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Exposure of some roofing systems
I \ Ser THl
I
I 'i
B92 no. 69 c . 2 byB.
F, Stafford I 3 3 Y E L G D l V l S r O N O F BUILDING R E S E A R C H-
N A T l O N A l R E S E A R C H C O U N C I L.
O T T A W A C A N A D ANO
r r r r
March 1970EXPOSURE OF SOME ROOFING SYSTEMS by
B, F, Stafford
In recent years, waterproof m e m b r a n e s m a d e of many new
materials have been developed f o r flat or nearly flat roofs, and f o r
roofs having unusual contours such as curved shells, hyperbolic
paraboloids, etc. Prompting this development has been the need for speedier, e a s i e r application and greater economy than that now en- joyed by t h e roofing industry.
During the l a s t hundred y e a r s , the most commonly employed roofing materials in Canada are bitumens, usually applied in
multiple ply built -up s y s t e m s , Some of the new systems still u s e b i t u m e n s either a s adhesives or waterproofing agents, but recent chemical technology has introduced m a n y new, thin, high
-
s treagth materials which are of a cmnpletely different nature, both in composi- tion and final appearance. Many of these new roofingmembranes have d i s t i n c t advmtages that could enhance, their attractiveness todesigners and owners. A few of the more obvious features are t h e i r relative e a s e of application, high reflective characteristics and good resistance to traffic.
F o r a better understanding of the performance of these systems
under Canadian climatic conditions, an outdoor exposure program was undertaken by the Division of Building Research of the National
Research Council of Canada. This report describes the roofing systems exposed, the method of t h e i r application, and the results of a n u m b e r of visual examinations taken over a 5-year period,
Photographs included at the end of this report show the extent of degradation of some of the materials that w e r e exposed for the full
5 years. A l s o included, i s inf ormathon regarding the performance over a 2-year period of a roofing system that w a s applied over the deck of a small, heated, instrument shelter constructed on the out-
skirts of Ottawa.
ROOF DECKS
A n u m b e r of small roofs, each measuring 1 2 f t by
4
f t w e r edesignated here as N o s . 1 0 , 11 and 12, w e r e prepared on site. W i t h
the exception of
No.
12, all the r o o f s ware joined together, forming one long roof. The materials employed and the method of applicationa r e described later.
The decks for these roof systems (except that of No. 12) w e r e
constructed from panels of 5/16 in. plywood nailed to a 2 by 2 in. l u m b e r
frame. A cant strip 2-in. high was nailed along one length of e a c h panel, s o that i t overlapped the edge of the adjacent roof section. Slight slopes were provided toward the cant strip, and f o r w a r d , to ensure water
drainage. The completed units were s e c u r e l y installed as a protective roof over stored, strucfxral-steel trusses in a way that permitted f r e e
air movement under the roof panels, N u m b e r s 1 to 10 w e r e exposed
fr-May 1964, but No. 11 was not installed until A p r i l 2 8 , 1967, A l l
systems were weathered in the Ottawa area.
Roof
No.
1 2 was installed during M a y 1967, overa
small enclosure approximately 1 0 miles f r o m the Ottawa site. This insulated buildingmeasured 14 f t by 1 0 f t ; an inside temperature of approximately 72°F
was maintained throughout the c o l d e r weather. The roofing s y s t e m
was laid o v e r an insulated wood deck constructed with a slight slope
f o r drainage,
T Y P E S OF ROOF-SYSTEMS EXPOSED Roof No.
1 - A polyisobutylene sheet bonded to a supporting
reinforcement m a d e of an elastomer-impregnated, asbestos felt, and topcoated with a white acrylic latex,
2 -
An
asphalt membrane, reinforced with g l a s s fabric and surf aced with a l u m i n u m -metal foil, bonded toa base sheet made f r o m glass or asbestos and saturated with asphalt.
3 - A black bvtyl sheet membrane composed of a c o p o l y m e r
of isobutylene and isoprene, applied t o the substrate with a contact -type adhesive
.
4 - A butyl sheet like the previous one (No. 3) in composl- tion, but white in celour.
5 - A thin-film roofing, produced b y the application of several liquid neoprene coats, and topcoated with successive layers of hypalon (chlorosulphonated polyethylene ).
Roof No.
6 - (a) a two component liquid-applied white rubber, used in conjunction with a silicone p r i m e r ,
(b) a g l a 6 s -fabric r e i n f o r c e d silicone sheet, applied with a contact-type adhesive.
7
-
A cold-process roofing s y s t e m , employing roofing felts, cold-applied s o l v e n t adhesive, and a cold-applied emulsified asphalt
.
8 - A single-ply roofing system, consisting of a white
polyvinyl -fluoride film, factory l a m i n a t e d t o an asbestos f e l t which is impregnated with a neoprene latex.
9
-
A white, liquid-applied, butyl latex s y s t e m , in whichis embedded a reinforcing, lightweight, g l a s s - f i b r e
mat, topcoated with chlorosulphonated polyethylene (hypalon)
.
10 - A conventional built -up membrane consisting of plies or layers of 1 5-pound type saturated roofing f e l t , bonded tagether with hot: asphalt, and topcoated with an application of gravel.
11
-
A
single-ply white roofing sheet, m a d e of ethylene propylene terpolymer,
and applied witha
contact-
type adhe sive,1 2
-
A single-ply sheet material, comprised of a white hypalon topcoating over a thin polyurethane foam backing, bonded to the substrate with an adhesive, METHODOF
APPLICATIONRoof
No.
1Liquid p~l~isobutylene adhesive w a s used t o bond this sheet
membrane to the deck, and the same adhesive, with asbestos f i b r e s
added, sealed the l a p s . A third type of polyisabutylene adhesive was u s e d to adhere the flashing, which consisted of a polyisobutylene sheet welded to a glass-fibre fabric. Finally, the system was painted with
Roof No. 2
T h e b a s e sheet was nailed at 6-in, intervals t o the plywood
deck. The asphalt, on the u n d e r s i d e of the f o i l - s u r f a c e d bitumen
sheet, was then heated almost to melting point with a n air -acetylene
torch, so that an adequate bond to the b a s e f e l t could be achieved. (An alternative method of application would have been to use h o t
m o p p e d asphalt. ) The edges w e r e flashed with the s a m e material.
Roof No. 3
The butyl-rubber sheet was cut to dimension, laid along
the roof deck surface, and d o w e d to relax. Half of the sheet was
then folded back onto itself along i t s l o n g e r dimension, and a c o n t a c t type cement w a s applied to the exposed underside and to the deck
with a r o l l e r . After the adhesive had b e c o m e dry t o touch, the
rubber sheet w a s unfolded back onto the deck, and a r o l l e r was used to smooth the surface of the membrane and e n s u r e a good bond. The
remaining half of t h e membrane was folded back onto the cemented
portion and the preceding technique w a s repeated. A 4-in. overlap
w a s allowed when the second sheet w a s laid; the same materials w e r e used in applying flashings around the edges.
Roof No, 4
This roof was applied using the s a m e technique as t h a t described i n the preceding paragraph.
Roof N o , 5
A thinned solution of neoprene was f i r s t applied to the plywood
deck to a c t as a primer. A f t e r drying, all the joints and flashings of the roof deck w e r e covered with pressure -sensitive cotton tape. T h e s e
tapes, and adjoining a r e a s of up t o 4 in.
,
w e r e coated with the uncutneoprene solution, After a 2 - h r d r y i n g period, the f i r s t neoprene. coat was applied with a b r u s h and roller, at a rate of 25 gal per 1 0 0 s q ft,
t o a wet-film thickness of 8 mils. A cure period of 3 hr was allowed b e f o r e the second application of neoprene w a s rolled on ta a wet-film thickness of 8 t o 1 0 mils, A f t e r drying o v e r n i g h t , the topcoatings of hypalon w e r e applied with s r o l l e r at the rate of l a g a l per 1 0 0 s q f t . The fir s t coat was applied to produce a wet film thickness of 8 mils and the final application was rolled on to a w e t film thickness of 1 0
Roof
No.
6A sheet of glass-fibre reinforced silicone, measuring 3 f t
b y 3 f t , was stuck to one end of the deck with a contact type of adhesive. This portion of the roof w a s exposed without f u r t h e r
t r e a t m e n t . The remainder of the d e c k area, including all the e d g e s
a n d the cant s t r i p , w e r e coated with a silicone primer, A l l joints w e r e sealed with a silicone rubber caulking material. The silicone- r u b b e r roofing mixture w a s prepared by adding 1 part of curing agent
t o 40 parts of the base material; it was applied to all areas other
than t h a t occupied by the silicone sheet. A f t e r an overnight cure, a sec- ond mixture was prepared and applied by roller and brush. This
second coat was cured and the surface was dusted with fine mica.
Roof No.
7
This was a 3-ply roofing system which consisted of 5 3 - l h saturated and coated felts, and a topcoat of asphalt emulsion.
A n u m b e r of
14
f t lengths of the saturated and coated feltswere cut and laid flat for a period of 18 hr. The first strip of f e l t
w a s laid lengthwise along the cant s t r i p i n such a way that it went
over and around the cant strip, and covered a 12-in. width of the deck, It was nailed to the cant s t r i p on 8-in. centres. One qt of cold-process adhesive was applied evenly o v e r this nailed felt, and
a second length, with its edge against the cant s t r i p , was l a i d o v e r the first felt so that it covered a 2-ft width of the deck. Because
this felt w a s t o o rigid to cover the cant strip, the cant was completed
with a g l a s s -fabric and asphalt emulsion. The portion of the felt that
was over the plywood w a s nailed on 12-in. c e n t r e s , and 2 qt of cold- process cement adhesive was applied over this second felt layer. Subsequent sheets, each 3 ft wide, were applied and nailed as before, s o that a 3-ply roof of 53-lb saturated and coated felts was obtained.
Roof
No.
8h this system, a 53-lb saturated and coated base sheet w a s
glued to the deck with an asphalt cold-process cement. The base sheets w e r e lapped 4 in,, and nailed to the deck and cant strip en
1 2 - i n . centres.
The first polyvinyl fluoride-asbestos sheet was then glued Eo the b a s e sheet with the same type of cold-process cement that was used previously. A second sheet, coated with adhesive up to within a n inch of one edge, w a s laid so that it overlapped the first sheet by
p o l y v i n y l fluoride tape, a n d the e n t i r e membrane was rolled to e n s u r e
f i r m c o n t a c t between the surfaces. The roof edges w e r e secured hy f o l d i n g the membrane under the deck and fixing w i t h the pressure- s e n s i t i v e tape.
Roof
No,
9A base coat of butyl latex w a s applied to the plywood roof deck
t o a wet-film thickness of between 1 0 and 15 mils. W h i l e still wet, the r e i n f o r c i n g scrim was laid in and rolled, and a small m o u n t of butyl Latex w a s applied over this glass-fibre mat t o wet it, Flashings f o r the
deck edge and the cant s t r i p were fixed in place with glass scrim
embedded in butyl latex. A 3-hr drying p e r i o d w a s allowed before
it was painted with butyl latex to a wet-film thickness of 1 2 mils. A f t e r another 2 hr had elapsed, a second coat was applied to a wet
-
f i l m thickness of 15 mils. After 72 hours, a third coating of butyl latex w a s applied, a g a i n t o a wet-film thickness of 1 5 mils. Finally,
a f t e r these coats had cured, half the roof was painted with hypalon to
a thickness of 1 2 mils.
R ~ o f
No.
10Two plies of asphalt-saturated r a g felts were first nailed to the deck; n o adhesive was used, Hot asphalt was then employed to adhere
two additional plies ta these nailed felts. The cant s t r i p was covered with rag f e l t ; at three edges of the roof, metal flashing was installed,
and rag f e l t was mopped over this flashing. T o complete the system, a top pour coat of asphalt was spread over the entire roof and gravel was spread onto this hot asphalt,
Roof
No.
11The material f o r this roof w a s rolled out and cut, so that two
equal lengths would cover the deck with a 4-in, overlap; the rnaterial was then allowed to relax. Before applying this membrane, the joints of the plywood deck w e r e bridged with a self -adhering, green, f a b r i c
tape, and the t w o lengths of roof material w e r e put into place along the deck centre-line, One-half of one length was carefully rolled onto
itself, and the r e c a m m e n d e d adhesive was rolled and brushed onto the exposed underside of the roof rnaterial and the corresponding plywood
deck, After the adhesive was considered dry to touch, the material w a s rolled back into place, and the second half of the membrane was adhered following the s a m e procedure, The second length of rnaterial
was applied in a similar fashion with a 4-in, averlap o v e r the first sheet; the e n t i r e roof was r o l l e d and pressed in place. All edges were adhered with the same cement and in s o m e c a s e s tacked with
nails t o ensure a complete bond. Roof
No.
12This roof w a s installed on site, over a plywood deck during a
s u m y , windy d a y with the temperature at 65'F. Four sheets were
cut ta 15;-ft lengths, which allowed t h r e e lap joints of 2-in. each
and enough material at all ends to permit a f o m - f i t around and under the edges. Guide lines were scribed lengthwise on the deck to ensure
the correct placement of the material, and a continuous coating of
special field adhesive was applied over the deck, W h i l e it w a s still w e t , the 4 lengths of sheet roofing w e r e embedded into it. A s p e c i a l l a p cement secured the lap-joints, and the field adhesive glued the sheet m a t e r i a l t o the fascia b o a r d . A wood trim was nailed over
the r o o f i n g material into the fascia board, and the e x c e s s roofing was
trimmed.
VISUAL EXAMINATION O F ROOFS
The first 1 1 experimental roof decks w e r e combined to f o r m
a continuous roof which was secured approximately 6 f t off the ground.
A wooden platform was constructed along one entire length which allowed shoulder height observation and photographs at periodic intervals.
W i t h one exception,
(No,
121, none of the roods tested encloseda heated space, and therefore the exposure i s not considered to be as s e v e r e as that encountered in normal usage. The decks were, however,
of a lightweight mate rial which would tend t o permit greater deflections
than normal. In addition, these roof surfaces w e r e initially subjected
to considerable foot traffic from interested visitors.
The following visual observations d e s c r i b e the performance of the f i r s t 10 roof systems o v e r a 5-year exposure period, Roofs Nos.
1 1 and 12, a l s o d e s c r i b e d here, were installed 3 years l a t e r than the
p r e v i o u s systems, and consequently their performance results are b a s e d on only 2 y e a r s of exposure.
Roof No. 1
After
6
t o 8 months exposure, small hairline cracks appearedw a s very pronounced after 2 years and there was s l i g h t damage d o n g the f r o n t edge. After 5 year's exposure, this effect had increased so that the distance between each hairline crack was reduced f r o m
$
i n .to
a
in, ; this cracking did not, however, appear to a f f e c t the polyiso- butylene sheet. Some small portions of the topcoat w e r e beginning to peel and the adhesive at the centre overlap had failed f o r a distance of1
approximately 10 in, to a width of 2 in. S o m e blistering along the cant strip, and s o m e slight chalking was observed, but t h e r e appeared
t o b e only s l i g h t d i r t retention. Roof N o , 2
S l i g h t dulling of the aluminum-foil surface had taken place by the end of the first 1 2 m o n t h s of exposure. After 2 years, the glass reinforcement at the lap was beginning to show; 3 m o n t h s l a t e r there
w a s a s l i g h t l o s s of bond in t w o locations on the lap joints, 4 f t apart. The find observation after 5 y e a r s of exposure s h o w e d some l o s s of adhesion in. inward on the overlap section covering the c a n t strip,
in addition to 3 l a r g e ridges running perpendicular to the length of the
deck. There were a l s o 8 ridges I - i n , wide running across the width,
Surface dulling was moderate and d i r t retention moderately high in an a r e a w h e r e water ponding took place,
Roof
No.
3A f t e r 1 0 months, the centre-lap joint began to l i f t slightly.
T h i s l o s s of bond was more noticeable after 2 y e a r s when the l a p
had lifted approximately
x
J 8 in. along the length of the lap. By then,there was also a lightening of colour and a small crack at the front
of the cant. A f t e r 5 years, the l o s s of bend along the lap joint had increased to a maximum depth of 1 in., chalking w a s of medium intensity, water staining along the l o w edge was severe, two nails
from the deck had lifted but had not penetrated the butyl sheet, and the averlap at one of the corners of the cant strip had lost its
adhesion, Roof No. 4
A f t e r 2 months, slight surface chalking was noticeable. At the end of 4 months, this effect was considered pronounced, and with
2 month" additional exposure, the chalking was washing over the
edge of the roofing. A f t e r 2 years there was a loss of bond at the centre overlap and d e f e c t s in the membrane w e r e quite noticeable; chalking continued t o be severe with large amounts of was h-off
5 years, adhesive failure had begun along the centre overlap to a
1
d e p t h of approximately y in., and surface defects in the form of $-in. long, oblong craters w e r e spread over the whole surface although not
penetrating the butyl sheet. A long crack along the f r o n t edge had
resulted in the separation of the deck and edge covering. A deep crack
had also developed along the top edge of the cant strip.
A s noted, it b e c a m e evident i n the e a r l y stages of this exposure
program that a major problem with the material was its s e v e r e chalk- ing characte ristic s, The manufacturer s submitted a second sample
that had been chemically modified i n an attempt t o irnprove the materialt s
resistance t o chalking; in a f e w months, however, it too had chalked heavily ,
Roof No. 5
Some minor cracking had developed i n this coating immediately following its application and before exposure, but it had b e c o m e no w o r s e after 1 yearts exposure, After 2 years, the flashing tape split
in two places and other small splits appeared on the cant strip, the surface was dirty, chalking had begun and a few of the nail heads under the roof material w e r e showing through. Six months later, the splitting
which ran along the long dimension of the deck, had become pronounced
and the membrane had opened at an edge (due to splitting) which allowed
water to enter the deck. After 5 y e a r s , s e v e r a l cracks had developed along the cant strip 1 to 2 in,
in
length, These cracks allowed w a t e r entry, and caused l o s s of adhesion along the length oaf the cant strip. Several nails pushed through the membrane with resulting r u s t stainsaccentuating the d i r t accumulation on the low side. The topcoat had cracked to moderate severity.
Roof No.
6
After 2 months, the sheet-applied system showed high d i r t
retention and a few small b l i s t e r s whereas the liqmid-applied material
did not appear to have changed, but after an additional
6
months e x -posure, both systems w e r e high i n dirt retention.
h
12 months timethis
effect w a s rated as severe. After 2 years, some l o s s of adhesion w a s found at the areas adjacent to the portions that had sufferedmechanical. ruptures. After
5
years, the sheet-applied partion of thisroof showed signs of heavy erosion, The entire roof was v e r y d i r t y and adhesion was poor near the damaged areas.
Roof No. 7
A f t e r 1 y e a r , slight chalking of the surface was noted. A f t e r
L
22 year" exposure, some damage t o the leading edge of the surface had occurred as a result of o b s e r v e r s climbing onto t h e roof, No f u r t h e r changes had occurred at the end of the 5-year period.
Roof
No.
8A f t e r 2 months, t h e r e was slight shrinkage of the tape at the joint. Except f o r the above-mentioned effect t h e r e was n o change after
1
2 2 years of exposure, After 5 years, t h e r e was a s l i g h t loss of gloss,
a f e w punctures in the topcoat (which appeared to have been the result
of mechanical damage) and a moderate l o s s of adhesion at the edges of
t h e centre tape. Roof No. 9
After 2 months, that portion not covered with hypalon showed slight d i r t retention. A f t e r 4 months, this d i r t staining on the butyl-
latex portion had b e c o m e quite severe, and the g l a s s scrim on the cant strip had pulled a w a y from the cant. T h e r e was a l s o some fracture of
the butyl-latex glass-scrim membrane at the edge w h e r e it had received w e a r from traffic. A f t e r 2 years, cracks had developed on the cant
strip. Three months Later, a crack appeased over the joint in the
substrate. The uncoated, butyl-latex p o r t i o n o f this test s m p 1 ~ appeared quite porous, and a large n u m b e r of holes w e r e evident.
After 2; y e a r s , it was observed that t h i s porous uncoated a r e a w a s allowing water penetration. After 5 years, w a t e r was getting into
t h e deck through the cracked joint, s e v e r a l small crater -like d e p r e s s ions
had a p p e a r e d over m o s t of the hypalon-coated area, and there w a s severe e r o s i o n of the uncoated butyl-latex portion.
Roof No. 10
After 2 months, s o m e gravel blow-off had occurred, and in
a few small areas of the roof, asphalt had bubbled through the gravel.
A f t e r 2 year's exposure, this bubbling effect was no w o r s e than slight. A f t e r 5 years, it was noted that there w a s some bubbling of
bitumen along the cant strip and o v e r a sizeable portion of the roof, notably over the joints i n the deck.
Roof No. 11
A f t e r 2 years of exposure, t h i s roof s u r f a c e had b e c o m e covered
w i t h black spots, approximately 1/8 in. in diameter, that appeared t o be a f o r m of mildew or fungus. There w a s moderate d i r t retention and
some dulling of the surface. Roof No. 12
A f t e r t w n y e a r ' s exposure, the white surface had hecome s l i g h t l y
d i r t y , and the lap j o i n t s showed just the s l i g h t e s t loss of adhesion.
DISCUSSION
A t a t d of 12 roofing systems w e r e exposed to outside conditions
f o r 2 or 5 years, 10 of the samples receiving the full 5-year exposure.
This p r o g r a m was considered t o be of sufficient duration to offer some indication of the service life that c a n be e x p e c t e d of the materials if installed i n the conventional manner, i . e . , w i t h the membrane un-
protected by insulation.
It:
should be mentioned that many of t h e samples investigated were experimental, and that some a r e no longer available at l e a s t i n the f o r m in which they were exposed,The performance of some of the new roofing s y s t e m s might suggest that their employment he specified only with g r e a t caution.
It w a s noted, however, that the principal f a i l i n g s in m a n y of these
systems w e r e the adhesives u s e d at the overlaps and f l a s h i n g s , and the
t h i n liquid-applied top-coatings which u n d e r w e n t r e l a t i v e l y rapid
f a i l u r e . W h i l e fully cognizant of their f a i l i n g s , one might still elmploy
t h e s e materials because of their distinct advantages: the o m i s s i o n of
g r a v e l from the membrane surface which simplifies inspection and
maintenance of t h e roof, and the fact that several of these materials
a r e acceptable bases f o r reflective and decorative coatings. F u r t h e r - m o r e , the e a s e of application of some of the liquid -applied r ~ o f i n g
systems make them especially suitable f o r membranes f o r i r r e g u l a r l y shaped surfaces. Finally, the light weight of these new roof coatings
could o f f e r appreciable relief to a building" s t r u c ~ r a l requirements. Some degredation of the surface of the materials, such as that
noted i n the white butyl sarmplc, could be t o l e r a t e d i f the wash-off
w e re not allowed to d i s f i g u r e the building's facade, The polyis obutylene s y s t e m s u f f e r e d marked cracking of i t s reflective, acrylic topcoat, but the sheet material itself appeared t o be in excellent condition,
I£
thiss y s t e m , t h e n , w e r e i n s t a l l e d i n an e a s i l y accessible area, periodic
recoating would probably ensure satisfactory performance for m a n y years.
It should a l s o be pointed out that the u s e of these materials d o e s not eliminate factors such as building movement, trapped moisture, and poor workmanship, which can cause failure in any
roof system i f they have not been taken into account by the d e s i g n e r .
CONCLUSION
The use of some of these new roofing membranes could be restricted to satisfying certain specific requirements; this exposure
program has shown, however, that of the I Q systems exposed f o r
the 5-year period,
4
a r e performing in a superior manner and might,therefore, receive wide application. These a r e the f o i l -surfaced bitumen sheet (No, 2 ) , the cold-process asphalt roofing ( N o . 71, the
polyvinyl fluoride -asbestos sheet (No. 8 ) , and the hot asphalt b u i l t - up roof (No. 10). Both of the roof systems that have been exposed f o r the 2-year period seem to be performing well and as y e t there is no evidence to suggest premature failure.
[>\. ..,.,,.,,,?,,;:!-
' I . .
ROOF
NO. 1-
5
years exposure:severe hairline cracking,
ROOF
NO. 2-
5 y e a r s exposure:slight dulling and s o m e ridging.
R O O F NO. 3
-
5 years exposure: colour change,
chalking andROOF
NO.
4-
5 y e a r s exposure: severe chalking, splitting and che cking ,ROOF
NO.5
-
5 years exposure: cracking and splitting.I
, ..,
ROOF
NO. 6-
5 y e a r s exposure: heavy d i r t deposition and surfaceROOF
NO. 7 - 5 years exposure:s l i g h t chalking.
ROOF
NO. 8-
5 years exposure: kos s af adhesion at taped joint.ROOF NO.
9-
5 years exposure: membrane cracked, severesurface erosion, and heavy d i r t
