Can I plaster over metal lath without a backing material?

Question

One alternative to traditional drywall is plaster over metal lath. Most of the videos I've watched use some kind of backing (e.g. brick, OSB, or plywood) with a layer of tar paper over the top behind the metal lath. Can I plaster over metal lath over a wall cavity with the lath secured to 2x4 studs (16" on center)?

Answer 1

Yes you can; however, I would recommend at least stapling craft paper/tar paper across the stud bay behind the lath to minimize loss of plaster through the mesh.

Make sure the lath is stretched tight.

Answer 2

Yes, you can apply plaster to metal lath without backing. That's exactly what you do for interior plaster and metal lath.

Type in "how to install interior metal lath and plaster" into google video search, you'll find what you're looking for. What you described looking at, with backing and a weather resistant barrier, was stucco.

Lath and Plaster takes a lot of skill, it's more expensive, and it's labor and material intensive.

Ceilings especially, if you are a first time DIY'er and your scratch coat is too thin, that can actually drop out on you and do some damage. It gets even trickier the more likely the ceiling joists will deflect (for example, undersized ceiling joists with you crawling around in the attic, or if there's living space above and the floor joists are just sized for the span and weight of gyp board like the floor system wasn't built for the added weight of all that plaster).

Plaster is not favorable if gyp board is an option, mainly for renovations. You will need to cut out with a powered grinder and metal cutoff wheels, a lot of cutoff wheels - you're easy peasy drywall saw won't cut either material; and, the over cuts for a new electrical receptacle box will be unavoidable because of grinder wheel diameter, the dust will be a nuisance and you won't catch it all even with a common home-owner shroud setup, and if you've ever had a grinder wheel break on you then you know you're going to want more than just safety glasses and a tee shirt... and it is a massive pain to make those cuts with the grinder guard on. On top of that, plaster with metal lath doesn't have common market solutions for retrofit work, receptacle boxes and so forth don't just screw into it. It doesn't cut out clean and it doesn't patch easy... more or less be prepared to back every joint, nylon every screw, and tie in is a pain because the different plaster mixes (old and new) can make it difficult to match the sheen and texture.

Even if you get the mix right, and even if it doesn't crack on you, you need to think about two things before you begin: finishing (consistency of flatness and texture) and next steps. You will be very lucky if you can pull off anything close to reasonable flatness and knock down every sweep. You will invite a world of mess if you have any lumps/divots/high-spots in the finish coat that you don't like. You will essentially be sanding down mortar or floating it out. Lots of dust, lots of effort, lots of materials, and then you might get into your scratch coat and increasing difficulty of getting it to match the sheen for paint becomes more of a factor.

Also keep in mind: Plaster will significantly raise the humidity for a prolonged period which can have other ramifications; and, four weeks is a good ballpark to being paint-ready for basic plaster mixes. These two in tandem can be a real thing to make sure you get your head around if you have a tight home, you don't want to seal moisture into a wood framed wall cavity without any way for the moisture to get out before the wood starts to mold. In most cases, you can usually get away with just waiting until any dark patches have evaporated.

If you only have a small section and you're basically just playing around, have fun! If you're thinking about doing your whole house, give some serious thought to the service-life considerations... how are you going to hang your pictures? have you ever tried to drive a brad nail through plaster for your trim? All those little things that are so easy with gyp board become cost and appearance considerations.

Added thoughts:

• You might try rib lath if you're worried about flex, don't go this route unless it solves some specific concern you may find as you get into things. A company, enzar, has various lath profiles on their website if you want to look at specialty stuff. Nothing special about enzar, not looking to promote.
• Check out ASTM C1063 for guidance.
• If you put kraft paper backing, you'll just be wasting craft paper backing. Get your mix right, if you're getting a bunch falling down, you're going to have other bigger problems.
• If you are doing much of it, you are going to need to cover everything you don't want plaster to grind into. Plastic wont be enough to protect walking surfaces.

Good luck!