Sound transmission loss of masonry walls: twelve-inch lightweight concrete blocks with various surface finishes

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Sound transmission loss of masonry walls: twelve-inch lightweight

concrete blocks with various surface finishes

CANADA

I

O/l V,' J4 Ser THI B92 no.

90

c * ₂

B

~

G

ANALYZED

SOUND TRANSMISSION LOSS O F MASONRY WALLS: Twelve -Inch Lightweight Concrete Blocks

W i t h V a r i o u s Surface Finishes

T.D. Northwood and D.W. Monk

Ottawa

SOUND TRANSMISSION LOSS OF MASONRY WALLS: Twelve -Inch Lightweight C o n c r e t e Blocks

W i t h Various Surface Finishes

by

T.D. Northwood and D .

W.

Monk

This is the f i r s t of a proposed series of notes r e p o r t i n g the l a b o r a t o r y measurements of sound transmission l o s s of m a s o n r y w a l l s . The t e s t p r o g r a m , which will extend over several years, will eventu-

ally include a range of block thicknesses and densities and will e x a m i n e the effects of various surface finishes. This particular note considers

six variations of a _{b a s i c 12-in. lightweight block wall.}

DESCRIPTION OF TEST SPECIMENS

The basic wall consisted of norninal 1 2 - i n , lightweight blocks, having actual dimensions of 7 -5/8 in, high x 15- 5/8 in. long x 1 1 -5/8 in. thick with insets at each lend and three cores. The centre core was

approximately 8 x 2-518 in. and the two outer cores w e r e 8 -1/2 x

2 - 5 / 8 in. The walls between cares were 1-114 in. thick, minimum, and the outer walls w e r e 1 - 5 / 8 in, thick, minimum. The average weight p e r block was 4 3 Ib. After t h e t e s t was completed a section of the w a l l , including mortar, was removed intact and found t o weigh

53 Lb per sq f t of wall surface, F i g u r e I , taken a f t e r the t e s t , shows typical mortar j o i n t s .

The wall was built in a t e s t opening 10 f t long x 8 f t high and con- sisted of twelve r o w s of blocks laid up with a Type N mortar (CSA

-

A1 79.1967) with 3/8 -in. mortar joints tcroled t o a concave finish. It w a s allowed to cure f o r 28 d a y s , a f t e r which a bead of caulking was applied

around the perimeter on both s i d e s of the wall a s a precaution against

pos:;ible shrinkage cracks. The following surface conditions w e r e then

tested:

W a l l 1A

-

B a s i c wall a s above, with no surface treatment.

W a l l 1B

-

One side of the basic wall was painted with t h r e e c o a t s of latex block filler applied with one-hour drying time between coats.

Application was by brush and deep pile roller.

W a l l

lC

-

O n the unpainted side of W a l l 1B

a

layer of 1/Z-in. gypsurn

f u r r i n g strips also ( F i g u r e 2 ) w e r e 24-gauge steelhaving a _{2-shaped cross} s e c t i o n , with one leg 1 / 2 in. wide and the other 1-114 in. wide and a connecting open web section 1/2 in. wide that provided a 1/2 -in. o f f s e t between t h e outer legs. The n a r r o w leg was f a s t e n e d t o the block wall

using 112-in, concrete nails, and the wider l e g then served as a mounting surface f o r the gypsum board, which was fastened on with

1 -in. self -drilling s c r e w s , The f u r r i n g s t r i p s we r e applied horizontally

at 2-ft spacing. The weight of the f u r r i n g added 0. 2 %b p e r sq f t of

wall a n d the g y p s u m board added 2. O lb. Thus the weight p e r s q f t of

finished wall was approximately 55 lb.

W a l l 1D

-

The basic w a l l was painted on both sides with three coats of block s e a l e r as described under Wall 1A.

WaLI PE

-

W a l l 1D w a s modified on one side b y the application of a 1 -in. -thick blanket of low-density g l a s s fibre and 1/2-in. gypsum -

board mounted an resilient furring as described under W a l l 1C

( F i g u r e s 2 and 3 ) . The f u r r i n g was mounted with 1 -in. nails over the

g l a s s f i b r e blanket compressing it against the block w a l l o v e r the a r e a

of contact under the furring strips. The weight per s q E t of glass

fibre w a s 0. 06 lb, and the weight p e r s g f t of finished wall w a s approxi- m a t e l y 55 lb.

W a l l 1F - W a l l 1D was modified on one s i d e by t h e application of 1/2-in.

gypsurn board mounted on r e s i l i e n t strips as described under W a l l 1C. W e i g h t per s q f t was approximately 55 lb.

TEST PROCEDURE

Each t e s t w a s done in accordance with ASTM E90-70-Laboratory

M e a s u r e m e n t of A i r b o r n e Sound Transmission L o s s of Building Parti- t i o n s . The results of the six t e s t s are given in Table I.

COMMENTS

ON

TEST RESULTS ( 1 ) Effect of Sealing

Block

Surface

h

F i g u r e 4 a comparison of W a l l s 1A, 1B and 1C shows the e f f e c t of sealing one or both surfaces of the wall with block f i l l e r . In the unsealed condition the wall performance i s governed by porous transmission through the block material rather than by the mass of t h e wall. Note that once one side is effectively s e a l e d , sealing the second

( 2 ) Effect of Extra Lcaf of Gypsurn W a l l b o a r d

F i g u r e 5 shows the improvement t o be achieved when an a d d i t i o n a l leaf of gypsum w a l l b o a r d is resiliently applied to one side, N o t e that in this instance t h e extra leaf is applied on the u n s e a l e d

side of the block wall. The substantial improvement is due in part to the absorption provided by the unsealed porous block wall.

Figure 6 shows a similar result when both sides have been sealed; here the improvement i s much less and i s , in fact, and

impairment at the law frequencies, Addition of a g l a s s fibre blanket

in the space between the block wall and the g y p s u m wallboard l a r g e l y

restores the effectiveness of the extra leaf except at the lowest

frequencies where a significant gain can b e achieved only by i n c r e a s i n g the spacing of the added leaf or by increasing the low-frequency

ab sorption. Leaving the block wall unsealed under the added Ie af is

a useful and inexpensive way of achieving better low frequency absorption

and avoids the reduction in transmis sion l o s s at the Eowe s t f requencie s

that may otherwise result with t h e added leaf.

ACKNOWLEDGEMENT

The t e s t s reported here were done as a cooperative project with the N a t i o n a l Concrete Producers "s sociation, who furnished the materials and constructed the t e s t specimens,

T A B L E

I

TRANSMISSION LOSS

IN DECIBELS

C e n t r e Band W a l l No.

Frequency Hz. 1A 1B 1C LD 1E

Sound Transmission

Figure 1 Block wall section after t e s t , showing extent of mortar coverage on horizontal and v e r t i c a l

0.50" GYPSUM BOARD R E S I L I E N T F U R ' R ~ N G S T R I P S 1" SELF - D R I L L I N G S C R E W S 1" T H I C K L.D. G L R S S F I B R E MOUNTlPlG F L A N G E (COMPRESSED

u n m

M O U M J I N G FLANGE OF FURRING S T R I P S ) _{Q P € # WEB F L A N G E} WdLLBOARD MOUNTING F L A N G E R E S I L I E N T M E T A L F U R R I N G S T R I P F I G U R E 2 S E C T I O N S OF W A L L S

I C

A N D I E S H O W I N G M O U N T I N G O F G Y P S U M B O A R D L E A F A N D D E T A I L

OF

R E S I L I E N T F U R R I N G S T R I P

Figure 3 W a l l

E

showing mounting of gypsum board over resilient furring strips and g l a s s f i b r e blanket.

F R E Q U E N C Y I N H z F I G U R E 4 COMPARISON O F W A L L S I A , I B A N D I D S M O W I N G E F F E C T OF S E A L I N G O N E A N D B O T H S I D E S O F W A L L W I T H B L O C K F I L L E R . W A L L I 0 I S S E A L E D O N O N E S I D E ; I D 15 S E A L E D O N B O T H S I D E S P P fLJ3P-2

F R E Q U E N C Y I N H z F I G U R E 5 E F F E C T OF A D D I N G E X T R A L E A F OF G Y P S U M B O A R D OVER U N S E A L E D S I D E OF B L O C K W A L L I B _{W A L L} S E A L E D O N ONE S I D E W I T H B L O C K F I L L E R I C

-

R E S I L I E N T L Y M O U N T E D GYPSUM B O A R D O N U N S E A L E D S I D E OF W A L L BP sa 1934-3

F R E Q U E N C Y I N H z F I G U R E 6 E F F E C T OF A D D I N G E X T R A L E A F O V E R S E A L E D S U R F A C E O F B L O C K W A L L , W A L L 1 D 15 T H E B A S I C W A L L ; Z F I S T H E W A L L P L U S R E S I L I E N T L Y M O U N T E D G Y P S U M B O A R D ; I E I S THE W A L L PLUS G L A S S F I B R E B L A W K E T P L U S R E S I L F E N T L Y M O U N T E D G Y P S U M B O A R D B P S Z ~ ~ - Q