how to make a bottle cap mural

(it’s not as easy as it looks!)

I used particle board for the base (peg board with the holes already drilled every inch is a good surface, and can be mounted with screws in the holes that show through). This is also a good way to size up your image, using the one inch grid already there with the holes.  I attached the caps initially with poster tac, to position them.  When I had a section I was happy with, I would use a hot glue gun.  You cannot use craft-store hot glue sticks, they don't have the binding material you need. You must use industrial glue sticks gotten on the internet.  I used Surebonder high strength high temp clear from http://www.glu-stix.com/.  They are sold in 5 lb boxes for ~ $100, and you will need high temp guns.  You need to make sure the glue is at hottest melt to really stick.  Even then, you will get occasional pop-offs.  I am not aware of any finish you can use to make it permanent, short of pouring resin all over it. 

Be aware that plastic has a short shelf-life, it will break down and crack after several years.  Especially caps of certain types of plastic, represented by those recycling numbers you find on some plastics.  Caps can be made of 5 different chemical compositions, some are more durable and some are more brittle.

One more thing:  you must carefully wash and sanitize each cap, rinsing isn't enough, even if it looks clean.  Otherwise, you could attract a lot of roaches and other insects and such.  I wash mine by hand, since I don't have a dishwasher.  other suggestions are putting them in a mesh bag in a washing machine, but the edges of some bottle caps are pretty rough, so they may tear through and you will have to buy a lot of the bags.