Different flours (both in terms of brand and even batches of the same brand) have different levels of absorbency, so you often have to experiment a little with new baking recipes. I always need much more water than the recipes in my favourite bread book call for, for example.
The best thing to do is add more flour gradually until you are happy with the texture, then you will have a better idea next time of how much you will need.
this is a technique that might help with the shell issue:
I suspect your croissants are losing humidity during proofing, possibly freezing the butter block, and possibly baking resulting in a harder shell. If you have a humidity controlled proofer and oven, then those parts may not be your problem. Otherwise, read on:
Peter Reinhart in The Bread Baker's Apprentice suggests pouring boiling water in a flat pan/container and placing in the bottom of the oven during the baking (of breads) in order to keep up the humidity. This Link has the recipe published with Peter's permission. Notice how the freezer doesn't come into play (freezer is a dehydrator and pretty good at it, too) although some recipes call the freezing part a must.
Croissants are lighter than bread loafs so they may require a different humidity profile than breads during baking (as noted by commenters). However, for proofing humidity levels should be high and the temperature around 80F or 27C.
To achieve that, for the proofing period keep the dough in a turned-off-oven and turn on the oven light a long with a the boiling water method. This usually prevents 'the skin' formation and a dried out crust. It also helps with getting a better rise during baking. The oven light bumps up the temperature but if you're room temperature is close, don't bother.
You may wish to read this piece on humidity and baking and generally the Maillard Reaction. Here's an excerpt that might explain the problem:
"Under dry oven conditions, the dough will have rapid evaporation of the water from
the exposed surface. This will cause premature formation of a dry inelastic outer shell
on the bread surface"
Best Answer
30C is a good temp for proofing. Proofing overnight in fridge allows for greater flavour development in breads (or any yeasted dough), but they still need to be proofed further at room temp before bake. Croissants I have never seen proofed in the fridge - not saying it can't be done, but I've never seen it. The only time you should be truly concerned about a hot kitchen (in my opinion) is when you're working with chocolate. Because breads and yeasted things rise best between 27C and 38C with the optimum temperature being 35C. Check out this link for more info http://www.theartisan.net/dough_fermentation_and_temperature.htm
Good Luck! Croissants are a labour, but a delicious one!