Yes, you can apply GhostShield 8510 without a densifier, however, you may use a lot more product than what you would have if you used a densifier. 8510 has a very small molecular structure and can penetrate deep into the many pores of concrete. The densifier helps to fill these pores as well as strengthen the concrete at the surface at the same time. As a result, the 8510 doesn't penetrate as deep and is more concentrated near the surface as it should be for the best performance.
If you use a densifier it's best to wait 7 days before application of 8510. Densifiers react with the concrete and can take up to a week for them to go through this process.