Testing a sodium aluminate solution
There are multiple reactions going on simultaneously. Aluminum metal reacts with the oxygen in surrounding air in order to create a plating of aluminum (III) oxide.

$$\ce{4Al(s) + 3O2(l) -&gt; 2Al2O3(s)}$$

Upon addition of sodium hydroxide, the oxide layer reacts with the base, leaving the aluminum free to attack by water for instance.

$$\ce{2 Al + 6 H2O -&gt; 2 Al(OH)3 + 3 H2}$$
$$\ce{Al(OH)3 + NaOH -&gt; Na+ + [Al(OH)4]-}$$

In summary, we can write the sum of the reactions as:

$$\ce{2Al(s) + 2NaOH(aq) + 6H2O(l) -&gt; 2Na+(aq) + 2[Al(OH)4]- + 3H2(g)}$$

The reason why the reaction proceeded slowly at first was due to the aluminum (III) oxide layer covering the aluminum metal.

From this link, http://www2.uni-siegen.de/~pci/versuche/english/v44-10.html:


  This reaction is used in drain cleaners. They are mostly made out of strong alkalis, to which alumunim or zinc has been added. The alkalis break down organic residues chemically. In addition, the formation of hydrogen leads to a bubbling effect which adds an additional mechanical cleaning mechanism.


Considering the properties of aluminates, one can go to PubChem hosted by the NIH which has a lot of information for almost every single compound necessary as well as literature linked to the specific compound in question:

http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=14766&amp;loc=ec_rcs