Plaster vs Stucco: What’s the Difference?

By Scott Sidler April 11, 2016

plaster vs stuccoA lot of folks confuse plaster and stucco in old houses. While they are similar in a lot of ways they are different enough that understanding when and where to use them, especially in renovations, is imperative.

Their differences are not readily apparent to the naked eye. Plaster and stucco can both be applied much the same way with the same textures and thicknesses, but the main ingredients in each are what make them different animals.

Today’s post might be a little more building geek than hands on preservation, but I think that understanding how and why your old house is the way it is makes you not only a wiser human but a better homeowner. So let’s get our geek on!

 

Plaster vs Stucco

Like I just mentioned the ingredients are what make the difference in these two similar building materials. Both are made with an aggregate of some kind, usually sand of various sizes and textures. Both need water to mix everything together and activate the curing process.

The big difference is the binder. The binder is what holds everything together and cures into the rock hard consistency we all know and love/hate.

I’m going to preface this post for all you plasterers out there by saying that this is a purposely oversimplified explanation of the topic. Plaster, stucco, render, etc have been around for millennia with so many variables and formulas that a 1000 page book couldn’t cover everything. My purpose is to help homeowners get their feet wet on the topic.

Plaster

Depending on what kind of plaster you have you will have one of two different binders, lime or gypsum. Let’s looks at both:

  • Lime – Prior to the early 1900s, lime was the primary binder in any plaster. Up until this time it was cheaper to acquire than the expensive gypsum plasters. Lime plaster is a rather laborious process of mixing water and lime and waiting for the lime to “slake” before it can be added to the sand for application. Lime also needed the addition of fibers like horsehair to help strengthen the wall. Lime plaster also takes an extremely long time to fully cure, sometimes taking as long as a year before walls could be painted or wallpapered.
  • Gypsum – You’ve probably heard of Plaster of Paris? Well, that is gypsum plaster. It got the nickname because in the 1700s Paris was built on top of some of the largest natural gypsum deposits in the world at the time. Most gypsum plaster came from Paris and so the name stuck. Unlike lime plaster, gypsum cures fast (only a few days) and sets even faster which is why we make casts for broken limbs with the stuff. It typically didn’t  require horsehair to strengthen it either like line plasters do.

Gypsum plasters are interior plasters typically not meant for exterior use because they do not do well with repeated exposure to water.

Like plasters however can excel outdoors under most weather conditions and with certain additives to ensure they have a long useful life.

If your house was built before WWII then your walls and ceiling are usually a combination these two materials. Pre-1900 homes likely have all lime plaster walls, while homes in the first half of the 20th century may have walls with a scratch and brown coat of lime plaster and finish coat of gypsum. Slowly but surely gypsum has replaced lime for interior plaster due to its faster drying time.

That doesn’t mean gypsum is a better materials simply that the building industry has gone to gypsum. Personally, I prefer an old like plaster any day even if most of the plastering I do these days is with gypsum.

 

mixing plaster

Stucco

So you know what plaster is and what it isn’t now, right? So, what is stucco then? Stucco, sometimes called “render” by our neighbors across the pond, is an exterior coating that historically wasn’t much different from lime plasters.

Like lime plaster is was made up of slaked lime (or a variety of other less typical natural binders, sand, and water but it was also given numerous additives to help it withstand the elements. According the National Park Service Preservation Brief 22 stucco sometimes contained any number of these unusual ingredients:

Mud, clay, marble or brick dust, sawdust, animal blood or urine, eggs, keratin or gluesize (animal hooves and horns), varnish, wheat paste, sugar, salt, sodium silicate, alum, tallow, linseed oil, beeswax, wine, beer, or rye whiskey. Waxes, fats and oils were included to introduce water-repellent properties, sugary materials reduced the amount of water needed and slowed down the setting time, and alcohol acted as an air entrainer.

All of these additives contributed to the strength and durability of historic stucco. In 1824 a new invention changed the way stucco was used in buildings.

Portland cement was invented in 1824 in England and named as such because its inventor, Joseph Aspdin, thought the cured concrete looked like Portland stone which was a popular building material in England at the time.

Portland cement mixed with sand and water creates a very strong stucco much harder and more brittle than like stuccos. While Portland cement gave us the ability to create harder stuccos than lime and natural cements typically did what we gained in strength we lost in repairability.

Portland cement made its way into all kinds of things like mortars too and it creates such a hard material once cured that it can do serious damage to old buildings if installed where lime plasters, stuccos, or mortars should be because it’s rigidity is so dissimilar to many historic materials that Portland cement can result in further damage to historic elements.

Unlike lime it cannot be renewed as time and Mother Nature slowly wear away at the softer lime coverings.

So should you ever use Portland cement in your stucco? Well, that depends on whether it was in your original stucco to begin with. I always recommend replacing materials with like materials. If you have Portland cement stucco then by all means patch and repair with a similar formula stucco, but if you have lime stucco then don’t even think about repairing with Portland cement unless you want more repairs down the line.

So there you have it! Stucco and plaster. Plaster and stucco. The same but totally different. I hope you enjoyed getting you old house geek on with me today. Until next time fight the good fight and save that old house!

 

25 thoughts on “Plaster vs Stucco: What’s the Difference?”

  1. I would the best solution for remolding. Basement walls and the brick sunroom. I would like to back with the other walls with sheet rock.

  2. I recently purchased an old Cajun house in South Louisiana. I have basically gutted the Interior down to the original shiplap long grain yellow pine walls. Interior construction like this was common at turn of the last century. The walls are very solid and will support the weight of plaster or stucco. The ceilings are old growth pine as well. The walls are ten feet tall. I have done exterior stucco and liked the textured look. I will put up wire lath and coat with latex twice before coating. I am thinking of using a redi-mix stucco. Two brown coats with white finish as the third coat. I have no concerns about the hardness and hanging pictures and what not. I will use a combination of masonry and regular drill bit and use dowels as hanger. I am looking for a southwest textured look. Should I use plaster or stucco.? Which will last longer? The ceilings won’t be coated.

  3. Hi, Scott. My community (dating back to 1928) plans to build a 14 ft. long monument sign at it’s historic entrance, and we have been doing fundraising to pay for it. We preferred that it be made of cement, however, for liability reasons the city said it needs to be a breakaway construction (aluminum with a thin exterior coating) held up by posts on a footer. The contractor suggested that it be covered with stucco; however, when looking carefully at a similar sign that they installed just three months ago, it already has significant damage from peeling, cracking, and separating. The contractor stated that it will last about ten years.

    What would you recommend as a coating? It has to be thick enough to hold recessed lettering. We were hoping that the sign would last a rather long time, say 100 years or so. We’d be grateful for any assistance that you can provide.

    Dina Wiley
    Friends of the Hollywood Riviera

  4. I didn’t know that there were such obvious differences between stucco and plaster. I totally agree that it’s important to know what your house is made out of though. I’m pretty sure my house has a lot of plaster in it, but a lot of the outdoor is actually done with stucco, so this was a pretty informative article! Thanks for sharing.

  5. I’ve read your blogs on all the plaster repair and this on plaster vs stucco. I have a 1938 house with stucco on the inside walls. The walls are as hard as concrete and it’s tough to hang anything in some places. I’ve even dulled drill bits.

    I would like to have smooth walls. One professional told me that I couldn’t sand them smooth because they may have asbestos. Can you give any ideas or a future article on smoothing the rough surface walls and pros and cons, please?

    Thanks!

  6. Scott, I, too, think you did a careful job of explaining in a simple way what binders a US homeowner might find in the finishes on their interior and exterior walls. It is a complex area of study.

  7. Scott, I think you have produced a very well balanced opinion on this subject, unfortunately some commentators do not seem to have understood the details of your Blog very well. Thank you for tackling a difficult subject from an informed position.

      1. I’ve a house that’s 124yrs. Three layers of brick. Ceilings 14ft. High with stone walls in basement. It’s in need of total renovation.

  8. Morning Scott, as you can see the blog was shared with some people that are engaged with this subject.

    I have been working with lime plasters, mortars and stucco’s mostly exclusively in the US and Europe for 25yrs. It has always been a touchy subject!! Over this time I have seen both materials used in the wrong context with terrible consequences for the building and usually the applicator.
    I usually advocate that ‘like for like’ material is used for repairs and conservation work, the basis of this being the original materials used. There are some arguments about substitution in certain circumstances, particularly where climate is adversely affecting the finish.

    Which effectively all that plaster/stucco is, a covering to protect the structure of a building from degradation. True these finishes have become decorative and artful in themselves over time, but there true purpose is protection.

    I am grateful that you write about OPC/ Lime on your blog, it is always a good thing to open up discussion about material use in preservation/Conservation and considering the debate about climate change and human intervention, to open up a debate about our basic use of construction material.

    However I would suggest that all the basic materials are covered and that some empirical facts are checked before publication, it may be an opportunity to prove the widely held belief in the preservation/repair community that re-use and repair is a much better way forward that demolition and new build.

    It may be an idea to publish a ‘lime cycle’ meme to illustrate the production of lime and maybe a further article clarify some of the discussion points in your blog?

    1. Richard, I’m already planning to take those steps since this post has stirred a lot of discussion and unfortunately more anger and rudeness than necessary in my opinion. I’ll be partnering with a couple heritage plasterers to offer up a more in depth post on the topic.
      This blog is largely aimed at homeowners and educating them about the old buildings they live in. The brevity and focus of most of the articles is to that end and so I don’t go into topics that require decades of training to perfect rather I try to explain in layman’s terms. This may be one of the few cases that a more thorough explanation is in order.

  9. Curious to know you technical sources for the merits of portland as a ingredient in exterior stucco? What are your historic references for this theory? Have you ever done any adobe restoration work…only to discover the damages done due to portland based stuccos? Do you have any contact with our fellow plasterers in Europe who use lime exclusively in exterior stuccos?

    1. Susan, my sources for this article were mostly pulled from The Secretary of the Interiors Historic Preservation Briefs on historic stucco and plaster and personal experiences working on 1880s-1950s buildings here in Florida. I have never done any adobe restoration, but I am well aware of the massive damage done to many historic buildings by adding Portland cement mortar and stucco where it does not belong. I don’t recommend Portland cement for any building that was built with lime because of the incompatibility, but here in Florida there are many early 20th century buildings that we restore that originally used stucco made with Portland cement.
      My work method for historic preservation has always been to repair like materials with like materials to assure consistent performance and maintain as much of the historic fabric as possible.

  10. If you want to destroy an historic building or allow your natural building to fail, use cement in your wall finishes. The worst advice ever.Cement lacks the necessary permeability which keeps a building healthy. Lime works inside and outside and is what should be used in restoration and in natural building. Do your homework Scott!!!!

    1. Bas, and what if that building was built using Portland cement? Shouldn’t learning to work with all materials matter? Yes, I agree that repairing like stucco with Portland cement is insane and will inevitably lead to early failure. But when you come across historic buildings built in the 1920s and 1930s that used Portland cement based stucco then the proper way to repair and restore them is with similar materials.
      If I built a house today I would use lime because I prefer it and know it to be a superior product, but that doesn’t mean Portland cement doesn’t have it’s place in repair and restoration work.

  11. Stucco based on slaked lime can be outside and last many centuries. If you add pozzolana, or volcanic pumice, it will dry faster, super strong and can withstand a couple of milennia. The addition of cocciopesto (brick powder) give it hidraulic properties to withstand even marine enviroments.

    1. Rafael, I agree and also know that there are numerous other ingredients or natural cements that can strengthen stucco. I don’t pretend to claim that Portland cement is the only answer, only to state what has happened in building science over the last century.

  12. I have never read such a disinformant article, you don’t even know that cement Portland is just lime heated to a certain temperature….and it contains gypsum!!!!
    I hope you will study a bit more before calling yourself an historic preservationists.

    1. Alberto, sorry you find it that offending. I understand the differences between lime, gypsum, and Portland cement and yes there are many of the same ingredients but you can’t deny that though it contains line or gypsum Portland cement is an entirely different material. You may have a preference for certain materials but that doesn’t mean that other materials are not appropriate or historically accurate depending on the building in question.

      1. Alberto is actually incorrect. Lime and Portland cement are not made from the same material burned at different temperatures.

  13. I find it misleading that you do not talk about permeability. Most of these old homes have survived for many years without vapor barriers because moisture would not be trapped in the wall system. As soon as you put cement on the building you are risking moisture issues. You also only talk about the downsides of lime. Not to mention, lime is far better suited than gypsum for exterior use, not marginally. Lime does not re-hydrate like gypsum for one. This is less building science and more an intro in to what is lime, gypsum, and cement. And a biased one. No one trusts lime even though it performed well for thousands of years because they don’t understand it.

    1. Frank, I appreciate your feedback. And I do trust line and find it an excellent building materials. You are correct that this is a introduction only into the basics behind some of the common ingredients in plasters, stuccos, and renders over the recent history. In an 800 word post there is no time to go into the complexities of the topic.

Leave a comment!

Keep the conversation going! Your email address will not be published.

*