As you can see above, different people will answer this question differently. And . . . there are different kinds of respirators, designed to protect the wearer from different contaminants. An organic compound respirator is designed to protect you from organic compounds, usually with replaceable cartridges. The lifespan of those cartridges varies with the contaminant and the concentration level of that contaminant in the air around you.

A particulate respirator has filters, not (necessarily) cartridges. Usually the lifespan of the filters depends on how much airflow is still able to pass through. Many industrial respirators are made to handle both cartridges and filters. Expect industrial prices for those.

I agree with the advice to check the Safety Data Sheet (formerly called Material Safety Data Sheet) supplied by the epoxy manufacturer. These are usually available online at the manufacturer's website.

You asked about two distinct circumstances - laminating and sanding. For sanding I would highly recommend that you wear an N95 particulate (dust) respirator. Wearing a respirator is not particularly comfortable. Respiratory disease is less comfortable. Your choice.