Do I need to prewash this fabric?

[Emerion]

I have bought some woven 100% cotton upholstery fabric, which was advertised as washable - one of my reasons for choosing it. It hasn’t been prewashed. I asked the seller if I should prewash it and she then said that they recommend dry clean only, although I could, at my own risk, wash it very gently & coolly. I know that fabric sellers sometimes say this about dry cleaning to cover themselves rather than because it’s really necessary. Do you think this type of fabric could and/or should be prewashed? I gather that prewashing is done because of shrinkage. Does woven cotton shrink? Obviously I’d rather not bother ( worried about unravelling and lazy!), but as it needs to fit snugly, I couldn’t afford shrinkage at a later date.

[sewingj]

I'd definitely wash it. I had some cotton upholstery fabric last year which I used to cover a box cushion. I washed it first and it shrank a lot!

[HooliganHeart]

I pre-wash just about every fabric before using. Not just for shrinkage but also to remove any left-over processes of manufacturing.

[sewmuchmore]

Woven cotton can shrink, but i would be wary of prewashing upholstery fabric if it has a finish to it such as flame retardant or it has a backing to it. Often upholstery fabric has a rubber type backing for durability. Is it upholstery fabric you have bought or is it curtain fabric and what are you going to use it for?
If is for furniture then i would treat it with scotch guard. If you are intending it for a piece of furniture that gets heavy use the perhaps cotton isn't the best choice as it can get grubby quickly. 
As with all soft furnishing you should vac them regularly and spot treat any stain.
Sorry this doesn't really answer your question. If you wanted to go down the pre washing route then i would overlock the raw edges so you don't get the ravelling.
One way of freshening up loose covers/curtains is to put them in a dryer with a tumble dryer sheet.

[BrendaP]

Cotton fabric usually does shrink, and unless you do prewash it you won't know by how much!

As to whether or not you do prewash depends on whether or not you expect to wash the finished item.

I have bought some woven 100% cotton upholstery fabric, which was advertised as washable - one of my reasons for choosing it. It hasn’t been prewashed. I asked the seller if I should prewash it and she then said that they recommend dry clean only, although I could, at my own risk, wash it very gently & coolly.

If it was advertised as washable then it should be washable.  If it's not then it was a contravention of the trades desctiption act and surely you would have a claim against the vendor (if you still have proof of how the fabric was described).

If you do wash it don't spin too hard or wring by hand, that could introduce creases which are hard to get out and even cause any printed design to rub and fade on those creases.

[Emerion]

Thanks all. It looks like I’m washing it then. It was advertised as upholstery fabric, @sewmuchmore, but has no special treatment or backing. I am using it as upholstery, so I will get some scotch guard. 

[Greybird]

@Emerion. Sorry I am late to this. Some upholstery fabric can be ruined by washing it. I had some that shrank so much that it went as stiff as a board and was impossible to handle. If you have enough, cut a 10cm or 20cm square (exactly) and wash that before washing the whole thing. It will not only give you an idea of the amount of shrinkage but also whether or not the "handle" of it will be altered.

[Emerion]

Thank you, that’s a good idea.  Luckily I hadn’t worked up the nerve to wash it yet, so I will try that.