Roofs are arguably the most critical element of the building envelope. The roof takes the most punishment from weather—rain, snow, hail, wind, extreme temperatures, ultraviolet light. All of them can and will damage a roof, and the results can be disastrous. Water damage is the most obvious result, but environmental control issues can be just as bad. Heating and cooling costs can go through the roof—literally—if the roof is damaged.
Correct preparation of the substrate before coating with a fluid-applied roof coating is the key to a successful, long-lived roof coating project. Neogard roof coating systems can have warranties of up to 20 years; if you want the roof to last that long, you must properly prepare the substrate.
We’ll discuss the five substrates over which Neogard roofing systems can be applied:
- Modified Bitumen
- Single Ply
- Spray Polyurethane Foam
For concrete, metal, modified bitumen, and single ply substrates, remove all abandoned, unnecessary and non-functional equipment, deteriorated and/or water-saturated roofing materials, adhesives, and any foreign materials.
Last time, we looked at concrete decks in detail. All of the problems discussed in that post apply to concrete roof decks. Moisture problems, surface contaminants, improper surface profiles, and deck repairs not being made apply to concrete roofs as they do to any other concrete deck.
Metal roof decks have a few critical preparation steps which must be performed to ensure the coating properly adheres and protects the substrate.
Remove rust: Rust will prevent the primer and/or coating from properly bonding with the substrate. It can also cause cosmetic problems by bleeding through the coating and discoloring the coating. Our preferred methods for removing rust are a wire wheel cup on an angle grinder, or sandblasting. Either method is effective; use the method most appropriate for your worksite. Panels with excessive rust must be replaced entirely.
Seam detail: This is required to prevent water from penetrating the roof, and to ensure that the system is sound and won’t split. Horizontal seams must be inspected, and any fasteners which have failed must be replaced. Ensure that seams with gaps greater than 1/8” are stitched as tight as possible with additional fasteners. Cover the seams and fastener heads with 70690 urethane mastic at 80 wet mils (or 70695 silicone mastic at 65 mils for silicone coating systems). You may also detail the seams using the system’s base coat material at 24 wet mils, embed 6” wide Tietex fabric, and cover with another 16 mils of base coat. Vertical seams should be treated as needed with mastic or base coat and Tietex.
Primer application: All Neogard metal roof coating systems require a primer. Metal can be difficult to bond to, so primer is essential. Apply the primer according to the instructions in our Guide Specifications and our online Summary Application Table. Proper priming of the metal will ensure that the coating—urethane, silicone, or acrylic—will stay put.
3. Modified Bitumen
Built-up/modified bitumen substrates need to be cleaned and have their seams detailed before coating.
Cleaning: We recommend dry vacuum cleaning the surface to remove dirt and debris, including any loose gravel. Dry vacuuming will remove the possibility of any water being introduced into the substrate. Also, the granules on the surface of the cap sheet can retain water, which will cause blistering and delamination of the coating as it is released. If you must power wash the roof, give it sufficient time to dry before applying the coating.
Seam detail: Just like a metal roof, the seams between the cap sheets must be treated to prevent water penetration and a properly sound system. The procedure is the same: cover the seams with 70690 urethane mastic 80 wet mils (or 70695 silicone mastic at 65 mils for silicone coating systems). Again, you may also detail the seams using the system’s base coat material at 24 wet mils, embed 6” wide Tietex fabric, and cover with another 16 mils of base coat.
4. Single Ply
Single ply substrates, such as TPO and EPDM, need preparation similar to modified bitumen. And like metal, priming is critical.
Cleaning: This is especially important on an older single ply substrate. Scrub the deck clean using a detergent like Neogard 8500 BioDegradable Cleaner and a stiff-bristle broom. That will remove contaminants which can prevent proper adhesion of the coating system.
Seam detail: Again, like metal and modified bitumen substrates, the seams between singly ply sheets must be detailed. And again, the procedure is the same: cover the seams with 70690 urethane mastic 80 wet mils (or 70695 silicone mastic at 65 mils for silicone coating systems). And yes, you may also detail the seams using the system’s base coat material at 24 wet mils, embed 6” wide Tietex fabric, and cover with another 16 mils of base coat.
Primer application: Using the correct primer is necessary for a strong bond. Neogard has special primers for single ply substrates that bond well with the substrate below and coating above. Our 7710 primer is for Silicone and Silicone HS systems over TPO and PVC. The 7720 primer is for Elasta-Gard urethane and Elastacryl acrylic systems over TPO. And our 7797/7798 urethane primer works for urethane and acrylics over other single ply materials, like EPDM.
5. Spray Polyurethane Foam (SPF)
SPF roofs don’t require quite as much preparation as direct-bond substrates, but there are two major items to consider.
Same-day base coat application: To prevent the SPF surface from accumulating contaminants that will prevent a proper bond, apply the base coat on the same day as the SPF.
Correct surface texture: Neogard coatings protect roof-grade spray polyurethane foam applications which are compliant with Spray Polyurethane Foam Alliance (SPFA) guidelines. We require that the SPF surface comply with the following SPFA surface textures. Each of these surfaces requires more added material for proper coverage (shown in parentheses), so it pays to have a smooth surface:
- Smooth (+5%)
- Orange Peel (+10%)
- Coarse Orange Peel (+25%)
- Verge of Popcorn (+50%)
Popcorn and Tree Bark textures are unacceptable for coating. For more information, refer to SPFA Technical Document AY-145, Surface Texture Of Spray Polyurethane Foam.
Surface preparation for roofs is essential for a long-lived roof coating system. It takes a little work, but it is worth the effort. Follow the guidelines in our Application Manuals and Guide Specifications, and your roof project will last a decade or more.
In the next installment of this series, we’ll look at the challenges of recoats.