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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