Sampling and Characterizing Plaster

Roger G. Morse AIA

Dyanki, Inc.

Sampling and Characterizing Plaster

A New System for Sampling and Characterizing Plaster in Three

Dimensions

• Homogeneous areas based on surface characteristics

• One type of plaster can have different surface characteristics

• Frequently results in large numbers of samples

Typical Survey Looks at Plaster in Two Dimensions

Example of Homogeneous Plasters in Two Dimensions

• Smooth wall plaster• Lumpy wall plaster• Wainscot plaster• Crown molding• Molded plaster• Sandy wall plaster• Spattered plaster• Knobby plaster

• Smooth ceiling• Lumpy ceiling• Applied decorations• Sandy ceilings• Highly painted

ceilings• Dashed ceilings• High relief molded

ceilings

Same Plasters in Three Dimensions

• Smooth white finish plaster

• Sandy white finish plaster

• Gray-beige base plaster

Plaster Classification

Report Results

Analysis Confirm s P laster Type

Analyze Sam plesG ravimetric Reduction

Augm ented Point Count

Verify that No. Sam ples meets AHERA Req.

Examine w ith Stereo M icroscope - Assign Plaster type

Clean Cores

Collect enough sam ples to m eet AHERA Reg

Initia l Inspection

Initial Inspection

• Make an initial determination of likely homogeneous plaster types

• Collect a sufficient number of each type to meet AHERA requirements for surface treatments– 1,000 SF – 3 samples– 1,000 to 5,000 SF – 5 samples– Over 5,000 SF – 7 samples

Sample Collection

• Core drill connected to HEPA vacuum

• Clean dust from surface of cores in sealed cabinet with HEPA local exhaust

Plaster Core

Evaluate Plaster Cores

• Evaluate with stereo microscope

• Assign plaster type to each layer

• Verify that number of samples meets AHERA requirements

Gross Characteristics of Each Layer

• Layer – (top, middle, bottom)

• Function – (finish, base, scratch)

• Gross Color – Munsell Color System

• Thickness

Components of Each Layer

• Cement• Aggregate• Fiber

Cement - Type

• Gypsum

• Lime

• Gypsum/Lime

• Portland Cement

• Clear Adhesive

Cement Color

• White

• Off White

• Gray

• Exact colors from Munsell Color System

Aggregate - Type

• Sharp mason’s sand

• Perlite

• Vermiculite

• Mica

• Washed sand

• None

Aggregate Color

• Colorless

• Tan

• Brown

• Black

• Red Brown

• Exact color definition with Munsell Color System

Fiber - Type

• Hair – cattle or horse

• Wood fiber

• Jute

• Fiberglass

• Cellulose

• Suspected of being asbestos

Engineering Properties

• Plaster strength

• Bond between layers

• Useful for engineering design purposes

Determine Plaster Type

• Atlas of plasters• Physical standards

Analyze Samples

• PLM• Gravimetric Reduction• Point Count (1000 points – Chatfield Method)• Report concentrations of plaster components• Report lime to gypsum ratio• Determine if analysis verifies plaster type

determination

Plaster Types

• Job mixed plasters

• Modern plasters

• Acoustical plasters

• Skim coats

• Plaster substrates

• Coatings

Job Mixed Plasters

• Colored sand plaster

• White smooth plaster

• White sand plaster

• Bond plaster

• Portland cement plaster (Stucco)

• Mortar and concrete

Modern Plasters

• Perlite aggregate

• Synthetic fiber reinforcing

• Gray granular gypsum cement

• Vermiculite aggregate

Acoustical Plasters

• Manufactured products

• Open porous texture

• Usually friable

• Each must be considered separately

• Frequently contain asbestos

Skim Coats

• Drywall taping compound

• Clear adhesive

• Fine aggregate (limestone, talc, marble)

• May be between layers of paint

• May not be able to find sufficient samples to meet AHERA requirements

• Evaluate separately for each facility

Plaster Substrates

• Gypsum lath

• Gypsum block

• Gypsum panels (drywall systems)

Coatings

• Textured coatings

• Heavy hard cementitous coatings (Thorocoat)

• May contain tremolite

Roger G. Morse AIA

Dyanki, Inc.

504 Snake Hill Road

Poestenkill, NY 12140