At the consecration of a church, wax-mastic is being used to seal in the relics into the Holy Table. Also the table top of the Holy Table is secured with wax-mastic and nails. Small reliquaries with relics are also have often the fragments of relics encased in wax/mastic to secure them.
The process to create wax/mastic is generally described in the order of the Great Consecration of the Church. However it seems that the ingredient list is also depending on local traditions.
The common ingredients of wax-mastic are:
- Gum Benzoin Sumatra
- Gum Olibanum (Frankincense)
- Myrrh Gum
- Ground Marble
- Rose Incense
- Rose Oil
- Pure Bees Wax
Some of these ingredients may differ depending on local customs and different scents desired, but this is the overall common list needed.
Note: Especially the resins (gums) and marble should be in powdered form. If they cannot be obtained in powdered form there should be ground before usage. An electric coffee grinder will help with this process.
Making the Wax-Mastic
Acquire all the ingredients needed, then crush everything that needs to be ground down in a coffee grinder or mortar and pestle if need be (although this will take much more time, esp for the incense). Heat the wax so it is boiling (it will look clear when hot) and then once it is hot enough, add all other ingredients. Then stir to keep them from boiling over and to give it an even mixture throughout.
Once everything is mixed in, you have your wax-mastic.
To then use it, you may want to turn down the heat and keep it just hot enough to keep it liquid, but not so hot that it'll scald you as you will need to pour it carefully for the various purposes during the Great Consecration.
Side note: It is probably best to get a metal pitcher than can be heated on a hot plate and then just have that ready before the service starts then you can just take it off the hot plate once it is time to use the wax-mastic.
Example suppliers for the ingredients
Some items on the ingredient list can be challenging to procure. Here are some example vendors for those items Gum Mastic:  Gum Benzoin / Gum Myrrh:   Ground Marble  Gum Olibanum / Rose Incense / Rose Oil: any Orthodox incense provider has those for example 
Russian Orthodox Church. The Great Book of Needs : Expanded and Supplemented. 4 vols. Vol. II, South Canaan, Pa.: St. Tikhon's Seminary Press, 1998.