His wary eyes caught movement as he added the last of his load to the wood already piled against Ivergan's hut.
Current version of sentence:
Most of his load had joined the wood already piled against Ivergan's hut when his wary eyes caught movement.
There was nothing wrong with the original sentence. The use of "as" to join two simultaneous events was perfectly correct. It was not a lazy "as-splice". Even I, the Ranter of As, assassin of -ings and persecuter of apostrophleas, had passed it. However, its being picked on by a slightly hyper critter made me think. I couldn't resist the challenge. So, while adding back some cut material that a wise beta regretted the loss of, I ran over the passage a few times and found a solution that did not add more words (my greatest fear *shudder*).
Gosh, it felt good.