A Comparison of Vallejo Pumice Types
by Legoburner
I've had the four main types of Vallejo Pumice sitting in my cupboard for ages, so thought I would finally get around to doing a quick comparison/review of them.
For starters here is what they look like:

You basically spread them onto a base with a spatchula and leave to dry. Drying time is 3-6+ hours depending on the temperature.
They go on wet:

But dry out and change shape:

Dried, Painted Pumice
To provide a more equal comparison, I've sprayed them black, then drybrushed with adeptus battlegrey, codex grey and fortress grey:

And for clarity here are close ups...
Sandy paste
very slick, could pass easily for ice or dust. So slick it is hard to drybrush if you have any moisture on your brush at all:

Black lava
goes on very smoothly and without drybrushing has the exact appearance of asphalt at 28mm scale. Very easy to control:

White pumice
very goopy and textured. A fair bit harder to control. Good texture though.

I use white pumice on my flames of war bases:

Grey pumice
easy to control but dries very differently to how it goes on. Looks the most like actual pumice stone.

Hopefully if you are considering a lazy basing option that is much faster to apply than sand, this comparison will help you choose a suitable pumice.