painting brickwork
No, "exterior brickwork paint" will be a latex masonary paint that's meant to be used on the exteriors of brick (or other masonary) buildings. Masonary paints are latex paints that allow H2O molecules to pass through the paint relatively easily, but are impervious to liquid water.
Most people wonder how something can allow H2O molecules to pass through it, but not water, and the answer becomes obvious once you recognize that the distance between H2O molecules in water is larger than the diameter of a single H2O molecule. And, surface tension keeps the H2O molecules in liquid water sticking together rather than dispersing like they would as humidity in air.
If you imagine a latex resin as being a wire scrunched up into a ball, then you can imagine that air could easily pass through that scrunched up wire because of the spaces between the various sections of wire. The acrylic resins used in masonary paint are chosen because the spaces between the wire sections are larger than the diameter of a single H2O molecule, but smaller than the average distance between H2O molecules in liquid water.
Consequently, individual H2O molecules can pass through masonary paint relatively easily, but not liquid water.
This is important when you're painting the outside of a brick building because any paint you use on the outside won't prevent moisture from migrating into the wall, it'll only prevent it from leaving the wall by evaporating from the exterior surface of the brick. So, if you use an impermeable paint like an high gloss oil based paint, then moisture will be trapped and can accumulate in the wall until you get pockets of water formed in the voids in the brick. That's cuz humid air can get into the wall at electrical outlets and gaps under baseboards and form frost inside the wall all winter long. Come the first warm days of spring, that frost melts and forms water inside the wall that may get absorbed into the brick or may form pockets of water within the brickwork. But, come the night following that first warm day, and you get subzero temperatures again, and that melt water freezes and expands. That can cause cracking of your bricks (called "spalling") due to water inside the brickwork expanding as it freezes.
So, masonary paints are designed to minimize the risk of freeze/thaw damage to masonary walls by allowing any water inside the wall to evaporate as readily as possible through the paint. That keeps the wall as dry as possible, and a dry brick is a happy brick, even if it's hot or cold out.
In your case, the brick face you'll be wanting to paint is on the inside, so painting it with any kind of paint will help prevent moisture from getting into the wall.
So, you don't need to use a masonary paint. ANY paint will work well. And, brick is rough enough that you don't need to worry about priming. Any paint will stick well to the rough surface of brick without priming. I'd clean the surface of the brick of dust and any loose mortar sand first, tho.
You might want to use a block filler over your brick if it's really rough brick, too, just to get a smoother looking surface.
Also, think twice about painting brick. It's easy to put the paint on, but it's not easy to remove that paint should you decide that it was a mistake to paint it. ANY paint you put over that brick is going to be softer than the brick and will therefore be more prone to getting marked and scuffed up, and that means you'll then be having to clean marks off the painted brick just like you clean marks off of painted drywall or plaster (and paint over really stubborn scuffs that won't clean off). You've got a near maintenance free wall surface now, why make work for yourself by painting it so that it requires more cleaning (and painting) instead of keeping the hard mark-resistant wall you have now?
Last edited by Nestor_Kelebay; 11-10-2008 at 03:00 AM.
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