NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

1000-30-1+731 June 19, 195>3

NBS REPORT

2 ^8£

a*

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REPORT OP

INSPECTION OP PLASTER WORK AT

ALASKA NATIVE. SERVICE HOSPITAL

AND TESTS FOR QUALITY AND

CHARACTERISTICS OF PLASTER MATERIALS

/ By

Nolan D. Mitchell

Requested by the

Bureau of Indian Affairs

The publication,

unless permlsslo

25, D, C. Such 1

cal ly prepared I

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 201 5.

or in part. Is prohibited

Standards, Washington

1 report has been speclflr report for Its own use,
fc#i J a iSt; S : mM

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REPORT OF INSPECTION OF PLASTER WORK

AT ALASKA NATIVE SERVICE HOSPITAL AND

TESTS FOR QUALITY AMD CHARACTERISTICS

OF PLASTER MATERIALS

1. INTRODUCTION

Pursuant to a request from the Bureau of Indian Affairs,

Department of the Interior, dated February 13, 1953, an inspection was made to determine the condition of plaster in the main

hospital building and the quarters buildings for nurses and

help at the Alaska Native Service Hospital, Anchora e, Alaska,

on February 21, §2, 23, 1953. Participatin’ in the inspection

were Messrs. Lansin? S. Wells, William C. Cullen, and Nolan D.

: itchell of the National Bureau of Standards. The report of

this inspection and related tests supplement a letter of this

Bureau dated June 16, 1952, and a report 9.3/--10015 dated

September 17, 1952, both signed by Lansing S. Wells.

Among representatives of the Department of Interior, Bureau

of Indian Affairs, who were contacted at the job were!

Hr. John J. Finley, Chief, Building A Utilities Branch, Wash. , D.C.

Mr. L. T. Burn, Architectural Engineer, Bldg. & Util, ir . , n Mr. H. T. McCurdy, Chief, liech. Engineers, l! Mr, J. C. Helfrich, Electrical Engineer,

Mr. Harry Halverson, Are a Chief,

Bureau Indian Office, Juneau, AlasP:a

Mr. V. P. Reimer, Project Engineer,

Alaska Native Service Hospital, Anchorage, Alaska

2. INSPECTION OF QUARTERS BUILDING

The first inspections were made in the quarters building

because the construction there was nearing completion. Fifteen

of twenty rooms and the corridors in the help’s quarters section

were found to have cracks in the plaster. Cracks were observed

in rooms 200, 201, 20?, 209, 212, ‘ 21k, 2l5, 217, 303, 309, 311,

321, 325, 329, 331, and in the corridor x^all in the vicinity of

room 303. A number of cracks extended from the corners of electrical outlet boxes. Some of the ceiling cracks extended from

electrical outlets toward the walls. The direction of the larger

wall cracks was usually more or less vertical. Many of these

more prominent cracks were intersected by narrower cracks extending laterally from the main cracks. Many of the thin cracks

were in random directions in a pattern known as map cracking.

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Not only were there cracks in the plaster but a number

of the ceramic wall tiles in the wainscots of bathrooms and

toilet rooms were found to be broken, and in a number of places

wall tiles were found to be loose from the backing of portland

cement plaster on metal lath. Wall tiles were removed from the

wainscot in one location, and equally spaced horizontal shrinkage cracks in the cement plaster base were observed in the

height of the wainscot.

3. INSPECTION OF MAIN HOSPITAL BUILDING

The inspection of the Hospital Building to determine the

condition of the plaster included visits to approximately sixty

percent of the total number of rooms and all corridors. A

careful inspection of the condition of the concrete of the

exterior walls was also made to determine whether defects of

concrete work might have contributed to the failure of the

plaster. The plaster on metal lath for corridor and room partitions, without exception, was found to be cracked or had been

cracked and repaired. A lar e proportion of the plaster surfaces had been painted, but cracking appeared to have continued

subsequent to the application of the paint. There were few

boxes for outlets for electrical services where cracks were not

found to radiate from one or more corners. The general cracking was of the pattern known as map cracking. The spacing of

cracks ranged from a few inches to about three feet.

Specimens of plaster for laboratory tests and analyses

were cut from rooms and corridor as shown In table 1. The

15- by l5-ineh specimens as cut from partitions for tests to

determine the stability of the plaster when subjected to

changes in relative humidity included the metal lath as well

as the plaster. Those for analysis to determine the proportions of plaster and aggregates were approximately 10 inches

square and did not include lath or plaster keys.

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Table 1 . Source or locat ion of ape cimens

of lath and plas ter for laboratory tests

Story

!

' Wing

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T Room

»

' Tests

t

Basement

t

1 South

f

t

i

1 Corridor

t

’ Analysis and stability/-

f Do ' do

t

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1 12 1 Analysisf First 1 East

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f 106 * A.nal3rsis and stability

I Do ' ¥e s t

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f 182 T Stability

f Second ’ Forth

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t Third ' East

r

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i Do ' We s t

1

1

f 318 r Stability

? Fourth ’ South

t

1

J 438 ! Analysis

i Fifth ? West

J

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T !<% ! Analysis

Do ’ South

?

I

? 523 ? Stability

? Do f do i ( Closet) ' Stability

i j

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( 523 )

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4. MATERIALS FOR AUXILIARY TESTS

Bags of materials were secured from the same sources

from which plaster, lime, and aggregates for the building

plaster came. The gypsum cement plaster, gauging plaster,

and finishing lime were bought from Pioneer Sand and ravel

Co., 901 Fairview North, Seattle, Washington. The plaster

supplied by this concern was from the Sigurd., Utah, plant

of United States Gypsum Co., and the lime was "miracle”

brand from U. S. Lime Products Corporation, Henderson, Nevada.

The vermiculite aggregate was from the Portland, Oregon, plant

of Vermiculite Northwest, Spokane, Washington, and the sand

was obtained by Mr. V, ?. Reiraer, Project Engineer, from

Anchorage, Alaska, who also forwarded retained samples of

plastering materials from his office.

5. CHARACTERISTICS OF PLASTERS

Characteristics of the plasters and hydrated lime are

given in tables 2 and 3. These materials conform to applicable Federal specifications. Analyses of plaster materials

found in specimens of the set plasters are given in tables

ij., 5, and 6. The proportions of gypsum cement and aggregates

in the set-plaster samples were determined by dissolving the

gypsum from weighed amounts of dried set plaster in ammonium

acetate solution, then washing and weighing the residue sifter

it had been dried at 70 v C. The gypsum cement plaster was

found to be 96.15 percent soluble; therefore, when the weight

of the soluble portion of the sample of set plaster was divided

by 0.96, the quotient gave the weight of the gypsum plaster

from which the percent of gypsum plaster in t he mix was computed. The ratio of sand to vermiculite in the a re ate

was determined from the weights of the two constituents. It

was found that the sand used in the plaster had a fairly definite proportion of a magnetic constituent. By the use of a

magnet a large part of the magnetic material could be extracted

from the mixture of aggregates. It was reasoned that the ratio

of magnetic material extracted from the mixed aggregate to that

of magnetic material extracted from the sand would be the ratio

of sand to that of the combined aggregates. The proportions

of sand and vermiculite and the number of cubic feet of each

per 100-lb. bag of gypsum plaster were computed on that basis.

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Table 2. Characteristics of gypsum islasters

|By federal Specification SS-P-402, except as otherwise stated]

Plaster

sample

designation

Type

Time

of

set

i

» Tensile

• strength

1

1

' Compressive

' strength

\

1 CaS04.l/2E20

1

1 hrs

1 ml 1 osi t U. S. Gypsum, 1 1 i t i fibered^ *

1 I 24 1 190

1 1

1

1 90.9

U. 3. Gypsum • 10 1/2

1 i » not fiberedv*

t

TJ. S. Gypsum, 1 medium set • gauging^/

1

1 * 225

t i

t

*

1

1

«

1

1

\

90.3

G 2 1/4 8 540

I 1

i

? 93-9

D. S. Gynsum, * fibered"^ * 1 ? 1/2 ' 240

t

’ ^ 1190

1A

Do • s 1 1 (with Alaska * sand) * H S 1/fc

1

* 185

t

1 ^ IO 3O

»

1 Do t 1 1 (fed. Spec. * SS-P-401) 1 K 8

t

* 350

i

* & 1930

1 92.6

Do * t ’(avg. 2 lots) 1 (fed. Spec. * 1 f t SS-p-401, ' but with ' 150 g

» needle for ’

1

1

1

1

1

1

»

t 7

«

1

1

1 consistency*

1 U. S. Gypsum ’ gauging^ 1

K * 365

1

»

* V 1880

1

1

t ,

1

8 Q 2 ' 540

t

* 2470

1

1

1 98.3

'V Sample of plaster approved for project.

^

Sample purchased from dealer who supplied material for project. All

of 25 g of gauging plaster passed through So. 100 sieve.

^The cubes of the four plaster mixes in this group exhibited volumetric

shrinkage as follows: 2.0 percent; 0.6 percent; 2.2 percent (avg.of 2

lots); and 3* 0 percent, respectively.

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•• V

;».< T

'> ' ? S .; •»

I • • •• -rw-»»c-* -it**- ... . ... ......

I .V- >• \

f .

. • r? i-

; ~ V-- ; ' i &

'

• " : - '-'i d •• •’"•'-
>, jj? -Pi

Table 4. Analysis of be t- e-coe t plaster for proportion of aggregates by

ammonium acetate method

(Basle: Material dried at 50° C)

Sample designation | Wei,ght of

. sample

t

1

1

•

1 Toti.l

insoluble j insoluble

1

1

1

t

1

Magnetic

content

extracted

U.S. G. "Red Tern” fibered

gyp sum plaster^

£

1 3-9945

f

I

t

t

£

1 0.1490 »

1~

3.73

ft

1

t

1

£

Do » 5 .OO 3O

t

» .1925 *1 3.85 1

1 —

Do 5-0037 1

» .1948 *

t 3-89 1 —

Do ’ 5.0032 1

1 .1992 '

1 3.9S 1

I —

Do

J 5.0033 i

1 .1901 *1 3.80 1

l —

Versieulite^ 1 4.9975

»

1

1

1

1

' (Avg. 3 . 85 )

1 5.0072 » 100.19

' (Soluble: none)

*

1

t

5

1

|

0.0000

Alaska * 19.9500 1

1

1

i

19.8635 1 99.57

' (Soluble: 0.43)

*

«

f

*

1

5

.7920

(Avg. of 6 detrminetinns)

bese-coat plaster^

B h£.ll

1 11 "

9.9905

t

» 4 . 633S

' 46.?8

?

I

1 0.1565

Do 10.0025 «

J 4 . 53OO '

« 45.29 I9 ,1580

Average 9 .9965 I

1 4. 5819 *

i 46.04 9

ft O .1568 * 12 9.9375

1 3.2155 »

1 32.20 1

1 .0318

Do 10.0010 1

1 3.4143 *1 34.14 ft

t .0220

Average 9 *9943 *

» 3.3149 *

ft 33.17 i

f 0.0319

38 106 9.9860 )

« 2.5108 * 25.14 1

t Do 10.0005 f

1 2.6432 't 26.43 1

ft 0.0000

Do 10.0015 I

I 2.6422 ’1 26.42 I

| .0000

Average 9.9996 I

1 2.5991 *

t 26.00 t

| 0.0000

I 245 9.9900 8

9 3.4605 *

1 34.64 i

1 0.0500

Do 10 . 000?

>

* 3 . 5V7

•

t 35.40 1

I .0375

Average 9.9954 »

> 3.5006 '

1 35.02 S

ft 0.C438

s 316 9.9925 i

1 5.4580 *

1 54.99 t« 0.1240

Do 10.0005 i

1 4, 594c

*

i 45 # Qii 1ft .1250

Do 10.0000 »

1 4.6195 *

t 46.20 ft

1 .1265

Average 9.9970 »

1 4.8905 }> 49.04 »

t 0 . 1252

S 438 9.9900 I

I 4.4013 *| 44.06 ft

* C .0915

Do 10.0002 t

1 4.4860 ‘

» 44.86 1

1

. A915

Average 9.9951 i

1 4.4439 '1 44.46 >

1 0.0915

W 504 9.9800

i 3.‘795 '

1 34,86 1

1 0.0650

Do 10.0005 »

? 3.7210 '1 37.21 1i .0560

Average 9.9903 i

i 3.6003 *1 35.04 1

t 0.0605

'©''Sample of plaster from dealer v.-ho sullied piaster for project.

^

Sample of vermiculite aggregate from Vernier,lite jfforthveet who supplied aggreg* te

for project.

\I/ Sample of sand supplied by Project Engine > / project.

Base-coat plaster from rails of hoepit:

-

! 1 res j actively: B, bee orient; , oxth; A, *t; 5, >outh; , ~t, fn’ flares ...enote the room number as given on rrehiteetur 1 >lan«. he ro portion of rg "< > tee ore determined from analyses if these sample*-,,

-7-
: 2'4:-'.:’4K. gliPM. 2 2

•. *

' •'• "£

; n i: •' )

i

• -r .*?

•y-» 1 «y y*.

‘

, , - ; -r '

•

• { • • ft . :T : b

r

{ $ / - j

1

f 'a

\

7 f

; ? } r/V t 4

1

.

J

? i

1 r

\

; V’ !

«

i t

:

3 * <r

< j 1 i

t ! *

.

!

i .» t

: •"

. ?

?

. ! 2'2\o i

i

M*. >: ; . r X;

' - y

i J

• f ?

i‘ sV *j - ^ J

.

>

;

; '

. r

. • .. S l

* >

r

r

!

Co

Oil

oC

2

'' l '

V’~~. 5 * ' '> ***@

?s* r

'

. *0 :

- v-'f

'? ? ". v f

‘

* *

ilsi- S

0*3 w;; • , v ‘ . '

i » r.cro. . 3 V . --V. •:

'

#? ;

!

.. 4r . &-•

' Swr.r.t

' li .

* : v; V'

j

t

. > . . .

;

J 424:;. oOI 4

•' .*

J i r ; t

i

! '^2.4.

< a®

J i.:^cv3 -v'- .

t

S':

• v .

1 ! 4" •

t

. C- • k

1 4'Ul^' f •4

"

_ ‘S’- .1

: i

4- -'4 •••;>.
e, Alaska

Sample , designation^

i

gO

eed

' Ratio, lice putty

1 to GSPO4 .1 / 211^0

1 in original mix

, Apparent MgO

, in lime used

fhicfcness of

the white coat

1 $ in.

h hall

: 11

' 3-5+ * 41.4 < 1/64 - 1/16

& 12 * 10

» * 0.95+ • 40 .0 1/16 - 3/32

& 106 • ii

l ’ 2.0- ' 38.7 1/32 - l/l6

S 245 • 10

! • 1.3- « 1/32

2 316 * 1C

1 ‘ 3-3- * 39*6 1/32 - 1/16

S 4-38 1 12

i

1 1 .4— * 39.8 1/16

% 504 t 4

i

• 0.81- • ^51.

< 1/64 - 1/16

\Vv setters signify,

I • ^Sample* aestgnal Klneral containin€ a percentage of MeO;

iirom ae uc.se coa

on assumption tnat the white coat consists of

rtotaing other trial

The excess HgG u
.

. V.

'

. 7

: _v V t .

' . * t ^ ... ?• * • - .

• 'i- ; )

. - .

*

. v . „

' ...... • .

. K •

• ; r- -r - -

• •! "' * '

•! . " ~

•~T

'

£

ti >

: - - ‘ r•<-

l

'

; ' ;

„

a

.

r- ;

' _

«

.(•r

.

*

- 1 V ' .•••./ ) % t' i :;.r\ s

- - .

: ' r

:

: X:

~ •

> f

’

• c-:, ; *

-

" :

.

.

. .

« v,

!

.

E .'.

c-C

N^p:.. .t

"

• ,•

t

7 L ..

i U

«Cl ;0

.

.

’

*

- :

42 ,

;M . -

a?.:*'-

, ;

s

' .

C> ,

;-

: r

: *r > -•••-

.

I

)

i

-• ctv

ye > «»

*

.

.

.

?^W,;r

?

1 C x'v.r

i -

.

f

. — CP. : .

j

;•

' -' C .

1

»

4

»

1 >

f Z-OQp.r.

' v

v

'*‘

. c-i ’

: -

. .. .

0*3

r 7

;

, ’t

'<

;;v “ *-•* ? 'V

’

i'l'iii ?

C-

: '•
nM* "•

<*MW. M.trri.1 dTM.ti"c) " ^

So^ole de.lm.tion Weight of , •uboIc

(

Total

f lneetable Totol Insoluble 1 Magnetic

content

extracted

O.S. 0. "Bod Ton" flh.red • C S * .

fi

gfpcixa p la«t 3.9905 0.1fc93 3.73

Do 5.00JO .1925 3.85 .

Do 5.0CJ7 .1998 3.89

Do 5.003? .1992 3.98

Do S.00J3 .1901 3.80

<A*k. 3.85)

VericT^llt•^',

9.9975 5.0072 100.19

(So tablet none)

Alaeva e»nd^ 19.9500 19.86J5 99.57

(Sotablot O.I13) (txg. of 6 det<ral netlone)

>M*-OMt plMter^

1 hell ' 9.9905 * 9.633s • 46.78

1

t 0.1565

Do ' 10.0025 9.5300 • 45.29 1 .1580

Awero«e

1

9-9°65 9.5819 ' 46.04 • 0.1568

12

|

9.9975 3.2155 • 32.20 .0318

Do • 10.0010 3-9193 • 34.14 • .0320

9.9993 3.3199 • 33-17 1 O.0319

* 106

1

9.9860 2.5106 * 25.14

1

1

Do • 10.0005 2.693? 1 26.43 « 0.0000

Do • 10.0015 2.6922 • 26.42 1 .000

0

Awero«e • 9.9996 •

t t

2.5991 ' 26.00 1 0.0000

245 * 9.9900 •

* »

3.4605 * 34.64

•

1 0.0500

Do 10.0007 • 3.5907 • 35.40 .0375

Average 9.9959 • 3. 5006 ' 35.02 0.04 TB

1 316 9.9925 ' 5.4580 • 54.99 1 0.1240

Do 10.0005 • 4.5940 • 45.94 • .1250

Do 10.0000 • 9.6195 46.20 1 .1265

Average 9.9978 ' 4.8905 » 49.04 t 0.1252

9 1*38 9.9900 ' 9.9018 ' 44.06 t 0.0915

Do 10.0002 ' 4.4860 • 44.86 .^15

Average 9.9951 • 9.9439 ' 4t.46 1 0.0915

W 504 9.7800 • 3.4795 1 34.86 • 0.0650

Do 10.0005 • 3.7210 • 37.21 1 .0560

Average 9.9903 ' 3.6003 •

• J5.04 1

1

0.0605

•J'Sujjl. Of plotter froo doolor who suppll .1 ple.trr for nrojeot.

^

"Sample of wernicullt. »«*re*ete froo VorriicT.il t« (orthveut who rraillod for project.

'J'S.apl. of .end supplied hy Project Bnelne.r n. reurceent-tliro of m*trriel need on project*

S».«e-co»t ulooter eeanlo. telr«n fron .11. of ho.pl tel hulldln*. letter. Minify

re.peetlwelyt B. huonoatt ' ,

' orths Boot; 9, oonth; W, set. end figures denote

the room number os eiwen on nrchlteetur/ 1 Onus. The proportion of e. royotee .ore determined from analyses of throe eenolee.
Table 5 . mlriM ol valte-coat plaster finish from valla of Alaska native 9»rrlw Hotpi tad. Anr^orm^rn

y ai ».

( -Mis: Material dried at ?>• C)

Saaple

deelgnatl

1 ixlde content 1 Cospound Composition

Total NgO

of lime

uydratsd

' Ratio, lima putty

1 to GaS0i^.l/2H20

* in original mix

Apparent MgO

in lime used

Thickness of

the whits coat

*

°'L

,

8

!

M

H20

(combined ;

lo2*“2o

3 CaO ' **0 s °3

:

G.SO4.2H2O > CaCOj 0.(08} j

H6(CH) 2 n*o

h2o

excess

sio2 h2o

3

• 5 % • * * i *

• f i * i t * * » In.

1 hail ' 11.87 21.16 • 1.12 35.62

|

18.02 12.49 1 26.86 26.99 15-52 26.07 3.72 0.00 1.12 79.6

;

3.5+ 41.4 = 1/66 - 1/16

B 12 • 10.02 16.67 • 1.21 3* 95

;

10.57 27.23 ' 58.55 • 22.79 4.11 10.42 3-37 0.00 1.21 68.1

;

0.95* 40.0 1/16 - 3/32

x 106 ' 11.52 17.5* • 0.60 36.87 ' 16.89 18.99 ' 40.84 • 26.20 11.76 19.88 1.15 0.00 0.60 92.3 • 2.0- 38.7 1/32 - 1/16

* 2*5 • 10.02 18.27 • 0.61 32.70 • 16.83 23-69 1 50.96 • 22.79 6.61 21.16 0.20 0.00 0.61 98.7

!

^67.9 1/32

s 316 10.62 23.36 • 2.18 36.58 • 16.86 12.70 ' 27.31 • 26.15 16.06 26.39 0.00 -3,6.19 ’J'a.lB 100.0

;

3.3- 39.6 1/32 - 1/16

S <>38 ' 12.22 17.67 • 1.09 36.51 12.66 22.38 • 68.13 1 27.27 5.00 18.00 0.00

^

0.62 ^1.09 100.0 • 1.4- 39.8 1/16

« JO* • 4.41

1

a.01 • 0.70 32.26 ' 12.77 29.03 '

•

62.63 • 10.03 8.31 18.67 0.00 .22 ^0.70 100.0 • 0.81- 'Vfi-T < 1/66 - 1/16

^.Letters signify, respectively: 1, basement I, north; B, east; S, south; V, woot. end figures denote the rooa number ms given on architectural plans.

N3''Saaplee designated 245 and V 504, respectively, apparently show abnormally high percentages of MCO in the lias used. Possibly sobs veralcullte (a mineral containing a eonsiderable percentage of MgO)

from the base coat was carried mechanically Into the white coat during the trowelling. If so, this would upset the validity of the calculations baaed on the assumption that the white coat eonalsto of

nothing other than lime and gypsum.

^The excess any be attributed Vo unidentified ainerals under S102 + &2°3*

-8 -
7

vnbi* 6. gjyif.Sat-&SE£sa&teg- .pAwfefBg

Coapatod trtzx weights »’»o In table !;) —r— —r— —*—~~—"—"

* t ^erregatca pm* 100- lb bag

Ss-mie t i'rpporUm , of uv&m c«l piaster

teetgni&fm ' In T

"

.., - n

t aggregate , v#mtcul?te . band

r * (1C lb/ft*} t (100 lb/.: t3

} t

: «

B hall 1 90 #0

B 12 ’ 26*2 1 •

i I E 1.06 *. 0*0 - *0

21*5 3c *0 ’ .3*1 .17

3.9 ‘

; ^ li3ii ft - ^ || *>o

E 31b ’ 66.,. .

i -- * • "• •*> f ,,

•• ••

, . _ i -_ W * 1(5.3 ; 2*1 • .23

-9-

i

Cn

TTiTmrm

TTT

<3

a9TTWT.Tr>

O^i

Tian

ncCfirio
: ,

.

' - s ’v : ;

*!•••'*

-JJ -

' K *1 {

^1-' :v

! If

* -5 :t /.

: - f

.. - • • - . .Vo-. v. >• - - *V v» - - - • --

?

*

t

. rife-:

r

c I -

.•H *»-• •

vl£

:>

; V

'

.. . - . .. •*: •».

-

r-
6. STABILITY OF LATH AMD PLASTER FROM THF HOSPITAL BUILDING

Five of the by lp-inch specimens of lath and plaster

cut from partitions of the basement, first, third, and fifth

stories of the hospital buildin ; were sawn, into 3 inch wide

strips and subjected alternately to hi h and low or low and

high humidity at nearly constant temperature. Changes in

length between gag© points 10 inches apart on l/i^-inch diameter thin brass discs cemented to the front and back surfaces

of the plaster were measured by means of an optical comparator

which was calibrated against a 10-ineh invar standard bar at

the time each set of readings was made. The changes in length

shown by the differences cf readings of the comparator indicated an initial shrinkage of many specimens followed by expansion when placed in an atmosphere havin'; high humidity and

shrinkage when in a container having low humidity.

The changes of length of the specimens in terras of percentage of the 10- inch gage length are shown in figures 1 and

2. These are typical of the behavior of the twenty-two specmens subjected to the tests. In some instances there appeared

to be evidence that the expansion of the plaster caused flexing of the lath, thus producing marked or anomalous differences

in the lengthening or shortening of the gage length of the

specimens during the period in which it was subjected to a

constant humidity. Some of these anomalies have been attributed to cracking of the base-coat plaster or both the basecoat plaster and the white-coat finish, thus allowing the

metal lath, already strained by the shrinking plaster, to

regain its length to the extent that the strain from shrinkage of the plaster had been relieved.

V

’

10
. 'idjgsl '-; I'JM to arrsnx >e<yg dor..!- -XX rd -r,X /id to mr.t%

'

. .: . mm * s

'

, ;. c . ohiM Fi:oziZ Z o:mi rpmn ^ovi /rlblxi/cT laflqitQti edz- io so’^oig

b SffoX wol - iigjtd :•: . X

•-

: £ ;, X <; ;

: g

• $ ' s 8 .. a 903 I'Z&S . 1 v£ O .0X13 ait'O'.i’l Oo b&o^emeO aOSi.O 3 8 SO .: ill d

r..o

riB qi?-a c i/iUiuqo no 'lo s $,:X ifc .-.•. .< e: e'to- : xsdo^Ior add- 10

' 16* ' * t ' at cfooi - . .. «

• I - sd

-

' .» s @ .

- •- - ‘tQte'mqyoo srfd lo vnil/^eo 'lo - oononoT: . o orid • X r-iwo.;fo

~' r s : ;-^oCIi 'r. q iBB .... , :;;o:x X.si;., .n 10 i ..

• ~ dX:/;i'-: /

‘

i x, X .! ’t .."il rsxi Bn . -xHoqX.r, ros n baoalq rioiw noIk.;j&o

OV--; X :,i j;; '

• ;XX OX. tO'. . -Oncd ,v '. x '

. . . •>

. bi-s X gsiyjXl at xmode ©-xe X i vx rfo/U-OI aid :.c. ©;• ' Xnso

. “-oil bszu.iTt. n&imZq G&& ..o aoZzrmqx® s rid dsrfq eoftabivs- ecf od

•'• ••« xe'>X.’;6 sooLinon^ *xc JtaafttftiB rdtio.oJbo crq; ax;;IX e .ntf.s.L :- to ' ,nt

- 4d i«X s o-.-n .: : te j

',

.. b od 0 jdo-x cfar. sj.hw :j X noJtd'u jui holloa ar': :Xooqs

o n . : : ..

•

r - i • ’o oo . o. , . : i I .

..’ x n/ ;:>

o

i*« ' 0 S 9 S .

- - t ia^3.:iXq n^.:Xi.XXi!'o orid v'd' oo-r Xinoo -b.ni anlB t xid.3l Xod-id

- '.Lun.ri'! .

r;o rXi 'txond .. ©..id X.xrXr jmti'X.o :. : oi .ddqnol add r-X^: ©re o

01
©

t»D aip©Ou©pHpo

Ti•HuuoV

+3P© * a >s © -p © -h © •d

jp «he § 2 O ,P u

tw P

*H

p© <a -p © ©

aJ P

3,5 d ° P o

08 4-3

+3

©

eg +3 fH O 2 © 3 m “r~> °. o ,0

UJ P s CO 83

Pt©

p

a©

-H ,P o s ®

P..P m +3W3 <H P O ©

(H

-P

+3

©

f*0 tuO P P © W) fHP P* -H -H( ra O © <H

W)p «a ^ Vi o o

-HF-4

!N3Dd3d ‘ Hd

100

/

//

Jo dW3i wnaa XN30a3d ‘S9NI0V3d 3SV8 W08J S39NVH9 H19N33 !N30d3d * H'8

«S Vto

a;W5

cj0

(li V

ft

C!

ft

TIME,

DAYS

gore

2»

Changes

in

length

of

specimens

of

lath

and

plaster

from

room

3

18i

10-in.

gage

length

when

subjected

to

changes

in

humidity.

7, BEHAVIOR OF FOLD PLAIT 'F 3AHS

Two test bars of plaster designated A and B were cast

in steel molds In order to study the behavior of the typical

plaster mix when subjected to changing conditions of humidity.

The bars were cast In molds to give an effective length of

10 inches between steel plugs cast into the ends of the bars.

The bars were made from plaster having the composition: 20

parts fiber-ed-gypsum cement, 8 parts vermlculite , and 5 parts

Alaska sand by weight. Bar B had 10 percent more water in

the mix than did bar A, The 1- by 7/8- inch bars had a l/l6

Inch thick white finish applied to one face after they had

been removed from the molds and measured for expansion. The

changes in length of the two bars are shown in figure 3. On

release from the constraint of the molds, the bars expanded

0.02 and 0,03 percent of their length at once, and after having

lain horizontally without other restraint than their own weight

for 4 days in a chamber at 70

J F and at 93 to 97 percent relative humidity, the bars were found to have increased in length

by 0,117 and 0,122 percent. During the next 10 days, at the

same humidities. Increases of 0,012 and 0.013 percent in

length were observed, making the total expansion from the

beginning of storage at high humidity 0.129 and 0.135 percent,

respectively. The bars were then placed in a chamber held at

70° F and at 30 to l\.Q percent, relative humidity for 2 days.

The shrinkage during these 2 days amounted to not more than

0.007 percent. During the next 8 days, however, after storage

in the chamber held at 18 to 20 percent relative humidity, the

shrinkage amounted to O.OljO and 0.043 percent for specimens

A and B, respectively. The shrinkage during the next 19 days,

under the same humidity conditions, amounted to 0.004 percent.

From the point of maximum expansion the shrinkage at the end

of 29 days' storage in chambers in which the relative humidity

was lowered by sta/es to 18 percent had reached 0,052 percent

and appeared to be continuing.

- 11 -
.

ris^s ©saw d bsm A be:Oa.o0 X a e.o

r r a aid - lo tfeetf owT

X»Olq^if sdd do -xoxvBrjdO *

« to dd'Biiel evljoajdt© xie ©yJEb or s&doa jsi ue.ao oi©w e-T.Ba edT

*®*JBo

r add to si; ns ode? o.xcii <faao gqj.Ia leecj ...-. iod eodo/ii 01

OS taoiiiaoqraoo >dd : rrx.YSx. v . rs&Ic 10 ,

••• r-bv 9

* 1: aw 2 x- :' edT

8tf**sq 0 brm t oilXiio.di’vev addBc, X . f.-©tf.©o :^g«;r -Xeigold adaaq

: : . krf djofi'j ‘xodl.c. ©oat ©ho o.t baXIqq/a xi® Xd.lt eaU.d'&? rloidd rioni

* ;. • 2 £isk a:, a a;c '.:

' a 7

.•: : 7

.' . ...

' do ' .

'

' ; s^Bd olid 4 ?bIo:r odd to $eLlM*t&%noo odd fiioTt qes®X^t

•

. > . d-iddow rrvro 'Tiaad iB.do drdx. ••?:'£ ©*s Txodcto jjjoddtw ^XXs^oosl*i:od alaX

-bI®*x dxi©o rx©q \ 0 od Cv .fs ri

' 0 V da *iodj, q do a ail a -,:o; qt *xot

ddqo.oX nl bear •• ; Offa io,l: od Onaol -.-xsw ft av. q da: jaaad o

v

0

, -oso’ioq £10,0 &rxs SJ .0

exitf ®o«xt xcoiaxxsqxe latfotf s ;

•*

.

, IX* -

> . 6 x*X OOoBlq .aerfs sibo &riT

I

- ' r

' : t© I . .. :. .xt.oid 0*toar doiS O j .Dadnaroa-B 0. os odd q ox. &:4xI*siLb odT

•

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8. FLEX'Cm? OF LAIT A AO FLASTFR

Twelve specimens for tests to determine the amount of

flexure of metal lath and plaster re suit in from expansion

or shrinkage of the plaster under different conditions of

humidity were prepared.. These were made by attaching 9 l/2

inch wide by 36 inch long strips of 3.4 lb, expanded metal

lath to l/4” inch diameter steel uprights mounted on a 6 by

l/8 by 36 inch Ion steel base plate. The uprights were

spaced 16 inches on centers in two rows of three each. Two

of the uprights of each row were welded in place while those

at one end were fitted into holes in the base, so as to be

removable. The lath strips were wired to the uprights so

that one end of the lath would be free to flex after the removable upright had been removed*

Fach coat of the base -coat plaster applied was made up

of 20 lb. gypsum cement plaster, 3 lb. verniculite, and p lb.

of Alaska sand. After the batch had been well mixed it was

halved. To one half, 14 lb. of water was added to give a

relatively stiff mixture; to the other, lp l/2 lb. of water

was added to produce a comparatively soft mixture. The

plaster coats were applied to the lath strips on two successive days to ll/l6-inch thickness as determined by wood

grounds, the drier mix being applied to the lath on the righthand side of the base. After storage under wet burlap over

night, the 12 specimens were transferred, four to each of

three humidity chambers. The relative humidities in the three

chambers into which the specimens were placed were p2, 72 , and

92 percent.

The large amount of water in the specimens increased for

a time the relative humidity above those fixed by the saturated salt solutions intended to keep the humidity at a constant level. After 3 days’ storage of the specimens, a whitecoat finish consisting of 4 parts lime putty to 1 part gauging

plaster was applied to the set base-coat plasters to thicknesses ranging from l/l6 to l/8 inches. The specimens were

returned to the humidity chambers as soon as the white-coat

finish had been applied.
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In the 60-hour interval between the application of the

brown-coat plaster and the white-coat finish, the free ends

of the metal lath strips made with the drier mix of plaster

were deflected from their original positions by expansion

of the plaster an average of 0.16 inch and those to which

the wetter plaster was applied an average of 0.13 Inch.

After the application of the white-coat plaster the specimens

continued to expand, thus causing increased deflections. A

pair of specimens having plaster of the two degrees of wetting

continued to deflect after lj.6 days in the chamber with high

humidity. The specimen with the drier mix, and without white

coat, has deflected 0,1^7 inch and the specimen having the

x^etter mix, with white coat, has deflected 0.1Ip inch* When

placed in chamber® conditioned to low humidity, the plaster

shrank, thus causing the strips to be deflected in the opposite direction. The four specimens which have been in a

chamber, the relative humidity of which has been lowered from

55 to 18 percent, have shrunk to cause deflections of the free

ends ranging from 0.197 to 0.276 inch. The shrinkage continues.

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9. CONCLUSIONS

From the observations made during the inspections of the

buildin ",s end the subsequent as well as previous laboratory

tests whiel indicated a high degree of dimensional instability

of the plafter when subjected to the range of relative humidities

not in excess of those encountered in buildings, it has been

concluded hat the cracking has resulted from this instability.

The relatir e effects of shrinkage of the fiber© d gypsum cement

plaster a? revealed by the volumetric shrinkage of cubes of

the neat aid sanded plasters, items k, 5, and 6, table 2, and

the expansion and contraction of the plaster bars having both

sand and isrmiculite as the aggregate in causing the plaster to

crack hav( not yet been determined. Doubtless both effects have

played a ]art in causing cracks in the plaster. The measurements

of chat ;:ei of length of specimens of the set plaster on metal

lath b*r roans of the comparator have shown that when subjected

to lame irariations in relative humidity the base-coat plasters

usually crack, and in a few cases the white-coat finish cracked

also. Sene of the 3 inch i^ride strips cut from the 15* by l5-inch

spec pent of lath and plaster taken from partitions in the hosbuilding exhibited decided curvature, which increased as

ests proceeded, indicating that the strength of the plaster

ufficient to cause progressive bending of the expanded metal

Some of these strips cracked during the tests, presumably

the strength of the plaster was not sufficient to cause

r bendin-' of the metal lath.

U. though the studies have not

sciable assurance, say that the

been completed, we can, with

cracking of the plaster has

yesuied from dimensional instability of the combination of lath

and xtak plaster. Dimensional changes have doubtless been a ravateeby "the humidity conditions prevailing within the buildin

duri]| and subsequent to the plastering operations.

It is quite probable that cracking of the plaster on the

metal lath partitions will continue through several seasons unless

sora© process for stabilizing the plaster against excessive expansion and contraction with the changes in humidity to which it

is ntmally subjected can be applied.

None of the contents of this report are released for publication or for use in sales promotion.

For the Director

Nolan D. Mitchell

Consultant, Buildin; Technology Division

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