The A to Z of adhesives, providing all the information necessary to ensure that the correct adhesive is used with the specific floor type to allow for a successful installation.
Flooring adhesives refer to a variety of solutions used to install a floor surface-covering material to the subfloor or underlayment. Adhesive is primarily used to permanently bond the floorcovering to the substrate to prevent movement and damage. Different types of adhesives are recommended for different types of flooring, although some multi-purpose solutions can also be effectively used with multiple materials.
When selecting an adhesive, there are a few important considerations to bear in mind, which include (in order of importance), the floorcovering to be installed, the manufacturer’s recommendations, the type of substrate, the condition of the substrate and the location in which the adhesive will be expected to perform. Climatic and localised conditions such as temperature, humidity, indoor/outdoor etc. will also need to be considered. When choosing the most appropriate adhesive applicable to each specific set of circumstances, sometimes requiring very specialised adhesives, these need to be considered.
Different types of adhesive have different characteristics, which will influence the decision to be made, from technical compatibility as well as practical application perspectives.
Basic Guide to Adhesive use with flooring:
Substrates and their impact on adhesive choice:
It is important to note that this is a guide – refer to the flooring and adhesive manufacturer for confirmation.
The table above shows Sand/Cement Screed or Concrete as the common factor. An important consideration now lies with the state of the substrate and the standard requirement for successful installation of flooring is that the screed must be sound, dry and free of contamination.
Sound: If the screed is sandy, dusty, friable or not properly bonded to its substrate, the entire system will fail if any stresses are placed due to shrinkage etc. The screed normally delaminates from the slab and comes up with the flooring, adhesive and any self-levelling compound.
Dry: Depending on the specific floorcovering to be installed, this will typically range between 3-5%; refer to the flooring manufacturer’s specification. If adhesive is applied to substrates that are too wet or moist, there is a possibility that the adhesive will not set properly, and in long term exposure, will re-emulsify and soften. The modern way to deal with moisture levels that are too high, is to apply a moisture barrier which then prevents moisture from affecting the adhesive.
Adhesive needs to penetrate into the surface of the substrate, and very closed surfaces such as power-floated concrete may prevent this. Other substrates such as epoxy coatings, old ceramic tiles, old vinyl flooring may also inhibit adhesion, and advice should be sought before proceeding.
Free of contamination: Old adhesive, paint, oils or putty must be removed or it must be appropriately sealed. For example, oils can soften the adhesive and prevent adhesion.
Common terms used with adhesives:
Coverage: The amount of adhesive to be used when applying the adhesive to the substrate with the specified applicator such as a notched trowel. The adhesive manufacturer formulates the adhesive to achieve specific performance related results, and requires the adhesive to be applied at that rate. This expressed as m² per kg or litre or as gms or ml per m².
Open Time: The maximum working time that the adhesive, after it has been spread on a substrate, remains able to receive the flooring. The same adhesive can experience significant differences in open time due to the following factors – atmospheric moisture (Cape Town in winter will experience a much longer open time than in summer), temperature (the colder the temperature the longer the open time), screed porosity will also influence the open time.
Flash-off Time: This is the time between the application of the adhesive and its readiness to receive the flooring. Even within similar types of adhesive this can vary considerably. European style adhesives tend to ready much sooner than local adhesives. This requires different work practices.
Consistency or Spreadability: This refers to the viscosity and workability of the adhesive. It should ideally be easy to spread over the substrate, adhere to the substrate and not “roll off” in front of the trowel. A buttery consistency will allow surplus adhesive to be picked up on the trowel and redeposited into the container.
Peel strength: The adhesive’s ability to prevent the flooring from being pulled up off the substrate.
Shear strength: The adhesive’s ability to prevent dimensional change in the flooring, in a horizontal plane.
Plasticiser Migration: Vinyl and PVC flooring contains PVC and Plasticisers which are prone to migrate out of the flooring very slowly over time. If the adhesive contains substances which create an imbalance, the plasticiser migration can be accelerated. The plasticiser thus released can soften the adhesive and can cause it to malfunction. The flooring can also be affected negatively.
Freeze-thaw stability: Water based adhesive will break down if they freeze. Storage is key to ensure that the adhesive is not subjected to freezing. In South Africa, the rule is not to install flooring below 15° C. Although this frequently happens, applying adhesive at low temperatures will present difficulties and even failure.
Clean-up: The adhesives used in a flooring project can be amongst the most difficult materials to clean up and remove from surfaces. In general, water-based glues will be easier to clean, but that will also make them susceptible to water degradation. Depending on the adhesive, different methods may be used to remove residual adhesive, including solvents such as Turpentine, Toluene or thinners. It is best to consult the manufacturer to obtain advice.
TYPES OF ADHESIVES AVAILABLE FOR SPECIFIC FLOORS
Acrylic Emulsion Adhesives
These adhesives are most commonly used for vinyl flooring of all types, and stick-down carpeting.
They are made from an emulsion comprising acrylic polymers, resins and binders as well as fillers etc. Most PSAs (pressure sensitive adhesives) are produced from acrylic emulsions. As a general rule most acrylics are pressure sensitive to a greater or lesser extent.
Once cured, high quality acrylic adhesives will be resistant to limited levels of moisture. The general purpose versions will have long open times which makes them ideal for installing sheet materials. Many will retain tackiness for a long time which enables installers to spread a whole room and cut in the edges afterwards. These adhesives tend to have minimal effect on plasticiser migration, and are widely specified.
Specialised versions with qualities aimed at solving specific floor covering issues, such as exist with LVTs are available and have eliminated many problems related to this type of flooring.
Pressure sensitive adhesives are mostly used where the flooring may need to be lifted periodically, such as access floors, so their permanently tacky properties are useful.
It is important to note that quality and performance vary greatly and the flooring manufacturers are generally the best people to contact to determine which are best suited to the job.
SBR Emulsion Adhesives
These styrenated butadiene rubber adhesives will often be incorporated with latex and are typically used with stick down carpets. They tend to perform poorly in moist conditions, have the potential to discolour products such as cushion vinyls.
This normally a wood glue, and is often used with solid wood flooring, where moisture is not an issue.
In Europe, use of solvent based adhesives has been terminated for several reasons – flammability concerns (many artisans have been injured or even killed where solvent based adhesive has been ignited accidentally) and non-flam adhesives give rise to serious concern relating to addiction, impaired lung function and potential heart problems.
Being solvent based, they may affect resin systems in stick-down carpeting. Use with care.
Neoprene Contact adhesives
These contain chloroprene rubber which is kept in liquid form by the use of solvent. These are pressure sensitive, and need to be applied to both surfaces to be bonded, allowed to flash off completely and then brought together, where they bond immediately. This is useful where high bond strengths are needed from the outset, such as hanging vinyl wall sheeting, flooring accessories such as skirtings etc. As they are not water based, they tend to be more resistant to moisture, but will accelerate plasticiser migration in vinyl flooring.
One part Polyurethanes
These very high bond strength adhesives originally were used in footwear, but are now used more commonly where high bond strengths are needed, with a very fast flash off, and working time.
Two part Polyurethane-based
This product is a reactive resin system where two components are mixed together and a chemical reaction takes place so that it cures and hardens sufficiently within four to six hours to take foot traffic. Polyurethane-based adhesives do not evaporate into the air, but instead form a solid structure between the bottom of the surface and the top of the subfloor. They have been available for several years and their durable properties are well known in the industry. Two-part urethanes tend to cure to a rigid film, which prevents movement. Under extreme pressure the film may fracture.
One-part polyurethanes are more flexible. Most polyurethanes do not become tacky, and cure chemically, which makes them difficult to work with.
Due to this strength of bond, polyurethane adhesives are used with flooring which needs stronger bonds, such as wood, rubber and injection moulded PVC tiles.
When selecting an adhesive for a carpet installation, one must consider the type of backing, necessary grab, traffic load, maintenance schedule, and quality and lifecycle of the carpet. The majority of today’s one-step carpet installations rely on the use of SBR-based adhesives due to their fast grab and excellent re-tacking characteristics. For builders and business owners desiring a short-term carpet installation, an economy-grade, SBR-based adhesive would be suitable.
A higher-end, commercial installation expected to last several years, which calls for glue-down application, would require a higher-grade adhesive. For carpets without design patterns where seams can be trace-cut, an adhesive offering ultra-quick grab should be used. This will allow the carpet to be rolled right away, which is ideal for today’s fast turnaround installation schedules. More extensively patterned carpets require a higher-quality adhesive with strong grab and appropriate slip time for matching up the patterns.
This tile adhesive is used for general tiling on solid concrete floors, and is generally cheaper than other types of tile adhesive. However, it should not be used on cracked cement floors or where there is the influence of acid-based chemicals or cleaners or where some movement is expected. It is supplied dry and is mixed with water and/or bonding liquid before being applied.
Contractors and installers looking to maximise profit while minimising the risk of call-backs need to stay abreast of the latest products when it comes to selecting floor adhesives. Being informed will ensure that they choose the correct adhesive for the correct application to allow for a successful flooring installation.
Wood flooring systems that make use of a tongue-and-groove fixing system should use a one-part polyurethane or a one-part SMP adhesive as it has elasticity for a bonded movement. This type of adhesive is also used where these floors are required to be stuck down, although a damp-proof sealer or moisture barrier should be applied to the substrate before installation commences.
Since wood products require a strong bond, urethane-based adhesives are excellent choices for holding solid wood in place. Once cured, these high-quality, solvent-free adhesives provide the flexibility and superior bond strength that sold wood installations demand.
SMP and urethane-based / moisture-cure adhesives offer the largest range of application and the highest installation security. For approved pre-finished, engineered wood, cork and parquet floorcoverings, a water-based adhesive is a choice pick due to its ultra-high tack and excellent re-bonding characteristics. Before any wood installation commences, it is advisable to consult the wood manufacturers to determine if their product is recommended for glue-down, as some engineered wood must be installed as a floating or nail-down system.
Acknowledgement and thanks go to iTe Products; Den Braven; FloorworX; Norcros SA; www.mariontile.com; http://flooring.about.com and https://en.wikipedia.org for the information contained in this article.