Step 5: Put in the lag bolt and finish up adding the mortar mix.
Put the lag bolt into the mortar mix. Because the lightbulb shape has some undercutting with the mold, the mortar mix wants to clump up in the middle of the bulb and not grip the sides. You can use the head of the lag bolt to tap down the pile in the middle of the bulb so it starts filling in all the gaps.
Keep adding mortar mix around the lag bolt to fill it up. Holding the lag bolt firmly to make sure it does not rattle, keep shaking the bulb and tapping the sides to fill in gaps and liquefy the mortar mix.
Take a coffee stirrer you "borrowed" from Starbucks and use that to tap down the mortar mix. You want to keep adding the mix, tamp and fill, tamp and fill. Finally the entire bulb is all done and you are tamping on the top. You want the mortar mix to be level with the top of the hole but not sticking out in a bulge.
When you are all done, put the lightbulb with the lag bolt pointing up in a spare plastic cup. The ones I used where also borrowed from Starbucks. Take a rag and clean up the metal threaded part of the lightbulb as well as you can - you don't want the mortar mix drying on it.
Set this to the side for at least 72 hours to let the mortar mix cure. I normally write the date it was made on the glass with a Sharpie so I can keep track.