I am a former art major in college who has discovered technical theater only recently.  I volunteer at a local community theater and have done so now for a few years.  I started initially because I am a painter and I wanted to learn and do some scenic painting.  The problem I have run into is the resident scenic designer (who is a very talented artist) prefers to do everything himself. 

All other aspects of producing a show are open for people to be involved, but unless all you want to do is prime flats and such, nobody ever gets a chance to lend a hand w/ painting.  Is this normal?  Or should I look to another area theater to get involved?  This is especially frustrating because I know I have the skills to help (just help, I'm not looking to impinge on his design) and the sets are NEVER complete by opening night.  Often many of the SD's design ideas (which again, are brilliant) get left in his head or on the drawing board because as 1 person working alone, he never has time to get it all done.

 I hate to say this, but this is life & he probably views everyone as a threat, to his perceived empire, status &/or standing within the group.
Which is very sad, when one becomes to believe, the place will fall down without you!
I think we all can be indited & found guilty of varying degrees of this from time to time!
I only hope I will have enough sense to pull the pin, when  I indulge in this type of caper!
May I suggest it is not a situation that has an instant fix, by pressing a button or mixing with water!
Therefore test the value to you of the water else where, without burning your bridges in this group completely.
Unfortunately I doubt intervention by the board or a crusade will have much of an effect, or you will even dent the barricade, as it does take time before he will  eventually implode! Which is a great pity, as he possibly whole heartedly jumped in to get it done from day one. With no assistance or support of the group & has been used & abused ever since.
One thing that could work, is for the group to pass around the hat or club together, to send him on an extended long service leave holiday trip!
I doubt my drivel will help you what so ever, as I only tend to run up against this situation, with dragons that run the front of house & rarely with techies, who are always perfect to work with!

I agree with Joan54! Just state it up front you want to help. If you get a "no thanks" time to try elswhere.

At the school I work at I NEVER have enough painters. We are currently doing Cinderella  (Shows are this weekend!)and did almost no building, all painting, I would have loved more painters!

Best of luck!