How much weight will the wood glue hold? Is it strong enough? These are questions I hear all the time.
I was wondering about this, too. So, I did a little research. This is what I found out:
How much weight can wood glue hold? Most wood glues will withstand about 3600 psi (pounds per square inch). The specific value depends on many factors, including the type of wood glue. Also, the glue is often stronger than the wood. So, the wood often breaks before the glue bond fails.
You must be wondering many things: What affects the weight wood glue can hold? Why? Let’s look into this …
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What Is The Weight Wood Glue Can Hold?
What do we mean by “the weight wood glue can hold”? It’s clear that when we drop a weight on a wood surface, we’re pushing down on the surface. This can be thought of as a stress on the wood.
What’s stress? In the context of Woodworking, a definition is:
Pressure or tension exerted on a physical object. The degree of pressure exerted on a material object measured in units of force per unit area.Oxford Dictionary
So, when you push down on wood, you put stress on the glue joints. Also, when you’re pulling apart a glue joint, you’re stressing the joint. This stress is measured in units of force per area. The unit for this is PSI (Pounds per square inch).
This seems to make sense. By measuring PSI before a wood joint breaks, you are measuring the stress that the wood glue can take. This can also be referred to as the strength of the glue.
However, there’s more to this issue: You’re not only interested in the stress that the glue joint will take, but the stress the wood itself will take before breaking. As a matter of fact, the wood can be the “weakest link” in the glue joint. When the glue joint is stressed, the wood can snap before the wood glue bond breaks!
In summary, the “weight wood glue can hold” is the stress on a glue joint before it breaks. This depends on the type of wood, as well as the glue strength.
So, how strong is the wood you’re using? The table below shows the strength for several different woods. It’s divided into two sections: The top part shows hardwoods (Such as Oak, Maple, etc.). The bottom shows softwoods (Such as Pine, Cedar, etc.).
Wood Strength Table
|Wood Name||Type||Strength (Shear parallel to grain)|
|Ash (White)||Hardwood||1,910 psi|
|Ash (Green)||Hardwood||1,910 psi|
|Ash (Black)||Hardwood||1570 psi|
|Cherry (Black)||Hardwood||1,700 psi|
|Chestnut (American)||Hardwood||1,080 psi|
|Elm (American)||Hardwood||1,510 psi|
|Elm (Slippery)||Hardwood||1,630 psi|
|Elm (Rock)||Hardwood||1,920 psi|
|Hickory (Shagbark)||Hardwood||2,430 psi|
|Maple (Bigleaf)||Hardwood||1,730 psi|
|Maple (Red)||Hardwood||1,850 psi|
|Maple (Sugar)||Hardwood||2,330 psi|
|Mahogany (African)||Hardwood||1,500 psi|
|Oak (Northern Red)||Hardwood||1,780 psi|
|Oak (White)||Hardwood||2,000 psi|
|Cedar (Northern White)||Softwood||850 psi|
|Cedar (Western Red)||Softwood||990 psi|
|Fir (California Red)||Softwood||1,040 psi|
|Fir (Grand)||Softwood||900 psi|
|Fir (Noble)||Softwood||1,050 psi|
|Hemlock (Eastern)||Softwood||1,060 psi|
|Hemlock (Western)||Softwood||1,290 psi|
|Hemlock (Mountain)||Softwood||1,540 psi|
|Pine (Eastern White)||Softwood||900 psi|
|Pine (Western White)||Softwood||1,040 psi|
|Pine (Sugar)||Softwood||1,130 psi|
|Pine (Ponderosa)||Softwood||1,130 psi|
Shagbark Hickory is the strongest wood listed in the table at 2,430 psi. This type of wood is often used for axe handles and related tools because of high strength. The weakest in the table is Northern White Cedar, at 850 psi. In general, we can see that hardwoods seem to be “stronger” than softwoods. This seems to make sense as hardwoods are usually more dense than softwoods.
How Much Stress Can You Put On Wood Glue?
However, the wood strength is only part of the story. We also need to see how strong the glue is to determine how much weight the wood glue can hold.
This table shows the stress/strength ratings for various popular wood glues. It contains three fields: Name, Type, and Strength.
Glue Strength Table
|Titebond Original||PVA||3,600 psi|
|Titebond II Premium||PVA||3,750 psi|
|Titebond III Ultimate||PVA||4,000 psi|
|Titebond II Premium Dark||PVA||3,750 psi|
|Titebond Polyurethane||Polyurethane||3,510 psi|
|Titebond Quick & Thick||PVA||3,000 psi|
|Titebond Liquid Hide||Natural Protein Solution||3,590 psi|
|Gorilla All Purpose Epoxy Stick||2 Part Epoxy||1,550 psi|
|Gorilla Epoxy||2 Part Epoxy||3,300 psi|
|Gorillaweld||2 Part Epoxy||4,250 psi|
The Name field contains the name of the glue product. With this information, you will be able to purchase the correct item or look it up in catalogs.The Strength field is the strength of the glue bond, measured in PSI (Pounds per square inch). The Type field describes the particular category that the glue is in:
- PVA – This stands for Polyvinyl acetate glue. These are common woodworking glues and are very strong.
- Polyurethane – These glues can be used outside where a waterproof bond is needed. They’re also very strong.
- Natural Protein Solution – This type of glue is made from natural materials. Hide glue is in this category.
- 2 Part Epoxy – This type of glue consists of a hardener and a resin. They are mixed together and form a very strong bond. Epoxy glue can be used with wood. Also, it’s very good for repair jobs involving wood and some other material, like metal.
Factors That Affect Wood Glue Strength
There are many factors that affect the strength of wood glues. So, even if the glue is rated at a high strength, your actual bond strength might not equal that value. Clearly, we want to get the highest figure possible So, how do we do that?
I’ll attempt to give some of the more important factors. This is certainly not an exhaustive list. A person could keep going and going.
There are many types of glue. These have different properties. What is true for one may not be true for another:
Type of Glue Used
There really are many types of wood glue. Some are stronger than others. However it’s not always best to use the strongest type. Other properties of the glue may be more important for your particular project.
Most woodworkers use one of the PVA glues. They are easy to use, clean up with water, and are very strong. Some are for interior use only. Others are resistant to some moisture. Still, others are classified as waterproof.
Temperature can affect the overall bond strength of the glue. Make sure you follow the manufacturer’s specifications for the glue you’re using.
In particular, you may need to heat your garage in the winter so that you can apply your glue at the proper temperature.
Make sure that the surfaces to be bonded are clean and free of dirt. Often, you can wipe it off with a rag to take care of this.
Porous Wood Surface
End grain is the grain at the end of boards. It can result from crosscuts made perpendicular to the grain. So, you often run into it when you need to join one board to another.
End grain is extremely porous and “soaks up” the glue. As a result, the bond can be very weak. Often woodworkers cut angles or put “fingers” into end grain. Glue can then bond to less porous parts of the grain and the resulting glue joint can be stronger.
Another option is to use an angle bracket or some type of metal plate along with glue to increase the strength of the joint.
Particular woods contain higher amounts of oil, sap, and resin. These substances can often interfere with popular woodworking glues. As a result, the joints can be weaker than they would normally be.
Some of the more oily woods include Oak, Maple, Teak.
To increase bond strength with oily wood it’s often good to use a glue that isn’t water based. For example, you could use polyurethane glue or 2 part epoxy glue.
Can Screws Make The Wood Joint Stronger?
Should you use screws with glue? After all, if the glue is stronger than the wood itself, will metal screws even increase the joint strength?
The glue may be rated to break after the wood itself. However, there is no guarantee that you will actually achieve this high stress figure with your joint. For example, you might be gluing end grains. Maybe you have not let the glue set at the proper temperature. So, screws, nails or other metal supports can actually make the joint stronger.
However, you need to make sure that you don’t crack the wood when you tighten the screw. This will introduce a weak area.
To avoid cracking the wood, you might want to drill a pilot hole for the wood screw. This will make it easier to turn the screw. However, you need to make sure that you don’t remove too much of the wood when drilling the hole. If the hole is too big, the wood can be weakened.
Also, if the hole is too close to the end grain, you can weaken the wood and the entire joint.
Is Hot Melt Glue Strong Enough For Wooden Furniture?
Hot melt glue guns are used with craft projects. However, can hot melt glue be used for furniture construction? Items such as chairs take a lot of “wear and tear”. Are there hot melt glues for projects like this?
The answer is YES! There are glue guns and polyurethane hot melt glues made specifically for projects like these. To find out more, read my post about hot melt glue and wood.
We have seen that wood glue strength is measured in terms of PSI (pounds per square inch). The total weight wood glue can hold depends not only on the strength of the wood glue but the strength of the wood itself. This is the case because the glue is usually stronger than the wood and it will snap before the glue bond breaks. If you look at the break, you will see torn wood fibers but the glue will be intact.
Many factors affect the strength of a glue bond, and then the weight that the wood glue can hold. These include the type of glue used and the application temperature.
Particular hot melt glues can be used for furniture construction.They are very easy to use: Just position the piece to be bonded and hold for a few seconds. No clamps needed! In addition, the joint is very strong.
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