Lazy Tips for Sewing Knits: Prewash, dang it!


I’m a bit obsessive about this tip: For the love of pretty fabric, prewash your knits! Wash ‘em in hot water, dry them on hot, and for good measure, wash and dry them again!

I learned my lesson on my second-ever tee shirt. I was so excited by the success of my first tee that I grabbed some brand new thin black polkadot knit from, and whipped up a cute Renfrew without prewashing it. And then, oh then… then I washed it. In just one wash it shrunk 3 inches shorter! Aghhhhhhh!!!!

Here it is, with a normal-length grey Renfew for comparison:

prewash collage

The pictures aren’t the best, but if you squint you might be able to see that the grey Renfrew covers the front pockets, but the black one only just covers the waistband. I find the black top too short to stay tucked into high-waisted skirts, and it’s even too short to comfortably wear as pyjamas. Too many drafts when I sit or bend!

Here are the two tops layered on top of each other:

layers tees

Now, I know it may not look all that dramatic to you… but I promise, it makes all the difference in the wearability of the tops!

Of course, there are a few factors at work. First and foremost, I should have prewashed the black knit.

Second, It’s a cheap tissue knit. Maybe a better quality knit would have shrunk less? I find that rayon knits shrink up quite a bit too though.

The sad thing is that I really like the idea of this black top! It is printed with a beige polkadot, which I thought might dizzying to the eye. Instead, I sewed the top with the wrong side of the fabric. One the left below is the shirt inside out… and on the right is the “good” side, with contrast neck and cuffs and just a hint of polkadot shining through. If this shirt fit, I’d wear it all the time!

inside outside

Nowadays, I always prewash knits twice before adding them to my stash – that way I’m ready to sew! I know that lots of people don’t prewash jersey, and that’s fine if it works for you… but if I’m going to put my money and time into making something, I want it to fit the way I intended!

How about you? Do you prewash? And if you do, do you use the heat settings that you’ll use forever after, or do you blitz it as hot as possible?

Ps. I missed this black top in my roundup of Renfrews in my closet, which brings my total up to 11!

Pps. The rest of my Lazy Tips for Sewing Knits are now gathered in the header bar up at the top! 

3 thoughts on “Lazy Tips for Sewing Knits: Prewash, dang it!

  1. I’ve just discovered you and love all your tips – thank you for a great series which I learnt about through handmade by Heather. Can I give you another lazy way to pre-shrink? I learnt from my aunt who was an adult during WWII and an amazing seamstress to soak fabrics in hot water in a basin and leave them overnight, then wash. Works like a charm, if I do it nothing ever shrinks any more. Saves you soap, power and water too:). I do it with everything – cotton, linen, viscose, woven, knits. Only things I don’t soak before pre-washing are silk and wool.


    1. That is the first time I’ve ever heard of that method – but it sounds like a great option! Thanks for the tip!


  2. This tip can’t be emphasized enough 😏. And I would add that the dryer part of it is the most important. I am usually a drying rack outdoors kind of washer, but (ahem) since that purple rayon mess I make sure to get to a dryer at least once with new fabric


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