Do employers mind a long work history?

I've always had itchy feet when it came to work, i just couldn't settle down long term for the same firm. I've done car mechanics welding steel erecting factory work warehousing forklift driving and construction. The longest i worked for one firm was 5 years and even that was an agency. I sent an application of recently for a new job, i have the skills they require but they might see my work history as a bad thing. 20 years and i had to put in an extra sheet for all the jobs i've done. One sheet wasn't enough. Would that be a bad mark against my name?