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Hi Daniel, The DPLF is PPG's premium epoxy primer. The number 50 indicates the color, by the way. It's available in several different colors - the 50 is gray. It's an outstanding product. I've used it in the past where it has remained on sheetmetal outside continuously for 10 years in NH weather, without a topcoat and without any hint of rust showing through. In my opinion, you cannot buy a better primer for bare metal. It is expensive however. Because of that, I have moved to PPG's OMNI epoxy, MP170 which is a similar product but significantly less expensive in PPG's OMNI "economy" line of paint products. The MP170 has a three day window instead of a seven day window so that doesn't help you out any. I am not aware of any epoxy from any manufacturer that does not have a topcoat time window attached to it. The similar DuPont epoxy has a 24 hr window. So I don't think you will gain anything by brand shopping. I don't think it's that big a deal though. The use of a 3M Scotch-Brite hand pad makes the scuffing job fairly easy in getting into the nooks and crannies. In my opinion that extra effort of scuffing and recoating the epoxy is a small price to pay
to get the better corrosion protection and adhesion that are provided by the epoxy over any other primer product. I am sure your idea of using a different primer over the epoxy at a later date would work. However, I don't think it would eliminate some type of scuffing operation so I don't see you gaining anything. I am not a fan of etch primers and don't use them at all. They generally have more restrictions on their use than epoxy does. In fact, I think you will find a similar time window for etch primers and I don't think you would get the corrosion protection that epoxy provides. For instance, PPG's OMNI etch primer, MP176 calls for sanding (scuffing) and recoating with itself after 24 hours before another product - and you can't topcoat it directly. I see no gain at all from the use of an etch primer in your situation. In fact it would be worse than an epoxy if not followed soon by something else. Surfacers, sometimes called filler/primers, are for filling sandscratches after a sanding operation in order to provide a smooth surface for the topcoat. They have no particular use on rough cast surfaces and they should be sanded prior to continuing anyway. The epoxy is non-sanding (unless you miss the window). My recommendation is to apply a coat of epoxy immediately (same day) after your sandblasting. That will provide the best protection until final assembly and ready for painting. After assembly, when the time comes, clean with a specialized cleaning product such as PPG DX330 Acryli-Clean, scuff with a Scotch-Brite hand pad, apply another coat of epoxy and proceed to topcoat directly within the time window for the exact product used. That's for the cast. For sheetmetal, you would usually be involved with sandscratches so a surfacer would typically be used between the epoxy and topcoat. By the way, since you have the main housings completely dissasembled, you might want to consider coating the interior surfaces also, if they are not already coated. Glyptal has been the standard product for the interiors of cast engine blocks and gear housings for many years.  Rod
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