- About EPDM
- Thickness and Width
- Splicing Seams
- Evaluation by Age
- Blisters
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1. ABOUT EPDM
By Kenton Shepard
Ethylene propylene diene M-class rubber (EPDM)
First introduced in 1962, EPDM is a thermoset, petroleum-based synthetic rubber formulated for extensive flexibility. Most EPDM used for roofing is vulcanized, but some non-vulcanized EPDM is typically used as sheet flashing for detailing.
Before installation, sheets should be unrolled and allowed to relax.
The difference between vulcanized and non-vulcanized EPDM
Vulcanized rubber has an intermolecular network of highly cross-linked polymer chains; non-vulcanized has polymer chains only.
After being mechanically stretched, vulcanized rubber returns to its original shape once the stress is removed; non-vulcanized doesn't.
Vulcanization changes the chemical composition of rubber. The chemical composition of non-vulcanized rubber is not changed.
EPDM has the following attributes:
Its typically black, but may be white when reflective qualities are desired. Although EPDM is available in black and white, there is little difference in performance;
- Roofing sheets thicknesses are usually either 45, 60 or 80 mil;
- Its use is acceptable on Low- and steep-slope roofs and roof of unusual shapes like domes and barrels;
- It may be adhered, mechanically fastened, or loose-laid;
- It may be used in exposed or concealed spaces;
- Highly impermeable to moisture;
- Good low-temperature performance;
- Good resistance to temperature extremes, ozone, UV radiation, weathering , impact, and abrasion;
- It is resistant to some acids, alkalis, and solvents, but swelling or distortion may result from exposure to other solvents, animal/vegetable oils, and petroleum-based products (not good above restaurants)
- Lifespan to 50 years depending on environment.
Mechanically Attached Membranes
On mechanically fastened roofs, fastener spacing will vary with roof height and wind exposure category. Fasteners will typically be spaced more closely around the roof perimeter. Seams will also often be more closely spaced around roof perimeters.
Adhered Membranes/Lightweight Concrete Problems
Adhered EPDM membranes are very effective in high-wind areas. When installed over lightweight concrete roofs (including LWIC), look for moisture problems. No good method exists for confirming adequate drying before installation of the membrane. latent moisture may interfere with curing of the adhesive, reducing teh wind resistance of the membrane.
Ballasted Membranes
Ballasted membranes will typically be fastened around the perimeter and the field held in place be gravel in the 3/4" to 1.5" range. Pavers may be used for Ballast. Eroded pavers will shed granular dust that can abrade the membrane over time.
Equipment and pipes should not rest on the gravel, but should be installed on platforms designed to effectively protect the membrane.
Areas Needing Reinforcement
T-shaped seam intersections should have reinforcement patches installed.
Roof-to-wall intersections DO NOT need cant strips but will have manufacturer-specified methods for keeping the membrane held securely against the corner.
Penetrations should be reinforced and sealed using an effective method.
2. THICKNESS & WIDTH
THICKNESSS
EPDM sheets are available from about 40 mils to 80 mils thick.
WIDTH
EPDM is available in widths from 7.5 feet to 50 feet, although 20 feet is a more typical maximum.
3. SPLICING SEAMS
By Kenton Shepard
Either of two methods may be used for splicing seams: liquid or splice tape.
Liquid splicing
1. Sheets must be unrolled and allowed to relax for a minimum of 30 minutes before splice assembly;
2. Overlap an minimum of 3 inches (or a manufacturer recommended dimension);
3. Overlaps should not impede the flow of runoff;
4. Areas to be spliced must be cleaned/primed with the manufacturer's recommended product prior to applying the splicing adhesive;
5. Liquid adhesive is applied and allowed to dry to a tacky state;
a. Over-drying must be avoided and may result in seam failure unless re-primed and adhesive is reapplied;
b. Some sealants need time for solvents to off-gas. If the membrane is mated to the substrate without allowing inadequate time of off-gassing, blisters may appear as a result.
c. Some systems recommend a bread of seam sealer be applied before the two sheets are joined.
6. The splice should be pressed together firmly and then rolled with a 2-inch maximum wide roller.
7. After waiting a time period specified by the manufacturer, a one-inch strip should be cleaned along the edge of the seam, and then a bead of lap sealant should be applied to the edge of the seam.
a. Some manufacturers may require a layer of splicing cement be placed over the seam before lap sealant is applied.
b. Special methods may be required where seams intersect with underlying seams lying perpendicular (a T-intersection).
8. Any imperfections should be repaired. These may include fishmouth, bubbles, blisters, or wrinkles.
Tape Splicing
1. Sheets must be unrolled and allowed to relax for a minimum of 30 minutes before splice assembly;
2. Overlap an minimum of 3 inches (or a manufacturer recommended dimension);
3. Overlaps should not impede the flow of runoff
4. Areas to be spliced must be cleaned/primed according to the manufacturer's recommendations;
5. If primer is specified by the manufacturer it should be stirred with a wooden paddle for at least 5 minutes. (kinda sounds like this was written by Howard Hughes)
6. Splice tape should be a minimum width of 2 inches or as specified by the systems supplier.
7. A small amount of tape should be visible after the splice is assembled.
8. Tape should overlap at least 1-inch at ends
9. The splice should be pressed together firmly and then rolled with a 2-inch maximum wide roller.
a. Special methods may be required where seams intersect with underlying seams lying perpendicular (a T-intersection).
9. If required by the manufacturer, a bead of lap sealant should be applied to the edge of the cleaned seam.
10. Any imperfections should be repaired. These may include fishmouth, bubbles, blisters, or wrinkles.
4. EVALUATION by AGE
By Kenton Shepard
Seam Technology History:
1. From the early 1960s until the mid 1980s seams were using white gas (cleaning) and a Neoprene-based splicing adhesive. The Neoprene polymer in the splice cement would sometimes break down and lose strength with prolonged exposure to ponded water.
2. In the mid-1980s, a butyl-based splice adhesive was developed that was very tolerant of ponded water, but the seaming process was complicated, leaving seams prone to problems caused by workmanship.
3. By the early 2000s, customized primers and double-sided seam tape emerged. These products dramatically simplified the seaming process and reduced workmanship inconsistencies.
4. Around 2005 EPDM became available with primer and tape factory-applied to one edge of sheets. This innovation reduced warranty claims by nearly 80%.
Improvements to Angle Transitions (flat roof to parapet wall)
Early in its history, wood nailing strips were used to secure ballasted EPDM where it up-turned at the base of parapet walls. As EPDM membranes experienced age-related shrinkage wood strips experienced pull-through. In the late 1980s, a new method emerged. Reinforced membrane attachment strips were attached to the roof with fasteners and a seam plate combined with adhesives improved this condition.
Puncture Resistance:
Early in its history, 45-mil non-reinforced EPDM was common, especially in ballasted systems common on commercial buildings.
In the mid 1980s, manufacturers began producing a 60-mil EPDM with an internal scrim, increasing puncture resistance by about 50%. The problem with an internally-reinforced membrane is that it contains less weathering material over the scrim. On 60-mil sheets of EPDM, the thickness of the weathering material was only 20-25 mils.
In 1996, an externally reinforced, fleece-backed EPDM with a full 60 mils of weathering material was introduced that increased puncture resistance by about 300%.
Flashing Improvements:
From 1962 to the mid 1980s, wall and penetration flashings were manufactured from uncured Neoprene. This material formed and spliced very well, but its UV resistance was poor. Over time, Neoprene flashing would crack and craze, and it became one of the most common courses of failure.
Flashing made of uncured EPDM was introduced in the mid-1980s. Uncured EPDM flashing offered dramatically improved weathering properties and none of the cracking issues.
Prefabricated pressure-sensitive inside/outside corners, pipe boots, and pourable sealer pockets for EPDM systems were developed and quickly gained popularity because they simplified the application process and improved quality.
Modern, pressure- sensitive flashings provide a full 60-mil EPDM weathering layer laminated to 30-mil cured adhesive for a 90-mil total thickness. This is a significant improvement over older methods.
5. BLISTERS
Blisters can develop in EPDM for several reasons:
Inadequate flash-off time: Some sealants need time for solvents to off-gas. If the membrane is mated to the substrate without allowing inadequate time of off-gassing, blisters may appear as a result.
Entrapped air/moisture: If the roof deck is damp or has gaps, when the membrane gets hot, moisture vapor/air will expand, causing the overlying membrane to lift, forming a blister.
Don't recommend that blisters be repaired unless they are damaged. Blisters do not affect the water-tightness of the roof, but a repair might. Also, warranties often cover water tightness but not blisters.