I agree, just prewash in hot water. I have done this and had some shrinkage in all wools, some more than others. However after the initial wash/dry have not had any issues with piecing wool into a quilt. But I have only done it twice, so don't have a huge experience to speak from. Hopefully you will get some more feedback too. I have also read that others have used old wool clothing as batting and it makes a really warm quilt.