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applying a certain thickness ?

6K views 58 replies 17 participants last post by  NACE 
#1 ·
A few weeks ago, someone posted something about varnish, it reminded me to start my pent-annual (every five years) re-coat of my pasting table.

today as I was laying on the fifth (or so) coat, I gots to wondering. . . .

Now I was never taught any method, but is there a simple trick to use to brush on a coat of a determined thickness?

Something like - To apply a coat of W mils, dip the brush X inches into the product, without any pressure on the brush and at an angle of Y degrees, apply for Z inches before re-loading the brush.

And then there is speed of the brush. And obviously viscosity of product.

or is this just something we learn how to feel over the years?

BTW, my table is 6 ft long by 30 inches wide. So it's just one medium sized horizontal surface, easily to control depth of coat - no issue with runs or sags.
 
#6 ·
John,

I understand there are mechanical methods of measuring, once the coat is applied.

I was just wondering if anybody was "taught" how to lay it on at a specific thickness.

It was just some of that brain candy we all snack on as we are laying it on. :thumbup:
 
#10 · (Edited)
I see what you're saying.

For brushing and rolling, I was taught before you even begin to consider wet film thickness, you want to get the paint on the surface and cover as much of an area as possible, while allowing you to lay it off before it begins to set up. Its at that point you will be able to roughly gage what your WFT will be by pressure and speed of your applicator. Ambient conditions, product characteristics, application devices, and applicator skill set will determine the limits of that area before you need to lay off. Spraying has a whole other set of rules.
 
#12 ·
I wasn't taught to specifically paint to a certain thickness. But it was always drilled into my head to not skimp on, or overwork the material.

The guy that trained was always saying, 'your not putting enough paint on' or 'your a good painter, but you don't put enough paint on'
Of course, I knew everything when I was young, so I had better ideas, like pulling paint down real smooth, brushing an rolling it within an inch of its life to get what I thought were the best results obtainable.

On the crew I came up with had a thing we would do sometimes when it was borderline whether a paint would cover in one coat or not.
We called it "petting" the paint. Double brushing over the cut in, putting a little extra on with the roller,... Really just trying to 'make' it cover.

Over time I began to see that when I 'petted' the paint it often looked better in a lot of ways to what I thought was standard painting procedure.
When I finally started checking myself (and others) I found that even when we 'petted' the paint, it generally wasn't going on as thick as is recommended.

I check thickness a lot these days, and I've found there are a LOT of variables in how thick your coat is.
For me, its worth paying attention too. I want to maximize the performance of whatever coating I'm applying. I wish I had listened to the old Codger, and figured this out years ago.. Its changed everything for me (for the better:thumbsup:)
 
#14 ·
With the exception of a 100% SBV plural component thermoset material, I consider a single component coating, that relies on solvent evaporation during the film forming stage, to be applied in stages in order to build the best thermoplastic film structure.

I liken excessive single component film build, to building a house on an uncured concrete foundation.
 
#20 ·
CApainter said:
.

The coalescing process that is critical to proper film formation in single component coatings, can only be achieved with effective solvent evaporation. If a paint film is allowed to dry on its surface before allowing all the solvents to thoroughly evaporate due to an over applied film thickness, molecular retardation can occur due to insufficient coalescence-compromising the coating's performance capabilities.

.

Well put. I've seen first hand the effects that incomplete solvent evaporation can have.


Lately, I've been thinking about the other side of of this effect. And how solvents (water) evaporating too quickly affects the properties of latex paints.
Especially newer paints designed to be "self priming" or "P&P in one".

I would like to know more about the chemistry of these new systems, (Aura,Duration, Behr,etc..) but from what little I think I understand, the paint film is almost asked to perform multiple tasks as it dries. To bond to and seal the surface, and form a uniform finished film.

If this is the case, it seems getting a thick enough film, (no more than specified of course) and that film having adequate time to dry and 'do its thing', would be crucial to that film performing like it should.
 
#23 ·
Josh,

There is so much about the science of coatings that I wish would be explained so that those of us without chemistry degrees could understand.

Only recently have I heard (but would still like confirmed) that acrylics re-emulsify the previous coat, forming a chemical bond, similar to what lacquer does. And I was brought up in this industry hearing that one needs to recoat alkyds within a certain time (before they cure) to also achieve a chemical bond.

These pieces of information were NOT given to me by chemists. I would love to know the facts.
 
#21 ·
I agree that a gauge is the best way, I don't got one and for me it is not a critical tool. I remember either owing one or using a partner's back when.

This was a concept I was just toying with while mindlessly applying coats on my table.
 
#24 ·
I will explain when I get to a computer. Don't forget too that alkyds dry by solvent evaporation and oxidation. Coalescence is the combining of latex particles as water evaporates. Wet Film gauges are really important in ensuring you are putting the proper amount of coating on a surface so that you are not cheating the customer or cheating yourself. Very critical in the application of Industrial coatings.
 
#25 ·
NACE said:
I will explain when I get to a computer. Don't forget too that alkyds dry by solvent evaporation and oxidation. Coalescence is the combining of latex particles as water evaporates. Wet Film gauges are really important in ensuring you are putting the proper amount of coating on a surface so that you are not cheating the customer or cheating yourself. Very critical in the application of Industrial coatings.
That's is the reason I insist on air-driven pumps.
You can easily count the cycle rate and determine flow. For example I'm using a Graco President 30:1 12 cycles and I have put on 26 oz

Say I'm using a .015" tip I know my flow will be about 1/5 GPM of trigger time. Now I want to spread at 200 sq ft a gallon. So I cover 40sq ft
In a minute of trigger time. 20 3 second passes
covering 4 feet per pass or about 1 foot 4 inches a second will give me my desired coverage.
 
#26 ·
I will follow up. Each cycle will last 5 seconds.
I will make I full pass. And on the second pass
2 feet 8 inches.

I will keep this pace the entire time until I have covered 40 sq ft. Then I'll wet gauge all corners and middle of the area.

If its too heavy I will speed up my pace if its too thin I'll slow it down. I recalculate and do another
40 feet and in my experience I'll have it all dialed in by now. Consistency is vital. Material, Pressure, Tip wear and Surface Porosity.

As John mentioned, 2 thin coats is better than 1 thick coat. Too thick increases surface tension
and you will get less wear time. In coatings it's easier to add than subtract.

Oh a SSPC C-12 certification doesn't hurt.
 
#32 ·
I will be slow and inefficient. And then I will sit there and watch the paint dry. :jester:

We have only run it once so far. Definitely looking forward to a couple of upcoming cabinet gigs to stretch it out.

It's a different level. My hat is off to guys like you who have that particular tiger by the tail. I would love to take a seminar where you, or someone like you, just lined it out...

I am very much a student of that particular game.
 
#33 ·
Rob

The only initial performance info I have is that compared to electric aaa, they do not line up psi for psi.

For example, the two products we ran, we ran 40-50% less fluid pressure than we would with the 395. With a shorter hose and an AAF, could not be more apples and oranges.

It's like some other hybrid between steroid ripped cupless HVLP and good old fashioned AAA.

My goal is to spray at the lowest pressure possible. I'll be the tortoise every time. :yes:
 
#50 ·
Rob

The only initial performance info I have is that compared to electric aaa, they do not line up psi for psi.

For example, the two products we ran, we ran 40-50% less fluid pressure than we would with the 395. With a shorter hose and an AAF, could not be more apples and oranges.

It's like some other hybrid between steroid ripped cupless HVLP and good old fashioned AAA.

My goal is to spray at the lowest pressure possible. I'll be the tortoise every time. :yes:
"good old fashioned AAA" . Has it been around THAT long? Or am I just that old?
BTW, great thread. :thumbsup:
 
#34 ·
VP the dead band on the 395 is greater than the DB on the Merkur.

Thats why every system is a little different. Kremlin
recommends more hydraulic pressure and less atomizing pressure.

Graco has double orifice so you can triple atomize with their system. I have actually gained sheen with theirs. Not always good turning satin to semi.

I notice you go as low as you can on hydraulic pressure and adjust atomizing pressure to achieve your desired fan.

I know I use a little more hydraulic and less atomizing than you.

Your spray is softer with less bounce back.
Mine is not as soft with more bounce back.

The only thing I gain is less overspray and slight production and transfer.

Your so soft that any overspray is easily manageable. I may do 5 doors to your 4.
Transfer maybe 6 oz in a gallon.

The Kremlin reps have their opinions. Graco and CAT Reps have theirs.

I go with the system in hand at the moment. Any way you slice it AAA is the way to get er done.
 
#35 ·
Oddly, and granted its early, the very first thing I noticed was the difference between how the Merkur receives the air supply, compared to the EOS 15:1. Very different experience, before even pulling the trigger.

We are really talking about 3 things here. Again, my mind looks at how low pressure can I deliver, and get what I want.

Airless is absurdly out of the question for me, unless spraying drywall, and maybe one or two other situs.

Electric aaa wins on mobility, and balance of production and quality (works for me and for many, but not for everyone). But, again, getting the air assist from external compressor is a very different experience.

Very intriguing combination of things going on there. And yes, it is the shorter deadband that is fascinating. Its like the difference in gearing between two fast cars.

I like your description above, except I do think you would bury me in production.
 
#40 ·
daArch said:
SERIOUSLY, no apology needed. This is actually turning into some very tasty brain candy.

I just hope NACE comes back and adds what he knows as he promised.
Yes Bill, my apologies for contributing the derail of the brush thickness thread.

There is relevance. Spray Guns have been the go to tool for consistent thicknesses for decades.

It's very similar at best. Load and release your brush at the best consistency as possible.

Covering the same distance each time to the best of your abilities keeping a WET edge.

CApainter, NACE, VP and many others keep at the top of my game. I thank all of them.

Now how about a twist on horizontal, vertical and overhead techniques with the Brush. Back on track Bill.
 
#42 ·
OH don't worry Rob, As I was formulating all this at the table, I fully "got" it that spray would be the best way, but then I thought, "even if I owned a spray rig, would I drag it out to coat 15 sq ft ???

But I couldn't answer that. Getting out of painting while the earth was still flat, spray technology was still like a burnt stick on the cave walls.

AND, I knew that what EVER was decided, could not be translated to any surface that was NOT horiz.
 
#41 ·
Bill

To your op, we do alot of Pettit Captains and Epifanes. Our go to system is to lay a couple of coats of captains gloss heavy (light sanding between), then do what the boat guys call "tip off" coats 2x with Epifanes (what they call) matte. Its a four coat system, but with these products (completely different from paints), each coat gets successively thinner. We do this system on all of the formal front entry doors we do. That'll be $7.
 
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