Hello:

I was wondering if anyone had some advice regarding potentially painting a newly parged exterior wall that goes from grade to about 2' above grade. Behind the parging is brick. The house is Victorian built in 1890 and in Toronto - so we get temperature extremes, particularly very cold winters with a lot of freeze/thaw.

We just had some brick facade removed and replaced with parging. It is drying to a light grey colour, which looks OK, but a little uneven in colour in spots - sort of like you can see the trowel lines.

In any case, I was wondering if it is recommended/OK to paint this surface. I have found contradictory information that says use great quality exterior latex but then another place says use acrylic. Some other places seem to suggest that painting it can cause it not to breathe which is bad for the masonry behind. Can't figure out which is right, so any advice would be appreciated.

Thanks!

 

Welcome to the forums!

If I understand correctly, parging is the same thing I know as stucco..... and I've painted miles of it. Most latex paints are breathable so there shouldn't be any issues if there is any moisture behind the paint.

Generally a coat of latex house paint thinned about 10% is as good as anything for a primer. The top coat should be latex house paint applied full strength. House [siding] paint is better quality than masonry paints. A quality house paint will hold up a LOT longer than any masonry paint.

I've heard anything from 3 days to 60 days cure time for the stucco although I've never had any issues if the stucco was 3 days old and quality paint used.

 

Ds281:

I wrote a big explanation of everything, and then my computer froze before I posted it.

So, here in point form is what I explained:

1. With utmost respect for Marksr, you're better off with a masonary paint than any top quality exterior latex paint.

2. The word "acrylic" simply means something is made of a plastic called "polymethyl methacrylate", which is the same plastic that Plexiglas is made of. ALL exterior latex paints will be made from polymethyl methacrylate resins and will form a film made of Plexiglas. To confirm, simply use some acetone to clean some Plexiglas and some top quality latex paint, and you'll see that they both dissolve in acetone.

In addition, all top quality interior latex paints, all Bathroom paints, all Kitchen & Bath paints and all primers intended for use on fresh concrete will be also be "acrylic".

Budget priced interior latex paints and all general purpose latex primers will be made with resins made of a plastic called "polyvinyl acetate", which you probably know better as white wood glue.

So, when it comes to house paints, most good quality latex paints are acrylic paints. If someone tells you otherwise, ask them to show you an "acrylic" house paint. If they point to a can with "100% Acrylic" written on the label, tell them that the term "100% Acrylic" is paint-speak for "Made with polymethyl methacrylate resins" and that "Vinyl Acrylic" is paint-speak for "Made with polyvinyl acetate resins". There's no such thing as 90% Acrylic or 80% Acrylic. There's three kinds of plastics used to make paint resins, and they're called "100% Acrylic", "Vinyl Acrylic" and "Styrenated Acrylic" for polymethyl methacrylate, polyvinyl acetate and styrene acrylate, respectively.

3. An acrylic resin can be thought of as a long wire scrunched up into a little ball. Even if you scrunch the wire down real hard, there will still be tiny spaces inside the ball (between sections of the wire) where a fine powder could pass through. In all latex paints, the space between the segments of wire is:
A) LARGER than the diameter of an H20 molecule, and
B) SMALLER than the distance between H2O molecules in liquid water.

That means that H2O molecules can pass through a latex paint resins in both directions, but liquid water can't pass it in either direction.

4. The ability of a coating to allow H2O molecules to pass through it is referred to as the ability to "breathe". Masonary paints are simply exterior latex paints that are made with acrylic resins that happen to be particularily good at breathing. That is, they allow H2O molecules to pass through them with ease, but are particularily impermeable to liquid water.

5. By using a masonary paint, you ensure that the masonary behind the paint stays as dry as possible. That's because the masonary paint resins are most able to allow any condensation that accumulates in the wall over the winter months to evaporate through the paint most readily. And, that keeps the masonary as dry as possible. Use an exterior latex paint on other kinds of exteriors like aluminum, vinyl or wood siding. Use a masonary paint on masonary exteriors.

Post again if you want to know why a latex paint is technically a "slurry" (and not an "emulsion" as they call it in Britain) and how latex paints form films. All of that was lost when my computer froze.

 

It's been my experience that masonry paint does not hold up well! Basically most masonry paints are poorer grade of house paint. I've painted over a 1,000 stucco houses and the ones painted with masonry paint needed repainting sooner than the ones coated with latex house paint.

I should probably add that the majority of my painting experience is in the S.E. USA. Exterior painting can change some due to different locales. It might be a good idea to ask the advice of the paint rep at your local paint store [not a paint dept] He would know what the pros in that area use and what preforms the best for any given job.

 

Marksr:

I have no doubt that what you are saying is true so far as how long each paint lasts.

And, that's entirely because the guy choosing a binder resin to make masonary paint is going to pick a different resin than the guy looking for one to make an exterior latex paint. And that only makes sense because the first guy has "breathability" as his top priority, whereas the second is primarily looking for the resin that stands up the best to the outdoor elements.

It's like designing a vehicle to win the Daytona 500 and designing a vehicle to take troops into battle. The designs won't be the same because the priorities are different.

When I read the original post, I understood that the poster was most concerned about moisture in the stucco causing freeze/thaw damage both because the bricks that were replaced were damaged and because the stucco was close to the ground.

If that is the poster's top priority, then his best bet would be a masonary paint even if it doesn't last as long. After all, I'm sure he'd prefer to repaint more often than replace bricks and repair stucco more often.

I think what's happening here is that you're comparing a known to an unknown. You can see paint that has peeled and deteriorated, but you can't see moisture evaporation. So, it's easy to come to the conclusion that the only difference between masonary paints and exterior latex paints is that masonary paints simply don't last as long. I expect that if you could see that the moisture evaporation through the masonary paint was considerably greater, you'd recognize that it's a different kind of paint designed with different priorities in mind.

After all, no reputable paint company would spend money making and marketing a poor quality version of it's good paint (and call it "masonary paint") just to hoodwink some gullible homeowner out of his hard earned money. Masonary is particularily subject to damage if it freezes when it's moisture content is too high, so masonary paints are designed to allow maximum moisture evaporation out through the paint film to avoid or at least minimize the damage. If they didn't do that any better than anybody else's exterior latex paint, then all of the consumer watchdog groups like Consumer Reports would be telling people not to waste money on masonary paint.

I don't think geography would change anything. Water expands as it freezes, and the ice it forms actually expands as it cools down to -4 degrees Celsius (or 25 deg. F.) Below that, the ice contracts as it gets colder, just as one would expect. Consequently, freeze thaw damage doesn't occur below -4 deg. Celsius because the ice is shrinking. So, freeze thaw damage occurs at relatively mild temperatures. I know Tennessee is warmer than Ontario, but I'm sure that you guys get down to 25 deg. F in winter too. So, there should be just as much freeze thaw damage where you are as here.

 

Thanks guys. I think if we do it, it will be with masonry paint. Our parging contractor said concrete paint, which I assume is pretty much the same as masonry paint. Or, is that a whole other debate?

 

He may have just been using the the term 'concrete paint' in a generic way. I normally think of concrete coatings as paints/stains for concrete slabs. Latex masonry paint will be fine. You'll need to 2 coats, the 1st be thinned a little to help it to suck into the stucco. The final coat should be applied full strength. I still believe a latex house paint would hold up longer, even better yet would be an elastromeric coating. They do a great job of sealing exterior masonry although a gallon of elastromeric won't go as far as a gallon of masonry or house paint.

 

There are "masonary paints" and "concrete primers".

We've talked all about masonary paints.

Concrete primers are special acrylic primers that will stand up the high alkalinity of fresh concrete. Typically, fresh concrete will be very alkaline from the hydrated lime used when mixing the cement. If left to it's own, the alkalinity of the concrete will gradually subside over the course of a year or two, and then it can be painted over with any paint, even without a primer. Typically, the fresh concrete is acid washed to neutralize it's surface pH, and a special acrylic primer applied after the concrete is dry enough to paint. Once the primer is dry, it can be painted over with any other kind of paint.

Concrete primers are needed over any masonary that's highly alkaline when it's fresh, and if stucco is made with portland cement and hydrated lime, then it would need a concrete primer if you wanted to paint over it. In this way, contractors can paint concrete construction projects without having to wait months for the concrete alkalinity to subside.

If it wuz me, I would leave the stucco unpainted for a few years for it's alkalinity to subside, and then use a masonary paint over it with no primer.

There are also "concrete block fillers" which are very thick paints meant for use on the rough surface of concrete blocks to make for a smoother looking coating on a concrete block walls.

 

My house is 12 years old. There are hairline cracks in the stucco. Can I just paint it with elastomeric paint to seal it?

 

Welcome to the forums Fitzjack!

Is your stucco painted? Elastromeric paint does a good job of sealing minor cracks. The stucco should be clean and dry. Unpainted stucco would need to be primed first.