Rolf,
That pic was made just for illustration as the resin had already cured and the trowel cleaned off with vinegar. I have a friend that had been at me for years to use vinegar but I assumed it wouldn't work. Turns out vinegar is a great cleaning agent for epoxy and at $1 per litre at the local supermarket it won't break the bank and much safer to use than a solvent, especially if you get epoxy on your skin. You can also stand your brushes in vinegar and the epoxy won't go off but you do need to wash all the vinegar out before reusing them so I use acetone just for this. I have a tall jar with a lid and acetone and stand my brushes in that. The lid stops the acetone from evaporating and I can just remove excess acetone by wiping them before reusing.
I'm using bote-cote epoxy for fairing and some other applications but not laminating (too thick). The standard bote-cote does not develop amine blush and this is just so convenient. I have used Gurit resin for all the laminating and structural work. Over the years I have used a number of diff resins and much prefer this as a laminating resin. I'm also using disposable Nitrile gloves . $10 for 100 pair at the local hardware store.