Sashing and checker board border help please
 

I have 9 x 9" blocks (seam allowance of 1/4" so blocks are actually 9 1/2") I need to join the blocks with sashing of two inches on all sides so the actual strips I cut will be 2 1/2" I believe. The I need to surround the nine blocks complete with the sashing with a checker board border that is approx 4" wide so two rows of squares. i need the squares to line up with the 9" blocks. Can someone kindly tell me the maths for cutting the checker border please? I want to use the tear method in which I stitch stripes together then cut to turn to restitch into the checker board.

You need your block and sashing to be an even number. Either add a 1 or 3 inch sashing

Here's the problem. If you want the checkerboard squares to line up perfectly with the 9" blocks, then you need the size of the checkerboard squares to divide 9 evenly. Yet the size of the squares must also divide 2 evenly. The only way to accomplish this is to have squares that are 1/2 inch finished.

There are two other ways to go. One would be to change your sashing to 3" (in which case you could use 3" checkerboard squares) or 1.5" (and go for 1.5" squares). The other is to accept checkerboard squares that do not line up perfectly with your 9" blocks.

If you want a 4" outer checkerboard border, you can also go with a checkerboard of four 1" squares across. This is another number that will divide evenly into 9 and 2. You would cut your strips 1 1/2". The problem with tearing is that it may distort the fabric up to 1/2" from the tear line. With such narrow strips, this may not work. Be sure and do a test tear before proceeding with all the fabric. You may have to punt & go with rotary cut strips.

Why did I not think of 1" squares? Still, I think that is rather small for the size of the main blocks.

I agree with Dunster. Your finished block size has to equal your finished checkerboard square. Don worry about sew a lot of 1" square. Sew strips (1.5" wide) of white and black and then sub-cut them down and you will have your checkerboard sashing much quicker.