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What is Mastic Adhesive?

By Jeri Sullivan
Updated May 17, 2024
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Mastic adhesive is a very strong bonding agent used in many commercial and industrial settings, but is perhaps most popular for setting tiles and sealing windows, walls, and ceilings in building construction. It is traditionally derived from the resin of the mastic tree, which is where it gets its name, though it is commonly manufactured synthetically as well. Depending on the application it is generally available in thin liquid, thick glue, or paste form. It can quickly and permanently bind many different materials together, though in most cases it works best on hard, non-porous surfaces. Over time it can and sometimes will seep into cracks and crevices, which can lead to discoloration and general weakening.

Where it Comes From

Originally, this sort of adhesive was made from the resin droplets or “tears” of the mastic tree. This tree, known scientifically as Pistacia lentiscus, grows most prolifically in the southern Mediterranean region, particularly in Greece and Turkey. In most cases the resin comes out of the tree the same way that sap comes out of many pine trees. Harvesting it is easiest if the whole tree is cut down, but killing the plant limits the supply dramatically. Traditional harvesters construct a number of shunts and filtration systems to capture the resin as it is produced, which saves the trees — but can make the end product very costly, both in terms of labor involved and natural limitations on supply.

A number of modern manufacturers create their own mastic in labs. In most cases it has the same intense adhesive properties and is chemically almost identical, but is a lot less expensive to make. Synthetic mastic is often a better choice for large projects and is more widely available in many places as well.

Construction Uses

When used in construction, mastic adhesive is typically in liquid form and applied with a caulking gun. It is squeezed out by hand in a thin line along wall or ceiling joints, and the strength of the adhesive helps hold load-bearing walls in place. The quick-setting adhesive eliminates the need to support heavy drywall for extended periods of time.

Construction adhesive is also used as a temporary hold for fixtures so they can be nailed or screwed in place by one person — that is, without anyone else there to help hold things up or double-check measurements. In these cases the adhesive can serve as a reinforcement, but it’s not usually intended as a final sealant. It’s often difficult to remove, though, so people in this situation usually have to be very careful to set things properly the first time.

Popularity in Industry

Industrial uses for this adhesive include repairing heating and air duct work in buildings and joining panels of concrete and asphalt in warehouses and storage facilities. Its ability to bind permanently to metal makes it really useful in certain auto and mechanical repair settings, too, thanks in part to its heat resistance and general durablility. Most of the time mastic adhesive comes in a finely ground powder that is mixed to form a paste in these sorts of settings; it is smeared onto the repair area and allowed to dry, usually for about 24 hours.

Potential Drawbacks

Even though it will bind to almost any sort of surface from tile to leather to rugged metal, mastic isn’t always the best choice. A lot depends on the intended use, as well as the likelihood of the adhesive coming into contact with excessive or prolonged moisture. It’s very common in tiling for instance, but most builders recommend it only for porcelain tiles, especially when used outdoors. Other tile types, such as ceramic, are less dense and more porous. Over time the adhesive can seep into these pores, causing discoloration.

There is sometimes also a risk of water damage if moisture is able to seep into spaces between the surface of the wall, joint, or tile and the adhesive strip. This is most common when porous materials are used in places like steam rooms and pool houses where there is a relatively constant amount of moisture and high humidity. Moisture doesn’t usually impact the integrity of the adhesive since it's generally waterproof, but it can lead to mold growth in the crevices of the building material which can be harmful to health, unsightly to look at, and difficult to remove thanks to the bonding agent's strength.

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Discussion Comments
By anon942706 — On Mar 28, 2014

Our LLC does acid stain concrete floors. I am looking for a product that can fill fine fractures and larger fractures in concrete slabs with a fast drying time and little shrinkage.

At the present time, I use rock-ite which is anchoring cement or a divit patch to fix the cracks or holes. My problem is when coloring out the fixed fractures my acrylic paint and acrylic sealer do not bond or achieve a darker enough color on top of these materials. I have even added a dark acrylic paint in the white rock-ite and the color of it remains white. Only with a great effort and several topical application can I color it but it still does not darken up in color much.

I have been doing this work for over 10 years. Amazingly, some of the floors that I have had to fix have had mastic all over the floors. My colors adhere perfectly to the mastic, and the colors do not lighten up.

Do you know of a product that I can use. This would greatly improve the quality of my work and make my life a little easier.

By anthemway — On Jan 05, 2013

What is the best adhesive for gluing wood trim to the front edge of a cultured marble window sill?

By anon293182 — On Sep 24, 2012

Can mastic adhesive be used for swimming pool tiles? Where can I purchase it in the Denver, Co. metro area?

By anon241101 — On Jan 17, 2012

Porcelain is extremely hard. Mastic will not seep into porcelain.

By indigowater — On May 11, 2011

Great tip on using mastic tile adhesive only with ceramic tiles. I had no idea mastic could seep into porcelain or marble and discolor the tiles!

I understand why organic mastic is the most popular because it's pre-mixed and is perfect for wall tiles. It sounds like an easy way to go. But is it heat resistant enough for a kitchen back splash?

By anon87901 — On Jun 02, 2010

Please can you give me the ratio of blending premixed adhesive with mastic and also as a thin set. can I have a list of manufacturers too. I want to start making my own mix.

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