Field note
Conventional plaster vs gypsum drywall
Conventional plaster is a thick, multi-coat gypsum (or lime-gypsum) system on lath or masonry, not a drywall wall with more compound. The product family sits in ASTM C28 (gypsum plasters). Lath and furring installation sit in ASTM C841. Application of interior gypsum plaster sits in ASTM C842. Metal lath as a product sits in ASTM C847. None of those are ASTM C840 / GA-216, and none of them are a GA-214 finish level.
This page is takeoff and qualification language for a drywall / wall-and-ceiling estimator who opened a spec and found plaster. Commercial restoration, civic, healthcare, and some luxury interiors still specify it. Residential production almost never does; custom historic work does. It is not a homeowner “plaster over drywall” tutorial.
Not a handbook reprint. This article is original Drywall Insider editorial. It is not a reprint of the Gypsum Construction Handbook. USG owns that book. Use the current official edition at USG’s handbook page and current USG product literature from usg.com for manufacturer procedures. Drywall Insider does not host that PDF.
Three systems, three crews
Keep the names apart on the bid form.
Gypsum board (drywall). Panels per ASTM C1396, hung per C840 / GA-216, finished with joint compound to a GA-214 level. Default commercial interior and default house. See choosing drywall type and how to hang drywall.
Veneer plaster. Thin plaster on veneer base, ASTM C587 / C843. Looks like drywall in the hang; finishes as plaster. Middle ground. See veneer plaster for the drywall sub.
Conventional plaster. Typically scratch, brown, and finish over metal lath, gypsum lath, or directly on suitable masonry. Thickness is measured in coats, not in a 1/2-inch or 5/8-inch panel. Labor is a plasterer. Accessories are plaster beads and grounds, not vinyl drywall trim by default.
A spec that says “plaster” without “veneer” is conventional until the finish schedule proves otherwise. A spec that says “Level 4 gypsum” is drywall. Mixing them in one room without an RFI is how a shop hangs board under a plaster inspection.
What conventional plaster actually is on a job
Lath and grounds. Metal lath (C847) on framing or furring (C841), or gypsum lath where the documents still allow it, or bond to masonry the plaster manufacturer accepts. Grounds set the thickness. This is not steel stud plus a sheet of Type X. Stud spacing, furring, and lath attachment are plaster-base rules. A drywall 24-inch o.c. partition is not automatically a plaster partition.
Coats. Scratch keys into lath. Brown builds the plane. Finish is the appearance coat (gypsum, lime, or a specified gauging mix). Two-coat work exists where the spec allows it over suitable bases. Do not invent a coat count to match a drywall Level 5 rate.
Weight and structure. Conventional plaster is heavy compared with a single layer of gypsum board. Limiting height, floor load, and existing lath in a remodel are the design professional’s problem — flag them. Do not hang metal lath on 25-ga drywall stud at a height the plaster load will oil-can.
Fire and acoustics. A plaster assembly can be listed. So can a gypsum assembly. They are not interchangeable hours. If the drawing says a UL design that is a gypsum panel wall, plaster is not a field substitute. If the drawing says a plaster-rated assembly, Type X drywall is not a field substitute. Read the design; see also the system-design takeoff companion.
Moisture. Wet plaster introduces water into the building. Sequence it like wet work: envelope closed, heat that does not dump combustion moisture, time to dry before paint or millwork. That is the opposite of a production drywall punch the next morning.
When a drywall shop should bid it — and when to qualify out
Bid it when the shop employs plasterers (or a plaster sub you actually control), when the scope is clearly conventional plaster, and when lath, plaster, accessories, and scaffolding are in the number as plaster — not as “board and mud, heavy.”
Qualify out when the company is a hang-and-tape or metal-stud shop with no plasterer. Write it: gypsum board systems per C840 / GA-216; conventional plaster (C841 / C842) by others. Do not leave “Division 09 interiors” unqualified if 09 23 00 plaster is in the book.
Joint-venture or dual-crew is common on commercial W&C packages that mix gypsum corridors with plaster monumental stairs or restoration rooms. Put the interface on paper: who frames, who laths, who plasters, who patches after MEP, who owns control joints and corner beads.
Residential. Production tract work is gypsum. A historic plaster-and-lath house is a plaster restoration or a drywall overlay if the documents allow overlay — those are different scopes. Overlaying gypsum on existing plaster (or the reverse) is a detailing problem (weight, fastener into framing, plane, cracking). Do not treat it as a weekend patch.
Spec words that change the bid
Watch the project manual for:
- 09 23 00 gypsum plastering vs 09 29 00 gypsum board
- Metal lath, diamond mesh, self-furring, paper-backed lath
- Scratch / brown / finish, gauging plaster, lime finish, Keene’s cement (the last is its own specified material — pull current mill data, do not substitute)
- Direct applied plaster on concrete or masonry
- Veneer language mixed into a conventional section — RFI which system
Manufacturer procedures for a named USG plaster or lath product live on usg.com, not in a drywall ATF trailer. Other mills: Manufacturers. Product door: Products. Guides: Guides. Handbook map: Using the Gypsum Construction Handbook.
Commercial vs residential in one paragraph each
Commercial W&C. Plaster is a scope decision at bid day. Monumental, restoration, and some institutional walls still want it. The rest of the floor is likely gypsum and maybe veneer. Split the estimate. Do not average a plaster productivity into a drywall unit rate.
Residential production. Assume gypsum unless the spec is custom and explicit. Texture and GA-214 are the finish conversation. Conventional plaster is a specialty hire, not an upsell of extra coats of all-purpose compound.
FAQ
Can we substitute 5/8 Type X for three-coat plaster to save money?
Only with a design-professional change and, if the wall is rated, a listed gypsum design that the AHJ accepts. It is a different system, thickness, fire listing, and finish. It is not a VE you decide on the scaffold.
Is veneer “conventional plaster light”?
No. Veneer is C587 / C843 on plaster base. Conventional is C28 / C841 / C842 on lath or masonry. Bid them apart.
Does GA-214 apply to plaster?
GA-214 is levels of finish for gypsum panel products. Plaster appearance is specified in the plaster section and mill notes. Do not punch a plaster wall with Level 4 raking-light language copied from a drywall job.
Who owns cracks in old plaster we are patching next to new drywall?
Write it. Mixed substrates crack at the joint if you do not detail a control joint or a proper transition. That is a design and a scope line, not a punch surprise.