Flooring Adhesives


Mastic or Mortar

Flooring adhesives can be one of the hardest challenges you face when you install flooring. To illustrate, you make up you mind to install flooring in your kitchen, so you go down to your local home improvement store and you look at all the varieties of tile they have on their shelves. You pick out a few designs you like and then think to yourself, ‘I need an adhesive to glue the tile to the floor.’ So you walk around the corner to the next isle where all the installation materials are located. Then you say to yourself, ‘Holy Cow there’s so many! Which one do I buy?’

Flooring adhesives can best be understood by simply reading the tile or stone manufacturer guidelines. Most floor tile manufacturers will recommend a particular adhesive and it’s always best to use this wherever possible. Most have common properties. Many of them on the market today contain a similar combination of chemicals to create an adhesion process and which fall into two basic categories; Thin-Set Mortar and Mastics. Where they differ is in their application. Some are designed to be applied on concrete sub-floors rather than wood sub-floors, and still others work better with an underlayment material instead of applied directly to concrete or wood.


Mastic resin, the basis for tile mastic is exuded from the bark of the mastic tree. The mastic tree (Pistacia lentiscus) is a Mediterranean evergreen. Mastics are a pre-mixed paste similar to a vinyl glues. Although inferior to a quality thin-set mortar in most tile applications, top quality projects can be achieved using this organic mastic.

Mastics are also convenient to use. They are conveniently sold in cans, tubes, and canisters that fit into caulking guns. These can be used to bond tile directly to concrete or wood subfloors. Mastic can be used with nails or staples to fasten plywood panels to floor joists for subfloors installations. The use of mastic helps eliminate squeaks, bounce, and nail popping. It also increases the stiffness and strength of the floor unit. Mastic can also be acrylic-based designed for bonding to all types of non-porous ceramic, stone and mosaic tiles, onto a variety of subfloors like brickwork, block work, and fiber cement surfaces. Non-porous subfloors include sealed concrete, concrete with curing compounds, ceramic tile, terrazzo, and natural stone surfaces. The easiest way to tell if the subfloor is non-porous is to sprinkle it with water. If the water beads up rather than absorbs into the surface, it is non-porous.

Thin-set Mortar

Thinset MortarThin-set mortar is a mixture of portland cement and sand used to adhere the tile to the subfloors. Portland cement is a hydraulic cement meaning that it not only hardens by reacting with water but also forms a water-resistant end product. These are produced by pulverizing composites of hydraulic calcium silicates, usually containing one or more of the forms of calcium sulfate. In addition are limestone, shales, and other naturally occurring materials. The manufacture and composition of portland cements, the hydration processes, and the chemical and physical properties have been widely studied and researched with innumerable reports and papers written on all aspects of it’s properties.

Some flooring applications call for Latex Thin-Set Mortar . It is the same as the standard thin-set mortar except latex or acrylic is added. The latex gives the mortar flexibility and additional bonding strength. The flexibility is required when going over subfloors, or often called substrates, that may experience minor movement such as wood subfloors. Also, the additional adhesion strength is needed when setting tile over hard-to-bond surfaces. Where ceramic tile is to be installed in exterior locations that must withstand freeze and thaw conditions most manufactures recommend a latex modified thin-set mortar. Porcelain tiles should always be installed using a latex modified thin-set or basic, non-modified, thin-set mixed with an acrylic latex additive. For installing ceramic tile over vinyl flooring or wooden subfloors, a latex modified thin-set mortar should also be used. These are often labeled as Full Flex, Super Flex, or Multi Flex thin-set mortars.

Floor Preparation

Floor prep is the key to well-bonded tile. Badly prepared subfloors and the use of improper setting materials are the cause of practically all major installation failures. Also remember that certain types of subfloors and conditions require different application methods. These treatments are neither expensive, time consuming, or complicated. The basics are that the floor should be entirely free from dust and loose material, the surface should be absolutely flat, and with no bumps and depressions. If the subfloor is concrete it should be slightly damp. This will stop the moisture being sucked from the floor too quickly. If the subfloor is a wood product, it should be completely dry.

(Article written by Charles Hayes - FloorBiz Senior Staff Writer)


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