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Old 03-10-2016, 02:46 PM   #1
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Default Spray painting

I am trying to understand how the DFT (mils) affects productivity when spray painting.

Will the time it takes to cover an area at 3.0 mils DFT take twice as long as that at 1.5 mils DFT?
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Old 03-10-2016, 02:55 PM   #2
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Quote:
Originally Posted by mms View Post
I am trying to understand how the DFT (mils) affects productivity when spray painting.

Will the time it takes to cover an area at 3.0 mils DFT take twice as long as that at 1.5 mils DFT?
Tip choice will determine rate of mil build. Also, the configuration of what you're spraying can determine tip choice. In other words if I need to have a DFT of 3 mils for a 50% solid material, I will have to apply a WFT at 6 mils. Applying six mils on a structure with a lot of tight angles, may need to be built up with a smaller tip and controlled passes rather than a steady pass with a larger tip.

Last edited by CApainter; 03-10-2016 at 03:03 PM..
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Old 03-10-2016, 03:00 PM   #3
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Whats DFT? What product are you using?
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Old 03-10-2016, 03:32 PM   #4
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Quote:
Originally Posted by Boco View Post
Whats DFT? What product are you using?
DFT = Dry film thickness. It is the amount of paint or coating left on the surface after the solvents have evaporated.

Quote:
Originally Posted by mms View Post
I am trying to understand how the DFT (mils) affects productivity when spray painting.

Will the time it takes to cover an area at 3.0 mils DFT take twice as long as that at 1.5 mils DFT?
Not necessarily. If a coating calls for 1.5 mils DFT per coat and you need a total DFT of 3 mils, then it will take twice as long (2 coats). If a coating calls for 3 mils dft per coat and you only need to do one, then that's that. Remember never to exceed the manufacturers recommended DFT, or you could end up with problems like this

As for how it affects productivity, refer to CApainters post above.
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Old 03-10-2016, 03:46 PM   #5
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Quote:
Originally Posted by mms View Post
I am trying to understand how the DFT (mils) affects productivity when spray painting.

Will the time it takes to cover an area at 3.0 mils DFT take twice as long as that at 1.5 mils DFT?
The absolute definitive answer to your question is yes...or no...or possibly. Do you know how to achieve a specific DFT? In order to do so, you must know the volume solids of the product you're working with - and you must have a way to measure your WFT - do you have a way to measure your WFT?

In CA's example, if you are applying a 50% solids (by volume) coating, you must be able to build a film at 6.0 mils wet, to achieve a dry film of 3.0 mils...which theoretically, would take no longer to apply than if you needed to achieve a 1.5 DFT. BUT, in this scenario, if the product you're applying can't, or shouldn't, be spread at 6.0 mils wet - then you'll have to apply two coats at 3.0 mils (each) to achieve a total of 3.0 mils of DFT....so then it'd take (theoretically) twice as long (very theoretically).

...and tip choice, by itself, won't actually determine the DFT (or WFT), but the proper tip size will certainly help you to establish, and maintain, the proper WFT to achieve the desired DFT. The speed, or deliberate slowness, of your spray passes, how far the gun is from the surface, whether you spray perpendicular to the substrate (or in broad sweeping arches), the psi level you set your pump at, the contours and angles of whatever you are painting, and many other factors will equally determine how much time is spent to finish a product...whether that time be spent efficiently or wastefully.

Again, what you will need, after knowing the spec'd DFT, is (1) what the product's volume solids are...(2) whether the product can (or should) be applied heavily enough, in 1 application, to achieve this DFT - or if 2 apps (coats) are required...(3) which you'll be able to find this info from the product's Tech Data Sheet...and finally, (4) how to measure your applied thickness to mathematically determine how to achieve your DFT goal (wet film gauge).
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Old 03-10-2016, 04:55 PM   #6
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Thanks for the replies.

I understand most of this, but here is the scenario of a current bid.

Engineer specifies Polyur 106 DTM Series paint.
Volume solids is 69% and recommended DFT is 4 to 8 mils.

Bid asks for a base price of single coat Polyur 106 to 4 mils thick.
Asks for an optional price for same paint but applied to 8 mils thick,
also in 1 coat.

I can calculate the paint product requirement difference easily, but
as I think about the labour difference, I'm thinking the productivity
(square feet per manhour) must be different also.

Will the painter not use MORE back and fourth passes on a given area
to achieve the 8 mil DFT than the 4 mil DFT?
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Old 03-10-2016, 09:12 PM   #7
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Quote:
Originally Posted by mms View Post
Thanks for the replies.

I understand most of this, but here is the scenario of a current bid.

Engineer specifies Polyur 106 DTM Series paint.
Volume solids is 69% and recommended DFT is 4 to 8 mils.

Bid asks for a base price of single coat Polyur 106 to 4 mils thick.
Asks for an optional price for same paint but applied to 8 mils thick,
also in 1 coat.

I can calculate the paint product requirement difference easily, but
as I think about the labour difference, I'm thinking the productivity
(square feet per manhour) must be different also.

Will the painter not use MORE back and fourth passes on a given area
to achieve the 8 mil DFT than the 4 mil DFT?
I'd check the TDS on that product before bidding a single coat at 8 mils DFT. I've never worked with a DTM that could be applied at 12 mils WFT and not curtain all over the place on me. Usually they like to be applied between 5 and 7 wet.
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Old 03-10-2016, 09:38 PM   #8
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Is this what you're looking for? How long does it take to apply 1gal over 180sf? Roll, splay? Ever though roll and 6+- mils..? But anyway, that's the chart for mh.
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Old 03-10-2016, 09:45 PM   #9
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Quote:
Originally Posted by Rcon View Post
I'd check the TDS on that product before bidding a single coat at 8 mils DFT. I've never worked with a DTM that could be applied at 12 mils WFT and not curtain all over the place on me. Usually they like to be applied between 5 and 7 wet.
If it is not reduced, 12mils possible in warm ambiance, although it will not spray but rather sprinkle)
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Old 03-11-2016, 07:47 AM   #10
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@ goga
I'm not seeing a sf/mh chart on the link you provided.
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Old 03-13-2016, 12:47 AM   #11
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So I've been thinking more about this.

If spray system can spray say 5 gallons per hour, and with an assumed 50% overspray loss, and applying paint to 3 mil thickness,
and 300 sf of coverage was achieved,
then it stands to reason that at same 5 gallons per hour, and same overspray loss of 50%, and paint applied to 6 mil thickness,
then theoretically only 150 sf of paint would be covered.

No?

ie
paint comes out of the gun at the SAME rate, no matter what thickness the paint is being applied.
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Old 03-13-2016, 01:03 AM   #12
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Quote:
Originally Posted by mms View Post
@ goga
I'm not seeing a sf/mh chart on the link you provided.
Mh chart = how many sf one man power can paint in one hour x hours to paint = sf per so many hours by one man power.

PS: chart is not in the link, it is in the logic from the provided sf per gallon on paint, sf per hour on man power, or how many gals can one man do on the wall per hour.

Last edited by goga; 03-13-2016 at 01:08 AM..
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Old 03-13-2016, 08:49 AM   #13
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Quote:
Originally Posted by mms View Post
So I've been thinking more about this.

If spray system can spray say 5 gallons per hour, and with an assumed 50% overspray loss, and applying paint to 3 mil thickness,
and 300 sf of coverage was achieved,
then it stands to reason that at same 5 gallons per hour, and same overspray loss of 50%, and paint applied to 6 mil thickness,
then theoretically only 150 sf of paint would be covered.

No?

ie
paint comes out of the gun at the SAME rate, no matter what thickness the paint is being applied.
Well, since we're speaking theoretically here...Your math seems correct, but you've also got to consider that, since the paint comes out of the gun at the same rate, you've got to either (a) double your application "passes" to achieve 6.0 mils (versus 3.0 mils), or (b) slow your application passes, by half, to achieve the higher build described (theoretically, of course)...in either case (theoretically), you have effectively double your application time to accommodate the heavier build...theoretically.

...and I realize we're speaking theoretically, which is kinda fun, BUT if you're using this actual formula to bid your work, you might want to either rethink your waste allowance for spray application, or go to a less wasteful means of application...While there will be some waste to apply product by spray, if you're experiencing a 50% loss (and I'm assuming you're speaking airless and not conventional spray), you are gonna need to (1) turn down the pressure on your pump, (2) stand a little closer to the surface, (3) invest in a new, and proper sized tip, (4) back off the material reduction a tad, and (5) learn a proper spray technique...if not, all the time/money you save by spraying will be lost due to extreme & excessive masking and drops, or equally excessive clean-up + add'l & unnecessary material charges for paint, rags, tape, filters, and associated equipment wear and tear (not to mention all the goggle wiper blades you'll need to be able to see with all the fog you've created). Think about it, at your waste allowance, for every 5 gallon pail you apply, 2.5 gallon is going somewhere that you don't intend for it to go...that's gotta be costly.

Last edited by Ric; 03-13-2016 at 09:06 AM..
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Old 03-13-2016, 09:41 AM   #14
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another thing to consider is if the area being painted is a smooth surface or roughened from abrasive blasting. a blasted surface could use up to 1/3 more paint than a smooth surface depending on the surface profile height and peak count / roughness since the surface area is increased per square foot. when painting a blasted surface, the profile valleys will be filled first and then wet film thickness is measure from the peaks / tops of the profile.
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Old 03-15-2016, 08:07 AM   #15
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Thanks for the additional replies.

@ Ric
Thanks for confirming my belief that theoretically 6 mil should in fact take twice as long as a 3 mil application (everything being equal).

With regards to the 50% overspray loss (or Transfer Efficiency) I realize this is subjective. Currently I am using 75% TE on 10' deep bridge girders, 25% on handrail, and 50% on everything in between.
Gallons per hour is something else that is subjective.

@ Mustangmike
I realized there was loss due to blasting profile but never realized it was 33%
Thank you for this!
We typically blast everything to SP6 unless specs call for something better.


Has anyone come across a site that discusses some of these, and lists some possible values?
- equipment gals/hr
- equipment transfer efficiency
- overspray due to part shape/size etc
- surface profile loss

Last edited by mms; 03-15-2016 at 08:11 AM..
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Old 03-15-2016, 08:25 PM   #16
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Quote:
Originally Posted by mms View Post
Thanks for the additional replies.



@ Mustangmike
I realized there was loss due to blasting profile but never realized it was 33%
Thank you for this!
We typically blast everything to SP6 unless specs call for something better.


Has anyone come across a site that discusses some of these, and lists some possible values?
- equipment gals/hr
- equipment transfer efficiency
- overspray due to part shape/size etc
- surface profile loss
http://www.google.com/url?sa=t&rct=j...2opRIF4HF2IKGQ
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Old 03-17-2016, 06:05 PM   #17
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Thank you!
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Old 03-19-2016, 11:49 PM   #18
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I'm trying to find a chart showing surface profile amplitudes that must be
achieved for defined blast cleaning levels prior to painting.

NACE 1 White Metal Blast (SP5)
NACE 2 Near White Metal Blast (SP10)
NACE 3 Commercial Blast (SP6)
NACE 4 Brush Off Blast (SP7)

I can't find anything.

Mustangmike?
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Old 03-20-2016, 07:50 AM   #19
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don't forget the tip orifice size can determine how quickly you can get a higher dft as well. Stepping up to the next size with a given volume solids will apply it at a higher dft. It's physics.
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Old 03-20-2016, 08:34 AM   #20
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http://www.sspc.org/sspc-vis-1.html
I'm not sure what you are looking for but the link is for SSPC Vis - 1. these are comparative pictures of the different blast cleanliness standards such as " SP 5 ". the pictures are examples of a steel surface that started as a specific rust grade or painted surface and what the end result should represent after blast cleaning.
other helpful documents can be found at SSPC such as SSPC-SP 10/NACE no. 2. these will only explain the different levels of cleanliness, not different surface profile size or peak count. surface profiles will be determined by the type, size, hardness and blast pressure used on a specific surface. cleanliness and profile should be listed in your product data sheets or job spec.
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