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  • Writer's pictureKat Zimmermann

Blocking: What it is and how to do it

Updated: Dec 31

Four swatches pinned to a blue foam blocking mat with gridlines. Top left: knit stockinette in weight 7 extra bulky yarn. Top right: crochet blanket square in green lagoon weight 4 yarn. Bottom left: knit lace with a leaf pattern in white cotton. Bottom right: crochet 8-pointed star in grey weight 4 yarn. In the background: maps of Westeros and Middle Earth. To the side: plaid tailor's ham and a tailor's sausage made of science print flannel.

If you knit or crochet, you've probably heard at least something about blocking. If you read this blog, you've definitely seen me tell you to do it! In this post, we'll review the types of blocking, how to do each type, and some considerations for making the right choice.

Q: What is blocking?

A: Blocking is the act of pinning pieces of knit or crochet work to a board (or block) and using water to get the fibers to set in that finished, corrected shape. Once the pins are removed, the piece should hold that shape without any help.

A long foam blocking mat sits on a coffee table. On it is one row of blanket squares, being blocked to 6x6 inches each. The colors are varied shades of green and blue with a few gold squares. To the side are the remaining finished squares layered in stacks by color. In the background, a small dog screams because he is not getting enough attention.

Q: Do I need to block every project?

A: No - blocking is often a good idea but it's not always essential. A general rule of thumb for making the decision is to look at the shape and size of the object. Some examples:

  • Large afghan made in one piece - ❌ too big to need blocking

  • Large afghan made of smaller squares - ✔️ block the pieces before you sew

  • Lacey shawl or doily - ✔️ any lace or delicate piece with fine details should always be blocked

  • Socks and hats - ❌ since these will be worn on the body, they will naturally block to fit the wearer. ✔️ However, if you're selling pieces or giving them as gifts, it may be worth blocking anyway.

Q: Is there anything I should avoid blocking?

A: Yes - ribbing or anything that is supposed to change its size when worn. See my post on the Fisherman's sweater for an example of why you should not block ribbing. If you block a piece that includes ribbing, block around the ribbing and leave the actual ribbing to its own devices.



You'll need some additional materials depending on the type of blocking you'll be doing, these are included at the top of each type's section below. Regardless of method, you'll need the following:

Blue blocking mats and knit and crochet sample swatches sit on an ironing board. In front of them are stainless steel t pins and a retractable measuring tape.
  • Blocking boards - I use these blocking mats from Humble Crafter, but there are a lot of similar products out there made of many different types of materials. What you want to look for is a set with gridlines made of a material that won't warp from moisture or heat.

    • --> if you don't have a blocking board (or space to store them), an ironing board or even a plush carpet will work just fine for a few projects.

  • Stainless steel pins - I use the set of T-pins (think biology class) that come with my blocking mats, but also use my regular quilting pins for sewing if I'm short a few. Again, we want materials that will not be affected by moisture or heat.

  • Ruler or a measuring tape - useful for larger projects and/or if your blocking boards do not have gridlines.

Once you've assembled your basic materials, it's time to decide which type of blocking will work best for the project at hand. First, we'll review the types of blocking. Then, we'll go over some considerations that will help you make an informed choice.


Blocking Type 1: Spray Blocking

Spray blocking is arguably the easiest type of blocking, which is why I have listed it first.

A crochet 8-pointed star made of grey weight 4 acrylic yarn is pinned to a blue foam blocking mat with gridlines. Pins are in each of the points and each of the troughs of the star. The star is soaked through with water. To the side of the piece is a blue glass spray bottle.

The only additional material you'll need is a spray bottle filled with cold, plain water (tap is fine although you may want to use distilled for very delicate fibers).

To spray block:

  1. Pin your project to the blocking board so the pins hold the shape in place.

  2. Spray the project with cold water so that it is wet through. For fuzzy fibers, you may need to pat the water in a bit.

  3. Let it dry.

  4. Unpin from the board.


Be sure to use cold water - warm could cause the dyes to run or the fibers to shrink.

This type of blocking can be used for any fiber. To speed up drying time, you can set the board under a ceiling or box fan or near an open window.


Blocking Type 2: Wet Blocking

Wet blocking is pretty similar to spray blocking. The only difference is we'll wash the piece prior to laying it out on the blocking board.

A white plastic wash bin and a bottle of Euclan brand unscented wool detergent.

You'll need an appropriate detergent (if you're using wool, I recommend Euclan unscented which works quite well and is appropriate for sensitive skin) and a wash basin for hand washing. I use a $1 dish washing tub from Target - any sink or basin that can be filled will work just fine.

You can use a washing machine if it's appropriate for the fiber. For example, 100% acrylic will probably be fine washed in cold water. 100% wool, however, demands hand washing. And no, the hand wash setting on your washing machine will not work (trust me on that - the wool will still try to felt).

To wet block:

  1. Wash your project by hand:

    1. Fill the basic with cold water and add detergent according to the label.

    2. Put your project in the water, squeezing it gently to soak the fibers in the sudsy water.

    3. Let sit 20 minutes.

    4. Dump out the water and rinse your project in clean, cold water using the same method as in b, above. You should only need 1 rinse if you used the right amount of detergent.

    5. Dump all water out and gently squeeze the water out of your project. Do not wring the fabric - this could damage the fibers.

  2. Pin your project to the blocking board so the pins hold the shape in place.

  3. Let it dry.

  4. Unpin from the board.


Be sure to use cold water - warm could cause the dyes to run or the fibers to shrink.

This type of blocking can be used for any fiber. However, I would not recommend it for extremely delicate projects as you could accidentally damage the fibers while washing. To speed up drying time, you can set the board under a ceiling or box fan or near an open window.

Wet blocking has the advantage of washing your project prior to setting its shape. This is great for projects you've been working on for quite a while, especially if you've traveled with the project or own furry pets that shed.


Blocking Type 3: Steam Blocking

Unlike wet blocking and spray blocking, above, steam blocking requires your fibers to tolerate heat. Because of this, I only recommend steam blocking for 100% natural fibers (e.g. cotton, linen, viscose, wool, etc.). Acrylic yarns can melt from the heat (remember that acrylic = plastic).

If you're using a blended fiber, I still recommend steaming with caution. You can always test how the fiber will react using a gauge swatch blocked on a piece of cardboard. This way, if it does melt, you won't have ruined your blocking boards or your project.

A piece of cream knit cotton lace is pinned to a blue foam blocking mat with gridlines. Stainless steel t pins are all along the outside of the rectangular piece of lace. A steam iron set to high heat and high steam hovers about 1 inch above the piece of lace.

The only additional material you will need to steam block is (a) an iron with a steam function OR (b) a handheld steamer.

Importantly - you must use 100% stainless steel pins to steam block as any plastic capped pins could melt from the heat (glass capped should be OK).

To steam block:

  1. Pin your project to the blocking board so the pins hold the shape in place.

  2. With your iron set to high heat and the highest steam setting, hover about 1 inch over your project (approximately the height of your pins) and let the steam do its work.

  3. Let it dry and cool.

  4. Unpin from the board.


In comparison, steam blocking tends to be the fastest because the fibers do not get as wet. However, you are still limited by the amount of steam that reaches the fibers so be prepared to spend some time with the iron, ensuring the fibers are all evenly dampened.


Tips for Pinning your Pieces

The actual act of blocking, pinning your pieces to the board, can be a little intimidating, regardless of the type of blocking you will do. Check out the video below for a quick look at what to look for when pinning - a description with highlights is below.

In this video, I've pinned an 8-pointed star. Because there are 8 points, keeping the piece even all the way around is a touch tricky. To get it right, I did the following:

  • The leftmost and rightmost points are both on the same line.

  • I then counted that the points were 7 inches apart which meant that the top and bottom points should also be 7 inches apart - 3.5 inches from the center line each.

  • To pin the "diagonal" points, I used the gridlines to check that the points were halfway between the North-South and East-West points and also aligned with each other.

  • Finally, I pinned the troughs of the points using the same method as for the points.

In all fairness, I probably should have used a ruler to check that the diagonal points were also 7 inches apart instead of eyeballing it - but it's OK for a sample swatch.

One other tip on the pinning process: pin around the fibers, not through them. It it tempting to stab the fibers into behaving, but this splits the yarn and can damage the fibers. It's best to go around the fibers, just as you would with a crochet hook or knitting needle, and then secure them in place.

Finally, I will also say use as many pins as you see fit. It's better to use too many pins than to use too few and end up with a project shape that's not where you want it.


Which type of blocking should I choose?

There are several factors at play here:

A crochet Midwife blanket (blanket made of repeating squares with flowers made of negative space and lacey borders between the squares) made of purple acrylic yarn is pinned to red and blue foam blocking mats with gridlines.
Pattern: The Midwife Blanket by Rebecca Langford
  1. Fiber Type

This is arguably the most important factor. The appropriateness of each type by fiber is included above, but here is a quick check list you may find helpful:

Spray Blocking

✔️ Appropriate for any fiber

Wet Blocking

✔️ Appropriate for any fiber

⚠️ Use cation with fine and delicate items that could be damaged by the washing process

Steam Blocking

✔️ Appropriate for any 100% natural fiber (e.g. wool, cotton, linen, viscose, etc.)

❌ Not appropriate for 100% acrylic fibers, which could melt from the heat

⚠️ Use caution with acrylic blends, which could melt from the heat. Use your gauge swatch blocked onto a piece of cardboard to test the fiber before blocking the final project.

2. Project Size

For most projects, this will not be an issue. However, you are limited by (a) the size of your blocking board and (b) the weight of the project when wet.

Consider, for example, whether you will be able to lift the object and squeeze water from it when wet. If this sounds too difficult, wet blocking is out as an option.

The front piece of the knit Fisherman's sweater pattern, prior to blocking and assembly. The cables are pronounced and the ribbing has elasticity, as it should. The neck stitches are bound off instead of being on hold as they should be.
Pattern: Fisherman's Sweater by Lion Brand Yarn.

3. Item Use

Consider how often the item will be used.

For example, a sweater will need to be washed regularly (although not after every wear), so wet blocking makes sense.

A lacy shawl, on the other hand, might only be worn for special occasions and would probably be fine steam or spray blocked, as appropriate for the fiber.


Some Special Cases

Q: What if I need to use starch?

A: First, read the directions and make sure your starch is fiber-appropriate! You will need to iron the piece for the starch to really take hold, so this is not appropriate for acrylic fibers (remember to test a swatch first for acrylic blends). Assuming the starch passes this test:

For spray starch:

  1. Block the piece first, but don't remove the pins after drying.

  2. Spray on the starch as directed.

  3. Press the piece (with pins in place) at a fiber-appropriate temperature setting.

For dip starch:

  1. Wash the piece as though to wet block.

  2. Before pinning in place, dip into the starch solution.

  3. Block as normal for wet blocking and let dry.

  4. Press the piece (with pins in place) at a fiber-appropriate temperature setting.

For delicate pieces and fine fibers, consider placing a layer of fabric between the iron and your piece - a cotton muslin will do nicely. Be careful the starch does not "glue" the fabric to your finished piece.

Q: How do I block items that aren't flat?

A: First consider if the item really needs to be blocked in the first place. If the answer is yes, find an object that is approximately the shape you need for the finished item and use it in place of a blocking mat for any type of blocking. Mixing bowls, for example, work well for hats.

A piece of cream cotton knit lace with a leaf pattern is pinned to a blue foam board with gridlines. A heated iron sits to the side.

I hope you've found this post helpful for your knit and crochet projects - please like the post and leave comments and questions below!

You can also join my mailing list using the form at the bottom of page to make sure you never miss a post.

Happy blocking!

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