Rubber Roof Sealing
- Apply self-leveling lap sealant to roof fasteners and terminations at the correct bead thickness.
- Differentiate between self-leveling and non-leveling sealant applications based on surface orientation.
- Prepare membrane surfaces and cuts to prevent premature material failure and running tears.
- Dicor 501LS — Self-leveling lap sealant used to seal screw fasteners and terminations on horizontal surfaces.
- Dicor 551LS — Non-leveling sealant used for applications on vertical or taller surfaces.
- Dicor rubber roof cleaner — Approved cleaning agent for preparing the membrane surface before sealant application.
- Caulk gun — Tool used to dispense sealant in the required 1/4" to 3/8" bead size.
Seal screw fasteners and terminations with self-leveling lap sealant (Dicor 501LS) in a 1/4" to 3/8" bead. Use non-leveling 551LS on vertical/taller surfaces.
Round all 90° cuts in membrane to prevent running tears. Don't stretch membrane.
Clean with Dicor rubber roof cleaner. Never use acetone or citrus cleaners.
How It Works
Sealant Viscosity and Gravity
The choice of sealant depends on the orientation of the surface. Dicor 501LS is self-leveling, designed to flow and flatten over fasteners on horizontal roof sections. Vertical or taller surfaces require 551LS, which is non-leveling and maintains its shape without sagging.
Stress Concentration Management
Sharp angles in roofing membranes act as stress risers. All 90° cuts must be rounded to redistribute tension and prevent running tears from developing at the corner. Additionally, the membrane should never be stretched during installation to avoid long-term shrinkage or pull-away.
Chemical Compatibility
The membrane surface must be cleaned specifically with Dicor rubber roof cleaner. Harsh chemicals like acetone or citrus-based cleaners can degrade the material and must never be used, as they compromise the integrity of the roofing system.
Diagnostic Chart
| Symptom | Check | Spec / Expected | Likely cause & fix |
|---|---|---|---|
| Sealant bead is too thin or fails to cover fastener heads adequately. | Measure the width and depth of the applied sealant bead. | 1/4" to 3/8" bead. | Insufficient material applied during the sealing of screw fasteners or terminations. Basis: Dicor DiFlex II Roofing Retro-Fit Installation Guide |
| Sealant runs down the side of the trailer or away from the vertical termination. | Verify the sealant product code used on the vertical or tall surface. | Use non-leveling 551LS on vertical/taller surfaces. | Self-leveling 501LS was incorrectly applied to a non-horizontal surface. Basis: Dicor DiFlex II Roofing Retro-Fit Installation Guide |
| Tears originating from the corners of roof cutouts. | Inspect the geometry of membrane cuts at 90° junctions. | Round all 90° cuts in membrane. | Sharp 90° cuts were left in the membrane, leading to running tears. Basis: Dicor DiFlex II Roofing Retro-Fit Installation Guide |
| Membrane surface degradation or failure to bond with sealant. | Review the cleaning agents used during surface preparation. | Clean with Dicor rubber roof cleaner; never use acetone or citrus cleaners. | Use of prohibited cleaners such as acetone or citrus-based products. Basis: Dicor DiFlex II Roofing Retro-Fit Installation Guide |
At the Bay: Diagnose the Case
CASE 1 / 4
Sealant bead is too thin or fails to cover fastener heads adequately.
- Test
- Compare
- Correct
Select the next check
Basis: Dicor DiFlex II Roofing Retro-Fit Installation Guide. A likely cause is a hypothesis; confirm it with the applicable service procedure before repair.
Common Bay Mistakes
- ✕ Applying self-leveling sealant to vertical surfaces where it will sag.
- ✕ Using acetone to clean the rubber membrane.
- ✕ Leaving sharp 90° corners on membrane cuts.
- ✕ Stretching the membrane during the installation process.
- ✕ Using citrus-based cleaners for surface preparation.
- ✕ Applying a sealant bead smaller than 1/4".
Quick Check
Practice only — not scored.
Source: Dicor DiFlex II Roofing Retro-Fit Installation Guide