Metal buildings are great and I personally am a huge fan myself but a lot of people don't really like the look of the siding, which is typically a series of ridges and valleys and seem to be reminiscent of a metal roof.
People often wonder if it is even possible to apply stucco to a metal structure and if it is, how that would look.
Is It Possible To Stucco A Metal Building?
The short answer to this question is...yes, it is possible to stucco a metal building but there are a few things to take into consideration that are unique to metal structures like weight, insulating properties and what systems would work best.
Weight should be a major consideration and knowing that a three coat system will be heavier than a one coat system or EIFS type of system is one thing to take into account. Metal buildings also have nearly zero insulating properties so adding or using foam would really help get some much needed R value from the structure.
The last thing you need to consider is what type of stucco systems would work best with the design of the metal, having high points and lower points and how you would even go about attaching anything to it in the first place.
Let's Talk Weight First...
Now stucco can be a very heavy material, especially if you use a three coat stucco system. For modern wood framed structures this weight is typically no problem, as there is plenty of strength to hold the added weight of the stucco. With a metal building however, weight is usually the first consideration for a lot of people, or it should be anyways!
A three coat stucco system can weigh on average of 10-12 lbs. per square foot! On the other hand a one/two coat stucco system can weigh as little as 4-6 lbs! This is a huge difference and on a small metal shed (6'x8'x6' tall) that is a difference of 1,500-1,800 lbs. to 600-900 lbs. if you had 150 square feet of wall to cover.
Remember that anytime you add weight to something, you will usually have to strengthen the frame of that structure in order to take and hold the added weight. Supporting a few hundred extra pounds would require some light structural modification while supporting nearly a ton more would usually require a more moderate amount of structural support.
Think About Insulating Properties...
Since metal has virtually no insulating properties on its own so adding additional insulation is going to be very enticing to some people and adding stucco can be one way to do that.
Styrofoam can be used with some stucco systems and it provides some additional R Value to a metal building. It can go on the exterior of the building, underneath the stucco base and finish coat(s) and gets attached directly to the metal siding.
You could also add Styrofoam to the interior wall cavities of the building for extra insulating properties and since foam is available in many different thicknesses, you can usually find a thickness that fits almost perfectly.
In some cases, you could even use standard insulation batting but this is usually for larger steel structures that have/use larger framing members.
Stucco Systems That Would Work Well...
I personally think that the thinner stucco systems would work the best on metal buildings due to the weight factor, which is the main factor, in my opinion.
A one coat (2 coat) system that uses foam underneath the base and finish coats is the absolute best stucco system to go with due to the fact that it is lightweight and adds great additional insulating properties at the same time, so it is the BEST option in my opinion.
You could also use a three coat stucco system if you would like but you will likely have to reinforce the framing/siding to accept the additional weight. This system is not really the ideal system and I would advise against it but it is important to note that it can work if precautions are taken.
What Kind Of Metal Building Are We Talking About?
There are many different metal buildings out there and they will be different as far as how they are constructed, how thick the metal is, whether they have vertical supports, how far the supports are spaced apart and so on.
For instance, a small metal shed that you would find from Home Depot or Lowes will have a very thin gauge metal that is used for the siding and the framing metal's thickness is also quite weak so keeping the weight of the stucco down as much as possible is crucial.
A larger metal structure, like a 40x60 metal building will have siding that is much thicker and framing members that are very thick in most cases and can support a little bit heavier load than a small garden shed.
Remember that you may want (or have) to add some additional framing support before applying the stucco to the walls. How much and where are difficult questions to answer but I like to look at traditional types of "stick built" homes and use that as a general rule for myself.