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Why should you prewash fabric ?
All the sewing experts recommend prewashing fabrics before sewing and all of them cannot be wrong. Here are the reasons why they do so.
To eliminate the possibility of fabric shrinkage – This is the number one reason why pre-washing fabrics is considered a pre-requisite to sewing.
Sizing is added in the manufacturing process of fabric to maintain the appearance of fabric as well as to increase the quality (feel, smoothness). It improves a lot of qualities of fabric but these ultimately washes off. After the weaving process itself, the fabric is de-sized at the factory but even then some sizing is retained. This is removed when the garment is washed at home.
The problem is, when the sizing is removed the fabric shrink and there maybe a difference in the size of the garment. I know for a fact that it will definitely fit differently after a store bought garment is washed for the first time.
When you sew with fabrics which shrink at different rates there can be puckers at the seams.
Prewashing is usually done for natural fabrics as well as blends of natural fabrics. Natural fabrics include cotton, silk, linen, wool. Knits almost always shrink. All these fabrics shrink in different levels. Zippers, interfacing, lining are all recommended for prewashing other than the main fabric.
Another reason for prewashing is to remove dirt, oil and other impurities as well as fats, waxes, etc.
Yet another reason is to pre-empt bleeding or color run. Pre-washing can remove excess dye and settle the dyes that should stay on.
There is one more reason – to easily get grain perfection. Some fabrics are difficult to be aligned in the correct grainline without removing the extra sizing etc. Some fabrics which look off grain may look perfect after prewashing it.
So when you buy fabric for sewing it is always preferred that you prewash fabric.
Which fabrics should be prewashed ?
Linen fabric may need to be washed more than once for the whole sizing to be reduced to usuable proportions.
Garments made of fabrics like silk dupioni should only be dry cleaned to maintain its looks – you will have to dry clean sillk dupioni before sewing as well. You maynot want to prewash fabrics with beads and sequins.Most silks are indeed dry clean only .
You can read more about sizing here https://en.wikipedia.org/wiki/Sizing
First and foremost, determine if the fabric will shrink or not. If it wouldn’t, may be you do not mind the other constituents.
How to know if you should Pre-wash?
Here is the foolproof method to know.
You can cut out a small square piece of fabric from your main fabric. Determine its size. Draw it’s outline on a piece of paper. Now wash this fabric piece and then press it dry. Now keep this back on your outline. Has it shrunk ? Or Is it the same dimesnion? If it has, you know that you have to pre-wash.
Before washing, ensure that you have enough water in your pan to completely immerse the whole fabric.
You can prevent the edges from fraying by sewing the short edges together with a loose stitch. This will make your fabric into a tube. After you have done the washing you can remove the stitches. Do not use any bleach or fabric softener. Use a mild detergent, preferably baby shampoo.
How would you prewash fabric ?
You have to treat the fabric the same way you would treat the garment. If you will be washing it in a machine, prewash the same way. Use cool water in the wash, low heat temperature in the dryer. Hot water will cause more shrinkage in natural fabrics like cotton.
When prewashing knit fabrics, lay flat to dry.
There is a pre-wash cycle in some washing machine – this is not as long as the usual washing cycles and is used for heavily soiled clothes. This will deal with the dirt in fabric first before the real washing. You can use this setting to prewash your fabric for sewing.
Or you can use a gentle cycle in your washing machine for prewashing with your regular washing machine.
Do not leave the fabric in the dryer for long after the work is done. You will have a very wrinkly fabric in your hands, otherwise.
Or you can hand wash. Infact you should only handwash delicate fabrics (eg Cotton lawn) Fill a bucket with enough water to thoroughly immerse your fabric. Put the detergent in this and mix thoroughly till everything is mixed. You can follow the principles used in handwashing here. I use baby shampoo to prewash. It is as gentle as any soap can be.
How to thoroughly pre-wash cotton fabric ?
If you want to remove all the sizing and all the impurities thoroughly from the fabric the following tips can help.
Add soda ash (washing soda) to water, along with detergent. Add 6 tbsp of soda ash to 1 kg of your fabric.
If you want a more thorough wash, you can boil the fabric. Simmer for some time to remove everything. You can keep it on low heat for about one hour or so. After taking out of the stove, wash in cold water.
A commercial product called Synthaprol removes excess sizing from fabric.You can use this in the washing machine ( no need to use detergent). This is a product of choice of many professional dyers, because it is essential to thoroughly clean fabric before dyeing.
How to prewash non-washable fabrics?
Fabrics like silk, wool, which you are thinking of dry cleaning after wearing, also need to be pre-shrunk before sewing. You can dry-clean them.
Another option is to steam shrink them using a steam iron, after testing the fabric on an inconspicuous place to see that the steam does not mark the fabric. Use a damp thin cotton cloth as your pressing cloth and steam press on the back. If using a normal iron, wet a pressing cloth and then keep it on your fabric. Now using a hot iron, press on your fabric till the pressing cloth becomes dry. This will be your steam pressing. Now remove the pressing cloth and press on the fabric and press till it is also dry/.
Even with the pressing cloth, do not press on the right side of the fabric. Keep it on the back of the fabric and press. Then press without the steam.
How to prevent color bleeding ?
If you have a fabric with color bleeding, you may want to set the colors. You can use a dye catcher sheet in the wash for this.
A natural remedy – After the washing is over, fill a bucket with cold water. Mix 2 tablespoon salt and 2 tablespoon vinegar to this water. Soak your fabric in this solution for 2 minutes. Rinse with cold water till there is no color bleeding. Blot the fabric with a dry towel and lay flat to dry.