# 5 gal paint... int or ext? how to tell?
**URL:** https://boards.straightdope.com/t/5-gal-paint-int-or-ext-how-to-tell/613324
**Category:** Factual Questions
**Created:** [February 19, 2012, 2:15pm UTC](https://boards.straightdope.com/t/5-gal-paint-int-or-ext-how-to-tell/613324 "2012-02-19T14:15:22Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@cedman](https://boards.straightdope.com/u/cedman)
#### Post date: [February 19, 2012, 2:15pm UTC](https://boards.straightdope.com/t/5-gal-paint-int-or-ext-how-to-tell/613324/1 "2012-02-19T14:15:22Z")
I inherited a 5 gallon bucket of never opened paint. I can determine the type of finish by dipping a stir stick and letting it dry. I can tell that it is latex by the smell (or lack thereof). However, is there an easy way, a hard way or _any_ way to tell if it is interior or exterior paint? There are no labels or printing on the bucket or the lid.
The color looks more like an exterior color (light gray) but could be an interior color as well.
I’d like to use it, (have you priced any paint lately??) but don’t want to make a bigger mess or have a bigger problem by using it in the wrong application.
Any ideas?
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### Author:  [@lawoot](https://boards.straightdope.com/u/lawoot)
#### Post date: [February 19, 2012, 2:55pm UTC](https://boards.straightdope.com/t/5-gal-paint-int-or-ext-how-to-tell/613324/2 "2012-02-19T14:55:00Z")
No idea - maybe if you have a local paint store they could look at it and tell. I THINK that exterior is generally fumi-er (is that even a word? It smells more, or at least puts out fumes that are more noxious).
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### Author:  [@jz78817](https://boards.straightdope.com/u/jz78817)
#### Post date: [February 19, 2012, 2:59pm UTC](https://boards.straightdope.com/t/5-gal-paint-int-or-ext-how-to-tell/613324/3 "2012-02-19T14:59:32Z")
if a paint store can’t help you, then paint something and leave it outside for a year… if it fades and/or cracks it’s probably interior paint.
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### Author:  [@Nava](https://boards.straightdope.com/u/Nava)
#### Post date: [February 19, 2012, 5:16pm UTC](https://boards.straightdope.com/t/5-gal-paint-int-or-ext-how-to-tell/613324/4 "2012-02-19T17:16:30Z")
> [@lawoot](#):
>
> No idea - maybe if you have a local paint store they could look at it and tell. I THINK that exterior is generally fumi-er (is that even a word? It smells more, or at least puts out fumes that are more noxious).
That would only apply to organic-solvent paint. The water-based exterior paints we made in the factory where I worked were all over the map re. smell, from the fast-drying varieties for painting roads (the ammonia would have knocked a wall out, or maybe wakened it) to others that smelled cheesy or which had virtually no smell. We didn’t make interior paints with ammonia as their only pH-adjuster, but the cheesy, oily, gluey, and no smell at all varieties were all present. The smells could come from ammonia, biocides (the same ones used for both applications), or from short-chain polymer.
Exterior paint needs to be more resistant than interior paint, but it can be used for interiors; I’d be more worried about making sure you use it on the right surface (walls, wood, metal).
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### Author:  [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)
#### Post date: [February 19, 2012, 6:11pm UTC](https://boards.straightdope.com/t/5-gal-paint-int-or-ext-how-to-tell/613324/5 "2012-02-19T18:11:54Z")
Is there a downside to using exterior paint indoors, if it smells OK? I could see the volatiles in exterior paint could be a problem, but wouldn’t you know that from the smell?
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### Author:  [@Cat\_Whisperer](https://boards.straightdope.com/u/Cat_Whisperer)
#### Post date: [February 19, 2012, 6:15pm UTC](https://boards.straightdope.com/t/5-gal-paint-int-or-ext-how-to-tell/613324/6 "2012-02-19T18:15:57Z")
According to my former professional painter husband, he agrees with **Nava** - you can use exterior paint inside, no problem. The idea of painting something and leaving it outside is about the only way you can tell if it can be used outside - an interior paint will flake and peel. The difference between exterior and interior paint is that exterior paint is basically more durable.
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### Author:  [@thelabdude](https://boards.straightdope.com/u/thelabdude)
#### Post date: [February 19, 2012, 6:31pm UTC](https://boards.straightdope.com/t/5-gal-paint-int-or-ext-how-to-tell/613324/7 "2012-02-19T18:31:07Z")
Without the original label, I doubt there is any telling. My guess is that the glossier it is, the more likely to be exterior. They do make high gloss interiors, and flat exteriors should be possible if hard to find. I am not even sure there is that much difference between modern interior and exterior paints. Exterior paints may get a bigger slug of anti mildew. (Some of them stink to high heaven.) They may get more light fast pigments. Many organic pigments break down in sunlight. The gray is mostly going to be titanium dioxide with a little carbon black, neither of which will fade in the sun.