If you're in a hurry, you can finish your crochet project, seam any separate pieces together, weave the loose ends and put it straight to use. But if you want your project to look as professional as possible, you should block the pieces before seaming them together. Taking the time to block your crochet sets the stitches, creates clean, even edges and ensures that individual pieces identical dimensions and come together easily when seamed.
Fasten each crochet piece to a blocking board. Pin the corners first, measuring and gently stretching the fabric to the appropriate dimensions. Then work along the edges, pressing T-pins through the crocheted fabric to hold it in place and create a straight, even edge. Expect to use quite a few T-pins, because you must place them very close together to create an even edge.
Spritz your crocheted pieces with a spray bottle until they're thoroughly wet, then leave to dry. Depending on your local humidity, this could take a day or two, depending on how thoroughly you saturated the fabric.
Remove the pins and seam the pieces together, as necessary, once each crocheted piece is completely dry.
Lay your crocheted pieces in a plastic tub or, for large items, in the bathtub. Fill the tub with just enough cool water to cover the crocheted fabric.
Lift the fabric gently out of the water -- wool is fragile while wet, and cotton can stretch out of shape -- and lay it on a flat towel. Lay another towel on top of the wet crochet and press down to gently squeeze as much water out as possible. Don't wring or twist the fabric.
Remove the uppermost towel and transfer the damp fabric to either a dry towel or a blocking board. Carefully stretch it to the desired dimensions, measuring and pinning as you go.
Remove the pins once the crocheted fabric is completely dry.
Pin the crocheted fabric in place on your blocking board, a sturdy towel, or a piece of clean, well-padded carpet.
Fill a steam iron with water and heat it until it produces full steam. You can also use a handheld garment steamer.
Move the steamer or iron slowly across the crocheted fabric, holding it just above the fabric's surface. Never let the iron and steamer touch the fabric. Continue steaming until the fabric is thoroughly wet. Don't use this method with acrylics, which may melt under the heat.
Leave the crocheted pieces to dry. Once they're fully dry, remove the pins and do any seaming necessary.
Choose your blocking method according to which fibers you crocheted with; wet or steam blocking is ideal for wool, but for silk, acrylics and other relatively fragile fibers, do spray blocking instead.
If you don't have a blocking board, make your own with fabric-covered foam, or pin your crochet to a clean, well-padded carpet.