Originally Posted by Bwildly
I am going to paint my exterior foundation "poured concrete".
Never paint concrete unless it's at least two years old. The reason why is that fresh concrete contains a lot of hydrated lime or Ca(OH)2 or HO-Ca-OH and it's those -OH groups in the fresh concrete that make it so alkaline that only certain kinds of coatings will tolerate it.
This web page explains why concrete and real plaster gradually become less alkaline during the first two years:What is Lime? | Products | Graymont
It takes AT LEAST a year for the CO2 in the air to turn that hydrated lime into limestone, with a resulting lowering of the very high pH of the concrete, thereby making it more neutral.
I have bought self priming masonary paint but was wondering if I should still use a primer first?
No, never use any primer under masonary paint, nor use any paint over it except another latex masonary paint.
Masonary paints are latex paints formulated specifically for exterior masonary (brick and block, normally) walls. When water gets into brick or other masonary walls, it has little deleterious effect on the brick (or other masonary) unless that water freezes. If it does freeze, the pressure of the expanding ice inside the masonary units as the water freezes can do considerable damage.
Masonary paints are formulated from from latex paint resins which can be thought of for the purposes of this explanation as long wires scrunched into balls. Even though the wire is scrunched up, there are still gaps between various segments of wire inside each ball. Masonary paints are made from latex paint resins where the distance between those various wire segments in each ball are larger than a single H2O molecule but smaller than the distance between H2O molecules in liquid water. So, only single H2O molecules can pass through a masonary paint film, not liquid water.
That means humidity can pass in either direction through a masonary paint film, but liquid water cannot pass in either direction through it, and so moisture inside the wall can evaporate through the masonary paint, but the paint will stop rainfall from outdoors from getting into the wall. In this way, masonary paint help keeps walls dry to protect them from the effects of freezing water.
Using a primer under masonary paint, or painting over it with anything but another masonary paint will defeat the purpose of using a masonary paint in the first place.
I have properly preped the surface for painting by scraping, power washing, and acid washing the surface but looks like its going to be a week or longer before I can do anything because of the weather.
You don't need to go through all that to get paint to stick to concrete. Unless it's polished concrete (like Costco has on their store floors) any paint will stick well to bare concrete without a primer, and with no more preparation than to ensure the concrete is reasonably clean.
The only time you need to prime concrete is if it's less than a year old. In that case you need to use an acrylic primer made specifically for this purpose. That primer acts as a physical barrier between whatever paint you use over it, and the highly alkaline concrete under it.
PS: You don't need to know this:
The reason why true drying oil based paints (like linseed oil based paints) won't last on fresh concrete is because of a chemical process called "saponification". This is the process whereby an animal fat or vegetable oil reacts with a strong alkali to make soap. So, if you paint over fresh concrete with a linseed oil based paint or varnish, the paint will literally turn into soap, with the associated loss of adhesion, peeling and disintegration as it gets washed away by rain. Alkyd and "alkyd based polyurethane" paints won't last either because alkyd resins are basically nothing more than a "clump" of souped up vegetable oil fatty acids, and those fatty acids would turn into soap too. Polyurethane resins are really nothing more than alkyd resins with strong urethane linkages inside them, so they'd turn into soap as well. Inexpensive latex paints and primers are more alkali resistant than oil based paints, but they're not alkali resistant enough to stand up well on fresh concrete or fresh real plaster.