I don't normally post here but I have just had exactly the same problem with relative humidity levels at over 80% in the workshop and so have been looking into the pros and cons of dehumidifying a workshop and some of the info in this thread is incorrect.
Ventilation, as has been recommended, will do no good at all unless the workshop is well heated. Otherwise you are just swapping one lot of cold moist air for another. In fact it will cause more problems, as the outside air is likely to be colder than the air inside, and you will end up further cooling the workshop.
Keeping the workshop warm with some ventilation would help but is likely to be prohibitively expensive unless the workshop is very well insulated.
The only practical solution if you want to run your workshop at 60%RH is to get a dehumidifier. The latest desiccant wheel dehumidifiers , like Steve has bought, are the ones to go for as they will work at low temperatures. They do take a fair bit of current; I have an XDry and that is rated at about 700W but it only draws that level of power when it is actually dehumidifying. It spends a lot of time with just the fan running when consumption is very low.
One problem with dehumidifiers is that they will not cope with fine dust as the rudimentary filters are just designed to stop household fluff. If you want to run one in the workshop it should be run overnight when you are not working. This is why I bought the XDry, it is one of the few dehumidifiers that can be used with an external timer.
Of course all this would be a waste of time unless the workshop is reasonably well insulated and sealed.
Keith
