help exterior paint keeps going YELLOW!!

[apj101]

Im painting the outside window cill/ledge on a victorian house with pillars and the like

I scrapped back to stone/cement in most areas!
I painted with Wickes exterior masonary paint brilliant white.
BUt it keeps turning yellow where i painted over the stone!!
do i need to apply a primer?
please i could really do with an answer this weekend.

 

[Robbie uk]

Try using some stabilising liquid first on the stone parts. Untreated,what ever was on the stone can bleed through. Or use Zinnser Bin primer.

 

[brushmate20]

use an oil based undercoat that should hold back the stain then ur top coat