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Fire performance of walls with plasters over extruded polystyrene

Shorter, G. W.; Blanchard, J. A. C.

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NATIONAL RESEARCH COUNCIL CANADA

DIVISION OF BUILDING RESEARCH

FIRE PERFORMANCE OF WALLS WITH PLASTER OVEREXTRUDEDPOLYSTYRENE

G. W. Shorter and J . A. C. Blanchard

F i r e Study No. 1 5 of the

Division of Building R e s e a r c h

OTTAWA March 1966

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FIRE PERFORMANCE OF WALLS WITH PLASTER OVEREXTRUDEDPOLYSTYRENE

by

G. W. Shorter and J. A. C. Blanchard

The increased u s e of f i r e -retardant

,

extruded-type, cellular polystyrene a s a building m a t e r i a l h a s prompted t h e F i r e R e s e a r c h Section of the Division of Building R e s e a r c h , National R e s e a r c h

Council of Canada, t o conduct a limited study of i t s f i r e p e r f o r m a n c e when it i s used a s a p l a s t e r base. One p r o p e r t y of t h i s m a t e r i a l that i s of great i n t e r e s t when considering i t s u s e a s a p l a s t e r b a s e i s i t s decomposition c h a r a c t e r i s t i c s at elevated t e m p e r a t u r e s ; i t rapidly decomposes and s e e m s t o "disappear". Thus the c r i t i c a l question i s whether the foam can support the p l a s t e r until the l a t t e r h a s p e r f o r m e d i t s f i r e enduring function. In o r d e r t o study t h i s problem a limited number of t e s t s , including laboratory t e s t s w e r e c a r r i e d out.

TESTS Small Scale

A wall specimen (30 by 30 in, ) was constructed of 8 -in. hollow concrete blocks. F i r e -retardant, extruded-type, cellular polystyrene 1 in. thick was secured t o the concrete blocks with portland cement m o r t a r approximately 1/4 in. thick (1 p a r t portland cement, 3 p a r t s

clean sand and 15 p e r cent hydrated lime by cement volume). Two coats of p l a s t e r w e r e applied t o the plastic foam, the f i r s t or s c r a t c h coat, 1/2 in. thick, the second or finish coat, approximately 1/16 in. thick. The s c r a t c h

coat was composed of 1 p a r t gypsum p l a s t e r and 2 1/2 p a r t s sand; the finish coat was lime putty. The specimen was then placed in a s m a l l e l e c t r i c furnace (1) and heated in accordance with the ASTM E-119 standard t i m e - t e m p e r a t u r e curve (2).

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The finish coat of p l a s t e r cracked at 10 min, and a f t e r 17 min smoke issued around the top edge of the specimen. After 3 2 1/2 min the s e a l on the side of the specimen was removed and it was observed that almost a l l of the plastic foam had disappeared. The p l a s t e r stayed in place throughout the t e s t .

In spite of the fact that t h e p l a s t e r did not come down during t h i s t e s t it could not be concluded that it would s t a y in place during a full-scale t e s t . Consequently, it was decided t o p e r f o r m f i r e t e s t s on l a r g e r specimens.

Full Scale

Two specimens ( I and 11) w e r e constructed in a l a r g e reinforced concrete f r a m e ( F i g u r e l ) , which had been used previously f o r special t e s t s s o that t h e opening i n the f r a m e was p a r t l y bricked in at the s i d e s and bottom. A single wythe of bricks 4 in. thick was built in the opening flush with one side of the old construction. During the erection of the brickwork a single row of bricks, 8 in. deep, was placed vertically at t h e c e n t r e of the construction, extending about 2 in. from the s u r f a c e

of the wall t o form a divider between the two specimens, which w e r e approximately 6 by 12 f t high. A m o r t a r consisting of 1 p a r t portland

cement, 3 p a r t s sand and 1 5 p e r cent hydrated lime by cement volume was then applied t o the flush surface of the specimens t o a thickness of approximately 1/4 in. This m o r t a r served a s an adhesive for the 1-in. thick fire-retardant, extruded-type, cellular polystyrene which was applied next. On specimen I, p l a s t e r was applied directly t o the plastic foam; on specimen I I, 1-in. m e s h

chicken w i r e was fastened with 1-1/4-in. staples t o the plastic foam before the p l a s t e r was applied. This technique was considered t o be in keeping with the p r a c t i c e outlined in Reference (3). The mixes f o r the p l a s t e r coats w e r e a s follows:

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Scratch Coat: 1 part gypsum plaster, 2 1/2 p a r t s sand, applied 1/4-in. layer.

Brown Coat: 1 part gypsum plaster, 3 1/2 parts sand, applied 3/8 -in. layer.

Finish Coat: 1 part lime putty, 1 part sand, applied 1/16-in. layer. Two observation ports were provided in each specimen on the unexposed side ( s e e Figure 1). Thermocouples were installed between the plaster and the plastic foam and in the mortar between the plastic foam and the brick a s the specimens were constructed. Thermocouples were also installed on the unexposed surface of the specimens, which were then allowed t o stand for a period of 148 days, at which time they were placed in the large wall furnace and heated in accordance with ASTM E -119 time -temperatur e curve.

Specimen I: The finish coat of plaster separated and fell within the f i r s t minute of test. At 6 rnin it was observed through the viewing ports that the plastic foam was very soft. At 7 rnin the whole of the plaster f e l l and the foam caught fire. The mortar used on the brick a s adhesive f o r the foam was still in place at the end of the test.

Specimen 11: Most of the finish coat of plaster separated and f e l l within the first minute of test. A t

6

rnin it was observed through the viewing ports in the brick that the plastic foam was very soft. At 10 rnin the plaster cracked. At 15 min no foam was visible from the ports. At

25 rnin flames appeared at the crack on the exposed side, and flames between the plaster and the brick could be seen from the ports. At 1 h r 20 rnin flaming was almost stopped, and the plaster bulged considerably. At 2 h r 24 rnin the test was terminated. At 2 h r 26 min, just before

opening the furnace, the lower half of the plaster fell. The remainder of the plaster fell about 3 min later. It could be seen from the exposed side that some of the staples used t o fasten the wire mesh were still attached to the wall.

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Temperature measurements for both specimens a r e shown in

Figure 2, which shows that the allowable temperature r i s e on the unexposed

s u r f a c e of specimen I was reached at 1 h r 44 min and that of specimen I 1

at 2 h r 17 min. The fact that the plaster stayed in place on specimen I I

is the main factor to which the 33 -min difference in f i r e endurance can be

attributed.

The plaster on specimen I 1 stayed in place for two reasons. The chicken wire provided reinforcing for the plaster membrane and the staples were long enough to penetrate the m o r t a r behind the foam, thus providing support for the plaster.

Laboratory T e s t s

In addition t o studies of the f i r e t e s t s others were made of certain

basic properties of the material using both thermogravimetric and dilato

-

m e t r i c apparatus.

The thermogravimetric apparatus i s an instrument that accurately m e a s u r e s the variation of the weight of a sample of m a t e r i a l a s the

temperature of the sample is steadily increased. Variation of the weight of the sample may be due to decomposition or change in the m a t e r i a l f r o m

the solid to the gaseous state ( s e e Figure 3).

The dilatometric apparatus i s an instrument that measures the

variation of the length of a sample resulting from a change in i t s temperature

( s e e Figure 4).

The foam i s thermoplastic and its mechanical properties a r e

considerably affected when i t s temperature reaches 175"F, the temperature a t which the cellular structure of the foam collapses. This may be seen in

Figure 3, which indicates a veryrapid deformation of the sample tested,

starting at 175°F. It is clear that a s soon a s this temperature i s reached the foam can no longer support the plaster, and that the temperature continues t o climb the foam becomes softer until it reaches 450°F when it s t a r t s to decompose and burn (Figure 4).

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CONCLUSIONS

1. Where cellular polystyrene i s used a s a b a s e for un

-

reinforced p l a s t e r , the p l a s t e r and polystyrene should not be considered t o add significantly t o the f i r e

r e s i s t a n c e of the wall.

2 . If t h e p l a s t e r i s reinforced with a s t e e l m e s h or chicken

wire, which i s itself secured t o the outer s t r u c t u r e (such a s by stapling it securely t o wood n a i l e r s a t the top of the wall or by embedding the staples in the f r e s h m o r t a r on the unexposed side of the cellular styrene) then t h e p l a s t e r should add significantly t o the f i r e r e s i s t a n c e of the wall.

REFERENCES

1. Blanchard, J. A. C. and T. Z. Harmathy. Small-Scale F i r e T e s t Facilities of the National R e s e a r c h Council, National R e s e a r c h Council, Division of Building R e s e a r c h , NRC 8207, November 19 6 4.

2 . Standard Methods of F i r e T e s t s of Building Construction and Materials, ASTM Designation E l 19 -61.

3. P l a t t s , R. E. P l a s t e r i n g on Polystyrene F o a m , National R e s e a r c h Council, Division of Building R e s e a r c h , Housing Note No. 9, March 1963.

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D o u b l e w y t h e t h i c k

S i n g l e

( 4

i n n u m b e r )

C o n c r e t e

b r i c k s u r r o u n d

B r i c k

w y t h e

o b s e r v a t i o n p o r t s

1 4 ' - 0 "

d e e p )

F I G U R E 1

U N E X P O S E D S I DE O F S P E C I M E N

B R 3 6 2 5 - 1

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0 10 2 0 30 4 0 50 60 7 0 80 90 100 110 1 2 0 130 140 TIME, MIN. @ P r e s c r i b e d f u r n a c e t e m p e r a t u r e @ A v e r a g e f u r n a c e t e m p e r a t u r e @ ~ v e r a ~ e t e m p e r a t u r e b e t w e e n t h e p l a s t l c foam a n d t h e p l a s t e r o f S p e c i m e n I @ A v e r a g e t e m p e r a t u r e i n t h e a d h e s i v e m o r t a r o f S p e c i m e n I @ A v e r a g e t e m p e r a t u r e b e t w e e n t h e p l a s t i c foam a n d t h e p l a s t e r o f S p e c l m e n I 1 @ A v e r a g e t e m p e r a t u r e i n t h e a d h e s i v e m o r t a r o f S p e c i m e n I 1 @ A v e r a g e u n e x p o s e d s u r f a c e t e m p e r a t u r e o f S p e c i m e n I @ A v e r a g e u n e x p o s e d s u r f a c e t e m p e r a t u r e o f S p e c i m e n I1

FIGURE 2 TEMPERATURE VS TIME PLOT

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1 0 0 2 0 0 3 0 0 T E M P E R A T U R E , OF

I

1

D i l a t o m e t r i c T e s t F I G U R E 4 D I L A T O M E T R l C C U R V E O F T H E E X T R U D E D - T Y P E C E L L U L A R P O L Y S T Y R E N E

-

- - -

I

& S t y r o f o a m - L e n g t h 3.00" T e m p . 0 - 2 1 0 ° F -

-

- - - -

-

-

T e s t t e r m i n a t e d d u e t o r a p i d d e t e r i o r a t i o n o f

I

I

S p e c i m e n

Figure

Figure  2,  which  shows that the  allowable temperature r i s e  on  the unexposed  s u r f a c e  of  specimen  I  was  reached  at  1  h r   44 min  and that  of  specimen I 1   at  2  h r   17  min
FIGURE  2  TEMPERATURE  VS  TIME  PLOT

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