*Should I use regular Elmer's Glue or Elmer's Glue-All?
The difference between the two is that the Elmer's glue all is not washable and is a more permanent glue. If you are planning on possibly getting your project a little wet, use Elmer's Glue All. For all other projects I would just stick with the basic Elmer's School glue since it is usually less expensive.
*Can I use this diy decoupage on photos?
I don't recommend it. But look, I did it anyway! Elmer's glue contains acid which can eat away the photo over time. But I have read online that some people have used watered down glue on photos and they are fine. I'm testing it just to see what happens. Maybe in a few years I will have a really cool old looking photo. Store bought Mod Podge is acid free so it is safe to use on photos.
*Is Elmers glue the same thing as PVA?
PVA stands for polyvinyl acetate and is the same thing as Elmer's Glue. If you are not from the USA, that is what you should buy to make this.
*Is it waterproof?
Paper decoupaged onto wood with Elmer's Glue-All mix
Under water...and it held up surprisingly well
Fabric decoupaged to wood with Elmer's Glue-All mix
Held under water and the edges didn't even come up. It passed the test.
So is it really waterproof? Yes and no. No you cannot go swimming with your project in water and expect it to be just like new, but yes it can handle getting wet here and there. If your hands are wet when you grab it or if you have to wipe it clean every now and then, it should be just fine. Elmer's Glue-All should be used on projects that you foresee getting wet since it is a permanent glue rather than a washable glue. I was impressed with how well it worked. You can also spray it with polyurethane or a sealer top coat to waterproof it.
*Is it a glossy or matte finish?
Matte. You can add some varnish to the mixture for a glossy finish.
*Why is it so runny?
Just because it's watered down. Don't worry, it still works wonders. If the glue is too thick, it can get crusty and hard. It just won't turn out the same. If it really worries you, just add a little less water and let me know how it goes, but from what I can tell, the watery solution works wonderfully. :)
*Can it be used as a fabric stiffener?
I think so! Here is a piece of yarn sticking straight up in the air. It was dipped in my decoupage mix and left to dry and it really did stiffen up. This opens the door to a lot more projects! I'll be making some doily lanterns soon :)
Any more questions? Feel free to ask.