Whether you’re new to wood veneering or a seasoned pro, at Oakwood Veneer we want you to have all the information you need to do the job right the first time. Contact cement, while not the best possible choice for laminating sheet veneer, has its place when doing a variety of “in place” applications. But understanding fully how and when to use contact cement, you can minimize grief and aggravation. Many seasoned pros, and certainly many new to wood veneer projects, have bought into myths about contact cement. Our purpose here is to bust these myths and help you have a successful experience with your wood veneered project.
MYTH #1: Contact Cement is the Adhesive of Choice for Wood Veneer Projects
Contact cement was originally designed for adhering high pressure laminates, like Formica-brand, for countertops and panels. While it can be used to adhere backed wood veneer, you need to take precautions. Wood veneers are prone to movement in the environment. Veneer sheets will expand and contract as temperature and humidity varies. This can cause failures in the topcoat of catalyzed finishes used today.
MYTH #2: Laminate Rollers are The Tools of Choice with Contact Cement
Using a laminate or j-roller is NOT appropriate forflexible sheet veneer application. Wood veneers are a “live” surface, meaning it reacts to its environment by expanding and contracting, you need a rigid glue line to “lock it down” to the substrate. This minimizes problems that can occur after finishing. It is extremely important to get as much pressure as you can when seating the veneer. Depending on the contact radius, using a veneer scraper will give you at least sixteen times more surface contact than you would get with a j-roller. So, ditch the j-roller and use a simple short-handled scraper.
MYTH #3: Contact Cement is Fine to Use with Raw Veneer Flitches
Using contact cement to adhere raw unbacked veneer is a complete failure waiting to happen for numerous reasons. Do not do it. Once again, contact cement is more suited for use with synthetic laminates, like Formica. It is best to use a two-part resin or PVA glue adhesive when working with raw wood veneer flitches.
MYTH #4: It’s Best to Use a Paint Brush to Apply Contact Cement
Since contact cement dries quickly it’s never a good idea to use a paint brush. Paint brush application to even a moderately sized area will cause an uneven rough surface and a spongy glue line. This can result in a wavy appearance when finished, as well as areas where you might get excessive movement which can cause the finish to check or crack.
MYTH #5: Using Contact Cement Allows for “Instant” Application
The solvents in contact cement need to totally evaporate before you apply the veneer to the substrate. Otherwise, you can get pressure bubbles between the veneer and the substrate as the solvents try to off gas but have nowhere to go. This can be corrected but, if you wait to let it completely tack up before application, this should not be a problem.
MYTH #6: Contact Cement is Perfect for Exterior Projects
Veneers can be used in exterior jobs, but you need to use the appropriate adhesives, like epoxy or resin glues, which are designed for exterior use. The nice thing about epoxies is they can also be used as a base finish to completely encapsulate the veneer for added waterproof protection. You need to use a UV-stable finish, as epoxies tend to not be as stable and can degrade after constant exposure to the sun.
MYTH #7: Contact Cement is Ready-to-Use
Contact cement needs to be stirred before use. The important part of the adhesive is the solids that are suspended in the solvent. The best glues for veneer will have a high solid content. As the glue sits in the can, the solids will drop to the bottom leaving mostly solvent and little solids. So, stirring will redistribute the solids, ultimately giving you a better bond.
MYTH #8: It’s Best to Be Generous with Contact Cement Application
Just as in any other woodworking project, when gluing up panels or doing joinery, it’s not as important where the glue is as where it isn’t. Dry joints or dry spots in the substrate will lead to surface failures. This is most important with contact cement! You need 100% coverage. It is also important to remember that too much contact cement is equally as bad as too little. Too much glue will cause a spongy glue line that will lead to excessive movement in the veneer. The idea is to apply a thin coat in one direction over the surface, followed immediately by a thin coat applied in the opposite direction. With porous surfaces like plywood, it is advisable to apply a thin coat, let it completely dry for several hours to size the panel, and then come back with a thin coat to create a good tack coat.
MYTH #9: The Floor is the Best Place to Store Contact Cement Containers
Because temperature affects the tack time of contact cement, it is best to store your glue OFF the floor in a room set to at least 65 degrees. Otherwise, it will extend the time it takes to come to a full tack which can lead to bubbles on the surface as well as excessive movement in the veneer.
MYTH #10: All Wood Veneer Backers Work Well with Contact Cement
Due to contact cement’s nature of being somewhat of a flexible glue line, it is important to select the appropriate backer for this application.
There are four different backer types to choose from:
1. 10 mil paperback: this backer while being the least expensive is designed for pressing or hard gluing.
2. 22 mil paperback: this would be the minimum backer thickness for contact cement application.
3. Wood-on-Wood and Phenolic backers are also good choices for contact cement applications.
MYTH #11: All Contact Cements are the Same
Contact cement is divided into two basic categories: water-based and solvent-based. In our experience, solvent-based adhesives perform better than water-based for flexible sheet veneer. That said, there is an even more important aspect to the glues available, and that is solid content. For adhering veneer, the rule of thumb is you want an adhesive with the highest solids-to-solvent ratio. Simply put, the higher the solids the more ridged the bond. Please note depending on your location in the country, some states have strict VOC (volatile organic compound) laws and solvent-based adhesives are just not available. If you choose to use a water-based adhesive, for best results it is very important to follow all the adhesive manufacturer’s guidelines for wood veneer applications.
MYTH #12: Contact Cement Works Well in Any Climate
Areas where there are large swings in temperature and humidity will test even the best application technique. In a perfect world, the goal for millwork is to be in a state of equilibrium, meaning there is a constant temp and humidity and the wood neither takes on, or expels moisture. Then there is the real world. Climate control is the first line of defense. In areas like here in Michigan, we have four seasons which display four distinct averages of temp and humidity. The key is, during winter months add humidity, and during the spring and summer months, dehumidify. This creates a more stable climate and reduces the chance of having problems down the road.
MYTH #13: Contact Cement is the One and Only Wood Veneer Adhesive
There are many types of glue for veneering and each one has distinct characteristics. Research is necessary to pick the right glue for each job.
The basic hierarchy of glue lines based on rigidity are:
1. two-part resin glues
2. specialized PVA glues designed specifically for laminating veneers
3. standard PVA glues, like carpenters’ glue
5. contact cement
Each has its own benefit for veneering, but saying some are better than others is an understatement.
MYTH #14 Contact Cement is Permanent
Contact cement will always be a flexible glue line and could fail to one degree or another, over time, on veneered millwork. For this reason, we recommend using a press and hard gluing whenever possible.