Glue or Screws or Both: Do You Need Screws for Wood Glue?
Wood glue versus screws for joining wood pieces has been an argument for a long time. Some woodworkers don’t trust wood glue to be enough by itself. They argue that at least screws should be added to the glue for maximum strength.
There really is no need for screws in addition to wood glue since a wood glue bond has been proven to be stronger than a screw bond. This is true because, in a glued bond, you have a continuous bond along the wood's entire face. The more surface area that is bonded together, the stronger the bond will be.
While wood glue may be the relatively new kid on the block, it often outperforms its predecessors. So, while you don’t want to glue your house walls together, it is perfectly safe to glue your furniture together. Let’s see why that is.
Which are Stronger, Screws or Glue?
Glue is stronger than screws. Not so much because of the chemical make-up of glue, but because of how it joins the wood together. The glue soaks into the wood fibers and essentially welds them together.
When wood is screwed together, you create a bond on the joint where the screws are. The bond holds firm wherever a screw is placed. This means that there are multiple points where the wood is not bonded.
In every place that the wood is not bonded, there is potential for structural failure.
With glue, however, you have a continuous bond along the entire joint. This factor is what makes wood glue so strong; in fact, stronger than the wood itself!
There is no gap in the bond so there is no leverage to pull the bond apart.
In tests, it has been proven that screwed joints break at the joint itself; glued joints break at some point away from the joint.
If you try to pry apart a glued wood joint, the wood will splinter, but the joint will hold.
So, while it may be tempting to “reinforce” your glued bond with screws, it is completely unnecessary. In fact, it may actually damage the bond since the screws will interrupt the adhesion at every point where they are placed.
Screws have a bad habit of cracking the wood or going in crooked, which compromises the joint's strength. Of course, the best way to avoid this is by drilling a pilot hole.
Furthermore, screws will shift over time. If exposed to extreme temperatures, screws will back out of the joint, leaving you with gaps or an unstable joint.
In humid regions, wood will swell and shrink according to fluctuating moisture levels. This will cause the screws to work loose and ultimately cause the joint to fail.
None of these issues arise with wood glue. The joint will last longer than the wood does.
Gluing Only Needs Time and Patience
Gluing takes more time than screws do, but in most cases, it works best.
Glue resists temperature and humidity changes better than screws do, and glue is not affected by weight in the same way that screws are.
While pressure can cause screws to shift or even break, glue is quite capable of tolerating significant pressure over prolonged periods without losing integrity.
But gluing a project together does require more preparation than screwing does. Let’s look at the process.
Keep Your Wood Joint Clean
Sawdust or dirt on the wood can prevent the glue from bonding properly. This should be removed before attempting to glue the joint. A few simple steps can ensure a tight bond.
- When preparing wood to be glued, be sure to remove all debris from the edges that are to be joined.
- In some cases, you can wash with soap and water, rinsing well. If this is the method you choose, give the wood a day or two to dry out before applying the glue. The presence of water will compromise the bond of the glue.
- Usually, the preferred method is to expose the new wood surface by light sanding. Just two to four passes along each edge with medium-grit sandpaper are usually enough to ensure a tight bond.
- Be sure to remove all dust particles after sanding.
Wood Should Be Created Equal
The strength of your bond is dependent in part on the wood. For this reason, the two pieces being joined should be as smooth and straight as possible.
If there are gaps between the two surfaces, this will result in glue having to fill the space. The bond in these cases will not be as strong as possible because of the discrepancies between the two pieces of wood.
You may want to sand or shave down both edges of the joint to make it as snug a fit as possible.
If there is still a bit of space between the boards at some point despite your best efforts, it can be remedied.
You can blend sawdust with wood glue to form a paste for tiny gaps to fill the gap. But this is not a one-size-fits-all tip. This does not work for large gaps.
If you want to stain or varnish your wood before gluing the joints, special care should be taken to keep the substances out of the joints to be glued. Glue does not bond well over stain or varnish.
An excellent way to protect your joint surface is to apply masking tape over the area that will be glued.
Spread the Glue Around
Applying an adequate amount of glue to the joint is vital to get a good bond. Too little glue will result in a weak joint, which may pop apart under stress. Too much glue will make a mess and cause flaws in your stain.
To prevent excess glue from squeezing out onto the surface of your wood, you can place masking tape on the upper surface all along the edge of the joint. This way, when the glue squeezes out, it squeezes onto the tape and can be easily removed.
It takes practice to learn how much glue is enough. Typically, you want the glue to squeeze out in a row of small beads along the joint's length. A scraper can remove these once the glue has set up a bit.
You will want to spread the glue to cover the joint’s entire surface area. Check out my video below on one way to apply glue.
If it is a small joint (two inches or less), you can apply the glue and rub the two pieces together a few times to spread the glue. This method is not recommended with joints larger than two inches and definitely should be done before the glue starts to set.
Apply Pressure To the Joint
Once the glue has been applied, it is time to clamp the joint while the bond sets. This is arguably the most important part. When glued bonds fail, it is usually because it wasn’t clamped tightly enough.
Official recommendations for clamping are 150 psi for softwoods. Most wood glues require at least twenty-four hours in clamps for the bond to cure.
A bit of caution is in order here: if you are using metal rod clamps, the glue contacting the rods can cause a dark spot on your wood.
This is easily remedied by covering the rods with wax paper before placing your bond in the clamps.
Screws or Glue Depends on Your Project
While the consensus is that wood glue works better than screws for most joints, of course, there are times when screws are necessary. It really depends on what type of joint you’re making. If you wonder if you can put a screw into the joint after the glue is dry, then check out my article on screwing into wood glue(Link Here) for additional information.
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