All About Concrete, Adhesives, Fillers and Sealants
Many projects require some kind of adhesive or sealant, and it is important to use the one most appropriate for each task. Learn how to choose the right adhesive for your project.
The most widely used adhesives are described here. Other types are designed for use with particular products, such as vinyl. Mirror adhesives, for example, do not affect mirror backings that might be stained by all-purpose adhesive.
Wood glue: Yellow in color, this is designed specifically for bonding sections of wood. Working time is about 15 minutes. It has a shelf life of about one year.
Contact adhesive (contact cement): A very strong solvent-based adhesive, this can be used to bond a large range of materials including wood, metal, many plastics and decorative laminates. It is not suitable for use with some materials, such as polystyrene and bitumen, or as a mirror adhesive, so check the manufacturer's instructions before using it.
Construction adhesive: Used to bond surfaces that cannot easily be joined with screws or nails, or combined with mechanical fasteners to form very strong bonds. Available in tubes and sealant-like cartridges. Most (especially water-based and solvent-free types) need at least one of the surfaces being bonded to be porous.
Resin: Made up of two elements that mix once they are dispensed from the cartridge, resin creates very strong bonds. Where a secure anchoring point for a wall fixture is required (on shelves, for instance), resin is injected into the hole before the fixture is inserted.
Expanding foam: Supplied in an aerosol can, this foam is used to fill large gaps, bonding to their edges.
Using a Resin Adhesive
Aim the nozzle into the hole in the wall, and discharge the resin adhesive into the hole (Image 1).
Immediately press a heavy-duty fastener into the resin, and allow the adhesive to set before hanging any heavy item from the fastener (Image 2).
Using Expanding Foam
Polyurethane-based expanding foam can fill large gaps or holes, and bonds the surfaces in the process. Some varieties have greater heat resistance than others. This is an important feature in some situations, such as when installing a flue. In this example, foam is being used to fill the gap around a drainage pipe.
Point the nozzle into the hole in the wall, and discharge the foam into the hole (Image 1).
After about five or 10 minutes, the foam will begin to bubble and expand. It will then set (Image 2).
Once it has set, the foam can be cut away using a saw to neaten the overall finish. Finer trimming can be carried out with a utility knife (Image 3).
Holes in the trimmed area can then be filled with an all-purpose filler compound, sanded, and decorated as required (Image 4).
Some sealants prime or seal a surface, while others create a decorative, waterproof or durable joint. Most joint sealants have a waterproofing element. Many sealants are made for specific uses, such as in kitchens, bathrooms or on windows.
Joint sealants usually come in cartridges and need a separate dispenser to apply them. Dispensers vary in size and design, so check for compatibility. Most sealants come in an extensive range of colors. Latex sealants can be painted but those made with silicone can not. Sealant remover is available, but can damage some surfaces.
The sealant must cope with movement, such as that caused by temperature changes, in the materials they join. Some sealants are not very flexible, but dry to a relatively hard finish, and are recommended for use in bathrooms — however, check for resistance to mold. Other types are more flexible, and are used in glazing.
Curing and longevity
Most sealants form a skin fairly quickly, but take several hours, or even days, to dry or cure completely. High-modulus sealants give off strong acidic fumes while curing. A few brands are "fast-cure." A sealant should never get completely hard, because of the need for flexibility. Be sure to check the cartridge for the length of guarantee. High-quality sealants may be expensive, but they are easier to work with and last the longest.
Types of Adhesive Dispensers
Hot melted glue is applied with a glue gun and has a variety of applications, according to the model. Solid sticks of glue are melted inside the gun at the time of use. Guns require electrical power, and generate considerable heat, so follow all the manufacturer's safety guidelines when using one.
Standard dispenser for all-purpose use. High-performance dispensers are also available and are better for regular use, and for use with the more viscous sealants such as construction adhesive.
Several variations are available, designed for specific tasks. An example is a repointing gun with a refillable cartridge for applying pointing mortar.
Easy to use and control, this is the top-of-the-line sealant gun. Batteries are recharged much the same way as those of a cordless drill.
Using a Sealant Dispenser
Cut off the tip of the cartridge. The opening at the tip determines the size of the caulk bead (Image 1).
Insert a metal pin into the tip of the cartridge and remove (Image 2).
Pull back the dispenser's plunger or rod and load the cartridge into the dispenser (Image 3).
To dispense the sealant, apply even pressure to the trigger. When you release the trigger, sealant will continue to dispense due to a buildup of pressure (Image 4).
Push the catch plate to make it stop. To store a half-used tube, insert a nail into its nozzle to prevent clogging, or replace the nozzle next time you use the tube (Image 5).
Water-based adhesives are an ecologically sound alternative to solvent-based products. They are non-toxic and low in VOCs (volatile organic compounds).
Health and Safety
Follow all manufacturer's instructions when using an adhesive or sealant, because the chemicals involved can be dangerous. Ventilate your working area and wear all recommended protective equipment and clothing.