I’m trying to make a water puddle decal I could put on the floor.
Here’s the material I’m using now:
If your roughness, metal, and emissive are just white textures, you don’t need to sample and multiply by anything, just feed the scalar value into the node and skip the texture (and associated overhead).
Don’t know how to fix your original question, but just an observation.
These are parameters in a master material. Place holders for actual textures that will be put there in the material instance. If I use a scalar I won’t be able to use alpha masks.
Ah, thought you were making a noob mistake, my mistake. I’ve seen ppl do…weird things in materials so 
Does Thin Transparent water work for decals?
If you mean the shading model, then I don’t think so
I don’t actually know if what you want to do is possible, and I say that as someone who spent a full week fighting the decal system for a convincing water effect and ultimately cutting the transparency.
The core problem as far as I understand it, is that decals can’t support what is essentially a dual-normal effect, as they are blending with the GBuffer instead of actually suplemenbting it. What I’d try if I were you (and what I would have done if I had the time) is replace the decal with a transparent quad that has your material setup, because that can at least support the visual effect (although almost certainly at greater expense).
Substrate addresses this to a certain extent, as their new model of transparency decouples transmittance (how much light penetrates/scatters through a material) and coverage (whether or not a material is affecting a given area).
