Buildings for paper mills. Part 1: A survey of existing machine rooms

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Pulp and Paper Magazine of Canada, 63, C, pp. T75-T81, 1962

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Buildings for paper mills. Part 1: A survey of existing machine rooms

Latta, J. K.

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Ser

TH1

N21r2

no.

151

c.

2

BLDG

NATIONAL RESEARCH COUNCIL

CANADA

DIVISION OF BUILDING RESEARCH

BUILDINGS

FOR PAPER

MILLS

Part I : A Survey of Existing Machine Rooms

BY

J.

K. LATTA

PULP AND P A P E R MAGAZINE O F CANADA, VOL. 63, NO. C C O N V E N T I O N I S S U E 1962, T75-T81

RESEARCH PAPER NO.

151 OF THE

DIVISION OF BUILDING RESEARCH

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This publication is being distributed by the Division of Building Research of the National Research Council. It should not be reproduced in whole or in part, without permission of the original publisher. The Division would be glad to be of assistance in obtaining such permission.

Publications of the Division of Building Research may be obtained b y mailing the appropriate remittance. (a Bank. Express. or Post Office Money Order or a cheque made payable a t par in Ottawa, to the Receiver General of Canada, credit National Research Council) io the National Research Council. Ottawa. Stamps are not acceptable.

A coupon system h a s been introduced to make payments for publications relatively simple. Coupons are available in denominations of 5, 25 and 50 cents, a n d may be obtained by making a remittance a s indicated above. These coupons may be used for the purchase of all National Research Council publications including specifications of the Canadian Government Specifica- tions Board.

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.

,

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Buildings

for Paper

Mills

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.." 7

Part

I: A

Survey of Existing Machine Rooms

J. I<.

LATTA

Resecc?.cl~ O f f i c e r , Co?~s11.~1ction

Sectioli, Division o f Bz~ilcli??g

Cjeseci?z/~,

hrutio?lctl R e s c n ~ ~ c l ~

Couizcil

In an endeavour t o meet the need \vithin the pulp and paper industry for information on building construction, a survey of existing nlachine rooms was carried out by means of a questionnaire and by visits t o several mills. During the visits, temperature and humidity readings were taken; the average condition within the machine

room was found t o be 94 deg. IF. aud 53 per cent relative

humidity. The quantity of water vapour released into the machine room from the wet end i s estimated a s being equal t o one third of that evaporated in the dryer section, and the need for enclosing the wet end i s stressed. T h e performance of different materials and types of roof and wall construction i s discussed and i t i s concluded that,, except for the use of a complete ceiling below the roof truss a s a protection for the roof deck, no one material or layout is superior.

T

H E PULP AND PAPERMAI<ING PROCESSES a r e largely mechanical and chemical ones requiring a large amount of complicated and expensive equipment rep- resenting a much larger capital outlay than do t h e lxildings housing it. Because of t h i s and also because of t h e natural preoccupation of t h e mill engineers with the performance and maintenance of the equipment the buildings have sometimes been relegated t o a secondary position. T h e Mechanical Engineering Committee of the Technical Section of the Canadian Pulp and P a p e r Association recognized t h a t there a r e some serious problems connected with t h e buildings in paper mills but t h a t t h e r e is, within t h e industry, a shortage of readily available information relating to these problems. They considered i t their responsibil- ity to t r y to remedy this situation but, lacking s t a f f and facilities of t h e i r own, turned to t h e Division of Building Research of t h e National Research Council f o r assistance. A f t e r discussion i t was agreed t h a t a study of all paper mill buildings was too large to be manageable, and so t h e investigation was confined to machine rooms in t h e f i r s t instance. I t is considered, however, t h a t t h e r e is no difficulty in estending t h e results of this study to other buildings. This, then, is the f i r s t paper of several which will result f r o m t h i s program ancl is confined to a discussion of the machine 'oom conditions and t h e performance of various types of coilstruction in use a t present.

I n the manufacture of paper, g r e a t quantities of water a r e used. T h i s introduces a number of problems

Paper presented a t the Annual Meeting of the Technical Section, Canadian Pulp and Paper Association, Montreal,

Canada, January 23-26, 1962; not to be reproduced with-

out pernlission of this organization.

in building design particularly in t h e paper machine rooms where much of this w a t e r is drained and evaporatecl f r o m t h e pulp to produce t h e paper. If t h e moisture given off in the machine room i s not con- trolled, severe damage to t h e roof ancl walls of t h e building may result. I n order to ascertain t h e magni- tude of t h i s problem, a questionnaire mas s e n t to all member mills requesting information on t h e type and performance of materials used in wall and roof construction. Sitbsequently t h e author a r r a n g e d through t h e Mechanical Engineering Committee to visit a large n ~ l m b e r of mills to observe t h e n a t u r e of t h e i r construction, t h e conditions within t h e machine rooms and to discuss with t h e owners the various problems t h a t had been encountered w i t h their buildings.

Replies to t h e questionnaire mere received from 5 1 mills. Thirty-three mills have been visited, of ~ v h i c h number 2 1 had previously replied to t h e question- naire. Thus, information h a s been collected on 63 mills. As any one mill may have a number of machine rooms and may have used several different types of construction however, 125 roofs and SO walls a r e reported on.

I t is clear f r o m the iliformation t h a t h a s been collected t h a t t h e most serious building problem in t h e machine rooms is the durability of the roof deck. TValls have usually been much more durable but i n many cases severe surface condensation h a s occurred which malces them extremely clirty and unsightly. Gefore reviewing the performance of t h e different types of construction, i t is desirable t o establish w h a t constitutes satisfactory performance.

Obviously t h e construction must be durable but t h e question of how durable now arises. T h i s i s a matter of economics which m u s t be solved by the designer of each mill, t a k i n g into account the cost of the materials, t h e ease with which they can be replaced, a n d t h e nuisance factor involved i n replacing them.

I t is also important to avoid anything t h a t inter- feres with t h e papermaking process, such as condensation clropping f r o m t h e roof. W h a t does n o t seem to be so \\re11 recognized is that a modern building cannot be considel-ed satisfactory if t h e r e is s u r - face condensation on a n y p a r t of the s t r u c t u r e . Quite a p a r t f r o m t h e harmful effects on t h e durability of materials, moist surfaces collect dirt and prevent t h e maintenance of a bright and pleasing work area. Slight condensation f o r short periods will not normally be harmful and s o it is convenient to adopt t h e 10 p e r cent w i n t e r design temperature as t h e a i r tempera- t u r e below which some surface condensation is toler- able. T h i s is t h e temperature below which 1 0 per cent

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of the January hourly temperatures fell d u r i n g the mechaiiical erigineeriiig problem, but a s the w a t e r periocl 1941 to 1950. Values f o r i t ailcl f o r many other vapciur in t h e machine room is the g r e a t e s t single fac- climatological phenomena such a s rainfall, snowfall, t o r contributing t o t h e cleterioratioii of t h e builcling, wind speecl and direction, can be obtaiiiecl from t h e sonie consideration must be given to t h e matter in Climatological Atlas of Canada published jointly by this paper. Excessive humidity also complicates the t h e Meteorological Division of tlie Department of inaiiltenaiice of a clean a n d bright work area, adds to Trailsport and t h e Divisioll of Euilcliilg Research [I]. the discomfort of t h e employees ancl increases mainte-

Accepting t h i s temperature a s t h e outside design nance costs i n the mill.

temperature i t is now necessary to ascertain what a r e The t e r m "a balanced supply a n d exhaust system" the conclitions curreiltly prevailing inside machine usually relates to a closecl hood installation in which rooms. the a i r suppliecl by mechanical means is adjusted to balance t h a t which is exhausted. I n actual fact, h o ~ v -

M A C H I N E ROOM CONDITIONS ever, all machine rooms have a balanced ventilating

system in t h a t the weight of a i r eiltering the room During t h e course of the visits, temperature a n d hu- must exactly balance t h a t which is exhausted. If, midity readings were taken a t various places in ma- therefore, t h e ~ v e i g h t of a i r supplied directly to the chine rooms. Owing to various factors in the individ- machines by nTay of Gi*ewin systems, etc., is deducted ual mills i t was not possible to take these readings a t from t h e total weight exhausted, the weight of a i r standard locations, but a n endeavour was made to which passes through the madline room can be ob- record conditioils under the roof and by outside walls tained. If t h i s f i g u r e is related to t h e tonnage of a t t h e wet and dry ends. production and if, furthermore, i t is assumed t h a t The average and extreme coiiditions m e a s ~ l r e d a r e this a i r while in t h e room has the same temperature summarized in Table I. aild relative humidity a s t h e general room air, i t is I n the questionnaire, the mills were asked t o report possible to assess t h e weight of w a t e r t h a t is removed t h e average inside minter conclitions in t h e worst f r o m t h e room per ton of paper.

location. The average and the extreme values reported This line of reasoning has been applied to 1 3 ma- a r e given in Table 11. The locations a t which the chine looms of 9 paper mills producing nenrsprint, readings were taken were not reported. and i t was fouilcl t h a t on the average 1,200 lb. of Room conditions a r e greatly influenced by the ven- water a r e evacuatecl f r o m the machine room per ton tilation system installed t o extract t h e hot humid a i r of paper produced. T h e w a t e r is over a n d above t h a t and to supply fresh air. The method of doing this is a which is evaporatecl directly from t h e d r y e r section.

T h i s f i g u r e is only approximate since the precise TABLE I Room Conditions in tl~e ~l/lills Visited. ~ v e i g h t s of a i r handled a r e not known, and in a n y _{case i t will vary with t h e stock temperature and t h e} design of t h e machine, b u t i t does indicate t h a t t h e

T ~ i n p . , R.H..

r / moisture picked up in t h e room is equal to approxi-

Locuiion O F _{mately one-third of t h e amount evaporated in the dry-}

Average . . . Highest temperatures Lowest temperatures Ilighest R.11.. Lowest R.H.

53 el. section. Therefore i t is clear t h a t t h e ventilation 53 of t h e room has considerable importance purely f r o m 43 the point of view of making paper. Furthermore, i t 67 is clear t h a t the bulk of this ~ v a t e r h a s come f r o m 56 the fourclriaiei* section a n d the various screens and headboxes preceding it. T h u s i t would be highly cle- sirable to enclose these p a r t s of the equipment in order t o prevent t h e escape of vapour i n t o the room.

37 When discussing t h i s problem with mill persoanel, i t 54 was almost invariably stated t h a t t h i s nras not a practical proposition since i t nras necessary f o r t h e machine operators to see t h e sheet a s i t i s formed 011

the mire and also f o r t h e wire to be changed easily.

73 Nevertheless, one cannot help but feel t h a t these a r e

64 the sainc types of a r g u m e n t as were used in other times t o oppose t h e introduction of closed hoods on

85 the d r y e r section.

53 Nearly all paper mills have their machine rooms op- e r a t i n g under a vacuum ancl in all probability t h i s is

9 the principal reason f o r t h e comparatively small number of mall failures. S t ~ t d i e s on other buildings, such

12 as office buildings, which a r e ventilated under pres- Over-all

Under roof a t wet end

" " a t dry end

By wall a t wet end " " a t d r y e n d

Under roof. dry end of dryers " " over dryers

Floor level, opposite breast roll

" " opposite reel Under roof, over headbox Floor level, a t wet end I n penthouse, over dryers In attic, above complete

ceiling

sui-e, have shown t h a t considel.able damage can be caused by w a r m moist a i r being carried o u t f r o m the TABLE I 1 Azrerage and Extreme Conditions Reported i n rooms into t h e cvall and roof structure through vari- the Qzrestionnaire. ous craclis and fissures. During cold ~ v e a t h e r the moisture coilcleilses oil t h e outer p a r t s of the wall, ice Tenzp., O F R. El.,

7,

lenses can build up, t h e materials become frozen when

wet a n d considerable damage can result. I f the build- 1 94 94 95 90 9'7 133 114 73 73 90 88 92 r - I / 1 0 , ~

63 _{ing is under vacuum, t h e colder a n d d r i e r outsicle a i r} 9 5 _{tends to bc drawn i n a n d these problems are mini-} 60- 90 _{mized. Nevertheless i t must be recognized t h a t t h i s} 95 _{vacuum does cause coiisiclerable trouble w i t h draughts,} Average

Ilighest temperature. . . Lowest temperature

Highest R.H. . .

Lowest R.13

.

. . .

.

. . 6 5 18 particularly ~ v h e n exterior doors a r e opened. The suc-

- 4 - 85

105 75 105

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Total

_-

TABLE I11 Roof Dech-s at the illills I'isifed.

No.

Toirtl No. of still i n Shortesl -

Type of Roof Deck No. Fnilzi~es service Longest

-- 'Still in service. Wood 34 13 Precast concrete 6 Gypsum

: I !

8 Concrete slab 4 1

TABLE IV Roof Decks Reported i ? ~ Q v c s l i o , ~ mire.

2 1

1

38'

2 5 50

2 36'

3 4 1 *

Asbestos cement 6 none

,

6 6 b

tion on the machine room in winter i s sometimes a s high a s

"4

in. of water. Steps should be taken t o re- duce t h i s considerably. W i t h existing buildings, one hesitates t o recommend t h a t t h e r e should be no suc- tion, but a f i g u r e of about

94

_{in. of w a t e r would be} much inore reasonable. Eefore t h i s f i g u r e could be reduced f u r t h e r t h e details of construction ~voulcl have to be examiiied carefully t o avoid t h e troubles outliiled above.

One solution to t h e problem of buildiilg dlirability arid t h e nuisance of d r a u g h t s i s to maiiltain a layer of d r y a i r against t h e walls and roof when t h e suc- tion could be virtually eliminated. Owing t o t h e difficulty of coiltrolliilg such a c u r t a i n of a i r \vhen clis- charged freely into t h e room, i t i s desirable t h a t some form of shielcl should be placecl between t h e hot humid a i r and t h e outer p a r t s of t h e s t r u c t u r e . I n the case of roofs this can readily be obtained by meails of a conlplete ceiling buspencled below t h e bottom chord of t h e truss, a s has been done in several mills. S o f a r , however, no a t t e m p t has been nlacle to extend this principle to t h e \valls, but i t i s possible t h a t some f o r m of inner shield can be provicled on t h e inner face of t h e wall coluinns. If w a r m dry a i r is then suppliecl to t h e a t t i c and wall spaces so formed, any vapour leaking past the ceiling o r inner lvall will be carried away before i t can do any damage to t h e roof o r m a i n wall. T h e need f o r t h i s a i r to be d r y must be stressed siiice economizers and other equipment, if in poor condition, can add coilsiderable quantities of water to the supply a i r .

F r o m these general considerations we may now t u r n to review t h e performance of the different types of construction t h a t have been used.

No1 Type of Roof Deck Total Srrl i ~ f ( ~ t l o ~ IJ Salzsf(tclo) IJ

- - . . -- - --- -

ROOF DECKS

A t t h e 33 mills visited, information was collectecl re- lating t o 85 different roofs. Of these, 28 had failed

Wood

I

12

and been replaced; the remaining 57 w e r e still i n service. Table I11 summarizes the number of roofs of clifferent types of construction ancl t h e service t h a t they have given.

An additional 40 roofs a r e reported in t h e question- nail-e, of which 26 a r e listed a s satisfactory and 14 a s unsatisfactory. Table I V summarizes the coilstructioil and performance of those roofs. Some roofs reported by the mill onlner as being satisfactory did not meet t h e clefinitioil of satisfactory performailce used i n this paper. T h u s , in some cases, a roof has beell trans- ferred f r o m one category t o t h e other a s a result of comments on i t s behaviour.

From Tables I11 and IV, i t is seen t h a t no oiie type of roof cleck i s markedly superior t o all t h e others, ancl even gypsum roofs which a r e usually n o t viewed favourably, have given good service. T h u s i t is neces- s a r y to look f o r other f a c t o r s that can influence t h e life of t h e deck. 9 9 - 3 Precast concrete Gypsum Concrete slab Asbestos cement Steel

Wood Roof Decks

3 6 5 1 - 15 5 1 3 4

The life s p a n of a wood roof cleck appears t o be quite variable, r a n g i n g from a minimum of 8 y e a r s to over 38 years f o r a roof which is still in service. The various lives which have been reported w e r e plotted against t h e relative humidity a t present existing i n t h e machine room. This plotting had a Jery scattered appearance ancl about t h e only thing t h a t w a s notice- able was t h a t all roofs t h a t have failed l a y in t h e upper half of t h e chart. I n plotting t h i s chart, it had been hoped t h a t some indicatioil would have been given to show t h a t roofs w i t h the s h o r t e s t lives had t h e highest humidity a n d vice versa, and, i n an endeavour t o f i n d out why { h i s was n o t s h o w n clearly, t h e case histories of t h e :nills visited were examined. This nllowecl some a d j u s t m e n t to be made i n some instances such a s allo~ving a higher humidity where a hoocl h a s been installed recently or i n anticipating a roof f a i l u r e where the roof w a s seen to be i n poor con- clition. Despite this readjustment, t h e plotted points still had q u i t e a wide scatter, but nevertheless a very tentative division coulcl be made a t about 40 per cent relative humidity in t h e machine room.

4 j -

Precast Concrete Roof Declcs

There a r e generally two m a i n agents t h a t cause t h e deterioration of precast concrete slabs : corrosioil of t h e reiillorcing steel a n d leaching of t h e cement. T h e f i r s t of these h a s been by f a r the more common and h a s caused consiclerable trouble by spalling of t h e concrete.

Some s i s f a i l ~ 1 i . e ~ of this type can be attributed t o a n early type of foamed concrete slab which is no

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longer o n t h e marliet, and i n w h i c h t h e r e i n f o r c e m e n t w a s not adequately protected against corrosion. T h i s m e a n t t h a t t h e material ~ v a s i n f a c t quite unsuited f o r use i n t h e h u m i d atmosphere o f a paper mill. E v e n so, t h e r e are still a number o f cases w i t h o t h e r precast slabs mhere severe corrosion h a s t a k e n place

a1 ures ancl t h e r e i s some evidence connecting those f ' 1 w i t h t h e bleaching processes i n various pulp and f i n e paper mills.

I t

has been shown i n other investigations t h a t cor- rosion o f r e i n f o r c i n g steel i n concrete can be caused b y a galvanic cell being set u p i n t h e concrete i t s e l f , particularly i n t h e presence o f t h e chloride ion. T h u s , t h e presence i n t h e atmosphere o f chlorine f r o m t h e bleaching process i n conjunction w i t h condensation could be responsible f o r t h e corrosion o f t h e rein- forcement. Although t h i s s t u d y i s confined t o m a - chine rooms, i t should be noted t h a t some similar cor- rosion problems have been observed i n bleach plants. I t m a y also be noted t h a t t h e use o f calcium chloride as a n additive i n concrete placecl i n w i n t e r call lead t o corrosion o f reinforcing steel.

T h e old precast dense concrete slabs have given good service, and t h e oldest roof encountered, w h i c h i s

50 years old, i s o f t h i s t y p e . I t i s reported, however, t h a t t h e underside o f t h e slabs started t o disintegrate some years ago, and t h e roof w a s replastered t o r e m e d y t h i s d e f e c t . F r o m observation o f a roof o f t h e same t y p e b u t w h i c h is only 35 years old, i t seems probable t h a t disintegration nras due t o a leaching o f t h e cement b y condensation. T h i s younger roof is n o w powdering o f f quite badly and loose grains o f sand can be seen on t h e underside. Small stalactites are also hanging f r o m t h e r o o f ; o n analysis t h e s e proved t o be m a i n l y calcium carbonate. I t is t h o u g h t t h a t mildly acidic w a t e r f r o m condensation i n t h e colder upper parts o f t h e hollo\~~ concrete beams r a n back out o f t h e slab, and i n doing so, leached t h e calcium f r o m t h e cement. A s f a r as is k n o w n , no paint or other vapour barrier w a s applied t o t h e exposed sur- faces o f t h e s e r o o f s .

Another d e f e c t w i t h precast b e a m s which is re- ported f a i r l y f r e q u e n t l y is t h a t t h e caulking between t h e individual slabs fails and drops o u t . I t has also been observecl t h a t some slabs tend t o t a k e on a per- m a n e n t d e f o r m a t i o n and t o sag b e t w e e n t h e purlins. T h i s w a s observed a t f i r s t hand a t only one m i l l , where i t w a s seen t h a t t h e floor slabs and roof slabs i n t h e i r penthouse had sagged approximately one inch over a span o f six f e e t .

Cost-in-Place Concrete Roof Decks

F o u r roof declis o f t h i s t y p e w e r e examined during t h e v i s i t s ancl one was reported i n t h e questionnaire. O f t h e f i r s t f o u r , one had failed while t h e other t h r e e continued t o give good service. T h e one i n t h e ques- tionnaire w a s statecl t o be u n s a t i s f a c t o r y because o f spalling and conclensation.

I n general, t h e r e f o r e , one can say t h a t concrete r o o f decks are s a t i s f a c t o r y i f t h e y have adequate insula- t i o n over t h e m t o prevent condensation. T h i s is also borne out b y t h e good performance o f precast dense concrete slabs as reported earlier. T h e y can be sub- ject t o t h e same t y p e s o f clestruction as are precast roof slabs, b u t clo not have t h e same n u m b e r o f joints which require caulking nor do t h e y have t h e same problems o f permanent cleflections.

Gypsum Roof Decks

During t h e v i s i t s t e n g y p s u m roof decks w e r e seen, and a f u r t h e r f o u r are reported i n t h e questionnaire.

O f t h e f i r s t t e n , t w o are still i n u s e a f t e r 36 and 34 years o f service, and have complete ceilings below t h e t r u s s . A n o t h e r mill h a s part o f a g y p s u m roof still i n use. T h e part which has been retained a t t h i s mill had insulation applied over i t some nine years ago, and i t i s now abundantly clear w h e n looking a t i t f r o m below w h e r e t h i s insulation has been placecl : t h e insulated part is clean and f r e s h , whereas the surroundings are v e r y d i r t y . O f t h e f o u r r o o f s reported In t h e question- naire, t w o are still i n use a f t e r 32 years' service each, and i t seems clear t h a t t h e s e roofs do n o t have a ceil- ing protecting t h e m .

O n t h e whole, t h e r e f o r e , t h e performance o f gyp- s u m r o o f s does not d i f f e r vastly f r o m o t h e r t y p e s o f construction, particularly w h e n protected b y a ceil- ing. T h e addition o f insulation would probably m a k e t h e m s a t i s f a c t o r y b y preventing internal condensation. I n general, t h e g y p s u m r o o f s failed e i t h e r t h r o u g h rotting o f t h e n700cl chips and general spalling or t h r o u g h r u s t i n g o f t h e w i r e r e i n f o r c e m e n t .

Asbestos Cement Roof Decks

Only s i x r o o f s o f t h i s t y p e were reported on d u r i n g t h e v i s i t s w i t h a f u r t h e r t h r e e b e i n g reported i n t h e questionnaire. All o f t h e s i x are v e r y y o u n g , the oldest being only six years old, and so i t i s t o o soon t o give any verdict a s t o t h e i r durability. All t h r e e roofs re- ported i n t h e questionnaire are stated t o b e satisfac- t o r y , and one is 26 years old, m a k i n g i t the oldest roof o f t h i s material w h i c h has been encountered clur- ing t h i s s t u d y .

I n general, i t ~voulcl s e e m t h a t asbestos cement roof clecks should be s a t i s f a c t o r y since t h e r e i s no rein- forcement i n t h e m t o corrode. I f stainless steel screws are used f o r fastening t h e y should give no trouble o n t h a t score.

Asbestos cement h a s various drawbacks, the prin- cipal one being t h a t i t i s v e r y b r i t t l e a n d , w h a t is more, t e n d s t o become m o r e brittle w i t h age. T h u s i t is not resistant t o i m p a c t .

I t

also t e n d s t o move ap- preciably due t o changes i n temperature and moisture content and tends t o s h r i n k considerably as atmos- pheric carbonation t a k e s place. T h i s last change i n t h e material is also said t o render i t m o r e slisceptible t o clamage f r o m f r o s t action.

For use as a roof deck, however, mhere i t would not normally be subjected t o impact loading or t o f r o s t action and provided allowance can be m a d e f o r t h e various movements w h i c h m a y t a k e place, there does not seem t o b e any reason w h y i t should n o t be dura- ble. I t is, i n fact, becoming a m o r e popular m a - terial and several engineers reported t h a t they w e r e considering i t favourably f o r replacement and n e w construction. T h e cement i s , o f course, subject t o t h e same agents o f destruction as t h e c e m e n t i n concrete.

Steel Roof Decks

No steel roof clecks w e r e seen d u r i n g the visits and only o n e mill reported t h a t t h e y had used t h e m on a n y building. I n t h i s instance, t h e y had not liked t h e material since t h e y considered i t expensive t o m a i n t a i n , requiring painting quite frequently. O n examining t h e questionnaire, i t i s seen that f o u r mills reported t h a t t h e y have steel roof decks over t h e i r machine rooms, and all are perforniing satis- factorily. One mill, however, is u s i n g all stainless steel w h i c h , while undoubtedly m o s t satisfactory, is probably v e r y expensive.

Taliing a broad v i e w o f t h e problem, t h e r e should be no reason w h y a steel roof cleck should n o t be used, provicled i t can be protected against r u s t i n g . T h i s can

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Total

1

33

1

27 5

1

10 22

- 7 -

be done b y maintaining reasonably d r y conditions is applied t o t h e mills reported i n t h e w i t h i n t h e mill, i.e. below about 50 per cent Relative using t h e i r reported temperatures and

H u m i d i t y a t t h e surface o f t h e steel, t h o u g h t h e pres- very d i f f e r e n t picture i s given as shown i n t h e ence o f salts or d i r t o n t h e surface will complicate t w o columns o f Table V I .

t h e problem. Several mills (including t w o o f t h e t h r e e usin

Alternatively a surface coating can be applied t o concrete blocks) did not report s u f f i c i e n t information t h e steel t o separate i t f r o m t h e corrosive agents. t o enable t h e calculation t o be made. T h e s e have been T h i s i s not particularly d i f f i c u l t w i t h some modern l e f t i n t h e category specified b y t h e owners. I t should materials, w h e n t h e m a i n expanse o f each sheet is be noted, however, t h a t t h e reported h u m i d i t i e s and considered. O n t h e other hand, there i s a v e r y d e f i n i t e temperatures m a y not have occurred adjacent to t h e problem a t t h e attachment points t o t h e steel purlins. walls. Nevertheless i t is considered t h a t t h e perform- I f a n y holes are punched through t h e material t o ance o f machine room walls should be judged b y take bolts or i f a n y welding is done, t h e protective rather higher standards t h a n are being applied a t

coating will be destroyed at these points and therefore present.

rust could spread f r o m t h e m . Possibly, t h e raw edges Considering generally t h e performance o f t h e walls o f metal could be reprotected i n some manner such as seen during t h e visits, i t can be said t h a t t h e y have using neoprene washers t o exclude t h e moisture, b u t not been as troublesome as roofs. T h e principal de- i n so doing one is relying upon t h e conscientiousness fects have been condensation on the inside, spalling o f t h e individual workmall t o ensure t h a t a proper f i t on the outside, some cracking, a certain amount o f

i s achieved. efflorescence b o t h inside and out, and i n some rare

instances icicle formation on t h e outside caused b y

WALLS vapour passing through t h e wall. T h e internal sur-

face o f m a n y o f the walls seen was d i r t y and drab I n visiting t h e 33 mills, 48 walls were examined and except i n those cases w h e r e i t had been painted re- a further 33 are reported i n t h e questionnaire. T h e cently. Painting or some similar t r e a t m e n t is re- particulars and ages o f these walls are summarized quired on m o s t walls as a vapour barrier b u t cannot

i n Tables V and VI. be satisfactorily applied over a damp s u r f a c e , and so

Judging f r o m t h e replies t o t h e questionnaire, i t i t m a y be assumed t h a t m a n y poor paint jobs can b e seems t h a t t h e mill owners are well satisfied w i t h t h e attributed t o t h i s factor.

walls as constructed a t present (see Table V I ) , b u t Only i n three cases did a wall have t o be entirely i t should be noted t h a t what is reported as a satisfac- replaced. T w o o f these were solid brick walls, both o f t o r y wall does not always f i t t h e requirement stated which failed due t o extremely severe external spall- earlier f o r no surface condensation. I f t h i s criterion i n g , t h e f i r s t one being adjacent to t h e economizers and the second one located b y some groundwood stor- age tanks. I n both cases t h e humidity was v e r y h i g h T A B L E V W a l l Constrtiction at the AIills Visited. and there w a s little or n o ventilation. T h e other case

concerned a t i m b e r stud wall which w a s erected o f necessity w i t h extreme cheapness during t h e early

Age years

-- -- - - 1930's and w h i c h rotted out a f t e r thirteen years.

Conslruclion No. Oldest Youngest Average Condensation on Walls

80 3 42 Average temperatures and relative h u m i d i t i e s in t h e

mills visited, as recorded i n locations adjacent to t h e

38 3 26 walls a t t h e w e t end, are 90 deg. F . and 67 per cent

Relative H u m i d i t y . T h u s t h e dewpoint will occur at a

- - 5 temperature o f 78 deg. F., and t o prevent condensa-

19 4 8 t i o n on t h e wall t h e surface temperature m u s t be k e p t

50 33 40 above t h i s figure. Furthermore, i f t h e outside tem-

21 7 14 perature o f 0 deg. F. i s t a k e n , and allowing for t h e

83 GO 72 thermal resistance o f t h e inside and outside a i r films,

- - 1 t h e n t h e wall structure itself m u s t have a resistance

4 2 4 5 14 o f about 3.22, i.e., a thermal conductivity o f 0.31. I f

t h e thickness o f t h e d i f f e r e n t types o f construction, which would be needed t o give this resistance are

Solid briclc .

Bricli face with terra cotta tile hacking . Brick face with concrete

block backing Terra cotta tile Solid concrete Concrete block . Stone masonry

Precast foamed concrete Sheet materials . Total . . . 20 7 1 4 7 2 2 1 48

T A B L E V I W a l l Construction as Reported i n thc Q~icstionnazre.

Reported Performance Modified Performance

---- - -

Construction No. Satisfactory Not Satisfactory Satisfactor!l Not Satisfactory

Solid bricli. . .

.

. Brick face with terra cotta tile backing . . . Solid concrete. . . .

Concrete block

Precast dense concrete . . Sheet materials. . . 8 1 4 1 7 2 3 - 1 - 4 1 (1 not specified) 9 5 9 3 1 G 2 7 0 5 2 7 2 1 0 1 4 1 (1 not specifled)

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considered t h e following values a r e obtained: Solid brick (common) 1 6 in. Solid brick (face) 29 in.

T e r r a cotta tile Between 1 2 and 1 6 in. Solid concrete 10 in.

Concrete block 24 in. Insulating board (fibre-

glass) Less t h a n 1 in. Insulating board (impreg-

nated sheeting)

llh

in.

Considering the resistance of a brick face w i t h t e r r a cotta tile backing, assuming a 4-in. brick w i t h a n 8-in. tile and :% in. of plaster, t h i s wall would give a resistance of 2.44. F r o m this, i t is clear t h a t to prevent condensation with all of the ordinary types of construction a t present in use, quite thick xvalls a r e required, and t h a t if t h e internal conditions a r e above average a n d / o r t h e external conditions below 0 deg. F., then even thicker malls will be required. On t h e other hand, i t can be seen t h a t quite small thicknesses of insulating board can maintain t h e temperature above the dewpoint, though they may pose other kinds of problems in providing adequate control over vapour flow and of preventing condensation within them.

Parapets

No review of malls is complete without some comments on parapets which a r e regarded almost uni- versally by maintenance personnel a s a prolific source of trouble. A l a r g e proportion of t h e expenditure which has been reported on repairs to walls has been caused by deterioration of parapets and necessary rebuilding and repointing. Most parapets, however, do not have a complete flashing on the inside face and over t h e top, and so i t is quite reasonable to expect severe troubles due to moisture penetration f r o m both sides.

Nevertheless, several mills have a policy of continu- i n g to use parapets, usually on the score of preserving t h e uniform appearance between old and new buildings. I n addition to t h e m a t t e r of appearance, parapets eliminate t h e possibility of icicle formation on t h e eaves of t h e roof. I n all probability, however, i t xvould be easier to achieve this effect by a reverse fall a t t h e outer edge of the roof and a suitable over- h a n g w i t h a d r i p on i t s lower edge.

Windows

T h e use of xvindo~vs in a paper mill machine room i s a very debatable subject. F r o m t h e point of view of building construction, i t is obviously easier to eliminate them, and, since t h e mills operate 24 hr. a day, i t cannot be claimed t h a t they a r e essential f o r lighting purposes. F u r t h e r m o r e , with proper ventilation they do not serve any useful purpose f o r admitting f r e s h a i r . T h e one m a i n a r g u m e n t i n favour of having windows is really a psychological one, and i t is argued t h a t i t i s good f o r t h e morale of t h e machine opera- t o r s to be able to g e t a glimpse of t h e outside nonr and then. The value of this morale-booster i s ques- tionable particularly when many ~ v i n d o ~ v s were seen to be so d i r t y and obscured t h a t i t is more likely t h a t they were a depressing influence, and i t ~vould have been better to have had a blank b u t clean xvall.

Condensation f r o m t h e ~vinclows, a p a r t f r o m being unsightly, can cause trouble w i t h t h e walls below t h e window. I11 many instances, i t was seen t h a t the xvalls themselves would remain dry, b u t below each window they w e r e soaked by t h e condensation running down. This can be minimized by providing suitable d r a i n a g e

channels, b u t like most industrial installations. unless these a r e of generous proportions they c a n very easily become clogged, and t h e n the w a t e r spills out a s before. On t h e whole, therefore, i t i s preferable to eliminate ~vinclows as f a r as possible. If some clear view panels a r e considered desirable ancl if t h e machine room i s small enough f o r the majority of the operators to benefit from them, clear glass block should be used w i t h generously sized drainage channels below them.

STRUCTURAL FRAMEWORK

I11 nearly all of the mills visited, t h e s t r u c t u r a l f r a m t - work consisted of steel columns w i t h a t r u s s support- i n g t h e roof. Some mills use reinforced concrete struc- t u r e s below the operating floor level, and, in one case, one extension of a machine room h a d been constructed in reinforced concrete.

Only two cases of serious deterioration of the struc- t u r a l steel were reported. One c a n be attributed to t h e corrosive influence of chlorine g a s actiilg on the flanges of t h e columns which were encased in brick malls. I n t h e other case, t h e trusses were only slightly higher t h a n the c h a r g i n g platform of r o t a r y digesters and w e r e subjected to a heavy concentration of sul- p h u r dioxide whenever t h e digesters w e r e opened f o r recharging. I n general, rusting of structural steel framexvorli h a s ilot been severe, although i t has been necessary to c a r r y o u t a considerable amount of protective painting. A n exception t o t h i s is where a complete ceiling h a s been provided below the t r u s s , t h u s obviating repainting f o r t h i r t y y e a r s or more. I t is preferable t h a t structural steelwork sllould not be encased in masonry b u t should be l e f t accessible f o r inspection and r e p a i n t i n g mhen necessary. Locat- ing t h e steelnlork w i t h i n t h e building will also keep i t w a r m t h u s lessening t h e danger of coildensation on it.

INSULATION

The fibreboard insulation which i s used i n the g r e a t majority of cases can be quite s a t i s f a c t o r y although i t does have t h e drawbaclc t h a t once moisture can g e t to it, i t tellcls to absorb aild to hold t h i s moisture. There is also the possibility t h a t i t may r o t mhen wet. Xeither of these objections applies to fibre glass which i s used in some cases, but it, on t h e other hand, has t h e drawback of being rather s p r i n g y when used on a roof. T h i s ti.ouble h a s been overcome in a t least one case by applying a top layer of fibreboarcl over it. Foamed glass ancl some types of foamed plastic have the advantage of being impervious to vapour, but a r e as yet more expensive in initial cost than fibreboard.

VAPOUR BARRIERS

I n t h e mills visited, p a i n t was t h e only vapour bar- r i e r used on the exposed surfaces of walls and roofs, but in m a n y illstances no effort appears t o have been made t o maintain t h i s paint film. T h e dampness of walls and also sometimes of the roof ilaturally makes a satisfactory re-application of p a i n t somewhat difficult. Most paint f i l m s f o r m satisfactory vapour bar- r i e r s provided they a r e thick enough. T h e i r effective- ness, therefore, depends largely upon t h e i r ability to adhere to t h e surface to which they a r e applied.

Most roofs have a mopped-on one- or two-ply asphalt ~ ~ a p o u r b a r r i e r betureen t h e deck and t h e insulation. T h i s forms a satisfactory protection f o r the

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~t of course leaves the deck itself e s p ity in t h e room.

ROOF MEMBRANE

W i t h few exceptions the roof membranes a r e made up of 4 o r 5 plies of bituminous felt. T h e exceptions usually apply to steeply pitchecl roofs where shingles of one f o r m or another have beell used. The use of shingles on a pitchecl roof such a s t h i s can have t h e advantage of permitting any vapour which h a s passed the vapour b a r r i e r to escape to t h e outside air. There appears to be some difference of opinion a s to whether i t is better to cover a built-up roof with gravel which may collect d i r t and promote plant growth, o r to leave i t exposecl ancl t o give a t r e a t m e n t with a light coloured coat which will reflect t h e sun's r a y s but which will have to be renewed periodically.

Roof membranes have not deterioratecl excessively f r o m natural causes and in most instances satisfactory lives have beell achieved. Where rapid failure has been reported i t call usually be a t t r i b u t e d t o a n escessive amouilt of t r a f f i c over t h e roof together with poor maintenance pi'actices which allow steel girders, f a n casings, etc., to be left lying on them.

VENTS

A t some mills i t mas noted t h a t in extremely cold weather overhead mires, faces of walls, and towers supportiilg conveyors were heavily coated with ice caused by t h e discharge of vapour f r o m vents, acl- jacent t o them.

Admittedly i t is a difficult task ~ v h e n designing a paper mill to ensure t h a t all vents a r e located where they will not cause a n y damage, but t h e r e i s no excuse f o r t h e case where a small pipe f r o m a v a t actually clischargecl acicl on to t h e roof of a n adjacent building.

NOISE

With the possible exception of slow-speed tissue mills, nearly all paper mills a r e extremely noisy. This i s particularly t r u e of high-speed nelvsprint machines which emit a most unpleasant howl. Despite this, only one mill was seen in which a n y a t t e m p t appears t o have been made to minimize t h e noise.

I n f u t u r e mills i t woulcl be desirable if this were given considerably g r e a t e r attention ancl where possible suitable acoustic materials applied to t h e walls and roof.

Noise not oilly affects t h e workers in t h e mills, b u t i t is also of consiclerable importance t o t h e nearby resiclents. Obviously open willdows will accentuate t h e noise level around t h e mill, and t h i s is possibly a

f u r t h e r f a c t o r in favour of eliminating \vindolvs entirely.

CONCLUSIONS I n conclusion, i t can be stated t h a t :

1. The excessive humidity in the machine room i s the m a j o r cause of t h e deterioration of t h e building.

2. The durability of t h e roof deck is t h e most serious problem in the building construction.

3. Although nlalls a r e much more durable t h a n roofs, i t is necessary t h a t g r e a t e r attention is paid t o t h e i r insulation value so a s to preveilt s u r f a c e condensation a t all outside temperatures above the 1 0 per cent winter design temperature.

4. The moisture given off illto the room f r o m the w e t end may be a s much a s one third of t h e amouilt evaporated in t h e d r y e r section. E v e r y e f f o r t should be made to control this m o i s t u r e and t o prevent i t f r o m reaching t h e walls and roof of t h e building.

5. The excessive vacuum under which machine rooms operate should be g r e a t l y reduced, but with nor- nlal constl.uction i t shoulcl not be eliminated entirely.

G. W i t h t h e exceptioil of ( 7 ) below, no one material or type of construction has been shown to be n~ai-kedly superior t o t h e others.

7. A full ceiling below t h e t r u s s with ventilation i n the a t t i c space has given good protection f o r roofs and in many cases h a s eliminated t h e need for repainting t h e s t r u c t u r a l steel. I t is recommended t h a t t h i s principle should be applied t o t h e walls a s well a s t h e roof.

S. S t r u c t u r a l steelwork should not be encased i n masonry b u t should be l e f t accessible f o r inspection a n d repainting when necessary.

9. Windows should be eliminated f r o m machine rooms.

10. G r e a t e r "xttention needs t o be given to t h e problem of noise aild to the location of vents and discharge pipes.

This paper, which i s t h e f i r s t of a s e r i e s on t h i s subject, i s a contribution f r o m the Division of Build- ing Research of the National Research Council of Canada, aiid i s published n-it11 the approval of the di- rector of t h e division.

R E F E R E N C E

1. TIIO~IAS, M. I;., Climatological Atlas of Canada. Joint publication of tlie Meteorological Division, Depart- ment of Transport and the Division of Building Research, Nat~onal Research Couacil. Ottawa, De- ceiliber 19.53. NRC 3151.