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TheHubbardBus 12-09-2019 09:04 PM

Paint pros, need help w/ coverage estimates
When dealing with 2-part paints (base + activator/hardener), do the coverage estimates supplied by the manufacturer include the activator, or only the base?

For purposes of example, I've included a dramatic example, which is linked to below. One of Dupon/Axalta's epoxy primers lists in its TDS a theoretical coverage of 1112 sq.ft. / gallon @ 1 mil of thickness. To mix it, you use 1 part of the Primer itself, and 1 part of the activator.

So, if I mixed up one gallon of base with one gallon of activator, for a total of 2 gallons, would that then cover 2224 sq feet @ 1 mil? Intuition tells me only the solid in the base matter, which means it would still be 1112, but it would be a big mistake if I was wrong.

Danjo 12-10-2019 12:34 PM

No replies? Well, I’m a total noob so I shouldn’t reply, but I’ve been doing lots of research.

The coverage is based on total volume Ready To Spray, so theoretical coverage a 1 mil dry thickness would be 2200 sf.

But that coverage is super optimistic, assuming 100% of the product is applied to The surface and 1 mil coverage is probably on the very thin side to cover that beautiful yellow.

Did you see that dry time in that stuff? PPG advertises 15 minutes dry to touch, though my experience is about 30 minutes. The longer a product stays sticky the more dust and bugs it has a chance to collect.

TheHubbardBus 12-10-2019 05:02 PM

Thanks Danjo! As always I appreciate your input.

I just used the 1 mil to illustrate the math. If I go w/ the example I included it will be as a primer & sealer, and at 5+ mil finished thickness. I do have a loss factor built into my calcs, as well as being pretty liberal w my measured coverage areas.

Dry times are for 5 mils in one pop, but with a roller application (which I plan), I'll probably need 2 coats to achieve that, which means dry-times will shorten accordingly. Still be long compared to 15 mins, though 'dry to touch' & dust free are 2 different things. Warning understood & appreciated, however. There's a fast-dry primer under the same brand I'm also considering.

Topcoat I'm planning on Imron 3.5hg+ polyurethane, from same manufacturer (Dupont / Axalta). They're made for industrial / heavy equipment applications, & unlike most auto paints, support roller/brush application. My plan is to roll & tip (still going back & forth on that though).

Danjo 12-10-2019 08:03 PM

Do you have a place where you can spray?

If you’re rolling look into those skinny foam rollers. I’ve only used them with latex, but with hi gloss latex on smooth door faces they produced a finish that is the next best to spray.

Danjo 12-10-2019 08:07 PM

I’m using PPG. Today I sprayed primer on rub rail that I’ve modified. I sprayed about 5 mil thickness and it was dry to touch in a few hours, so about the same.

Danjo 12-10-2019 08:12 PM

I have a bicycle painted with Imron. It’s showing it’s hard use now, but considering what I’ve put it through I can attest to its durability.

TheHubbardBus 12-10-2019 08:27 PM

Good to hear about the Imron. I've heard really good things about it, & I know it's popular on the bicycle scene. Some guys on the airstream forums were raving about it as well. I can get great industrial paint for the same price of non-so-great auto paint. No place to spray. I've considered renting an area, but then I still have to worry about PPE, & frankly I'm not comfy spraying this stuff in an enclosed area w/ just a filter mask. We can roll here together, plus we have family that are willing to pitch in. I appreciate the advice on the rollers. If we do roll - which is highly likely at this point - I'm going to order some extra white to practice with on some of the interior panels we've removed before we do it 'for real'. I am a little concerned about the rivets though. Any tips?

musigenesis 12-10-2019 08:38 PM


Originally Posted by TheHubbardBus (Post 363117)
I am a little concerned about the rivets though. Any tips?

Try SEM self-etching primer on your SS rivets prior to painting (also scuff them a bit before applying the primer).

SEM is weird stuff - feels more like painting with watercolor than proper vehicle paint, but it adheres extremely well to bare metal, even SS.

Danjo 12-10-2019 09:30 PM

Have you seen this?

Probably the same dust to bug ratio as rolling outdoors.

Just need a big enough place that you don’t send overspray on the neighbor’s new Cybertruck.

I’m using one of those harbor freight HVLP sprayers with a 5 CFM compressor to do the rub rails and small parts with good results.

ACamper 12-11-2019 10:35 AM

I am going to paint my bus next spring or summer, I decided on using rollers. I talked to the guys at the paint store and they connived me on using a good primer. I can't remember the amount they told me. They have been good in the past about estimating amounts. I am sure a roller will use more but I don't want to deal with a sprayer and the type of masking it takes to prep for one.

I am going to do mine outside in the woods. I am going to hopefully wait until the ground is moist and their is no wind(fingers crossed). If it gets some dust or pine needles,, it is a 84 school bus, lol. I am mostly concerned about a good coat of paint sticking.

The prep is going to be big.. I will probably try to do it in a couple of stages. Deep clean, more clean, scuff and sand. Big job.. but it will be nice I am sick of looking at yellow.

Sorry I can't help you with the paint estimate. The guys at your local auto body supply or paint store might have some good insights.

TheHubbardBus 12-11-2019 11:29 AM

EDIT: Danjo's spot on.

Danjo 12-11-2019 11:54 AM


Originally Posted by TheHubbardBus (Post 363198)
I've found some info that would seem to contradict going off the total prepared volume, Danjo (I hope that doesn't come off sounding a-holish. It's not meant that way). I'd like to hear your opinion on the following.

A few different resources have all said about the same thing: the theoretical coverage listed in spec sheets is based entirely on the solids content of the paint. From what it sounds like, activators/hardeners/catalysts do not contribute to the final dry film volume. So if it says 1000 sq ft @ 1 mil for the base, that's what you'll get, assuming zero loss. If this is the case, I guess it would make sense thinking of the term 'catalyst' in it strictest sense.

That number would then be modified by the transfer efficiency (& other losses). Again, just going off stuff I found on the internet. But roller/brush application appears to have the best efficiency (by far) (Of interest to us both, @ACamper), with HVLP a distant second, and less efficient spray applications even worse.

For reference:

Calculating Coating Requirements

Yep, roller is almost 100% efficient.

The coverage of that primer is based on total volume, Ready To Spray, so if you have a gallon of base and a gallon of activator, that is 2 gallons. They are including the activator in the volume.

If not too apples-to-oranges, the PPG primer Iím using advertises 975 sq ft per gallon. Itís a 4:1 mix so the activator would have a lesser effect on the total volume calculation.

TheHubbardBus 12-11-2019 12:54 PM

Thanks again, Danjo! I just called Axalta with a different question about rolling & tipping (they got nothing), but they did confirm exactly what you said. You definitely saved me a lot of paint. And a lot of $$!!!!

I'm stupid. You're smart. I was wrong. You were right. You're the best. I'm the worst. You're very good-looking. I'm not very attractive.

Danjo 12-11-2019 02:03 PM


Originally Posted by TheHubbardBus (Post 363213)
Thanks again, Danjo! I just called Axalta with a different question about rolling & tipping (they got nothing), but they did confirm exactly what you said. You definitely saved me a lot of paint. And a lot of $$!!!!

I'm stupid. You're smart. I was wrong. You were right. You're the best. I'm the worst. You're very good-looking. I'm not very attractive.

Nah man. Well except for the good looking part.

Danjo 12-11-2019 02:08 PM

Try rolling it to see if you get the finish you want. Hit it with some spray rustoleum and roll that over top and see if that’s acceptable. I used to think rolling was too janky and then I did a bunch of research and it changed my mind. I’d sure try those skinny 6” foam rollers. I was really amazed on the quality of finish that is possible on a smooth surface.

TheHubbardBus 12-11-2019 02:25 PM

I used the exact same rollers you're talking about on our floor, w/ the kbs (water-cured urethane). The floor itself was hosed, so a good looking job was impossible even if I had been trying to achieve one, but on the few spots that were relatively smooth, it came out pretty good. I'm fairly certain with actual prep on the outer shell - not my rusty floor - those rollers will easily meet my expectations. Not looking for show-car perfection, just a super-durable coat that looks decent.

Are you / have you sprayed your entire bus, or just parts? I do plan on spraying the small stuff I can remove, like mirror assemblies, marker light guards, etc.

Danjo 12-11-2019 03:02 PM

1 Attachment(s)
Iím building a tent over the bus with .9 mil plastic and Iím spraying the rub rails in the driveway. In a couple weeks Iím going to a rental booth to spray the whole bus.

TheHubbardBus 12-11-2019 09:45 PM

Sweet! You must be so excited! Can't wait to see how it turns out. What colors / paint scheme you going with?

Danjo 12-11-2019 11:51 PM

1 Attachment(s)
I’m down to the wire on prep so no time to get excited. This green and a cream color for the rub rails. IDK with the humongous black grille how it’s going look. I’ve debated painting the plastic cream also, but I worry that might look bad after a while

TheHubbardBus 12-12-2019 12:14 AM

1 Attachment(s)
Sweet. Like those colors a lot! You can always re-do the grill later if you decide. Seems like light colors and bugs would be a bad mix.

This is a photo-chop of what we hope our bus will end up looking like. Same thing, I think the mirrors, grill, & bumper would look great in white, but only until we started moving.

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