Working with outside graphic designers

If the designer provides (and works with) design specs, then it generally takes one or two days to implement a static design. The trouble starts when designers do not provide you with those, or expect a pixel perfect responsive rendition (which falls in the Contradictio in terminis category).

Demand design specs. Carefully control expectations. If the designer and client expect you to create a fully responsive page layout without providing exact design specs for mobile, tablet, and large screens (minimum), then ask for those. You cannot be expected to make up things as you develop.

Communicate with the designer before he/she starts designing. For example, set up some ground rules, such as the base grid that will be used. Explain about Foundation/Bootstrap type like 12 or 18 column grids. This will also simplify the design process on the designer's side.

Document everything. Before collaborating, speak to the designer in person (or over the phone) in order to assess the knowledge and experience level. Based on that conversation you decide on the risk level. I use 15-20% for low risk, 25-33% medium risk, and 50 up to 100% for high risk. I calculate the expected number of hours, and multiply with that risk factor. Also, I add an additional 10% hours per person working on a project (multi-person drag).

Add a planning phase during which you communicate with the designer. DEMAND DESIGN SPECS even if he/she never worked with those before. I cannot tell you how important this bit is. You cannot be expected to hunt down every margin size, font property, and so forth, in a mockup - it is the designer's job to document this exactly for you, including differences in styling between break points.

Send the designer this if he/she feels it is too much work to create design specs:

“Developers at all stages of projects expect and demand strong documentation. Although documentation is never the most exciting aspect of design, it’s a critical step in ensuring smooth working relationships, timely delivery and a successful hand-off at the end. Ultimately, design documentation acts as a life-support system, ensuring that your vision is executed properly.”

Introduce something like Specctr​​ to the designer. This will really make your life as a developer easier, since it also exports directly to CSS rules, which you can copy.

Keep the lines of communication open at all times. Keep asking for updates.

If the designer expects interactive stuff/animated effects, then he/she ought to use some kind of prototyping or animation tool to demonstrate what it should look like.

If the designer and/or client opine that you are asking for too much, then it is probably not worth your time and energy to work on the project - it will just be very, very stressful in my experience.

PS and everything Liam said :-)

It's reasonable for the client to ask you to collaborate with the other designer. Do your best to make it work.

I've done this quite a few times.

The only real issues are: what medium does the other designer predominantly work in and what's their skill level?

If it's a print guy/gal and they're going to design the website and you're supposed to then piece it together in HTML, you're going to need to explain some of the differences involved going from print to the web. Responsive Design, for example, can be a foreign concept to a lot of print designers. You may want to explain it along the lines of "Create a catalog page, then reformat to fit both a post card and a movie poster. With the web, you're not designing for a set size" (desktop to mobile to 4k huge screen).

You are "the web expert" in that situation. You need to educate their designer in what works online and what doesn't. If they don't take your advice, their site isn't going to work right and that's not going to be your fault.

If he's another web designer, all I can do is say good luck, it's going to be a bumpy ride. It's rare that you end up working with another web designer with the same, or even relatively close, skill level. If they're beyond your skill or far beneath it, there will be a lot of butting heads if "the lead" isn't worked out early in the contract.