What's the white substance that's showing up on my deck?

Question

I stained/sealed my deck a few weeks ago; now there's a white substance appearing randomly on the railings and floor. Any idea what it might be, and how I can get rid of it without removing the sealant?

Answer 1

Did you clean your deck with TSP (Tri-Sodium Phosphate) prior to sealing, maybe to get rid of some mold or mildew stains?  If so, unfortunately the fix will be neither fast nor easy.  See my source link for info on how to fix this.