Are you asking me? I'm just remembering and reporting on what others have said. Some opine that it's fine to paint stucco, many others say absolutely not. Yes, it absorbs water, but it also lets go of it. Supposedly stucco is also a very poor substrate for paint.
I'd like to address this issue of whether or not painting stucco will prevent it from "breathing", and thereby eliminating moisture from the walls of the house.
Moisture gets into the exterior walls of a house through leaks in the vapour barrier, such as at electrical outlets in exterior walls. That moisture accumulates over the course of the winter, forming condensation and frost during the winter, and that frost melts in the spring time. It's true that mold needs moisture to survive, but an occasional wetting once per year isn't enough to support mold growth.
People should be aware that all latex paints (both interior and exterior), "breathe", whereas neither interior nor exterior oil based paints "breathe". The term "breathe" means that humidity can pass through the dry paint film, but not liquid water.
Oil based paints don't breathe because they crosslink so densely that there isn't sufficient space between the oil molecules or the parts of the alkyd resins to allow water molecules to pass through the paint film.
Both interior and exterior latex paints "breathe" because the gaps within and between acrylic resins are larger than the diameter of a single H2O molecule, but smaller than the distance between H2O molecules in liquid water.
Consequently, individual H2O molecules can pass through a latex paint film relatively easily, but liquid water cannot pass through it. It's that ability to allow humidity to pass, but not liquid water that's really what's meant by that term "breathe".
An acrylic resin can best be thought of as a long copper wire scrunched into a small ball. No matter how strong the person doing the scrunching, tiny gaps will remain between the segments of wire that make up each ball. Those gaps will be wide enough to allow a sufficiently fine powder, like sand say, to flow through the wire ball. Water molecules attract each other, and so liquid water cannot pass through that scrunched up wire ball unless the gaps between the wire segments are wider than the distance between H2O molecules in liquid water, and in latex paints, they're not.
So, I don't see why painting stucco with a latex primer and exterior latex paint is going to prevent moisture inside the wall from evaporating through the paint film.
Masonary paints are latex piants that have particularily wide gaps between the wire segments, but not so wide that they allow liquid water to pass through the paint film. That allows for the greatest "breathability" of the paint film to minimize freeze/thaw damage in masonary walls from moisture getting inside the wall and freezing.
I really don't know how well elastomeric coatings breathe.
Yes, our home has a screen at the bottom edge.
I remember someone saying that paint stopped water, but would let through moisture vapor. is that possible?
Thanks for the detailed explanation.
It is my understanding that here in Arizona the moisture barrier is reversed compared to homes in areas that are cold/freezing. Think about it we run AC here, making the interior colder than exterior at least 9 months a year. I don't run it at all if I can help it. but you see the concept of the inside being cooler than the outside.
However, when working on the exterior wall to reposition the stove top vent hood; the barriers looked like they were still set up for a 'freezing' climate. consisting of interior paint joint compound skim coat gypsum drywall nylong netting[ chicken wire gaps fluffy fibre glass insulation blown in between the studs
1/2 inch sheathing two layers of tar paper stucco exterior paintUpon running the stove top fan am convinced the house is, nor could ANY house could be, tight enough to need super breathing requirements.
I don't think you'll have any problem either.
Not only is Arizona a dry climate, but cold air escaping through a hole in your vapour barrier is going to warm up and absorb any moisture in the walls, which is the opposite of what happens in the winter where I live.
I'm just surprised that it's taking three coats to get a decent looking coating over your stucco. I expect that's because the first coat you're putting on is acting as a sealer for the second coat. I think priming with a latex primer would reduce the amount of elastomeric coating you have to put on.
PS: All acrylic and PVA resins have enough elasticity to stretch and shrink with wood outdoors, and primers don't need to have UV resistance and mildew resistance because they're meant to be covered by a top coat that would keep the sunlight and moisture off of them. If you ever see latex primers listed as an "Interior Latex Primer" or an "Exterior Latex Primer", it's likely that the only difference is that the latter uses a coalescing solvent that smells a lot, whereas the former uses one that doesn't. In hospitals and commercial settings it's often important not to have the latex primer or paint smell as the coalescing solvents evaporate because some people can get headaches from inhaling those fumes, and generally, the less the solvent smells, the less people will be affected by it.
There seem to be 2 opinions on painting.
One is for stucco over concrete block which is common in the south. It is very common to paint the stucco.
The other is stucco over wood frame. The advice is to redash, which is the thin stucco material used as the surface on the original stucco. Paint turns the stucco into a surface that requires relatively frequent repainting. You don't have to redash very often. (I don't know why that logic doesn't apply to cement block stucco.) Redash can be pigmented.
Thanks for your usual detailed information.
The advice on painting stucco, in particular, is do not use oil paint, which prevents 'breathing'. The outer surface of the wall has to 'breathe' better than inside the house surface. It can be a particular problem on older houses that do not have the vapor barriers common on newer houses.
I would note there is also EFIS. Don't know if it is still being used, but there were some horror stories, which may have been from improper use, where there was extensive mold inside the walls. Very expensive to fix.
Electronic Flight Instrumentation System? I'd rather have steam gauges.
When I did the exterior walls as a SECOND coat over previous attempts, I got these vertical 'llines' that show up because of pattern recognition. Someone said wait a month they'll disappear, but I think the lines come from a change in surface 'smoothness' which will never change with time. They do seem to be diminishing with time, not sure why.
As an experiment, I painted only half a cupalo(sp?) tower on the south side of the home. A week ago, I only painted half vertically because of the height and difficulty to reach. Today I painted the second haf and there is absolutely NO vertical line caused by an overlap! There is an apparent change of color, which could be attributed to drying time. We'll see.
So here it is. Wet overlap shows up, but dry overlap does not ?! That makes no sense to me, but if it's true I'll simply adjust my painting around it.
Both wet and dry overlap should result in the same increase in colour density until you reach complete hide of the substrate colour. Once you're at complete hide, adding more coats or more paint anywhere won't cause any change in colour density.
Why does that surprise you? If you overlap wet paint you are retarding what was already there - partially dried - from drying further. It will, eventually. In addition to difference in color, you will also get a difference in sheen.
IIRC, you are painting over previous paint that is chalky. On an old house. Lord knows how many coats of paint are on it but that old, chalky paint is going to suck moisture out of the new paint. Put on a coat, moisture is sucked; come back later and apply more paint overlapping the old and you are going to get a stripe where they overlap because the overlapped area has been sealed. Not hard to understand.
Not sure I'm fighting 'colour density' because
I don't see any pattern, well not much, burning through from the first coat's blotches.
The more and more I look at this, the more and more I think I'm fighting surface textural changes. Less coat - surface is slightly rougher. More coat - the surface is slightly smoother. And, the eye is quick to perceive a pattern, any pattern.
But, your point is well taken, I have completely discounted the potential for colour density changes. From memory, the eye is supposed to be more sensitive to colour shift than to light/dark shift. With that in mind, it would explain why the first coat hasn't burned through to the second, only the second shows. No, if colour density were an issue, it should show up in the second coat over the first, and does not seem to. I'm caught between hoping it's only a matter of true curing/drying time and just careful applications.
I add Floetrol at 4 oz per gallon [recommended amount] and the paint seems to still be sticky, gooey, and dry before I can go very far along the wall. The paint even forms a slight scum on top of the surface in the container. Keep in mind this is evening painting, and is painting on the shaded walls, not in the sun, nor any surface in the sun. So there should be nothing except our 10% humidity accellerating the paint's drying.
What?! retarding paint's drying changes its colour?! Difference in sheen I believe. But that's due to the surface gumming up. I used to use Easy OFF Window Cleaner, comes in an aerosol spray can, to lightly mist the surface of latex and be able to brush over any variation making it uniform, but alas, they've discontinued that product. Used to be able to use that product to go back hours later nd still make corrections, too.
First, coat should be sensitive to what's underneath. That's why I chose to water wash and physically scrub the old coat. Which did show a colooured run off of chalky paint and dirt from wherever. I saw a difference with the way the paint went on and recommend always cleaning the base surface. But, the problem that prompted me to post is NOT with respect to the first coat, but the second coat, which of course is going over an almost acceptable surface of paint. Second coat was actually an experiment. I don't want to do two coats on this house, too expensive, and too labor intensive.
I didn't say that. I did say that paint can take many days to completely dry/cure and that the color and sheen won't be uniform until that time has passed. __________
Let me try to clarify...
I'm trying a new section that has been physically scrubbed with brush and plain water. We'll see what happens over that.
I hope all these problems are just a matter of drying. However,
Where I put the two coats has the 'decidedly' obvious stripes ONLY from the last coat. Been drying since I started this thread.
On the tower which was difficult to reach so I painted one half side, waited three days, painted the other half; has absolutely NO line at the overlap, but does appear to be two diffierent colors! Oh well, win one lose one.
No appears to have been done all at one time. Plus, thiis specific area is not large, around 8 feet high by 10 feet wide.
I have seen their starts and stops, but this is not it. Their patterns are horizontal. My painting patterns are vertical, since I paint from top to bottom.
Same thing...new paint will dry, next coat will dry except any overlap will which dry more slowly. Ultimately, all will look the same assuming you mixed the paint well.
Out of curiosity, why do you paint from the bottom up? Gravity is your friend.
I thought I said I painted from the top down.
Don't get me started on my ability to use the English language! I absolutely say the opposite of what I mean. In meetings, people marvel at that trait.Up is down. Down is up. Spent too much, yeah.That kind of thing.I say it's all part of dyslexia that is getting worse while aging. What's really irritating is that with dyslexia the sentence looks absolutely correct until finally noticed!
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