The Causes and Effects of Common Adhesive Problems

Adhesive concerns surface in all types of situations. Often, we believe that the only role an adhesive plays is to hold down a piece of material. But frequently, extenuating circumstances arise to create problems. The following are several of the more common adhesive-related concerns and their possible causes.

Adhesive on the surface of materials

Adhesive on the surface of a piece of resilient material can be a result of many different causes. Sometimes, spilled adhesive is tracked onto the surface of the floor material. Other times, it's due to adhesive oozing or bleeding through a tile joint or seam. The adhesive will be sticky, attract soil and appear dirty. Most adhesives, with the exception of epoxies, can be cleaned from the surface of the material. It is best to attempt to identify the source of the adhesive so that the cause of the problem can be positively identified.

Bleeding of adhesives can occur for a variety of reasons. Among these are:

Excess adhesive, deposited from a trowel notch that is heavier than what was specified by the manufacturer of the adhesive or resilient material, can leave a film of adhesive that is simply too thick. This thick film tends to migrate when subjected to foot or rolling-load traffic.
Open time of the adhesive was not honored. With few exceptions, adhesives are designed to have open time. Open time allows the adhesive to lose some of its moisture and develop body. The professional installer must know how to judge the proper open time in accordance with individual job-related variables, such as temperature, humidity and substrate absorbency.
Moisture problems can impact adhesives within days of their application. In most cases, a moisture problem will occur within 48 hours, but the adhesive may require more than five days to fully cure. Thus, the emergence of a moisture condition can cause the adhesive to re-emulsify and ooze.
A maintenance problem, often the result of either stripping the floor or starting the floor maintenance regimen too soon, can cause adhesives to bleed. New floors should not be stripped. Strippers are highly alkaline, and their alkalinity attacks the adhesive - especially when the adhesive is new. Subjecting newly installed resilient materials to excessive moisture, perhaps by aggressively mopping the floor, will create the same effect as a moisture problem if the adhesive has yet to fully cure.

Compatibility of adhesives with the substrate

Residues on the surface of the substrate can cause de-bonding, discoloration and adhesive deterioration issues. Any residue left on the surface of the substrate introduces one more variable that can cause adhesive failure. Some common residues, and the concerns they create, are as follows:

Oily residues create bonding and discoloration issues.
Sealers and curing compounds create bonding and adhesive compatibility issues.
Parting compounds create bonding issues.
Overspray of paint creates bonding and adhesive compatibility issues.
Gypsum wall textures/taping compounds create bonding issues.
Solvent spills create discoloration and adhesive deterioration concerns.
Heating oil spills create discoloration and adhesive deterioration concerns.
Existing adhesives can create compatibility problems with the new adhesive.

The substrate's porosity often dictates the type of adhesive to use and the amount of open time it requires. Many times, a floor in a renovation project is assumed to be porous when, in fact, the substrate is non-porous. Porosity conditions are of most concern when installing resilient products with a non-absorptive type of backing, such as when heterogeneous- or homogeneous-backed sheet materials are laid over a substrate that has had a moisture remediation treatment and was skim coated with a cementitious underlayment.

Bonding failures

The causes of adhesive bond failures are varied. Some of the more common situations are detailed below.

Dirt and dust on the surface of a substrate can create enough of a barrier to negatively impact the adhesive's bond and cause installation failure once the floor is placed into service. Dusty surfaces can also cause adhesives to "ball-up," which creates a show-through problem in the finished floor.
Residues from sealers, curing compounds and parting compounds serve as just one more layer of a substance that can fail. Most of these residues are made to degrade or decompose over time. How can you be sure this has transpired?
Insufficient open time for adhesives usually leads to bubbling, indentation of the material's surface and adhesive migration.
Excessive open time usually results in a poor bond between the resilient material and the adhesive. This is usually the case whenever there's a lack of adhesive transfer to the back of the material.
Moisture damage to an adhesive manifests itself in two ways: either in re-emulsification, or in a poor bond of the adhesive to the substrate. Either condition tells you that the adhesive was not allowed to cure. Adhesives that re-emulsify were exposed to moisture prior to the adhesive's cure, meaning the substrate was too wet to install over. Adhesives that initially cured but were then subjected to moisture will usually de-bond from the surface of the substrate, leaving most of the adhesive stuck to the back of the flooring material
Alkalinity damage appears in two guises: the adhesive will have a crystallized appearance and be somewhat brittle, or it may virtually disappear and leave only a few traces of residue. To the untrained eye, alkalinity attack on an adhesive can create the impression that too little adhesive was used. In reality, the adhesive was just eaten up by the alkaline salts.
Adhesives that dry too soon due to the effects of an overly absorptive substrate can cause the adhesive to appear chalky and somewhat crystallized. When allowed to dry too quickly, the plasticizers in the adhesive can be removed with evaporating water, which limits the adhesive's elasticity.

Excessive adhesive application

Excessive adhesive application is usually the result of the installer selecting an improper trowel notch for the job. In fact, the notch trowel is the installer's single most misused tool. All adhesive manufacturers specify the trowel notch requirements for their adhesives and for the type of substrate to which the adhesive may be applied.

So, why is there a problem? Well, if you were using a trowel with 1/16-inch wide and 1/16-inch deep notches spaced 1/16 of an inch apart, and the specifications for the adhesive required a trowel with 1/16-inch wide, 1/16-inch deep notches spaced 3/32 of an inch apart, you'd probably question what harm could come from using the trowel that had notch spacing a mere 1/32 of an inch smaller that what was specified. How could such a minute difference affect an adhesive spread? The answer is almost 20% more adhesive will be applied to the substrate.

Excessive adhesive applied to the substrate is responsible for indentations in resilient material caused by static loads, such as furniture, and rolling loads. Undulations in the material can result from knee, knuckle and footprints that leave permanent impressions in the excessive adhesive film left on the floor. Ridges may also develop in the adhesive during the rolling of the floor. Other problems caused by the application of excessive adhesive include oozing of adhesive, adhesive contamination of seams, bubbles in the floor covering, and curling of materials.

Rolling materials into the adhesive

I hear a lot of comments regarding the use of a roller. To get excess air out from beneath the freshly laid floor covering, some installers use a broom, a wet towel wrapped around a piece of lumber, a wall roller, their hands, and any number of other means. The bottom line is they are too lazy to carry in the appropriate tool - a roller - to complete the installation in the specified manner.

Why do you think a manufacturer would specify the use of a 100-lb. roller if a 25-lb. one would do the job? Why would a manufacturer specify a 150-lb. roller for rubber tile if a 100-lb. roller would suffice? Are manufacturers trying to be difficult? I don't think so! The reason is application of a specific, straight-line static load is necessary to force the material down into the adhesive while maintaining a uniform pressure on the surface of the material. Do you think that could be accomplished with a wall roller? And how do you think the installation will look once it has 10 coats of high-gloss polish applied?

Adhesive removal

Removal of adhesives must be done with the greatest of care. Some adhesives must be completely removed, while others may be removed to a thin residue. In no case should a new adhesive be applied over the trowel notches of an old adhesive.

Adhesives can be removed by either mechanical or chemical means. If there is no asbestos concern with the old adhesive, it can be removed mechanically through the use of some type of power scraper (either a wet or dry method). Chemical removal requires much more attention to detail.

Chemical adhesive removers must be cleaned up thoroughly, because they exert the same removal action regardless of whether they come in to contact with an old existing adhesive or a freshly applied new one. When remover residues are left behind, the results can be disastrous.

Beware of adhesive abatement companies that are not familiar with the flooring industry and its standards. These firms can leave you with what appears to be a clean substrate even when it is loaded with adhesive remover residues that are not readily identifiable.