When planning exterior tile installation, such as over a concrete slab for a patio, you'll need the right exterior tile adhesive to stand the test of time and the elements. There are many bonding materials, ranging from modified and unmodified mortars and thin-set adhesives to polyurethane-based construction adhesives. Read on to find the best exterior tile adhesives for your next exterior tiling project. Choosing the right adhesive and grout products is essential to a successful exterior tile installation, but getting started with choosing the right product for your project can be a minefield. If this sounds like you, then fret not, as we're here to provide a comprehensive guide to exterior tile and adhesives to answer some frequently asked questions about which types of adhesives and grouts are best suited for deployment in outdoor environments.
If you are laying an exterior wall, you must first ensure that the substrate on which you are going to install the tiles is suitable. Brick and plaster walls are acceptable, but first, you need to make sure they are level and able to support the load of the tile you are attaching to them. Primers are essential when it is necessary to reduce the absorption of surfaces such as plaster, plywood, plaster, drywall, and sand: cement mortar. Many homeowners dread taking on DIY projects because buying the right products and then using them correctly seems like a daunting task. For exterior decks, you'll almost always use modified thin-set mortar as a binder. Modified thin-set mortars set tiles or stones on surfaces such as cement or concrete. The additives in the "modified" flakes will help it stand up to weather and time. Adhesive materials such as unmodified adhesive or mortar do not contain any additives resistant to water and temperature variations. The improved slim assembly contains more cement and polymer, which helps it perform better. You can pay between $10 and $25 for 50 books. 
Depending on the tile application, 50 lbs. can cover 25-50 square feet of unique tiles or specialty pavers that require thicker applications; or, if adding single mosaic tiles, 50 pounds can cover 200 square feet. Another standard adhesive used for outdoor tiling projects is PL adhesive. It is a moisture-curing polyurethane adhesive that is much stronger than ordinary construction adhesives. PL adhesives are expensive compared to low profile, costing around $10 for 28 oz. tube. Great for fixing loose tiles or if you're putting together a small custom project. Always refer to the tile manufacturer's recommended adhesive for your specific application. It is a mortar composed of Portland cement, fine sand, water, and latex additives. The unmodified low profile contains no latex additives. These additives help reduce water absorption, improve bond strength and minimize movement due to temperature changes.
You can buy modified thin-set mortar at most home improvement stores (Home Depot, Lowes, etc.) and tile stores. Be sure to let your sales representative know that you are working on an outdoor project so they can recommend the right tile adhesive product for you. Avoid using adhesives and other premixed tile adhesives outdoors. Thin mortar is a dry mix, usually in 50 pound bags. Sometimes smaller bags are also available. Check the coverage chart on the back of the bag to determine how much tile adhesive you need. On average, a 50-pound bag will cover 60 to 100 square feet, but the project and type of tile will affect the thickness you need to apply the adhesive. You will need a power drill and a paint paddle/stirrer. Most modified thin mortar products are mixed with water. Some are used in combination with latex. Always check the instructions on the packaging. Mix with water:
- Pour about 2 inches of clean water into a 5 gallon bucket.
- Pour a small amount of fine powder into a bucket.
- Mix water and powder well. Add more water or powder as needed to make a paste the consistency of cake icing.
Each type of tile adhesive may have a different mixing procedure. Some need to be mixed, let sit for ten minutes, then mixed again. Your bag of modified thin mortar should contain mixing instructions. When building an outdoor patio, follow them explicitly for the best results. The most common adhesive brands for exterior tiling projects in the United States include:
- Versabond: Polymer-modified, high-bond, multi-purpose mortar that bonds to most surfaces; used indoors and outdoors; can also be installed in cold weather
- Laticrete 254: Polymer-reinforced thin mortar for interior and exterior; suitable for thin tiles, thin tile pa,nels and glass tiladhereeres to exterior plywood and concrete
- Loctite PL Premium: This modified thin mortar alternative is also offered by LePage PL Premium in Canada. This polyurethane-based construction adhesive is highly effective in all outdoor conditions. It comes in a caulking tube; it is a thick - good consistency for laying tiles.