Lime Time: Lime Plaster on Faswall Exterior

by ziggy on May 13, 2017 -- 2 comments -- Follow

Lime plaster base coat on Faswall block

Applying the first coat of lime plaster over the faswall block

Lime plaster is the source of a lot of confusion for folks, myself included. It’s taken a long time to understand even the basic ins and outs of hydraulic lime, hydrated lime, slaking, carbonation, blah blah blah. When you start to read and hear about lime plaster, it sounds a bit like alchemy. Which it kinda is. Lime is totally unlike clay plaster, which seems so simple and innocent in comparison. Lime plastering is, after all, a chemical process that you really want to ensure goes according to plan.

The challenges of lime plaster are increased when your wall substrate is not even, such as a coarse straw bale wall. That’s because you cannot build lime out in thick layers, nor should it be applied unevenly either.

Attached greenhouse with plaster

South side of home, first coat of lime completed

Lime Plaster on Faswall Block Home

So, thankfully… all that to say… doing the lime plaster over the walls of this faswall block home was a relative dream, since the wall surface was already fairly flat. The fussiness of building out many thinner coats was avoided, and the pleasure of working with lime was much more apparent. It was fun, in fact. I still prefer working with clay for a variety of reasons, but lime has its place, ya know?

lime plaster - faswall east

Elaborate staging on east wall — very important to get this right before starting actual plaster work!

My crew and I applied the lime plaster base coat to this faswall block home in relatively short order. The weather was cooperative, which is always very important when working with lime. Too hot or too cold is no bueno. We had some very interesting staging situations, but once we had a plan we were able to focus on the work.

Like Gabe of The Art of Plaster told me before starting this job, planning is the most important step. No kidding! Getting set up to actually plaster the walls seems to take fully half the time, especially when you’re working off the ground or up on a roof. Geez.

First coat of lime plaster on faswall

Freshly completed base coat in greenhouse

We’re using Type-S hydrated lime for the plaster work, which for some reason was incredibly difficult to source in this part of the state. I guess it’s just a reminder of just how rare this type of work is around the US these days. Sad fact but true.

Japanese jigane trowel for lime plaster

Applying lime with Japanese jigane trowel

We used steel trowels to apply the plaster and compress fiberglasss stucco mesh, which should help immensely with the longevity of the plaster work. Actually, most of the walls are blessedly well-protected, except for the large east-facing wall. Even though lime is much more resilient than clay plaster, it’s still a good idea to protect your walls as much as you can.

Floating fiberglass mesh in lime plaster

Embedding stucco mesh in first layer of lime plaster

After embedding mesh, we used a sponge float to create an open pore texture. Working lime plaster too much and leaving the pores closed can be bad news. The sponge also left a nice surface texture for when we go back and apply a thinner finish coat.

Lime plaster, open pore surface

A close-up look at the open pores after using a sponge float

Eventually the whole wall will with finished with Keim mineral paint, which I’ve never used before. This job has been a fantastic opportunity to try new things out.

Wetting down lime plaster

Keeping the walls misted to allow for slow curing


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  • Yosi Almog

    Thank you for the nice post. What is the lime mix that you used – did you add any fiber?

  • I used 2.5 sand to 1 lime for the base coat. (The finish will be 3 sand to 1 lime.) I didn’t add fiber since we used fiberglass mesh.

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