This benefit is a major time and money saver for any contractor. It has helped propel silicone into the spotlight as one of the fastest-growing roofing technologies in the industry. Although rare, there are times when a primer is actually necessary. In this article, we will be looking into the following substrates and whether or not a primer is necessary for each:
■ metal roofs
■ spray foam
■ single-ply (TPO / Hypalon / PVC / campers)
■ mod bit / aged asphalt / gravel BUR
■ EPDM.
Metal roofs are great substrates for silicone roof coating restorations. If in good shape, your metal roof will require no primer at all. This is not always the case, however. In cases where rust is affecting the roof, rust inhibitive primer (RIP) is recommended. By applying 1 gallon per 200 square feet, you can almost entirely stop rust. Although, there’s nothing that can completely stop rust, RIP slows it to a degree that it is no longer considered a threat to the roof. RIP can be sprayed or rolled on and, once dry, it adheres to your silicone coating. It’s a safe and easy way to make sure rust doesn’t take over a metal roof. Of course, if rust damage has created major holes or gaps in a roof, some panel replacement may be necessary. In most cases, however, RIP offers enough protection to keep the metal roof’s rust at bay. The only other time a PM primer may be necessary on a metal roof is if Kynar roofing is used. In rare cases, we have seen poor adhesion on Kynar. Thankfully, there is a solution for that as well. Single-ply primer (mostly used on single-ply substrates) will coat over Kynar and offer tremendous adhesion for the silicone coating.
As with most substrates, primer is seldom required on spray foam. There are, however, times when you’ll want it handy. As you know, exposed spray foam can be damaged quickly if left in direct sunlight. Fortunately, night seal primer (NSP) has been
developed to help with this issue. Here are a couple instances in which NSP is necessary:
■ Prior to coating on top of foam, be sure that the foam is not exposed to the sun for longer than a day. If you will be working on a foam roof for multiple days, you will want to make sure you prime the foam to maintain its integrity. NSP goes on easily while holding the foam’s integrity, allowing you the time you need to finish the job.
■ You may also want to consider NSP in your tie-in lines. Foam does not adhere to silicone, but it will adhere to NSP. The NSP coat will allow the new foam to adhere to the previously installed silicone, allowing you to finish the job the right way.
The “no-primer-necessary” trend continues for most single-ply roof jobs. However, like metal roofs and spray foam roofs, there are a few instances where a primer is recommended.
On TPO, PVC and Hypalon roofs, a primer may be necessary on roofs under five years old. These roofs can sometimes be oily, making it difficult for silicone to adhere. If you are working on a newer TPO roof, single-ply primer (SPP) will help the silicone adhere even better. This primer is designed to cut through these oils and create a nice surface for the silicone to stick to.
Recently, we’ve seen an uptick in silicone usage on campers and RV roofs. If you’re coating a camper or RV, you could have similar issues to TPO and Hypalon. Once again, SPP is the recommended primer for this type of job.
For modified bitumen and aged asphalt systems, primer is not necessary. The silicone will hold and maintain a strong bond, but there has actually been a primer developed for these roof types. With modified bitumen and asphalt roofs, silicone can begin to yellow quickly after the silicone is applied. This yellowing is due to activating asphalt bleed-through from the asphalt and bitumen. Although this bleed-through does not negatively affect the silicone’s integrity, it can be unsightly if you were expecting for a dazzling white roof.
To help prevent yellowing, bleed block primer (BBP) was developed. This primer has been designed specifically to stop this bleed-through, offering protection for white rooftops. If you or your client aren’t concerned with roof color, you can skip this step. The watertight roof will still last decades. If, however, your roof is a point of pride, this primer is a must-use on these substrates.
EPDM is typically known as the most stubborn substrate when it comes to silicone adhesion. If it’s too new, the silicone may not hold. If it’s too old and dirty, the silicone may not hold. EPDM gave silicone experts a headache until the right method was finally
discovered.
The first key to silicone application over EPDM is to use rinse-able cleaner (RC). Although not technically a “primer,” this cleaner is definitely necessary before coating on EPDM. After power washing the roof, RC is applied onto the EPDM. Let RC sit for ten minutes
and then rinse it off. This quick step will help silicone roof coatings adhere very well to the EPDM. If, after the roof has been washed and cleaned, adhesion tests are still showing less-than-desirable performance, SPP may be used to offer optimal strength. In some extreme cases, when additional adhesion is necessary, SPP can be used to offer maximum hold. Between RC and SPP, you can guarantee great silicone adhesion on EPDM.
While primers are not necessary on most silicone coatings jobs – most of the time a good power washing will offer enough prep work for good adhesion – knowing what primers are available will be useful on the unusual jobs you encounter.
Klaus Schlimm is the Marketing Director for Progressive Materials Silicone Roof Coatings. He graduated from Northern Kentucky University in 2009 and has spent the past eleven years in sales, proposal writing and marketing. For the past five years, Klaus has been working in marketing and public relations in architecture, construction and roofing. Klaus builds marketing campaigns for Progressive Materials and their clients to help win business. For more information, feel free to reach out to Klaus at
klaus@pmsilicone.com.
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