar mix contains Portland Cement, Hydrated Lime, and Fine Sand. It is designed to produce 1800 psi at 28-days using a water-to-cement ratio of around 0.80. I figure lowering that should up the strength and might make an acceptable mixture. I will be developing a series of iterative mixtures to determine one with acceptable properties. The selected mixture will be used as the top for the grill. The primary concern with using mortar for countertops is shrinkage. Hopefully lowering the w/c and possibly latex will help control any problems with cracking.
Stay tuned for updates and results.