Wallpaper Primers: The Foundation of A Quality Paperhanging
Introduction: Why Primer Matters
In its most basic form, primer is simply an adhesive. For paint, primer provides an adhesive layer for the paint to stick to. And we have various primers formulated to adhere paint to various substrates (metal, plastic, drywall, etc). For wallpaper, primer is still an adhesive. It’s still primer. But wallpaper primers provide a few additional features that standard paint primers lack. When painters say things like “the wall is primed”, they’re not generally giving us enough information about how that wall is primed and whether the primer and the application of the primer is appropriate for installing wallcoverings. This isn't about whether the painter's primer is good; it's about whether it's appropriate for our specific installation.
PVA Primers: A Misfit for Wallpapers
PVA primers are inadequate for wallpapering and should not be used. Period. They're typically used under paint, especially in new builds. And they offer the bare minimum in terms of adhesion since we only need paint to adhere to them.
Wallpaper primers, on the other hand, are typically hard, acrylic primers that are specially formulated to not just have greater adhesion than PVAs, but also to ensure the material can be repositioned on the wall, to protect the wall surface from softening under the slow-curing process of wallpaper paste, to create a barrier on the wall protecting it from being scored with a knife, and to assist removal down the road without causing damage to the walls that would've resulted in needing major drywall repairs.
I prefer using a penetrating sealer primer as my base since they tend to lock in whatever paints and primers may already be on the wall (and I don’t want to spend time dissecting decades of decorating choices). And then I use an adhesion-promoting wallpaper prep coat on top of the primer to give a little more tooth to the surface, helping to lock in seams so that the material has even greater resistance to its propensity to change shape on the wall as it cures.
The Science Behind Wallpaper Primers
Wallpaper primers are formulated to provide the best foundation for wallcovering installations. These primers are specifically formulated to have more adhesion than paint primers, while simultaneously allowing "slide" (movement for repositionability). This is important because many materials will stain if adhesive touches the face of them. So in order to install them safely, it’s best to slide them in place. The primers do this by providing a crystalized surface for the paste to bite into. Since most wallcoverings reshape when exposed to moisture or temperature changes, the extra adhesion of the primer provides additional resistance to the materials' natural propensity to reshape during the curing process.
Some wallpaper primers additionally allow for the wallpaper adhesive to tack up more quickly by an increased ease for moisture and gasses to escape into the underlying surface (or by including other agents that will help dry out the adhesive). As the moisture content decreases from the paste, the tackiness increases, quickly holding the wallpaper in place against the wall so it has greater resistance against shrinking. Managing the rate that adhesives cure can be done in a few ways. I think the most effective way is by using an a liner paper.
Selecting the Right Primer for the Job
Not all surfaces are created equal, and neither are all wallpaper primers. Non-porous (or slick) surfaces, for example, need a prep coat that can handle the smoothness without failing. Products like ROMAN R-35, Benjamin Moore's Wall-Grip, or PPG's SEAL GRIP are formulated for these sorts of tasks.
My go-to primers are GARDZ, a product by Zinsser, and DRAW-TITE, a product by Scotch Paints. But there are other great products on the market. PRO-977 by Roman, is fantastic for vinyls and dries harder than many other primers. And Shieldz by Zinsser is a wonderful prep coat (though I prefer Wallpaper Prep Coat by Swing Paints). However, when working with some materials, prep coats could reduce your ability to reposition the material on the wall because they’re drying out the paste faster than you may prefer. Many paperhangers love Benjamin Moore’s Fresh Start, which is a hard acrylic primer. I'm always inclined to want to use something other than R-35 if possible, as it adds a lot more adhesion to the surface and really negatively impacts future removal. Some projects might call for a different primer (or to expressly not use a specific primer), emphasizing the need to have a good understanding of the surface and the material you're working with. But most of the time you’d be safe to use GARDZ or DRAW-TITE.
All of these products ought to be applied in a manner that penetrates the surface. If someone is spraying it on, they ought to at least backroll the product in order to get a good application.
Application Tips and Tricks
Primer generally goes up like paint. However, if it's thinner primer like GARDZ or DRAW-TITE, you start rolling it on from the floor upward, as opposed to your normal technique (from the center, up to the ceiling, and then down). Also it helps to not put too much pressure on the roller. Just let it relax as you're rolling it on (and be sure your roller doesn’t run dry). Also note that wallpaper primers generally get better coverage than paint primers. A gallon of GARDZ, for instance, covers about 450 sqft, about 50% more than your standard PVA primer. So though the gallon's more expensive, it goes further. Drywall should be sanded or scraped down to remove any dimples and then any loose particles should either be swept off with a brush or washed off with a microfiber cloth. After this, prime the walls and let them cure.
For some materials, you can hang them a few hours after priming (assuming a dry climate). But if you're installing a vinyl, metallic, or another non-permeable material, you'll need to wait longer because the off-gassing from the primer curing won't be able to escape through the substrate. In this case, even if the can says you can hang over it in 3 hours, you'll likely need to wait a day to prevent off-gassing from causing bubbling. The devil is always in the details and it's not possible to encapsulate all of the details on the side of a paint can. Hopefully this information helps ensure you're not setting yourself up for failure before the wallpaper even goes up.
Wrap-Up: The Primer Takeaway
If there's one thing to take away from this, it's that choosing the right primer is not just grabbing the first thing you see off the shelf at the paint store—it's one of the most important steps for any wallpaper installation. It may very well stand between a stunning wall treatment that lasts and one that's peeling at the seams or bubbling due to failing paint before you've even had a chance to really enjoy it.
Understand the requirements, choose wisely, and don't cut corners.