Hi everyone,
I am working on a diorama using putty and fine sand and i was wondering about using a primer or something that definitely improves the adhesion of the acrylics on those materials (I am gonna airbrush the whole job with acrylics once it is prepared).
I came into Liquitex Matte mediums.. are they good? Have you any other suggestions? Are there a "best stuff for a proper job" in this case?

Thanks a lot and keep on rollin' on you tracks

You can't go wrong with Tamiya Surface Primer from the can, it always works well.

Vallejo primers work well. Some people have had trouble shooting them through an airbrush but if it's just for groundwork, you can always use a regular brush.

Kimmo

Someone who has actually used this brand & type of paint will confirm or deny, but I've used similar Fine Art stuff for err art, but so last century...

My thoughts are they belong to the extenders/modifiers & are used to modify the behaviour of the acrylic paint on canvas.

Go to the Mfr's website & read up before shloshing on your latest creation?

Also, I'd go with priming, many choices:
rattle can primer Halfords/£/€/$ store
Tamiya primer
Vallejo Polyeurethane Primer
many others.

Something that I see strongly recommended for painting and weathering model railroading rolling stock is 'adhesion promoter', primarily for the acetal plastic commonly used to mold handrails. You should be able to get it at an auto parts store, and it functions as a clear primer while providing enough 'tooth' for a subsequent coat of paint to adhere. A search on Google should give you a number of choices for brands.