NATIONAL BUREAU OF STANDARDS REPORT

7489

] PERFORMANCE OF ROOFING IN PUERTO RICO

by

William C. Cullen

and

William W. Walton

<3JBS>

II. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1004-12-10447 20 April 1962 7489

PERFORMANCE OF ROOFING IN PUERTO RICO

by

William C. Cullen

and

William W e Walton

Organic Building Materials Section

Building Research Division

Sponsored by

Office of the Chief of Engineers

Department of the Air Force

Bureau of Yards and Docks

NATIONAL BUREAU OF STANI

Intended for use within the Go^

to additional evaluation and revi listing of this Report, either in v the Office of the Director, Natioi however, by the Government agi

to reproduce additional copies f

IMPORTANT NOTICE

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 2015.

jress accounting documents

lly published it is subjected

roduction, or open-literature

i is obtained in writing from

:h permission is not needed,

pared if that agency wishes

<NBS>

li. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

PERFORMANCE OF ROOFING IN PUERTO RICO

1 . INTRODUCTION

The many problems involved with roofing materials and systems exposed to

tropical conditions has long been recognized by the construction agencies

of the Defense Department. Heretofore, little information has been

available regarding the performance of roof systems in the tropics to

assist those charged with design and maintenance responsibilities. Therefore, in response to request of the Bureau of Yards and Docks, U. S. Navy;

Directorate of Civil Engineering, U„ S. Air Force; and the Office of the

Chief of Engineers, U. S. Army, a study of roofing was conducted on the

island of Puerto Rico as a task under Project No. 10447, "Performance of

Roofings" of the Tri-Service Engineering Investigations of Building

Construction and Equipment, NBS.

This report gives the results of the performance of the various roof systems

which are employed on both military and civilian structures. In addition,

it identifies the failures which are common to roofs in the area and describes

the maintenance and repair methods employed to keep the roofs in a serviceable

condition.

The survey of roofing was conducted on March 20 through March 24, 1962,

primarily in the vicinity of the cities of San Juan and Ponce, Puerto Rico.

The following Military Installations were included in the survey:

Fort Buchanan, San Juan, P. R.

U. S. Naval Station, San Juan, P.R.

Naval Communications Station, Sabana Seca, P.R.

Fort Brooke, San Juan, P.R.

U. S. Naval Station, Roosevelt Roads, P.R.

Fort Allen, Ponce, P.R.

Personal contacts were made with contractors, military and civilian engineers,

and with maintenance personnel experienced in the performance, construction

and maintenance of roofing systems in the Puerto Rico Area.

1 / 2 . CLIMATE*1'

The climate of Puerto Rico is tropical marine, slightly modified by insular

influences when land breezes blow. Radiational cooling frequently causes

land breezes at night; consequently, somewhat lower night-time temperatures

uSource: Weather Bureau, U. S. Dept, of Commerce Local Climatological Data,

San Juan, Puerto Rico, 1961.
!
2

occur than would normally be experienced with sea breezes. The air drainage

from the higher altitudes (peak elevation 4,000 ft.) gives relatively cool

night breezes during December, January, and February.

Characteristic of all tropical marine climates, the coastal areas of

Puerto Rico have a small annual range of temperature. The difference between

the average temperature of the warmest and coolest months is only about

5.6°F. This is also true concerning the absolute range of temperature.

The highest temperature of record is 96°F. and the lowest 62°F.

The coastal areas of Puerto Rico have an average rain fall of 60 inches per

year with a fairly even distribution throughout the year. Rainfall is

generally the showery type, except for continuous rains which occur in

connection with the passage of tropical storms.

Puerto Rico is in the tropical hurricane region of the eastern Caribbean

where the season for these storms begins June 1st and ends November 30th.

Several hurricanes affect this area every season, but weather records show

that only five of these storms have caused winds of hurricane intensity

in the San Juan area during the past 50 years.

The normals, means, and extremes for temperature, precipitation, wind, and

humidity in San Juan, Puerto Rico, are as follows:

Temperature: Normal for year, Daily - max. 82.8°F.

Daily - min. 73.2®F.

Precipitation: Normal Total for year - 60 inches.

Wind: Mean hourly speed for year - 8.4

Relative Humidity: Mean for year at 2:00 A.M. - 877.

at 8 :00 A.M

at 2:00 P.M,

at 8:00 P.M

3. ROOFING SYSTEMS

A number of roofing materials and roof systems were observed during the

survey and it is believed that the following types are typical of a large

percentage of the roofs used on structures in Puerto Rico.

- 3

-

3.1

Exposed Concrete Slabs

The predominate type of roofs employed on both civilian and military residential

structures in Puerto Rico was reinforced concrete slab. The thickness of

the roofing slabs varied from 3 to 6 inches with the 4- inch slab being the

most common. Figures 1 through 4 illustrate typical residential structures

which were protected with exposed concrete roofs. In addition, exposed slabs were often employed on relatively large roof sections, such as the family

housing structure illustrated in Figure 5. Generally, the slope of the

roof decks varied from level to about one inch fall per foot run. In some

cases, exposed slabs were used on structures of modern architecture with

almost vertical slopes, as on the cathedral illustrated in Figure 6. The

exposed slabs were either broom- or steel-trowel finished depending on the

surface desired. In many cases, the surface was coated with various materials

to provide solar reflectivity and/or for aesthetic reasons.

3.2

Built-Up Roofs

Conventional 4- or 5-ply, surfaced, built-up roofs were used to protect both

military and civilian structures where it was not practicable to utilize

the monolithic concrete deck. This was generally true of industrial

installations, shopping centers, and on large military structures where

precast concrete slabs or wood planking were employed for the roof deck.

The built-up roof was also used to repair exposed concrete when it became

uneconomical to isolate and repair cracks in the deck. A typical structure

employing such a roof is shown in Figure 7.

3.3

Metal Roofs

Corrugated metal roofings were quite often observed on relatively steep

roofs (slopes in excess of 3 in. per foot), on temporary military structures,

on warehouses and factories, and on extremely low cost housing.

3.4

Asphalt Prepared Roofings

The use of "wide selvage", mineral-surfaced, prepared roofings was observed

on some military structures at Fort Buchanan, Fort Allen, and the Naval

Station, Roosevelt Roads. Prepared roofings were generally restricted to use on temporary buildings having wood decks with a slope of approximately

5 inches per foot.



3.5 Miscellaneous Roofings

Roofing systems other than those described above, which were observed with

a passing interest, included:

a. Thatched roofs

b. Asbestos-cement roofs

c. Mission tile

d. Bituminous protected metal

4. OBSERVATIONS

4.1 Exposed Concrete Slabs

4.1.1 Performance

Exposed reinforced concrete slabs were used for roofs in many areas of Puerto

Rico and had apparently performed very satisfactorily. It was reported and

confirmed by observation that no leakage or seepage occurred in the slabs

unless some defect such as a crack was present. However, the inspections

revealed evidence that few exposed concrete slabs on military structures

escaped cracking to some extent. One of the common difficulties which was encountered in the construction of the concrete buildings was the attainment of a sufficiently stable foundation to prevent cracks in the roof

slab due to the unequal settlement of load-bearing walls. Typical cracks

which were observed on Officers’ Housing, Fort Buchanan, and attributed

to the unequal settlement of foundations are illustrated in Figures 8 and

9. It was reported that cracking also resulted from shock due to blasting

in the vicinity, shrinkage, and from thermal stresses and movements due

to temperature changes.

The exposed slab of one relatively large structure (EM Barracks, NCS,

Sabana Seca, P.R.), illustrated in Figure 10, was relatively free of

cracking and the occupants reported it to be watertight. This two-story

structure was of reinforced concrete construction and was built in 1952.

The roof slab had a broom finish. A biological growth, common to the

exposed roofs in Puerto Rico, contributed to the dark roof surface, as shown in the photograph.

In cases where multiple roof levels were employed, some trouble was encountered at the junction of the deck with the vertical surface. A

grout coating of concrete was unsuccessfully employed to remedy this

condition. Cracking, as illustrated in Figures 11 and 12, soon developed

and, in addition, the adhesion between the grout and the dense concrete

was poor and water was invariably found in that area. Interior examinations

generally revealed leakage in these areas.





5

Obviously, the most serious problem involved in keeping the exposed slabs

watertight is the development of cracks. Therefore, the methods and

remedies set forth for the repair of cracks have been many. For examp le,

it was reported that a method effectively employed by the natives to

render a cracked slab waterproof was the application of a boiled G.I.

soap solution. We were unable to confirm the effectiveness of this

procedure. Among the more conventional methods used to repair cracks

were the following:

A. Grouting with Concrete .

This method consisted of applying a cement grout directly over the crack,, as illustrated in Figure 13. Our observations indicated that this method

was not effective due to the poor adhesion to the dense concrete deck.

On the other hand, if proper adhesion was obtained it is predicted that

the crack in the substrate would soon be transferred to the patching

compound due to its relatively poor elasticity.

B. Plastic Cements and Other Mastics .

This method consisted of applying a bituminous plastic cement, caulking

compound, or other mastic directly over the crack. These methods

appeared to be adequate for temporary repair only (less than one year).

It was apparent that these materials oxidized, cracked, and lost their

adhesion to the substrate. These defects were observed in such systems

after less than 6 months exposure.

The patching of cracks with an elastomeric type of material was observed

at the Naval Station, Roosevelt Roads. This system was performing quite

well after three months exposure which, obviously, was too short a period

for evaluation.

C. Bituminous Material and Reinforcing Medium.

The repair method consisted of applying a mastic (bituminous emulsion,

asphalt plastic cement, or proprietary materials of similar viscosity)

over the crack and extending 4 to 6 inches on both sides of the crack.

A reinforcing strip (generally woven glass fabric or glass mat) was embedded in the mastic and coated with a similar material. A typical

roof employing such a system is illustrated in Figure 14.

This method of crack repair has proven the most successful of the many

methods tried. However, it has many limitations. Our observations

indicated that movements in the deck at the crack due to expansion and

contraction sometimes resulted in a break in the system over the crack.

In addition, poor adhesion between the fabric and the deck was observed,

indicating poor preparation of the surface.

'

.5

m

m

6

D. Repair Membrane Over the Entire Roof .

The application of a waterproof membrane over the entire deck was deemed

necessary in cases where the cracks became so numerous that the isolation

and the repair of each individual crack became uneconomical. A case in

point was the Lanham Act Housing at Fort Buchanan. This development was constructed in 1940 and consisted of 200 units in 25 two-story buildings,

one of which is shown in Figure 5„ The exposed concrete slabs performed

adequately until 1957, when due to the high maintenance cost of crack

repair and the relative ineffectiveness of the repair, a complete roof

system was applied. The roof system consisted of asphalt emulsion (5 gal.

per square) - glass mat combination, followed by a reflective aluminum

coating. It was reported that leakage has almost been eliminated with

this repair system.

Our observations indicated the condition of the membrane was good after

five years exposure, as shown in the general view in Figure 15. Two

deficiencies were noted in the system. Ruptures of the membrane, as illustrated in Figure 16, were observed in two areas. However, these

cracks were not typical of the irregular cracks generally found in the

exposed decks. Therefore, they were attributed to other causes. In

addition, many blisters were observed which ranged from a few inches in

diameter up to 15 inches or more, as shown in Figure 17. The blisters

apparently occurred between the deck and the membrane and were possibly

caused by poor preparation of the surface prior to the application of the

membrane. The blisters have caused no particular problems and, therefore, no action to eliminate them is indicated at this time.

The aluminum coating had weathered to a dull finish exposing the bituminous

material in some areas and its condition after 5 years exposure indicated

that additional coatings are warranted.

4.1.2 Coatings for Exposed Slabs

Protective coatings of various types were observed on many of the exposed

slabs. These materials were, in many cases, employed for aesthetic

reasons, but were primarily used to reduce temperatures by reflecting solar

energy and, therefore, were pigmented white, alumimum, or other pastel

shades. The use of these coatings apparently had little effect on the

waterproofness of the slab. However, it was obvious that the lightcolored coatings exerted a dominate influence on the temperatures attained

by the slab. There is a tendency to think of unpainted concrete slabs as white in color, but this is not true in Puerto Rico where exposed slabs

are quite dark due to biological growths, as illustrated in Figure 8.

As would be expected from a wide variety of coatings, the performance varied

from poor to good and it is felt that the type of material, the quality and

quantity used, and the proper preparation of the substrate are of great

importance. Experience should be used to dictate whether a particular

material will perform adequately.

The performance of an elastomeric type of coating identified as "Hypalon"

(a chlorosulfonated polyethylene roofing solution) was observed on the

parabolic roof of the Santa Maria Reina Cathedral in Ponce, P.R.,

shown in Figure 6. The roof consisted of a 3-inch reinforced concrete

shell supported by a series of 54-foot span cantenary arches and had

an area of about 240 squares. It was reported that two coats of "Hypalon"

were applied by conventional pressure pot-spray equipment in January 1957.

Our observations indicated the material had weathered quite well and no obvious defects were observed after 5 years exposure. A general view

showed a somewhat mottled appearance indicating either unequal coverage

or unequal weathering. It was felt that an additional application of the

material should be applied in the near future.

4.2 Built-Up Roofs

Although it was reported that both asphalt and coal-tar-pitch built-up

roofs have been employed in Puerto Rico, only surfaced asphalt roofs were observed. As previously indicated, this type of roofing was used

where it was impracticable for one reason or another to leave the slab

exposed

.

It was interesting to note that roof insulation was seldom used in the

Puerto Rico area.

The built-up roof protecting the Public Works Shop Building, Roosevelt

Roads, was the oldest built-up roof observed. It was a 5-ply, surfaced,

asphalt built-up roof applied in 1941 over a 2-inch T & G wood deck on

a low slope (approximately 1/4 inch per foot).

The appearance of this roof was good after about 20 years exposure, as shown in Figure 18. An examination of the asphalt showed it to be

very hard and brittle even at the high temperature of the roof. However,

there were no other signs of deterioration and it was apparently performing its basic function. The only defects observed were a number

of bare areas where the felts were exposed. Some 41 leaks were reported

in this roof. However, our observations indicated that most, if not all,

of the leaks resulted from defective flashings, as shown in Figure 19.

Obviously such deficiencies could be prevented by adequate and timely

maintenance.



8

In our opinion, this roof could be expected to perform for another 10 years

with adequate repair and maintenance procedures. The performance of this

roof compares favorably to the performance of similar roofs in the

continental United States.

Built-up roofs used to render cracked slabs waterproof were also observed

on residential buildings at the N.C.S., Sabana Seca, P.R., illustrated in

Figure 7. The membranes were applied in 1961 to the main roof sections

,

as shown in Figure 20. The roofs were in excellent condition and were watertight. However, some leakage was still apparent in the interior.

It, no doubt, resulted from cracks observed at the angles formed by the

intersection of the roof slab with vertical surfaces.

An examination of the asphalt revealed it to be very soft (135°F Softening

Point or less) at roof temperatures. The use of this soft material

between the deck and the first ply of felt resulted in an asphalt

drippage through a crack in the slab. This, of course, was a matter of some concern to the building occupants.

4.3

Metal Roofing

Corrugated, galvanized steel roofing was observed on many temporary

structures and low-cost housing (slum areas). This material had apparently

given good service on sloping roofs with little maintenance. It was reported

that wind damage was common to this material during the heavy winds in

connection with the passage of tropical storms.

4.4

Prepared Roofings

In the course of the survey, a few "wide selvage" asphalt-prepared roofs

were observed on sloping roofs (5/12 slope) on one-story temporary

structures at both Fort Buchanan and at Roosevelt Roads. Our observations

indicated that this type of roofing gave adequate service for approximately

10 years in the Puerto Rico area.

Asphalt shingles were not observed, but it is predicted that they would

perform at least as well as the "wide selvage" roofing on relatively steep

slopes, if they were adequately protected from wind damage.

4.5

Miscellaneous

Various roofing materials other than described above were observed with only

a passing interest. No attempt is made here to describe their advantages

and limitations.

9

5. DISCUSSION

The majority of roofs used by the military on Puerto Rico consisted of either

the exposed concrete slab or the mineral-surfaced, built-up roof. Therefore,

this discussion will be limited to the two systems.

The exposed concrete slabs have performed very satisfactorily on roofs of

low slope (0-2 inches per foot) in the Puerto Rico area. However, our observations indicated that cracks resulting in leakage occurred in the

slabs and can be attributed to one or more of the following events:

a. Foundation settlement

b. Shrinkage

c. Thermal movements and stresses

d. Effects of blasting

e. Substandard concrete.

Some of the factors can be controlled to some extent, while others cannot.

For example, defects due to shrinkage and substandard materials may be

reduced somewhat by proper design and construction practices combined with

adequate inspection during construction. Further, the initiation and

propagation of cracks due to thermal movements and stresses may be reduced

by the proper selection and application of a heat-reflective coating. It

is our opinion that the thermal movements are quite large on exposed slabs

in Puerto Rico due to the dark color resulting from the biological growth

and therefore, the application of a reflective coating would prove effective.

Some methods have been discussed by which cracking may be reduced, but it

is extremely doubtful if cracking can be entirely eliminated. Therefore,

methods of repair to render the cracks leakproof are considered essential.

The repair of cracks may be accomplished as follows:

a. Isolate and repair each individual crack.

b. Application of a waterproof membrane to the entire roof.

It is felt that the former method should be employed as long as it is

economical. Now the question arises, when does it become uneconomical to

isolate and repair the existing cracks? This point we cannot define.

It is suggested that an analysis of repair and maintenance costs to keep

the slab leakproof together with the opinion of competent engineers at

the camp, post or station involved should largely govern.

10

In regard to crack repair, it is our opinion that the one-component systems,

such as cement grouts, various bituminous mastics, and cauling compounds,

generally have not been satisfactory except as temporary expedients. It

is felt that a reinforcing medium in conjunction with a suitable mastic,

emulsion, or plastic cement offers the best possibility of permanent

repair. The selection of both the reinforcing medium and waterproofing

agent should be based on past experience or research, where experience

is lacking.

In connection with crack repair, we are of the opinion that the placement

of a 2- to 3-inch wide paper or plastic strip over the crack prior to the

installation of the repair system will permit the stresses set up by

movement in the slab to be distributed over 2 or 3 inches of the repair

membrane instead of in the very small area above the crack. This system

should prevent premature cracks in the repair system.

The installation of a waterproof membrane over the entire exposed slab is

indicated when the isolation and repair of cracks becomes uneconomical.

The selection of the type of membrane will be influenced by the type of

structure, and its predicted future life and use. In the case of

permanent structures, the 4- or 5-ply, mineral surfaced, built-up roof

appears to be the logical selection and, based on past experience, should

provide 20 or more years of service. The type of bitumen selected for

these roofs should be commensurate with the slope of the roof and precautions should be taken to prevent drippage through existing cracks to

the interior.

A more economical repair system may be indicated depending on the type

and future use of the structure. In this case, the membrane, consisting

of the glass mat or woven glass fabric-asphalt emulsion combination, has

given adequate service. This membrane should be further protected with

a reflective coating compatible with the asphalt emulsion. Best results

are usually obtained by allowing the emulsion to weather 3 to 6 months

prior to the application of the reflective coating.

No doubt, there are other systems which may prove satisfactory in this

capacity.

The conventional 4- or 5-ply, bituminous, built-up roof, surfaced with

gravel, has performed very well over wood decks, precast concrete slab

decks, and other decks having many joints, and the continued use of

these roofs in these situations appears warranted.

11

6. CONCLUSIONS AND RECOMMENDATIONS

(1) Exposed reinforced concrete slabs have provided excellent service on both military and civilian structures in Puerto Rico.

(2) Built-up roofs should be employed only where the use of the exposed

concrete slab is impracticable.

(3) The conventional surfaced, built-up roofs have provided excellent

service both as new roofs and as repair membranes for defective

exposed slabs.

(4) Mineral-surfaced prepared roofings will provide approximately 10 years

of adequate service on sloping roofs.

(5) In the warm, humid climate of Puerto Rico, concrete slabs become

quite dark due to biological growths on the surface and, therefore,

reflective coatings should be employed to reduce thermal movements

in the slab.

(6) Methods for the repair of cracks in exposed slabs should be investigated,

since experience has indicated cracking will occur in such slabs. A

system for providing the distribution of stresses over larger areas of

the repair membrane should be investigated.

(7) Repair methods employing a mastic and reinforcing medium have proven

most successful.

(8) A membrane type roof should be employed when it becomes uneconomical

to repair cracks. The type of roof should be determined by the type

and future use of the structure.

7 . ACKNOWLEDGMENT

The cooperation and assistance provided to the authors by Mr. Raymond Angueira

and other members of the Design Division, Caribbean Area Public Works Office,

U. S. Naval Station, San Juan, are greatly appreciated.

USCOMM-NBS -DC

II. S. DEPARTMENT OF COMMERCE

Luther II. Hodges, Secretory

NATION AL HL’RKAT OF STANDARDS

A. V. Aatin, Director

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