Almost all watercolor paper will curl will it gets wet. You can actually use that to your advantage. I prefer paper that has a good, strong curl. If you're seeing one long upward cup/curl down the length of the paper, you're coating correctly to the grain. If you coated the other direction (i.e., against the grain), you'd be seeing 'washboarding' -- guaranteed to produce uneven emulsion. But, if you coat with the grain, and then immediately stick something round under the curl when the paper is wet and leave it there for the whole drying time, you will never get any emulsion pooling that can leave you with too-thick spots. I use cut lengths of the pool toy things -- plastic noodles (??) I think they're called -- made of plastic foam.