Not insulated?
I'm not sure how much condensation you have to deal with in your colder climate, but I'm saying you should get an oil based primer and use two coats of that.

My contractor advised us to use oilbased primer in our bathroom because it is more resistant to the effects of moisture. I have no recommendations on brands, but I'd get only the very best you can find, as the foundation of any future paintings in a new structure.

I actually hope that the drywaller used a setting-type mud, like Durabond or Easysand, and not regular premixed mud. IMO premixed will fail due to the wild temperature swings that will set the stage for condensation on the walls (or within them) and the moisture will lift the mud/tape.
Oil primer for sure.
Casey

This is really why you don't see garage drywall jobs hold up very well unless the space is heated. I don't see what you are going to gain by using an oil primer though...perhaps I am missing something. I would use an acrylic primer and follow that with two coats of some high quality exterior satin paint.

Sombreuil mongrel......yes, he used Durabond but I'm not sure if he did it adequately (I don't know anything about it). I know he used it for the first round of mudding (mixed with the ready-to-use drywall compound) but after that I think he just used the premixed.

Our garage is not heated but it is insulated. The walls still look great 12 years on. I hope we didn't make a mistake by using drywall in our poolhouse.

Anyway, I was at the paint store (supposedly experts) and they didn't think exterior or interior made a difference in this application and told me that oil primers are not what they used to be (they've taken out a lot of what made them so good because of new environmental laws and for lower toxicity, etc.) and that now they are not much better than the acrylic ones. His demeanor made me lack confidence in what he was saying (he didn't seem to know much when I asked for details), but I went ahead and bought an exterior acrylic primer.

Someone tell me its going to be OK because I've just cut in the edges!

It will be OK!

...yes, he used Durabond but I'm not sure if he did it adequately (I don't know anything about it). I know he used it for the first round of mudding (mixed with the ready-to-use drywall compound)

Hopefully this will not come back to bite you. It might be OK, it might not. These should NEVER be mixed together.Applied one at a time OK but not mixed up together.

Oh dear!

What might happen if he mixed them? (Well, he DID mix them, that I know. The Durabond was a powder that came in a box and he said he'd put the powder into the mud to strengthen it - makes it like concrete he said. He went through 2 small boxes of it...)

Concrete? Oh my. Do you want or need concrete in your walls? Concrete is good for sidewalks and runways, not walls.

I have been a drywall and painting contractor in northern michigan for 25yrs. it is ok to mix durabond with certain types of plaster (mud) the mud can or should only be all purpose, never topping or light, mid-wheight mud. both all purpose and durabond have the same ingredients. the only difference is durabond has an excellerator in it. youll notice on the package different setting (when its hardened) times. 90minutes, 45min. all the way down to 5min.. note when mixed they should be mixed really well..