When Laticrete founder, Dr. Henry M. Rothberg, launched the company’s 4237 Latex Thin-Set Additive, he introduced a strong, weather- and shock-resistant “thin-bed” mortar, using equal parts sand and cement. It replaced thick, heavy and labour-intensive mortar bed installations. As acceptance of this problem-solving technology increased, ceramic tile and stone became more common choices for flooring and building facades.

Early in their development, tile adhesives won out over mortar for one very simple reason: weight. Writing in the mid-1990s about the evolution of tile adhesives, Henry M. Rothberg, then chairman of the board for Laticrete International, recounts the story of the first major project he was involved in during the 1960s where adhesives replaced mortar.

“For example, 30 years ago, I met with the designers, including the architect I.M.Pei, who were developing two100-storey buildings in New York City. We reviewed the problems of ceramic tile in such structures when installed by the traditional mortar method. We created a study reviewing costs and savings of ceramic installation with the new adhesive method and traditional mortar method.”

What that study showed was that, using mortar, some 2268 metric tonnes of the material would be required. When all the costs of elevator time and loading/unloading were added up, it came to, in 1960s US dollars, USD168,000.

Comparatively, adhesives would require less than 250 tonnes of material, which would cost only USD 16,800, a savings of USD151,200. Adjusted for inflation to 2017, that’s equivalent to USD1.236 million.

Additionally, with a reduction in structure weight of over 2000 tonnes, the building engineers estimated there would be further savings of USD100,000, which in 2017 terms would be USD817,000. So an overall savings, in 2017 terms, of over USD2,000,000.

As Mr Rothberg points out, the reality was that without the use of adhesives, the architects would simply not have chosen to use ceramic tile:

“If the adhesive method was not available for ceramic tile or if the technology was not advanced enough, there would have been little or no ceramic tile sold on this project. The owners would have chosen carpet, vinyl or thermoplastic flooring.”

Adhesive qualities

There are around four highly important characteristics that tile adhesives need to have, namely:

  • Adhesive strength
  • Water retention, i.e. open-time and adjustability-time
  • Resistance to excessive strain development
  • Flexibility (deformability)

The ability of the adhesive to keep the tile in place can be measured in terms of tensile and shear factors. These two factors are frequently connected when it comes to stress being placed on tiles.

For example, if the substrate on which the tiles are placed shrinks, this will create an initial shear stress, which seeks to move the tile on a horizontal or vertical plane. When that force is resisted by the adhesive, the tile will instead tend to bulge outwards, which places a tensile stress on the adhesive.

“Open-time” refers to the length of time the tile layer has to place the tile on the bed of applied adhesive. If the adhesive loses water rapidly to the substrate, or reacts quickly to exposure to the air by forming a skin over its surface, the adhesive will not form a strong enough bond with the tile. “Adjustability-time” refers to how long the tile layer has to move and adjust the tiles after contact with the adhesive. Again, this largely depends on how fast the adhesive loses water to the substrate.

The expected standard for most adhesives is open-time and adjustability-time of around 15 to 20 minutes. It is typically promoted and controlled by the addition of organic additives, which tend to be limited in cheaper adhesives, due to their high cost.

If the adhesive has an unbalanced formulation, or is applied at too great a depth, shrinkage in the adhesive will introduce strain on the tiles.

Flexibility is the ability of the adhesive to adapt to shifts and changes while retaining adhesion to the tiles.

Types of adhesives

The development of adhesives has largely followed the path of attempting to meet these requirements in a variety of circumstances, and with different balances between them, while keeping costs low and ease of use high.

There are, in general terms, five different types of adhesive: “Thinset” or standard mortar; one-part adhesive (also called paste/mastic adhesive); latex-based adhesive; solvent/resin-based adhesives; and epoxy/reactive resin adhesives.

Thinset/mortar cement adhesives are the simplest of the adhesives and consists of Portland cement, sand and an organic ingredient to help the mixture retain water to improve its open-time. That ingredient is quite typically an alkyl derivative of cellulose.

One-part adhesive is primarily a resin or latex based adhesive with filler substances such as quartz or marble dust. While this adhesive is easy to use, it is not suitable for use where exposure to moisture will occur, or where heavy stress will be placed on the tiles, such as in flooring.

Latex-based/cement adhesives were the first tile adhesives developed that could withstand external application, with good waterproofing and frost-proofing properties. Sometimes also known as “two-part” adhesives, they are made by mixing liquid latex with a mixture of Portland cement and sand.

Solvent/resin-based adhesives are factory-prepared, ready-to-use mixtures consisting of fillers dispersed in a solution of an organic binding agent in volatile solvent. Environmental concerns mean that these formulations are no longer used much.

Epoxy/reactive-resin adhesives is a speciality adhesive that provides a high level of resistance to exposure to cleaning chemicals, and is frequently used in areas such as dairy production and food factories.

Impact on building

As Rothberg relates in his history of the early use of tile adhesives, the move to adhesives also required some changes in the way that buildings were constructed. He said, “When I developed the first latex Portland cement adhesive suitable for both exterior and interior ceramic tile installations, I met great resistance from the construction industry because it was not traditional. Forty years ago, it was necessary to instruct both architects and building contractors in floor and wall surface preparation. I would then teach ceramic tile installers how to use a notched trowel in applying a thin layer of cement based adhesive.”

Architects needed to be informed because the types of building surfaces we take for granted today were not the norm back then. Rothberg goes on to say:

“The traditional method accommodates variations in wall or floor surfaces because mortar can he applied from 20mm to 70 mm in thickness. This allows the tile installer to accommodate poor quality concrete floors, or uneven brick and masonry walls.

“The introduction of adhesives has dramatically changed many phases of construction. With adhesives, the floor surfaces must first be flat, true and level or the walls must be flat and plumb. This is usually the responsibility of the concrete worker for floors, and the plastering worker for preparing the walls. It is necessary for the architect and builder to understand the adhesive technology limitations so they can prepare the building properly.”

Adhesive technology also developed in step with advances in producing ceramic tiles. Pre-World War II tiles tended to be small mosaic tiles fixed with cement mortar, and the rough backs of these tiles helped the mortar to secure them in place. The mortar was applied with a minimum thickness of 25 mm. This thickness ensured that the cement would retain moisture over a period of time in order to develop strength and cure.

The move to ceramic tiles with smooth backs, produced in larger sizes meant that the standard methods no longer worked well. Rothberg said, “Technology advances in the adhesives industry supported technology advances in the ceramic industry. As the ceramic industry produced larger and more impervious tiles, they required new adhesive technology to provide problem-free installations. So, adhesives technology moved hand in hand with ceramic technology.”