How To Glue Metal To Concrete
There are many different types of adhesive that can bond metal to concrete. Epoxies, urethanes, and silicones are the most common. These adhesives will provide a strong and permanent bond as long as they’re applied properly. In this article, we will go through the best ways to glue metal to concrete, from first preparation to final setting.
Which Glue Is Best For Bonding Metal To Concrete?
There are three types of glue we would recommend for the task of gluing metal to concrete
Epoxy
Epoxy adhesive is one of the most popular adhesives for bonding metal to concrete. It has great versatility and can be used in a variety of applications.
There are two materials that makeup epoxy: an epoxy resin and an epoxy hardener. The two main types of epoxies are thermoset and thermoplastic. Thermoplastic epoxies set rapidly at room temperature, typically within five minutes or less, while thermoset adhesives require heat to cure properly.
Epoxy resins are cured with heat and are considered slightly superior to thermosets. Epoxies provide a good bond strength for metal to concrete, but they do have some drawbacks. First, epoxies are not recommended for use on concrete that contains fiberboard. The reason is that fiberboard reacts with the epoxy resin to produce a brown resin blob called “bloom”. Bloom can cause serious damage to treated surfaces if left on too long.
According to the National Concrete Masonry Association (NCMA), epoxies are safe and can be used on concrete that contains fiberboard. In general, temperatures hotter than 180 degrees Fahrenheit and more than 60 psi of pressure are recommended.
Epoxy resins can be mixed with many different hardeners to produce a wide variety of adhesive characteristics. For example, the epoxy-hardened steel connectors used in timber-framed construction require an epoxy resin that is extremely flexible and resists cracking while under compression.
Urethanes
Urethanes have the advantages of epoxies with the added benefits of good flexibility and longer reaction time. Urethanes are also compatible with fiberboard, so they have fewer drawbacks.
The most commonly used urethane is a two-part adhesive that cures with heat. This type of adhesive is called an aromatic urethane and thermosets and cures at room temperature or slightly above. It can be applied to concrete immediately after mixing, but it should set up within about one hour.
Silicone Adhesives
Silicone adhesives are great for bonding metal to concrete because they adhere well, but can be removed later through heat and pressure. Silicone is also flexible and can withstand high temperatures without getting brittle.
Because silicone can be removed with heat, the siliconized surface does not have to be waterproofed or sealed and the final bond is unaffected by water. Most silicone adhesives are applied using a caulking gun or other similar tool.
Preparation
Before bonding metal to concrete, it is important to be aware of the various hazards that can be caused by using the wrong types of glue.
The first hazard is a chemical attack. Because many types of glue react with the concrete to produce harmful compounds, using glue that will react with the concrete can cause damage. Your end result may look and function correctly, but if you allow the reaction time to go on too long the resulting bond could become brittle and break over time.
The second hazard is fire. If the bond becomes hot enough, it can melt the surrounding concrete and cause a fire hazard.
The third is heat shrinkage. The heat created by the cement reaction can cause the adhesive to shrink and contract, making it more brittle and liable to break.
Applying
If you are using epoxies or urethanes, the best way to apply them is to use an electric trowel. This type of tool is used commercially by contractors for concrete installation and can also be purchased from specialty retailers. A standard trowel has a thick handle, which can be used to apply the adhesive without heat.
Before bonding the metal, it is important to mark where you will need a hole for drilling. Then, make a hole in the concrete using a hammer drill. The hole should be slightly smaller than the threaded ends of the metal. This will allow the metal to be fastened securely to the concrete.
Before gluing, flush all dust out of the holes by spraying them with water. Then, clean up any remaining dust that got inside the hole and around its edges by flushing it out with water and wiping it away with paper towels or rags. Remove hair, lint, and other debris by using a vacuum.
To glue the metal to the concrete, use a rubber mallet with a 1/4 inch socket or an adjustable wrench to fasten it in place. Then apply adhesive to the threaded holes and insert them into the hole in the concrete. Place adhesive around each hole and tighten evenly but firmly.
Allow time for the adhesive to set for at least 24 hours before using it. The entire bond should be completely cured within two weeks of application.
Setting
After applying the adhesive and fastening the metal to the concrete, you should allow time for it to set. A good rule of thumb is to allow 24 hours for epoxies and 12 hours for urethanes. After the set time is up, it is important to completely cure the glue so that it does not soften in use.
If you are using urethane glue intended for concrete, then you can use a high-temperature heat gun to cure it in place if the conditions are correct. If you are using an epoxy adhesive, you can use a heat gun with a temperature of around 120 degrees Fahrenheit, but not more. If the temperature is too high, the adhesive and surrounding concrete can get brittle and break off.
Safety And Guidelines
Before starting any project, you will want to make sure that you have the proper safety equipment. This includes gloves, eyewear, and a respirator. Epoxies and urethanes can be damaging to your lungs if inhaled, so it is important to protect yourself when using them. Respiratory protection may also be necessary to prevent any inhalation of fly ash and cement dust, which can cause lung irritation.
