Residue on newly painted concrete

[Bigsnack]

Hi Folks

I've recently patched up some old sills + external walls with some Cementone render repair stuff and painted over with Sandtex Black exterior.



As you can see from the pics, I'm getting a white residue coming through. Any idea what this is and how I fix it?

Cheers,

Pat

 

[Old Salt]

Has it rained recently? It looks like water marks to me like you get on a car that’s been washed but not dried.

 

[Bigsnack]

Yep shows up after rain. any idea how to get rid?

 

[Old Salt]

If that is what caused it I would be thinking about a good wash with detergent, dry it off and once really dry perhaps trying a clear waterproofer or silicone spray or something to get the water to bead off.

https://www.toolstation.com/everbui...MIro6Y04_37wIVU-N3Ch3y2AtoEAQYAiABEgJud_D_BwE

The only other thing I can think of is a lighter coloured Sandtex