Here are some instructions from Sabrina Pearson from Golden Software on utilizing the Grid Mosaic feature in Surfer. There is also apparently a script for doing this though I haven't had time to check it out!
You can use the Grid | Mosaic command with all of the grids in a single directory. This is actually a pretty quick process to select all of the grids using the dialog. Here are the steps I would use:
1. In Surfer 12, click the Grid | Mosaic command.
2. In the Open Grid(s) dialog, navigate to the desired directory.
3. Click on the first grid file. Hold down the SHIFT key and click on the last grid file.
4. Click Open.
5. Set any options in the Grid Mosaic dialog and click OK. A new grid is created with all of the mosaicked grids.
You will most likely want to set the # of Nodes in both the X and Y direction. I would recommend setting this to a value less than 10,000, but you can set it up to 2,147,483,647 rows and columns. You will likely run out of memory before hitting that maximum number of rows and columns.
There is a GridMosaic scripter command available. This allows you to read the grids in from an array. You could populate the array using all of the grid file names in a directory. I recommend taking a look at the example in the Surfer help. Click Help | Contents in Surfer 12. Then, click the + next to Surfer Automation and + next to List of Methods and Properties. Click on the GridMosaic page. You can use this in combination with a loop.
There is a recent example of something similar to this on our blog at
http://www.goldensoftware.com/blog/scripter-example-read-all-data-files-in-directory.