Three-quarter-inch hardwood is one of the thickest forms of flooring available today. Most hardwood manufacturers discourage the use of glue as an installation technique for hardwood. This decision is based on the way that hardwood flooring works. Wood is a material that contracts and expands with temperature and humidity. When glue is used to hold down the planks, the wood is unable to breathe, expand and contract when it needs to. Glued wood flooring can pull away from the adhesive or even crack under the pressure. This is not as big of an issue with thinner floors or engineered floors because the thinner wood is more flexible than 3/4-inch hardwood.
Most hardwood manufacturers and retailers recommend nailing down ¾-inch hardwood floors. If hardwood is to be used over concrete, manufacturers recommend you place a rubber or plastic moisture barrier between the cement and the plywood subfloor, followed by a layer of black felt paper. If the flooring is to be installed over a plywood subfloor in a pier and beam house only the felt paper barrier is necessary under the floor. Use cut nails or 8 penny finish nails to nail the planks in place.
If you still think gluing your ¾-inch hardwood floor is the best option, there is one kind of adhesive you can use. A urethane adhesive allows more flexibility and breathability than other floor adhesives, so it is the only kind of adhesive that should be used. Before purchasing, determine if the product is safe for use with hardwood floors. If the package does not say it can be used for hardwood, then you should not use that adhesive. Follow all installation instructions exactly or else many companies will not honor their warranty if something goes wrong. A combination of glue and nails can sometimes be used to install hardwood floors.