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LEV testing - spray booths
If your spray booth is overspraying - paint mist escaping the booth, drifting where it shouldn't, or settling on surfaces it shouldn't reach - it's a sign the booth isn't controlling the mist as it should. Since the booth's whole job is to control the isocyanate mist and protect the sprayer, overspray is a warning worth understanding. Here is why a spray booth oversprays, what to check, and why it matters for more than finish quality. This is general information.
The short answer
If your spray booth is overspraying - paint mist escaping the booth, drifting where it shouldn't, or settling on surfaces it shouldn't reach - it's telling you something important: the booth isn't controlling the mist as it should. Because a spray booth's whole job is to control the paint mist (drawing it away from the sprayer and containing it) and that mist is an isocyanate hazard, overspray is more than a nuisance or a finish problem. Here's why a spray booth oversprays, what to check, and why it matters. This is general information. How the booth is supposed to control the mist. A spray booth controls the paint mist by moving air - typically a downdraught, drawing air (and the mist in it) down and away from the sprayer and the work, out through the extraction and filters. This airflow is what sweeps the mist away and contains it, keeping it off the sprayer, off surfaces it shouldn't reach, and out of the wider workshop. So the airflow is the heart of the booth's function - and overspray (mist going where it shouldn't) means that airflow isn't doing its job of controlling the mist. The clue in overspray is that the air isn't managing the mist. The common causes. Why might the airflow not be controlling the mist? A few common causes. Clogged or dirty filters: the booth's filters (the intake filters, and especially the extract filters that catch the overspray) block up with paint over time. Clogged filters choke the airflow - the booth can't move the air it needs to draw the mist away - so the mist escapes, lingers, or isn't swept away cleanly. This is one of the most common causes of overspray, and it's why booth filters have to be changed regularly; a booth with neglected, clogged filters will overspray. Weak or disrupted airflow: the airflow may be inadequate for another reason - a failing or worn fan, blocked or restricted ducting, or the booth simply not moving enough air - or it may be disrupted: draughts, doors left open, obstructions in the booth, or a poorly-balanced booth (intake and extract not matched) can all break up the clean airflow pattern so it doesn't sweep the mist away properly. Spraying technique or setup: how the spraying is done matters too. Overloading the air with too much paint (spraying too heavily, wrong gun setup or pressure, spraying too far from the work) can produce more mist than the airflow can handle; and the way the work is positioned can disrupt the airflow around it. So technique and setup can contribute, though the airflow-side causes (filters, fan, disruption) are the usual culprits. Often overspray is a combination. Why it matters beyond finish. Overspray is often first noticed as a finish-quality problem: mist settling back on the work (a rough, contaminated finish - overspray in the literal sense), or drifting onto other surfaces, cars, or equipment. That's a real cost in itself (spoiled finishes, rework). But it matters for more than quality: if the mist is escaping or not being contained, the booth isn't controlling it - which means the isocyanate paint mist isn't being properly controlled. Isocyanates are respiratory sensitisers that can cause incurable, career-ending asthma, so mist that's escaping or lingering can be reaching the sprayer or spreading into the wider workshop, exposing people. So overspray is a health warning as much as a quality one: the same failure that spoils the finish means the hazardous mist isn't contained. This is why overspray should be taken seriously, not just tidied up. What to check. So if the booth is overspraying, check: the filters first (are they clogged with paint? change them - it's the commonest and easiest cause to fix); then the airflow (is the fan and system moving enough air? is the ducting clear? is the airflow disrupted by draughts, open doors, or obstructions? is the booth balanced?); then the spraying technique and setup (too much paint, wrong gun setup, work disrupting the airflow?). And, importantly, because the booth is an LEV controlling a serious health hazard, have its performance properly tested: a thorough examination and test measures whether the airflow is actually controlling the mist (the airflow, the containment), which both diagnoses overspray and confirms whether the booth is protecting the sprayer (covered in the how-a-spray-booth-failure-was-traced-back page). So testing is both a diagnostic and a health check. The takeaway. So a spray booth oversprays because its airflow isn't controlling the mist properly - most often clogged filters or weak/disrupted airflow, sometimes spraying technique or setup, often a combination. Check the filters first, then the airflow, then the technique. And take it seriously beyond the finish: overspray means the isocyanate mist isn't being contained, so it's a health matter, not just a quality one - which is why having the booth tested (to confirm it's actually controlling the mist) matters. This is general information. This is general information.
Key points
The airflow controls the mist
A spray booth controls the paint mist by moving air - typically a downdraught, drawing air (and the mist in it) down and away from the sprayer and the work, out through the extraction and filters. This airflow is what sweeps the mist away and contains it: keeping it off the sprayer, off surfaces it shouldn't reach, and out of the wider workshop. So the airflow is the heart of the booth's function.
That means overspray - paint mist going where it shouldn't (escaping the booth, drifting, settling on the work or other surfaces) - is a sign that the airflow isn't doing its job of controlling the mist. If the air were sweeping the mist away and containing it as it should, the mist wouldn't be escaping or settling where it shouldn't. So the clue in overspray is that the air isn't managing the mist properly - which points the diagnosis at the airflow (and the things that affect it). This framing is the key to understanding overspray: it's fundamentally an airflow-control problem, whatever the specific cause. So the airflow controls the mist - overspray means the airflow isn't managing it - is the starting point: read overspray as an airflow-control failure. The common causes of that failure follow. So overspray signals the airflow isn't controlling the mist. This is general information. This is general information.
Clogged filters
One of the most common causes of overspray is clogged or dirty filters. A spray booth has filters - the intake filters (cleaning the incoming air) and, especially relevant here, the extract filters that catch the paint overspray as the air leaves. These filters block up with paint over time as they do their job of catching the mist. And clogged filters choke the airflow: the booth can't move the air it needs to draw the mist away, because the blocked filters are restricting the flow.
So as the filters clog, the airflow weakens, and the booth can no longer sweep the mist away cleanly - the mist escapes, lingers, or settles where it shouldn't. This is why booth filters have to be changed regularly: it's the routine maintenance that keeps the airflow up and the mist controlled. A booth with neglected, clogged filters will overspray, and it's often the first thing to suspect and the easiest to fix. It's directly analogous to a clogged filter choking a dust extractor's suction - the same mechanism (a blocked filter restricting airflow), here showing as overspray rather than lost suction. So clogged filters - the commonest cause of overspray - are where to start: check and change the filters, because clogged ones choke the airflow that controls the mist. Other airflow causes follow. So check and change the filters first - clogged ones choke the airflow. This is general information. This is general information.
Weak or disrupted airflow
Beyond the filters, the airflow can be weak or disrupted for other reasons. Weak airflow: the booth may not be moving enough air because of a failing or worn fan, blocked or restricted ducting, or a system that's lost performance - so even with clean filters, the air isn't strong enough to draw the mist away properly. This is the booth's equivalent of a dust extractor losing suction, and it undermines the mist control the same way.
Disrupted airflow: even adequate airflow won't control the mist if its pattern is broken up. Draughts (from open doors, gaps, or the workshop), obstructions in the booth, badly-positioned work, or a poorly-balanced booth (where the intake and extract airflows aren't properly matched) can all disrupt the clean airflow pattern the booth relies on, so it doesn't sweep the mist away cleanly and overspray results. So the airflow can fail either by being too weak (fan, ducting, lost performance) or by being disrupted (draughts, obstructions, imbalance) - both stop it controlling the mist. These, with clogged filters, are the airflow-side causes of overspray. So weak or disrupted airflow - a failing fan, blockage, or broken pattern - is the second cause area: check the fan, ducting, draughts, obstructions and booth balance. Spraying technique and setup follow. So weak or disrupted airflow also causes overspray - check the fan and the pattern. This is general information. This is general information.
Technique and setup
How the spraying is done matters too. Overloading the air with too much paint - spraying too heavily, wrong gun setup or pressure, or spraying too far from the work so more paint atomises into drifting mist - can produce more mist than the airflow can handle, so some escapes control and shows as overspray. So a technique or gun-setup problem can cause or worsen overspray, independent of the booth's airflow.
And the way the work is positioned in the booth can disrupt the airflow around it - a large or awkwardly-placed item can block or divert the downdraught, creating areas where the mist isn't swept away cleanly. So the setup (how the work is arranged relative to the airflow) can contribute to overspray as well. That said, while technique and setup can play a part, the airflow-side causes - clogged filters, weak or disrupted airflow - are the usual culprits when a booth starts overspraying, so they're where to look first. Technique is worth reviewing, but a booth that's suddenly overspraying more often has an airflow problem (filters, fan) than a technique one. So technique and setup - too much paint, or work disrupting the air - complete the causes: spraying and positioning can contribute, alongside the primary airflow causes. Why overspray matters beyond finish follows. So technique and work position can contribute, but airflow is the usual cause. This is general information. This is general information.
Why it matters beyond finish
Overspray is often first noticed as a finish-quality problem: mist settling back on the work (a rough, contaminated finish - overspray in the literal sense), or drifting onto other surfaces, vehicles or equipment. That's a real cost in itself - spoiled finishes and rework. But overspray matters for much more than quality.
If the mist is escaping or not being contained, the booth isn't controlling it - which means the isocyanate paint mist isn't being properly controlled. Isocyanates are respiratory sensitisers that can cause incurable, career-ending occupational asthma, so mist that's escaping the booth or lingering rather than being swept away can be reaching the sprayer or spreading into the wider workshop, exposing people to a serious hazard. So the same failure that spoils the finish - the airflow not controlling the mist - also means the hazardous mist isn't contained. Overspray is therefore a health warning as much as a quality one, and should be taken seriously as such: not just tidied up or worked around, but investigated and fixed, because it signals the booth isn't protecting the sprayer. Because the booth is an LEV controlling this serious hazard, its performance should be properly tested (a thorough examination and test measures whether the airflow is actually controlling the mist), which both diagnoses overspray and confirms whether the booth is protecting people. So why it matters beyond finish - the isocyanate mist isn't being contained - is the crucial point: overspray is a health warning, so check and test the booth, don't just live with it. So overspray means the hazardous mist isn't contained - treat it as a health warning. This is general information. This is general information.
Questions
Usually because the airflow isn't controlling the mist properly - most often clogged filters choking the airflow, or weak/disrupted airflow (a failing fan, blocked ducting, draughts, obstructions), sometimes spraying technique or setup; the booth controls the mist by airflow, so overspray means that airflow isn't doing its job. Your spray booth is overspraying because its airflow isn't controlling the paint mist properly. The booth works by moving air (typically a downdraught) that draws the mist away from the sprayer and the work and out through the extraction and filters - so overspray (mist escaping, drifting, or settling where it shouldn't) means that airflow isn't sweeping the mist away and containing it as it should. The common causes: clogged or dirty filters - the booth's filters block up with paint over time, and clogged filters choke the airflow, so the booth can't move the air needed to draw the mist away (this is one of the most common causes, and why filters must be changed regularly); weak or disrupted airflow - a failing or worn fan, blocked ducting, or a booth not moving enough air (weak), or draughts, open doors, obstructions, or a poorly-balanced booth (disrupted) breaking up the clean airflow pattern; and spraying technique or setup - too much paint (heavy spraying, wrong gun setup or distance) producing more mist than the airflow can handle, or work positioned so it disrupts the airflow. Often it's a combination, but clogged filters and weak airflow are the usual culprits. Check the filters first, then the airflow, then the technique. So it's an airflow-control problem - usually filters or airflow. So because the airflow isn't controlling the mist - check filters and airflow. This is general information. This is general information.
Yes - clogged extract filters choke the booth's airflow, so it can't move enough air to draw the mist away, and the mist escapes or lingers; it's one of the commonest causes of overspray, and why booth filters must be changed regularly - changing them often fixes it. Yes - clogged filters are one of the commonest causes of overspray. A spray booth has filters, including the extract filters that catch the paint overspray as the air leaves the booth. These block up with paint over time as they do their job of catching the mist. And clogged filters choke the booth's airflow: because the blocked filters restrict the air trying to pass through, the booth can't move the air it needs to draw the mist away. So as the filters clog, the airflow weakens, and the booth can no longer sweep the mist away cleanly - the mist escapes the booth, lingers, or settles where it shouldn't, which is overspray. This is exactly why spray booth filters have to be changed regularly: keeping the filters clear keeps the airflow up, and the airflow is what controls the mist. A booth with neglected, clogged filters will overspray, and it's often the first thing to suspect when a booth starts overspraying - and the easiest to fix, since changing the filters often restores the airflow and stops the overspray. It's the same mechanism as a clogged filter choking a dust extractor's suction - a blocked filter restricting airflow - just showing here as overspray rather than lost suction. So if your booth is overspraying, checking and changing the filters is the first thing to do. So yes - clogged filters choke the airflow and cause overspray. So yes; clogged filters are a common cause - change them. This is general information. This is general information.
No - overspray is often noticed as a finish problem (mist spoiling the work or drifting onto surfaces), but it also means the mist isn't being contained; since the mist is isocyanate (a respiratory sensitiser that can cause incurable asthma), poor containment is a health matter, so overspray is a health warning too. No - overspray is not just a finish-quality problem, though that's often how it's first noticed. As a quality issue, overspray shows up as mist settling back on the work (a rough, contaminated finish) or drifting onto other surfaces, vehicles or equipment - a real cost in spoiled finishes and rework. But it matters for much more than that. Overspray means the mist is escaping the booth or not being contained - which means the booth isn't controlling the mist. And the mist is isocyanate paint mist: isocyanates are respiratory sensitisers that can cause incurable, career-ending occupational asthma. So mist that's escaping or lingering rather than being swept away and contained can be reaching the sprayer or spreading into the wider workshop, exposing people to a serious health hazard. In other words, the same airflow failure that spoils the finish also means the hazardous mist isn't being contained - so overspray is a health warning as much as a quality one. This is why overspray should be taken seriously and investigated, not just tidied up, cleaned off, or worked around: it's a sign the booth isn't protecting the sprayer. And because the booth is an LEV controlling a serious hazard, confirming whether it's actually controlling the mist means having it tested. So overspray is a health matter, not merely cosmetic. So no - it also means the hazardous mist isn't contained. So no; it's a health warning, not just a finish issue. This is general information. This is general information.
The filters first (clogged with paint? change them - the commonest, easiest cause), then the airflow (fan and system moving enough air? ducting clear? airflow disrupted by draughts, open doors or obstructions? booth balanced?), then spraying technique and setup; and have the booth's performance tested, since it controls a serious hazard. If your booth is overspraying, check things in this order. First, the filters: are they clogged with paint? Clogged filters choke the airflow and are the commonest, easiest-to-fix cause - change them and see if the overspray stops. Second, the airflow: is the fan and system moving enough air (a failing or worn fan, or blocked ducting, weakens it)? Is the ducting clear? Is the airflow being disrupted by draughts, open doors, obstructions in the booth, or a poorly-balanced booth (intake and extract not matched)? These disrupt or weaken the airflow that controls the mist. Third, the spraying technique and setup: is too much paint being applied (heavy spraying, wrong gun setup or pressure, spraying too far from the work) producing more mist than the airflow can handle? Is the work positioned so it disrupts the airflow around it? Between these - filters, airflow, and technique/setup - you can usually find the cause, with the filters and airflow being the usual culprits. Importantly, because the spray booth is an LEV controlling a serious health hazard (isocyanate mist), have its performance properly tested: a thorough examination and test measures whether the airflow is actually controlling the mist, which both helps diagnose the overspray and confirms whether the booth is protecting the sprayer. So testing is both a diagnostic and a health check worth doing. So check filters, then airflow, then technique - and have it tested. So the filters, the airflow, the technique - and get it tested. This is general information. This is general information.
It can - overspray means the mist isn't being contained, so if the airflow isn't controlling the mist, the isocyanate mist may be reaching the sprayer or the wider workshop; you can't assume the sprayer is protected when the booth is overspraying, so it should be tested to confirm whether it's actually controlling the mist. It can, yes - overspray is a warning that the sprayer may not be protected, and you shouldn't assume they are while the booth is overspraying. Here's the reasoning: overspray means paint mist is escaping the booth or not being contained, which means the booth's airflow isn't controlling the mist as it should. Since the booth's job is to draw the isocyanate mist away from the sprayer and contain it, an airflow that isn't controlling the mist may be failing to protect the sprayer - the mist could be reaching their breathing zone, or spreading into the wider workshop where others are exposed. Isocyanates are respiratory sensitisers that can cause incurable, career-ending asthma, so this is a serious matter. Now, overspray doesn't automatically prove the sprayer is being exposed above safe levels - the sprayer also normally wears respiratory protection (RPE) as a second layer, and the extent of the exposure depends on the specifics. But overspray does mean the booth's primary control (the airflow containing the mist) is compromised, so you can't rely on the booth to be protecting the sprayer while it's overspraying. That's why overspray should prompt having the booth properly tested - a thorough examination and test establishes whether the airflow is actually controlling the mist and protecting the sprayer, rather than leaving it to assumption. So overspray is a reason to check the sprayer's protection, not to assume it. So it can - so test the booth to confirm the sprayer is protected. So possibly - don't assume protection; have it tested. This is general information. This is general information.
By keeping the airflow working: change the filters on schedule (clogged filters are the commonest cause), keep the fan and ducting maintained, avoid disrupting the airflow (draughts, open doors, obstructions, poor balance), and use good spraying technique; and have the booth thoroughly examined and tested regularly to confirm the airflow is controlling the mist. You prevent a spray booth overspraying mainly by keeping its airflow working properly, since overspray is fundamentally an airflow-control problem. The key measures: Change the filters on schedule - clogged filters are the commonest cause of overspray, because they choke the airflow, so keeping them changed (before they block up) keeps the airflow up and the mist controlled. This is the single most important routine measure. Keep the fan and ducting maintained, so the booth keeps moving enough air (a worn fan or blocked ducting weakens the airflow). Avoid disrupting the airflow: keep draughts out (don't leave doors open), keep obstructions out of the booth, position the work so it doesn't block the airflow, and keep the booth balanced (intake and extract matched). Use good spraying technique and setup: don't overload the air with too much paint (correct gun setup, pressure and distance), so you're not producing more mist than the airflow can handle. And, importantly, have the booth thoroughly examined and tested regularly - as an LEV controlling isocyanate mist, it must be tested (at least every fourteen months), and the test confirms the airflow is actually controlling the mist, catching a decline before it shows as overspray or exposure. So the combination of filter changes, airflow maintenance, avoiding disruption, good technique and regular testing keeps the booth controlling the mist rather than overspraying. So prevent it by keeping the airflow working - filters, fan, no disruption - and testing. So change filters, maintain the airflow, spray well, and test it. This is general information. This is general information.
Overspray means a spray booth's airflow isn't controlling the mist - so the isocyanate hazard isn't being contained; we thoroughly examine and test spray booths, measuring whether the airflow is actually controlling the mist and finding why it isn't, so overspray is diagnosed and the sprayer protected, as COSHH requires. Ask us to test your spray booth. This is general information.
