Adhesives

Adhesives by definition are non-metallic pastes that are used in the process of bonding two surfaces together. They can come in the form of runny liquids as well as malleable pastes. Adhesives are applied between 2 surfaces out of a bottle/tub or tube and are governed by a “working time/open time”. This period of time is different for each type of adhesive and refers to the amount of time that an adhesive is able to be worked before it begins to cure once removed from its container.  

Once dry, an adhesive forms a strong bond between two materials and resists forces of separation up to its working load. Some forms of adhesive remain malleable once set, others take on a moveable but firm character, whilst others dry to be completely solid. There are many different types of adhesives that are used in construction applications, here we shall take a look at them.  

PVA Wood glue

Wood glue is a very affordable and widely used adhesive that is used for glueing two timber materials together. The base of regular wood glue is PVA (polyvinyl acetate), a workable viscous fluid that dries into a hard material. When utilised correctly, PVA dries harder than most timber, and as such is a great choice of adhesive for bonding wood materials. Many manufacturers produce their own PVA based wood adhesives, with particular additives that increase the durability and strength of the glue being added to the formula. Certain types of wood glue can be used in exterior scenarios. PVA has a relatively long open time in comparison to other adhesives, meaning it can be worked for a while before it sets. As it begins to set the PVA becomes tacky. PVA that is applied in cold weather can dry into a brittle state that does not bond properly to the materials it is in contact with. Most PVA dries a whitish clear colour but can be mixed with sawdust or colouring to create a colour match when dry. This glue is water based and is nontoxic, making it a very suitable adhesive to work with.  

Silicone Sealant

Silicone sealant is a waterproof sealant that is used throughout the construction industry for a variety of different applications. Silicone is applied with a sealant gun to a dry and dust free surface and can be used to either bond or waterproof an area. Common applications for silicone include lightweight bonding such as sticking window boards or skirting in conjunction with nails, as well as sealing baths, shower trays, sink basins, and kitchen worktops. When silicone sealant is squeezed out of the tube it is a viscous and sticky liquid that can be easily shaped or moulded with profiling tools. When the sealant dries it becomes rubbery and capable of flexing slightly with the movement of other materials. As such it is good for use in moist environments such as bathrooms where the humidity rapidly changes. Silicone also has a fairly long open time and ordinarily cures overnight, though fast drying formulas are available. There are many manufacturers that produce specialist formulas that possess properties such as mould resistance and increased strength. Silicone comes in a variety of different colours suitable for use in many applications. These types of adhesives may also be referred to as mastic, an older term used for these products due to the use of mastic resin in their creation. Whilst some products do still contain mastic resin, synthetic silicone is more commonly used.  

Chemical anchor resin

Chemical anchor resin is a form of adhesive used for structural applications. The most common application for this type of adhesive within domestic construction is securely fastening threaded rods into masonry or concrete. This adhesive typically has a very short open time, meaning that it dries hard in a short space of time. The resin dries hard and waterproof, forming a strong bond with most materials provided the surface is clean and dry. Once dried the resin is capable of resisting much shear force as well as draw out and is stronger than the masonry that it is pumped into.  

Flooring adhesive

Flooring adhesive is a type of glue that is used specifically for securing modern chipboard or OSB flooring to timber and other dust free substrates, typically in combination with the use of mechanical fixings such as nails or screws. The glue is applied to the substrate before the sheet is laid, as well as in the tongue and groove of the sheets. As the glue sets, it expands into a foam-like substance. This foam fills any small gaps between the boards, as well as ensuring there are no gaps between the flooring and the substrate. This gap filling technology helps to eliminate squeaks in the floor later on down the line. Whilst this glue is very effective at holding down the floor, it can be a nightmare to remove sheets after the fact if required. Unlike traditional non glued floorboards, glued boards are near impossible to remove without damaging the floor joists, due to the high strength performance of the adhesive. Additionally, the chemicals involved in the glue are particularly unpleasant, with many manufacturers issuing a known carcinogen warning with their products. As such, it's imperative to wear gloves and cover up to prevent contact with skin. That being said, there is typically no inhalation danger, as the glue does not give off vapour. 

Construction adhesive

Construction adhesives are a heavy-duty form of adhesive intended for use in the dirty and rugged construction environment. There are many manufacturers with varying formulas and products that all fall under this category, though they are each sold under the description of varying characteristics. Generally, they all share similar properties, namely extreme bonding strength and fast setting actions. All weather applications, gap filling, and non-toxicity are among the other properties that are common with this type of adhesive. When wet this adhesive is very thick and tacky, capable of giving a good instant bond for holding materials in place. When dry this adhesive is still flexible and capable of moving in environments with varying moisture contents. Many types are UV resistant and shrink and crack resistant, making them perfect for bonding in external scenarios. These adhesives are typically thixotropic in nature - a descriptor that means they are capable of returning to their original set state after having been stressed. This property is good for environments that suffer from frequent material movement.  

Contact adhesive

Contact adhesive is a lightweight spray adhesive that can be used to adhere materials to large surfaces. This adhesive is not suitable for use in structural applications due to its low comparable bonding strength, though it finds uses in other areas. Sticking down paper templates, tacking carpet, or applying veneers are a common use for this adhesive. Generally speaking, it does not find much use in residential construction, though it's still useful to keep a can handy. 

Bitumen

Bitumen is a petroleum-based product that presents itself in a thick, sticky liquid. This material is viscous and waterproof and is commonly used for sticking down felt on flat roof assemblies. This product is black and softens with heat. It can be purchased in tins for use in flat roofing. It is poured onto the area in which the felt is being adhered and can be spread with a roller. As it dries/cools, the adhesive becomes harder and bonds to the felt and roof surface. It remains somewhat malleable once dried and moves in response to the heat from the sun, preventing the felt from cracking. Some types of felt come with hardened bitumen as a backer. This felt can be rolled out and heated on its back side to soften the bitumen before/during installation. 

Super glue/CA glue

Cyanoacrylate, more commonly known as super glue, is a fast-curing adhesive that will bond to most materials. This adhesive can be used for lightweight bonding. Common applications include joining mitres in skirting and architrave, as well as applying veneers. This adhesive dries hard, though it can be brittle when dry. In most cases it can take up to 24 hours to fully set and can be applied in a wide range of temperatures. Super glue intended for use in construction is often sold in a set alongside a spray can that is full of activator. When the activator comes into contact with the glue, the glue sets in a matter of seconds. 

2-part resin/epoxy

This type of adhesive is created by mixing two components together, in a similar method to the glue and activator CA glue kits. These products are sold with the resin alongside a catalyst that is used to activate the resin. When the two are mixed and allowed to dry, the resulting material is incredibly hard and durable. Cured resin can be bonded to most materials and is resistant to water and temperature. Dried resin can be sanded and painted. This type of adhesive sees much more use in factories or boat building and is not commonly used in construction. When used, it is mostly in repair applications.  

Construction foam

Construction foam is a modern type of adhesive that sees a lot of use due to its fire-resistant properties. Fixer foam is a type of adhesive that expands to bond materials together. This type of bonding is strong as is typically used for filling the gaps around door linings or window openings. This foam is fire rated and as such is often called for in the regulations and specifications of a project. Expanding foam is another type of foam that is used for filling voids where drafts are found. This type of foam expands to multiple times its size and is able to fill deep voids that can’t be accessed from the surface of a structure. Both types of foam are very sticky and tacky when first sprayed out from the can. Once the foam has dried the excess can easily be cut away with a saw or knife. This foam can be sanded, filled, and painted, though this is a makeshift solution to some problems. Specialist foam can be purchased with the intention of fixing plasterboard to masonry.