MBC-DBU Shootout

I am generally a fan of the PPG OMNI line of economical automotive paints but I have heard many complaints about how inferior their basecoat (MBC) is. I have found the single stage OMNI urethane MTK to be very good but I was concerned about the MBC since I had never used it. I decided to do a comparison test sprayout of both the OMNI MBC and PPG's auto refinish standby - a basecoat in the premium Deltron line known as DBU. I purchased a quart each (minimum buy) from the same store and mixed by the same counter person. My test sprayouts were about 3 or 4 square feet each on vertical sheetmetal panels. Both had a catalyzed jet black base (from previous sprayouts :o)). Both paints were cleared with OMNI MC161 urethane clear. Both the MBC and the DBU sprayed well but I noticed that the MBC was noticeably thinner even though it was not reduced as much as the DBU. I wound up using 4 coats of the MBC but three would probably have been satisfactory. I used 3 coats of the DBU but two probably would have been satisfactory. My conclusion is that an extra coat of MBC is needed to obtain coverage similar to the more expensive DBU. I had heard of people using six or more coats of the MBC to cover but I found no need for that many with red on black.

Here's a cost comparison of OMNI MBC to PPG DBU in bright red:

Basis for comparison: Same gun. Same assumed area covered (1/2 qt RTS req'd per coat). Full credit taken for unused reducer . Full credit also taken for unused/unmixed DBU. Basecoat only - no clear considered.

MBC = $21.41/qt
MR187 reducer = $14.27/gal
Mix = 1:1
21.41 + 14.27/4 = $24.97 for 2 qts RTS
1/2 qt RTS/coat x 4 coats = 2 qts RTS required = $24.97 total (no MBC left over)

DBU = $87.90/qt
DRR1185 reducer = $37.20/gal
Mix = 1:1.5
1/2 qt RTS/coat x 3 coats = 1.5 qts RTS required
0.6 qts DBU + 0.9 qts DRR = 1.5 qts RTS 87.90x0.6 + 37.20x0.9/4 = $61.11 total (0.4 qts DBU left over)

DBU:MBC = 61.11/24.97 = 2.45

Therefore, the PPG DBU costs about 2-1/2 times as much as the OMNI MBC. This comparison favors the DBU since it takes credit for the left over unmixed DBU color and presumes that it can be used effectively later. If that is not the case, then the left over DBU should be considered waste. The DBU would then cost over 3-1/2 times as much as the MBC to properly cover the same area.

Can one justify the extra cost for the DBU based on using less material to cover the same area? I think not, considering the above.

The overall "quality" appearance of both paints is essentially the same. However, I concluded that the color match with the OEM paint is better with the DBU than the MBC. If matching existing panels well is an important criteria, then the extra cost appears justified. I will definitely do the bumper with DBU. For overalls though, you would not be able to tell the difference unless one was parked right next to the other. For complete jobs, like tractors, I would not spend the significant extra for the premium basecoat.

Another factor that might tip the scales in favor of the DBU would be a significantly better long term durability. I don't know about that but would be surprised if there was a major difference. They are both cleared with a urethane. Perhaps a premium PPG clear would be more appropriate long term but that would make the cost difference even greater. In any event, as Dozerboss has noted, even the OEM clears have a nasty tendency to peel away after about 8 or ten years - at least for vehicles not shedded. I know, since I have had three of 'em that did that. When that happens, a complete repaint is really the only fix.

Comments or criticism welcome.

Rod

I tend to agree with you. I can see no significant advantage of BC/CC over single stage urethane or even hardened enamel for overalls. The one advantage I will admit is that it probably is a lot easier to spray metallics using base/clear because you don't have to be concerned with both gloss and metallic appearance at the same time. That would seem to be a valid argument. I haven't done any metallics in years but I will give base/clear an advantage there, even without trying it. I haven't yet figured out why the basecoats (not including the clear) appear to be more expensive that a single stage in the same color and in the same quality level. Pigments are a big cost factor in paints, hence the several levels of cost for the same chemistry, depending on color. Basecoats would seem to use less pigment for the same coverage than a single stage (0.5 mil film build per coat compared with 1.0 mil for SS). I always thought that was one of the key reasons that the OEMs moved to BC/CC...lower pigment cost for similar resulting quality...at least for typical modern auto ownership periods. That's probably not a valid comparison though since the OEM paint is not the same stuff we all buy at the auto paint store.

Unfortunately, the days of the shadetree mechanic are about over, except for antique cars and tractors. Just after I got my latest truck I was looking under the hood trying to find the distributor. Come to find out there wasn't any! Camshaft and crank position sensors send signals to the on-board computer which determines when to fire which cylinder. So much for filing the points and tinkering with the timing :o). A similar series of sensors completely control the air/fuel ratio. Fine if everything works as it should. When it doesn't, it's time for a tow to the expensive high-tech diagnostic center.

Anyway, I would also like to hear any arguments in favor of base/clear for anything other than panel matching of existing BC/CC systems. It's possible I could be convinced...

Now for the rest--that's a new subject. I remember "the thing" but can't visualize it. For sure it has an engine you can tune and repair and probably has replacement parts that cover decades instead of a few years. Are you sure the motorhome has a steel roof? Someone approached me about repainting an RV but its aluminum top and bottom with brush on cool seal on the roof. Never tackled aluminum and i'm unsure of the proper primer. Any tips for repainting aluminum and what is the name of the spray version of cool seal? What about the old cool seal don't you have to remove it first? Anyway it's something differant and interesting but i won't be going on any roofs until there is cooler weather. Plus it's 38 feet long--will need to buy a 2 gallon pot!