# Thinning latex? Weaker paint?



## Bennylava (Mar 22, 2013)

Hi all. I was wondering about thinning latex. Also oil base, if there is a difference? I'm a bit of a paint noob. 

Some sprayers require you to thin the paint in order to spray it. Others do not. But wouldn't thinning the paint be counterproductive, in the end? I mean, the paint was designed to be the way it is, right? So if you go thinning it out, how can you guarantee that you'll get the desired longevity out of the paint?

If you thin it out, how can the paint possibly be as durable as it was before you thinned it? Why would anyone want to thin their paint? It seems that it would just weaken the paint.


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## joecaption (Nov 30, 2011)

Just makes thinner not "weaker".
May need more coats to get full coverage.


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## Gymschu (Dec 12, 2010)

I rarely thin my paint. I know when I do decorative painting with glazes added to the paint, well, let's just say the paint is easily rubbed off of the walls unless protected by a clear coat. Adding Floetrol to latex paint doesn't seem to affect the paint as much although I don't have a full-fledged trust in how it will perform over the long haul even though the Flood Co. says the Floetrol doesn't affect the paint qualities at all.

I would only thin as much as necessary for the paint to be applied with a sprayer. If not spraying, you would rarely, if ever, have to thin the paint.


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## Bennylava (Mar 22, 2013)

joecaption said:


> Just makes thinner not "weaker".
> May need more coats to get full coverage.


How could it not weaken it? Say you thin some oil base so it can be sprayed onto a fence. You now put a lot more space in between those oil molecules, which are the UV barrier. Leaving more room for the UV to be able to penetrate. 

Some sprayers claim no need to thin ANY type of paint. Perhaps that would be the reason?


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## ToolSeeker (Sep 19, 2012)

The reason for sprayers is the pump, some have a pump that will spray it straight. Some with smaller pumps that will not spray the thick latex paint without thinning it. Some paints today dry so fast that to thin them make them easier to work with. This does not necessarily translate to easier on the painter, it means the paint has more time to level itself as it dries. Some paints such as pro classic, I will use this because it is what I am familiar with, to thin it or use of additives will hurt it's performance. The reason for this is it has levelers already in it and to do this will affect those levelers.
There is a super contributor on here named ric knows paint who will hopefully come along and explain it a lot better than I can.


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## ric knows paint (Oct 26, 2011)

Bennylava said:


> How could it not weaken it? Say you thin some oil base so it can be sprayed onto a fence. You now put a lot more space in between those oil molecules, which are the UV barrier. Leaving more room for the UV to be able to penetrate.
> 
> Some sprayers claim no need to thin ANY type of paint. Perhaps that would be the reason?


Good questions, Benny...

The definitive answer to all your questions is...it depends. 

When thinning paint, it is possible to over-thin and reduce the products ability to protect as intended...but that's not necessarily the whole story. Paint, in it's original packaging, is designed to provide protection - when applied at a specific mil-thickness. If the paint were applied at 1/2 the recommended thickness (or at twice the recommended square footage) it would be impossible for that coating to provide the type of protection you'd expect. In that respect, thinning does the same thing. By adding a liquid solvent or diluent to a packaged product, you've increased the product's theoretical spread rate, without adding any additional solids (solids are those components of paint that stay on the surface after the solvents have evaporated) thereby decreasing the finish, and proper, mil thickness needed for maximum protection. 

Example: 1 gallon of paint will cover 400 square feet (theoretical), if you add 1 quart of thinner (water, solvent, diluent, whatever) you now have 1 gallon and 1 quart of material with a new theoretical spread rate of 500 square feet. Now if that can of paint was a 50% solids product, and was applied, unthinned, at the theoretical rate of 400 square feet per gallon, that would result in an application of 4 mils wet film thickness (WFT). But since this is a 50% solids product, it would dry down to 2 mils of dry film thickness (DFT)...But now you have added 1 quart of evaporative solvent (with no solids) creating 1 gallon and 1 quart of material. Now your solids content is only 40% which, at 500 square feet, yields the same 4 mils WFT. If the recommended DFT of the coating is 2 mils to last, for example, 10 years - you can see how 4 mils WFT @ 40% solids will yield only 1.6 mild DFT and would theoretically diminish the coatings ability provide necessary protection by 20% (or 8 years in this hypothetical scenario)...

In this example, you could control your application spread rate to stay at 400 square feet and still maintain the recommended DFT of 2 mils - but when thinning paint at a rate of 20%, it'd be very difficult to apply at that rate without runs and sags...

But would that "weaken the paint?" Well again, that depends. Earlier I mentioned "thinning" products with either a solvent or diluent. And even though the industry kinda refers to all "thinners" as solvents (even water), that's not exactly proper nomenclature. In the case above, thinning a latex paint with a diluent (water), no harm would be done to the latex resin as water only dilutes the resin - doesn't destroy it. So thinning to that degree with water would only weaken the products ability to protect due to the resulting inadequate film thickness. 

In that same example however, if the latex product were to be thinned with denatured alcohol (solvent), it would absolutely "weaken" the paint as the resin is actually dissolved by the alcohol. A film may still form, but without all the attributes and expectations of a latex coating...the film will not properly coalesce, and without proper curing, latex paints are just un-bound color on the surface subject to all negative effects of UV light.

Final point...and this is a tricky one. With latex paints, most manufacturers will say thin up to 1 pint per gallon with water - that's a lot actually, and usually not necessary to thin that much - But it won't hurt or weaken the paint...nor will it significantly diminish the ability to achieve the recommended dry film thickness (DFT)...

With oil base (alkyd) products, it's a little different story (even though everything I said about solvents vs. diluents is equally true with alkyd products). Paint manufacturers will usually say "do not thin" ...but it has little to do with what I've described above. Manufacturers are under very rigid guidelines regarding the amounts of solvents (VOC's) they can legally add to the product - and most legal oil/alkyd products are offered at the very limit of those restrictions. If a manufacturer were to bless the end user with the license to thin their product, they would effectively be encouraging the user to alter the formulation and create a non-compliant coating (as it relates to allowable VOC's) - putting both parties at risk of environmental polluting. 

I really hope this information is more helpful than confusing. Happy painting.


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## Bennylava (Mar 22, 2013)

Thank you for the well articulated reply. Yes that clears up a lot for me.


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## ToolSeeker (Sep 19, 2012)

Thanks Ric


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## Will22 (Feb 1, 2011)

*Aside from affecting the performance, thinning may cause overspray.Product
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## Will22 (Feb 1, 2011)

Aside from thinning affecting the intended performance, it may cause overspray.


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## KD PAINTING (Nov 8, 2012)

Thinning your paint does not mean that your weaken the product and affect its durability, it is just easier to work with and for some spray machines it helps them run and spray a lot smoother. When your paint is thinned, you will most likely have to apply another extra coat to get the desired coverage. As long as you do not over-thin your paint, I don't see any issues with it whatsoever. Good Luck!


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## chrisn (Dec 23, 2007)

KD PAINTING said:


> Thinning your paint does not mean that your weaken the product and affect its durability, it is just easier to work with and for some spray machines it helps them run and spray a lot smoother. When your paint is thinned, you will most likely have to apply another extra coat to get the desired coverage. As long as you do not over-thin your paint, I don't see any issues with it whatsoever. Good Luck!


 
did you read post #6???:huh:


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## Bennylava (Mar 22, 2013)

KD PAINTING said:


> Thinning your paint does not mean that your weaken the product and affect its durability, it is just easier to work with and for some spray machines it helps them run and spray a lot smoother. When your paint is thinned, you will most likely have to apply another extra coat to get the desired coverage. As long as you do not over-thin your paint, I don't see any issues with it whatsoever. Good Luck!


According to Rick it can, but doesn't always. You have to let the situation be your guide.


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## SeniorSitizen (Sep 10, 2012)

Think of thinning paint and straight from the bucket as if it were two buddies bellied up to the bar. One orders shots and the other orders mixed drinks. The end result will be the same but one will just take longer.


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## ToolSeeker (Sep 19, 2012)

Maybe I'm reading it wrong but I think he's saying some thinning is acceptable with no ill effects but if you go overboard you can hurt it. I guess my question is latex paint is water based if you add small amount of water to thin doesn't some of the water evaporate during the drying/curing process? And the water you add is just that water it has no resins or binders mixed in, I don't think just stirring it would give it the same effect. But hey I could be wrong. What about an additive like flotrol or xim extender would the effect on the final film be different?
HEY RIC.


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