A properly fit N95 should block out all dust. If you are getting plaster in your nose, try different types of masks (folding), or a half-face respirator.
One of the justification for not advising N95s to the public was the fact that most people don't know how to properly wear one. As if they couldn't be trained in a few weeks, or duration of the pandemic.
Also, N95s filter out particles smaller than .3 microns (the 95% part). You can look it up, but it has something to do with the electrostatic media and physics. It definitely does not work like a sieve. (https://www.usatoday.com/story/news/factcheck/2020/06/11/fac...)
Actually it DOES work like a sieve on larger particles. The electrostatic mechanism works on smaller particles, while the larger ones are indeed filtered "mechanically".
The 0.3 micron size is used in the specification because it's the "worst" case... too large for maximum electrostatic attraction, too small for mechanical filtration...it's the worst case.
You are here talking specifically of N95 masks, not cloth masks, and this is only true for the very few that properly use masks. Doctors are required to not touch N95 mask and dispose of them after each use. Viruses can live for up to 24hrs on a mask and spread from you touching the mask then another surface.
Covid survives for 30 seconds in sunlight, so wearing a mask outside is bad on balance as you breathe in your own CO2 and reduce oxygen intake which both have negative health effects (especially during exercise).
Unless you have a valve, and hardly breath at all, exhaling pushes the N95 away from your face enough to let some unfiltered air in. There’s a similar (though smaller) effect with the thin paper valves, but regardless of how good the fit is, you need a much better valve than that to actually filter all air through the fabric.
I’ve had both with and without valves since 2015. Would never buy one without a valve again if I can find one with a valve (in the last year at some times could only find valveless)
Fwiw, in Israel it was illegal to use a valved mask without covering the valve with cloth/paper/surgical mask. The official statement was that the pressure out of the valve disperses virions much farther, and is thus more dangerous to people around you if you are presymptomatic than having no mask at all.
One of the justification for not advising N95s to the public was the fact that most people don't know how to properly wear one. As if they couldn't be trained in a few weeks, or duration of the pandemic.
Also, N95s filter out particles smaller than .3 microns (the 95% part). You can look it up, but it has something to do with the electrostatic media and physics. It definitely does not work like a sieve. (https://www.usatoday.com/story/news/factcheck/2020/06/11/fac...)