How to Spec Lime Plaster So Your Architect Actually Understands It

How to Spec Lime Plaster So Your Architect Actually Understands It

You’re knee-deep in a custom Oklahoma home design. The client wants “breathable, historic-looking walls that won’t trap moisture or smell like chemicals.”

You spec lime plaster.

The architect sends back a redline: “Use drywall + latex for code compliance.”

Sound familiar?

Here’s how to write lime plaster specs that stick — and get architects/builders on board without the back-and-forth.

Step 1: Lead with the Why (Performance, Not Hype)

Don’t say “beautiful eco-finish.” Say:

“Lime plaster system (hydrated Type S lime + aggregate sand, ASTM C5 compliant) for vapor permeability >10 perms (ASTM E96), zero VOC off-gassing (per CDPH 01350), and Class A fire rating (ASTM E84). Suitable for humid Oklahoma climates to prevent mold per IRC R806.”

Step 2: Nail the Materials Breakdown

Be specific — architects love checklists:

- Base Coat: Hydraulic lime (NHL 3.5) mixed 1:3 with sharp sand (0–4mm). Thickness: 8–12mm.

- Scratch Coat: Same mix, cross-hatched for keying.

- Finish Coat: Pure lime putty + marble dust (or mineral paint topper). Thickness: 3–5mm, troweled matte.

- Source: Organic Finishes LLC Type S Lime Base (OK-sourced, tested for local aggregates).

Step 3: Address the Objections Up Front

Preempt the “too slow/expensive” pushback:

“Curing time: 24–72 hours misted (faster than cement in humidity). Cost: $2.50/sq ft material (vs. $1.50 drywall, but 50% fewer callbacks). Code: Meets IBC 2021 Section 2506 for plaster systems; no variances needed.”

Step 4: Include a Simple Detail Drawing

Attach a one-page PDF sketch (we can send you a template):

Wall section showing three-coat build-up, vapor barrier placement (none needed!), and mineral paint compatibility.

Real Spec Example from an OKC Project

On a 4,200 sq ft Tudor revival in Nichols Hills, we spec’d:

“Lime plaster interior walls per Organic Finishes system. Breathability: 15 perms. Finish: Tadelakt-style polished with beeswax. Total: 8,000 sq ft, applied in 12 days by 3-man crew.”

The architect approved in 48 hours. No revisions.

Your specs aren’t just words on paper — they’re the blueprint that protects your vision (and your paycheck).

Need a free spec sheet template or lime sample for your next bid?

Email shawn@organicfinishesllc.org or call 918-947-9390. We’ll customize it for your OK project.

Spec smart, build better,

Shawn Reeder

Organic Finishes LLC

Lime plaster systems for Oklahoma’s signature homes