Vad "wash primer" är förefaller bero på vem som säger det och i vilket sammanhang!!!

"primer" är "grundfärg". The "wash" har med rengöra och/eller förbereda att göra.

Från referenser:

http://www.wjleigh.co.uk/Glossary.asp#W

Wash Primer A paint containing phosphoric acid which gives an etching effect for use on aluminium and galvanized steel to improve the adhesion of the subsequent layer of paint.

http://www.elcometer.com/glossary/Wash Primer.html

Wash Primer
Priming paints which are generally supplied as two separate components requiring be mixing immediately prior to use and remain usable for a limited time.
The thin film that is applied is generally very sensitive to water during and immediately after application.

http://www.paintinfo.com/mpi/store/glossary/gloss-m.htm

Metal Conditioner A solution that chemically reacts with the metal surface to prepare it for subsequent painting. A wash primer is considered a metal conditioner, as the phosphoric acid component forms a chromic phosphate complex with the polyvinyl butyral binder and bonds to the metal.

http://www.hghouston.com/glossary.html
wash primer

A thin, inhibiting paint, usually chromate pigmented with a polyvinyl butyrate binder.

http://www.sherwin-williams.com/aerospace/primers.asp

Conventional exterior primers

wash primer - promotes adhesion to clean, deoxidized surfaces

Se även de svenska referenserna noterade nedan!