Fiberglass is a difficult surface to work with. The trouble is it's nonporous surface which is so smooth that regular adhesives have trouble sticking to it. To successfully stick tile to fiberglass, you need an adhesive strong enough to cling to a smooth surface. The exact type of adhesive you use largely depends on the job you need to accomplish.
Fiberglass Pools and Showers
Pools and showers are perhaps the most common fiberglass surfaces to which tile is adhered. These applications require specialized pool and shower adhesives. Only adhesives labeled for pool or shower use are designed to work well with fiberglass subjected to high levels of moisture, pool chemicals and extreme temperatures.
Small tiles are sometimes laid on mesh fiberglass sheets. The mesh fiberglass keeps mosaic and other tiles uniformly spaced and easy to apply to walls and other surfaces. To stick tile to fiberglass mesh, you need a universal industrial adhesive. These adhesives are designed to adhere well to restricted, flexible surfaces like fiberglass mesh and to hold tile securely.
Epoxies are some of the strongest and most common adhesives on the market. These thermosetting polymers come in two parts: an epoxide and a polyamine. When mixed together, they form an adhesive strong enough to keep tile adhered to a slick, nonporous surface. There are many different epoxy adhesive formulations designed to work in wet, high-heat or any other conditions necessary to suit your project.
Read the Label
The key to finding a suitable adhesive for your needs is to carefully read the label. Any adhesive suited for sticking tile to fiberglass will clearly say so on the label. If you do not find references to fiberglass or tile it is best to look elsewhere. When choosing an adhesive, also consider your other needs. Some adhesives are suited for high temperatures, high moisture, flexible surfaces and any other conditions necessary to suit your project.