aggressively thinning latex paint?

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Is it OK to aggressively thin latex paint with distilled water? My aim in doing so is NOT to increase coverage, but rather to improve the penetration into splits and cracks and rough areas. My intent would be to allow this first thinned coat to soak in and dry thoroughly, then apply two more coats of the same product, unthinned.
If the answer is "no", could you please give some technical explanation why it is not a good idea.
I already tried this on some old treated pine deck boards I used to repair portions of an exterior porch stairs. I washed and rinsed the boards, then let them dry thoroughly. Then I painted them with an exterior acrylic latex porch paint thinned 50/50 with distilled water. This first coat had remarkable penetration. After it dried thoroughly (a couple of days in 85 degree weather in the garage) I put 2 more coats of the same product, unthinned, allowing thorough drying between coats. I used these boards to replace some worn exterior porch stair treads, but they've only been in place for a couple of weeks so far so I won't know the results for a couple of years.
In the past, I've used an oil primer, followed by 2 coats of latex topcoat, but haven't had very good results. The latex bonded tenaciously to the primer, but the primer blistered and peeled away from the wood. This exterior application sees lots of sun, rain, snow, and foot traffic.
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oil base paint dosen't breathe so any moisture will lift the paint. latex does so some moisture will come through without any issues. I have used floetrol (sp) available at DD Lowes, and sherwin williams to thin it and extend drying time (on Latex) which lets it penetrate more and although some paints do not reccomend it I have not had a problem. Penetrol is for oil based paints but not as easy to find

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Ether Jones writes:

Isn't that ordinarily done with sprayers?
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Ether Jones wrote:

Thinning aggressively is a bad practice, you may get the color to move into cracks but you end up with mostly pigment and very little base to hold the pigment to the wood. If you look at most latex primers it says to not thin or to use a maximum of 10 percent thinning fluid. BTW, thinning with distilled water is overkill, any drinkable water would be acceptable.
Latex paints don't really penetrate, they just lie on the surface. So your idea of penetrating doing something good is false. Paint won't fill in cracks effectively. What you want to do is lay on a coat that cover thoroughly to seal the wood by coating it. If there are cracks you should be sealing the cracks with a caulk before you paint. Or, preferably, use sound board with no cracks.
A really good undercoat that dries on your hands takes a lot of work to get it off, even if you skin is oily. Your thinned paint will come off your hands relatively easily.
What you need for a long lasting application is not aggressive thinning, but aggressive coating. The wood needs to be smoothed, cracks filled, and the surface coated with a high quality porch paint.
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George E. Cawthon wrote:

Thanks for your lengthy response George. Some of your comments puzzle me so I'd like to ask a few questions.
I don't understand your statement that I "end up with mostly pigment and very little base to hold the pigment to the wood". If I thin 50/50, doesn't the ratio of base to pigment stay the same? In other words, what happens to all the base? Isn't it still there, just like the pigment is? Or is there some sort of chemical reaction where the water destroys the base? I realize that by thinning, I don't get as thick a coat as I would otherwise, but I figure that "something" is better than "nothing", since the unthinned paint simply does not get down into the fine cracks in the wood.
The cracks I am talking about are not large cracks that could be caulked. I'm talking about many fine splits in the wood; of the order of the thickness of a piece of paper. The unthinned paint simply cannot get in there thoroughly, no matter how aggressively I brush it. And, as it cures it leaves pinholes where the splits are; pinholes where water could get in. If I thin the paint 50/50, it's still fairly thick, but it is able to soak down into the splits instead of just bridging over them. Then when I let it dry and paint over it with unthinned paint, I get a continuous coating with no pinholes.
I tried scraping and washing a portion of the porch floor, then letting it dry thoroughly and painting it with 50/50 thinned latex. You can see the paint soak in to the fine splits, and when it dries it absolutely doesn't rub off - it is very tenecious. I intend to cover this first thinned coat with 2 additional coats using unthinned latex. I'm not trying to go cheap on paint; I'm trying to get the wood coated. Also, there are nooks and crannies in the porch where it's very difficult to get the unthinned paint to go; a prime example is between the deck boards. If I use unthinned paint, it wants to "bridge over" adjacent boards instead of soaking down between them. Then, when you walk on the boards, the slight relative motion between adjacent boards causes the paint "bridges" to fail and expose bare wood. If I paint these areas with thinned paint, it penetrates between the boards and coats the hidden edges (where water drips down through). In this case, when putting the unthinned overcoats in these areas, I would be carefull to brush out any paint bridges.

The label says "do not thin" but it does not say *why*. Since I intend to thin only the first coat, and then go over it twice with unthinned paint, I would like to understand if (and why) thinning is still objectionable.

I understand that this would be optimal. In another universe I'd love to do that. But I don't have the time or money to rip up my porch floor. I'm constrained to work with what I have, with the wood in place. There is no rot, but in many areas the wood is weathered, and the paint is blistering and peeling (actually, the latex topcoat is adhering to the primer, but the oil primer is peeling from the wood). It's because of my unsatisfactory experience with oil primer that I am exploring other approaches.

In the painful process of learning, I've had the "pleasure" of using several different paints, some of them awful. The one I am using now, and with which I am fairly impressed, is "Best Look Premium 100% Acrylic Latex Satin Porch & Floor Enamel" from the local hardware/paint store. It says on the fine print on the label that it's made by Sherwin Williams. It costs about 25 bucks a gallon. It is very thick and creamy, easy to apply, and coats very well.
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Ether Jones wrote:

Sure the ratio is the same but the base needs to be a certain concentration to provide a good a reasonable coat, that is why manufacturers caution against thinning. You don't need to get the paint down in those thin cracks, you just need to be sure that the paint seals over the cracks. I suggest that you take a good board, and paint small sections with 100%, 90%, 70%, 50% and 40% paint thinning with water. Then scrub a dub with water after 24 hours. That will show what the paint you are using will do with thinning.

If that is true then do it. However,you would be much better off filling the cracks with something other than paint, maybe glue thinned about 10 percent (use Elmers carpenter glue (the yellow stuff). Not only will you have the cracks mostly filled they will be glued together.

You are trying to fix a structural problem with paint. The board should not be moving in relation to each other. If the boards are moving a tiny bit you can seal with a flexible paint, but a paint you walk on is not flexible to any extent.

Maybe you have the problem in hand. OTOH, the peeling may be due to moisture absorption from below, if the porch is over uncovered soil.
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George E. Cawthon wrote:

Good suggestion. I wasn't as scientific as you suggested with all the different percentages, but I did run a "sanity" test before I committed to using the thinned paint in my actual application.
I took a representative sample board and power-washed it to remove the old blistering paint, then I let it dry and gave it a single coat of aggressively thinned latex (I would guess 50/50 although I didn't measure it). After letting it dry thoroughly I blasted it with the power washer (1700 psi) and it didn't budge. So I figured, on that basis, that using the thinned latex as a first coat, to be overcoated with 2 coats of unthinned latex, was a reasonable thing to do. My reason for posting here was to try to get some additional technical reasons, if there are any, why the process I described is bad practice. So far, to summarize what I am hearing, the gist of most of the counter-arguments is that thinning the latex causes a thinner coat to be applied, therefore resulting in a "weaker film". But no one so far has suggested (at least not in clear language) that adding too much water actually interferes with the paint's chemistry. Since I intend to overcoat the first thinned coat with 2 coats of unthinned latex, it seems to me that the "weakened film" argument is moot.

This is very interesting because this is exactly the sort of thing I wanted to do initially, because it seems to make so much sense, but I couldn't find _anybody_ to confirm the idea, despite talking to contractors and paint-store people. Is this really a viable approach?? Would Elmers be the right stuff to use, or might there be something even better? It has to be water-based for this project. Is Elmer's really paintable?

My deck, which I built myself with 5/4" deck boards on 2x10 joists 16" on center sitting on doubled-up 2x12 beams 6' on center supported by posts every 5' along the beam length, you could drive a tank on it and it wouldn't budge.
The porch is a different story. It is certainly not built as sturdily as I would have done it myself, but it's not unlike many decks I have walked on. The boards DO move slightly relative to one another when you step on an area between joists. This absolutely kills the paint if there are "paint bridges" joining the boards, as I discovered the hard way. So when I re-paint it, I plan to avoid paint bridges between adjacent boards.

Yes, it's over uncovered soil. It is going to be very interesting to see what happens over time to the newly-refinished treads on the rear stairs. I discussed this in a separate post in this thread. I used a different process on each of the 11 treads and risers.
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It sounds like you've invented primer. The unknown is how long it'll last.
Why not just use a real primer? Oil-based primer should sink in better, but even a latex primer will have a better chance of a long life. Both can be topcoated with latex.
--
Warren Block * Rapid City, South Dakota * USA

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Warren Block wrote:

How is latex primer chemically different from latex topcoat paint? Does it have a different binder system than latex paint?

Why not oil primer for this job? Here's why:
Many claim that oil-based primer penetrates better, but the caveat is that the wood must be BONE DRY. The least bit of moisture appears to greatly interfere with absorption and adherence. By contrast, latex seems to be fairly forgiving: to apply latex, the wood can't be wet or damp, but it doesn't have to be baked dry for a week. This is a significant issue for this outdoor project, especially at this time of year, when finding a whole week where there is no rain and the humidity is low and there is no dew in the morning is next to impossible.
The area to be painted is a high-use area; it is a great inconvenience to take it out of service. If I power-wash it, I have to keep traffic off it until it dries or it will get dirty again. For oil primer, that means a full week of dry weather after washing. If it rains, I have to wait another week.
Once the wood is dry and the oil primer is applied, it takes several days to dry properly so that it can be painted with latex. If it rains during this period it seriously compromises the primer. All during this period, the area must be off-limits to traffic.
Once the latex is applied, I need another 24 hours of dry weather or the latex will be compromised.
On the other hand, if I use latex:
After power-washing, the wood is ready to accept a coat of latex within 24 to 48 hours. Within 4 hours I can apply a second coat. Within 24 hours it is rain-proof and ready for foot traffic. Done.
Besides the significant inconveniences of oil (as detailed above), my experience will oil-based primer has been highly disappointing. See my other posts in this same thread for more details, but here is the gist of it. I tried using latex topcoat over oil primer previously and the system failed within one year. The latex topcoat bonded to the oil primer, but the oil primer started blistering and peeling away from the wood in large chunks. I tried to follow all the rules. I do not know if I somehow did something wrong, or if oil primer just isn't the right solution for this particular application (exterior, wood, horizontal, foot traffic, sun, rain, snow). Some boards were coated all six sides, and some were coated on the top and ends only. All of them failed prematurely.
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What you're looking for is a "block filler" paint/primer.
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I use a product called Floetrol for thinning Latex paints. It also adds a lot of good properties like helping the paint flow. This is good for doors when you want the paint to lay flat and not have brush marks. Available most anywhere.
Steve
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clipped

I think label instructions are good advice, and wouldn't recommend more thinning than the label advises, especially for high wear and outdoors. It might work, but why tempt fate for a tough condition? Primer should not blister unless applied to damp or dirty wood or in hot, direct sun.
Start with clean, dry wood. Scrape and sand as needed. To fill cracks (which invite disruption of paint film and intrusion of moisture), apply paintable, flexible caulk after primer dries. Prime the caulk after it dries. Paint. Cover all sides of the boards.
I don't buy cheap paint, and I hate paint prep work, but I am a fanatic about the prep when I paint or paper because I don't want to have to do it over. Why use poor quality paint, or ruin good quality paint? Paint stores have product specifically for thinning both types of paint and which don't weaken the film. The logic in not thinning too much is that you dilute to the point that you are applying little more than colored water. Of course, it would have "remarkable" penetration. Buy some new wood or Trex.
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Norminn wrote:

"doesn't weaken the film" is the part I want to understand better. Why doesn't this product "weaken the film" but water does? I'm not saying you're wrong, I just want to understand how it works.

So... it doesn't matter if I thin the latex 50/50, as long as I apply enough coats that the total amount of latex I use is the same as I would have used if I didn't thin it?
For example, say I pour out two equal portions of unthinned latex into separate containers. I paint one board with 2 coats using the first portion (using it all up). I thin the second portion 50/50 with distilled water, and paint the second board with that, applying coats (and letting them dry) until the second portion is used up. Both boards now have exactly the same amount of pigment and binder on them. Will the paint on the second board fail because I thinned it? _Why_? (It's the "why" part I am seeking to understand).
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Look at the two. The product is every bit as thick as latex paint. It has the consistency of latex paint. It has the same polymers and surfactants as latex paint. It has added polymers and surfactants to help the paint flow and "skin" properly. Pour a cup of it in your hand. Watch what it does. Feel it.
Now do the same with a cup of water.
Here's yer sign.
Steve
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Steve B wrote:

I just looked at a container of Floetrol today. Until now, I'd never heard of it.

Very cheap latex paint maybe. Floetrol is nowhere near as thick as the latex paints I have been using.

How do you know this? The label on the container lists no ingredients. The MSDS doesn't list any ingredients (it does say the boiling point is 212F though). Where did you get your information?

Do you personally find that to be a satisfying technical answer to the question?
If I paint one board with 8 ounces of high quality latex paint, using as many coats as it takes to use up the paint, and I paint a second board with 8 ounces of the same high quality latex paint plus 2 ounces of distilled water, again using as many coats as it takes to use up the 10 ounces of thinned paint, are you saying the second board has a "weaker" film? And if so, _why_?
OT, just heard on the news - Pluto has been stripped of its planet status.
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Ether Jones wrote:

MSDS doesn't list the chemicals, but does say that it is 90% volatile. The other 10% is magic potion :o)
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Norminn wrote:

... and the boiling point of that 90% is, guess what? 212 degrees F. Does that number sound familiar?

Apparently a tightly held secret? Steve B claims they're "polymers" and surfactants. I wonder where he got that info. Seems weird that they would put polymers in it. You'd think they'd use monomers, like the original latex, so it would boost the binder.
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Let me just say this. I have used it. I like it. It works for me. Your mileage may vary. Use it or don't. It's as good a solution as any proposed.
Surely as good as water. Maybe even a little better.
Steve
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On 24 Aug 2006 14:04:23 -0700, with neither quill nor qualm, "Ether

Floetrol is a latex medium with additional binders which are not in water. It's good stuff. (I have a quart of it on my kitchen floor waiting to be used with the latex enamel I'll use to repaint all the interior house trim this month.)

Perhaps here: http://www.flood.com/Flood/CustomerSupport/FAQ/DIY/Floetrol+FAQ.htm

Yes. Take an ounce of Elmer's glue. Thin it with water. Does it still work as well? You've thinned out the chemical bonding. Ditto your thinned paint. Most manufacturers ask you not to thin more than 10% because it messes with the durability of their paint formula. You're thinning 25-50% and it'll come back to bite you, ah gare-on-tee.
If you're low on engine oil in your car, it is recommended that you don't add water to that, either. ;)

This just in: Everything We (You) Know Is Wrong. The sun isn't going down, the horizon is moving UP!
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Larry Jaques wrote:

Or not. I've read that link. There is no mention at all of polymers or surfactants. All its says is that Floetrol contains "conditioners". My shampoo contains "conditioners" too... maybe I could use that? It's cheaper... :-)

It's also recommended in my car owner's manual that I do NOT add third-party additives to my oil, either. Just like the label on my latex which says "Do not thin"... not "Do not thin, except with Floetrol, which, although made by our competitor, contains the exact same chemistry as our proprietary acrylic binding system".
I'll probably pick up a gallon of Floetrol today and give it a try on some of the boards I am refinishing and give it a fair try. It would be nice to have more information about it though. Like what's in it.
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