The application of hot asphalt to built-up roofs has traditionally been done with cotton mops. Old timers prided themselves in their selection of cotton and their skill at making their own mops. In the old days cotton was purchased by the hank, bundled together in large bales. Today cotton may be purchased either as ready-made mops or in the traditional hank to be made into mops on "rainy days." Owens Corning's development of fiberglass created the possibility of substituting fiberglass in place of cotton for hot mopping roof decks. The first use of fiberglass for hot mopping a roof was implemented shortly after the second World War. The immediate benefit of fiberglass as a roofing mop is its longer life due to its heat resistant qualities.

The acceptance of fiberglass roofing mops has been slow; today however, fiberglass mops are used on one-half of all roofs hot mopped in United States. The change from cotton to fiberglass by roofers is occurring more rapidly today and forecasts predict that within another decade most roofers will have been exposed to fiberglass roofing mops and will make the change from cotton to fiberglass. The following information will examine both cotton and fiberglass roofing mops and will present information that will enable one to see the benefits of using fiberglass roofing mops.

Cotton is an organic fiber that is tough and absorbent. The use of cotton as a kitchen mop easily demonstrates these qualities. For roofing, a 2 1/2 lb. cotton mop is the average. Cotton mops, however, do range in size from 1 1/2 to 5 lbs. The durability of a cotton hot mop is solely dependent upon the quality of the cotton and the temperature of the asphalt. Cotton varies from very soft to hard; the latter more durable in hot asphalt.

A major portion of hard cotton in the past was scrap cotton obtained from the tire cord manufacturers. Today, there is little demand for cotton tire cord; therefore, there is little hard cotton scrap for roofing mops. This greatly increases the cost of good hard cotton. Softer cotton is generally what the roofer must use.

Most of the cotton roof mops today are made from scrap from the garment industry. For instance, a blue cotton roofing mop is scrap from the blue denim clothing industry. To make the situation even worse, the clothing industry is using more and more cotton blended with synthetic fibers. When this material is used for hot mopping it burns faster than pure cotton would.

After a short time in hot asphalt, cotton starts to char and burn. The cotton strand will separate near the top of the mop hear, leaving long and undesirable strings of cotton on the roof deck. A roofer may use 2 to 5 cotton mops per day, per hot crew, depending upon the quality of the cotton and the temperature of the asphalt. The cost and availability of cotton for roofing mops is dependent upon the quality of the yearly harvest and the demands of the different major cotton markets.

WEARING... As a roofing mop, however, fiberglass must wear out rather than burn up as does a cotton mop. This enables a roofer to re-use a fiberglass mop for several days. The length of time a fiberglass mop can be used depends upon the surface being roofed and the type of fiberglass material used in the mop. Since fiberglass has low abrasiveness, rough surfaces tend to increase wear more so than smoother surfaces. Fiberglass wears at the end of the strand, becoming shorter until there is not enough length for good pick up or spread. The more heavier plied fiberglass wears longer than lighter plied yarn or roving.

PICK-UP... Since fiberglass is non-absorbent, asphalt is retained within the mop through surface tension. Because the heavier plied strands have less surface area pound for pound than lighter plied yarns and roving, pick up and wear are opposed to each other. Heavier plied yarns either sacrifice pickup or require more strands and consequently more weight to match the pickup of lighter plied strands. On the other hand, lighter plied yarns and roving, because of their increased surface area, have high pickup but wear out faster. A practical solution to this problem is to mix these materials to reduce wear and increase pickup as much as possible.

Pickup... can be further increased if the fiberglass strands are spaced apart so that there is room for the asphalt to bridge from strand to strand. This principle can be easily observed through an examination of a paint brush. The bristles are spaced so that paint is suspended in between the rows of bristles.

FLOW... Because fiberglass roofing mops are non-absorbent, they allow asphalt to flow off the strand easier than cotton. This coupled with fiberglass' ability to conduct heat provides a more uniform flow and distribution of asphalt on the roof deck.

CONSTRUCTION... Fiberglass roof mops are made in a variety of types. Many of the first were designed like cotton mops. Because fiberglass and cotton are not similar materials, this created many unsatisfying experiences for the roofer. Today relatively little fiberglass is sold in hanks, primarily because of the difficulty of securing the fiberglass to the handle. Some of these old traditional methods of mop construction allowed the more slippery fiberglass to string out all over the roof. The more sophisticated fiberglass mops today use newer methods of construction which overcomes these past problems.

Today there are two major types of fiberglass roofing mops. The first type is composed of rings or grommets which hold approximately one pound of fiberglass. These are then slipped on to a metal sleeve and compressed together to form a mop. This type of construction allows a roofer to make whatever size mop he chooses. Roofers are also able to add rings as the mop wears down, enabling them to have a more consistent day-to-day performance.

Most manufacturers of ready-made fiberglass mops have attempted to create something unique about their mops. Some have focused upon increasing pickup while others have worked to increased the life of the fiberglass roofing mop. Kirby Fiberglass, Inc. has worked to increase pickup and yet maintain long life by using a combination of fiberglass strands in the mop.

SELECTION... Choosing the style of fiberglass mop that best meets the needs of the roofing contractor is determined by many factors: personal preference, number of crews, type of roof (new or re-roof). About 80% of the roofing contractors prefer ready made pinhead fiberglass mops. The rest of the roofing contractors use either a screw head mop or assemble their own by using circle or ring fiberglass hanks held together with a compression head. Many contractors like to vary the size of the mop depending upon the job, or like to add hanks as the mop wears; these contractors use circle or ring mops. There are others who do not want the trouble or mess of making a mop. Their choice is pinhead or screw head mops. The ultimate in a pinhead mop is a K.F. Applicator which has spacers in the head to add to its pick-up and spread.

Whichever fiberglass mop is chosen there is a basic rule that must be followed: it must weigh 2 1/2 times more than its cotton equivalent. Both mops will weigh the same when fully immersed in asphalt. The fiberglass mop, because it is not saturated with asphalt, will deliver more asphalt to the deck and feel lighter than its comparable cotton mop.

USE... Basically a mop is a mop and therefore they all work somewhat the same. The performance of a fiberglass mop differs somewhat from the performance of a cotton mop. Since fiberglass does not absorb asphalt, the asphalt merely coats the surfaces of the yarn allowing a faster flow than cotton and making it important to get the mop from the bucket to the deck quickly. This is only a slight adjustment for the mop man. The only other major difference between cotton and fiberglass occurs when the asphalt stops flowing from the fiberglass mop. When this occurs with a cotton mop, more asphalt can be forced out by scrubbing, however with fiberglass there is no more asphalt left and scrubbing can harm the bare fibers, so there is one big rule with fiberglass mops: "Do not scrub a fiberglass mop."

CARE... The biggest objection to fiberglass roofing mops is mainly attributed to the difficulty of cleaning and storing a mop at the end of a day. Crews who used fiberglass mops have little problem with the brief care a fiberglass mop needs. In fact when comparing the time and effort that is needed to keep a crew in cotton mops, cleaning a fiberglass mop is less of a problem. There are only a few simple steps to insure that your fiberglass mop will be ready for use the next morning. At the end of the day it is best to drain the excess asphalt from the mop. Then using a 2 x 4 or any smooth object gently squeegee the mop, be careful not to overdo this, with the asphalt on the fiber, you can damage the bare fibers. After you have squeegee the mop, fan and set the mop on some material that can be peeled off the next morning. If the crew is using packaged asphalt, the waxed wrapper is perfect. The next morning, peel the paper off and place the fanned mop in a mop cart. It shouldn't take but a few minutes and the mop can be rolled over and totally submerged in "hot," ready to go in minutes. Even if the mop is left overnight, fully loaded with asphalt, it should only take a few minutes longer to thaw.

Many roofers reheat their mops in the kettle, while this does speed up the reheating, there is a possibility of the mop ending on the tubes where temperatures reach 2000 degrees, enough to melt fiberglass. So if you feel that you must reheat the mop in the kettle, be careful.

Fact: The dry weight of comparable fiberglass and cotton roofing mops is different. Fiberglass mops should weigh 2 1/2 times more than cotton when both mops are dry. However, after both of the fiberglass and cotton mops have been soaked in hot asphalt and used to apply asphalt to the deck, the cotton mop will retain absorbed asphalt and will weigh a little more than its comparable fiberglass roofing mop.

Fact: Fiberglass is not like cotton. It does not have a large amount of absorbed asphalt trapped in the fibers. Fiberglass transmits heat to the core of the mop, speeding up the reheating process; however, properly cleaned and fanned the night before, a fiberglass mop can be reheated in 3 to 5 minutes. Even when not cleaned the night before, it should only take 10 to 15 minutes to reheat. A word of caution, it is recommended that fiberglass mops should not be reheated in the kettle. There is a danger that the mop will sink to the bottom and lay on the tubes. This contact with the extreme heat on the tubes will damage the fiberglass mop and could damage the tubes.

A roofing crew will use 2 to 5 cotton mops per day. One fiberglass roofing mop will last for one week of hot mopping. This means that one fiberglass mop will replace 10 to 25 cotton mops. The initial cost of a fiberglass mop is higher, however, the savings per week can range from 20 to 40 dollars per hot crew. A large roofing firm may save up to $20,000 per year.

Roofers using cotton mops have trouble achieving equal flow of asphalt because cotton absorbs asphalt and prevents it from flowing uniformly. The absorbent cotton holds the asphalt, causing the end of the mop to cool rapidly. The head of a cotton mop remains extremely hot, yet the heat is held in the head because cotton is an insulator. The cotton mop will then drag on the deck as the end cools. This requires more effort to swing the mop and leads to areas where there is insufficient asphalt for quality roof construction.

The non-saturated fiberglass roofing mop allows asphalt to flow much quicker. The asphalt flows off of the strand instead of out of the strand. This flow is helped further by the transmission of heat by the fiberglass mops. The first is that the more uniform flow provides a better coverage of asphalt, thus less chance for voids or holidays. Secondly, the fiberglass mop glides on the deck rather than dragging as does cotton. This easier application of asphalt reduces the effort required by the hot roofer.

Review Points

Fiberglass roofing mops will save 20 to 40 dollars per hot crew per week.

Fiberglass roofing mops glide rather than drag on the roof deck, mopping is easier.

More asphalt is more uniformly applied with a fiberglass roofing mop.