I am setting a basketball hoop at my house. I picked up 11 80lb bags of quikrete for the job and inadvertently got 2 bags of fast setting. Is it ok to the 2 bags of fast set with the 9 of regular?

Ive had a window leak for a while. It only leaks in a heavy or wind driven rain and the leak is above the window, which is on the first floor. I had a roofer/remodeler out and he said the roof looks fine (and ive never had water in the attic or anywhere in the walls). He said the stucco doesnt look like it was done correctly, its looks as though someone just put a skim coat directly over the cinder block and then painted it. Its not thick enough and he doubts there is any waterproofing material under the stucco. You can even slightly see the grout (?) lines along the block through the paint in places. His suggestion was to waterproof the current stucco with 2 coats of elastomeric paint/sealant. He believes water is seeping through the thin skim coat and throught the block and going down the wall and out above the window. So heres my question, has anyone had expirience with this type of paint or sealant? And i was also thinking if I decide to go this route will it actually work? Should i have him check the flashing on the 3 windows along this wall before the painting is done...i honeslty dont know if they are flashed properly, if at all. im still waiting on my estimate and Im working on getting estimates from other masons/plaster companies before I decide which route to go...but any opinions? thanks!