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B---, Oh yes, there is absolutely no doubt that using a manufacturer's recommended complete "system" from the ground up is the best way to minimize problems - at least problems due to the paint or the additives. Automotive paints are usually more complex to deal with than hardware store or tractor store paints but the same thinking applies. It seems to me that many of the problems that crop up on this forum are a result of not following the manufacturer's written instructions. The instructions on the can labels of the basic alkyd enamels found in hardware and tractor stores are there for a reason. They are also pretty simple. While most can be applied by spray, they are really slow dry products that are intended for brush application. I have never seen such a paint specifically call for or specifically recommend a hardener additive on the can label. Perhaps that's because of a liability problem, I don't know. However, I do believe that most of the potential users of such paint products are probably totally unaware of the safety issues involved and would not be expected to have the proper equipment to safely spray such products when used with a hardener. But that's only my opinion. There's also a reason why most automotive paint products carry that "For Professional Use Only - Not For Sale To The General Public" wording on the label. I suspect the legal departments had some influence in that. The thinning requirements, if there are any, are also pretty simple for the hardware/tractor store paints. It should say right on the label if thinning is required at all and if it is, exactly what to use and how much to use. There are many types of thinners used that are generally available in home centers or where the paint was purchased - turpentine, mineral spirits, VM&P naptha, xylene and others. One should not make substitutions here. There should be no such questions as "can I use something else", or "what should I use" or "how much should I use." They should use what is called for on the label. If they don't have it, go buy it. And if it's not clear on the label, find another paint. Mixing and matching stuff between chemistries and manufacturers can be a recipe for disaster. Those products are cheap. There is no reason not to use what the manufacturer recommends. I have never seen a non-automotive paint call for an automotive reducer or any other type of specific automotive paint additive. You won't find Rustoleum calling for a PPG additive or vice versa. Use of generic ingredients intended for acrylic enamels in alkyd enamels or vice versa is also a poor practice that is just asking for trouble. And using lacquer thinner to thin an enamel is simply a crazy idea. As far as the slow drying goes, I have never had a paint that did not dry to the touch by the next day if instructions were followed. You may be able to gouge it with your fingernail if you try but you should be able to handle it carefully w/o a problem. I recently painted my truck roof with DuPont Centari AE. It was a small quantity and I used 3 oz paper drinking cups as measuring devices. My mixing area was overflowing with crap and I didn't notice until the next day that the measure cup that I had used for the color got tipped over at some point and the remnants of uncatatlyzed Centari that had stuck to the sidewall and bottom had spilled over onto the work surface. It was dry, even though it was thicker than any film one would normally apply. I could gouge it with my fingernail but I had to try at it. The following day, it was difficult to even dent with a fingernail. If any paint is not dry to the touch in a days time, something is definitely wrong with the materials, assuming reasonable painting temperatures. I don't know about the epoxy chemical bonding issue you raise but believe (perhaps incorrectly) there is some type of a chemical bond with "most" of the usual products applied over it. The ones that I am familiar with (PPG's DP/DPLF and their OMNI MP 170) are not specific about overcoats but indicate their respective time windows w/o regard as to what is going over them, even body filller in the case of DPLF. There is no caution that sanding is recommended within the window if an alkyd or other product is used over them. The window seems applicable to pretty much the entire product line w/o any stated reservations. If you look at an old (1983) DP epoxy tech sheet, it indicates that the old DITZCO alkyd enamel (both catalyzed and uncatalyzed versions )(also no longer available) is one of the recommended topcoats, applied within that 7 day window with no mention of sanding. So I wouldn't expect there is anything about a basic alkyd enamel (or an acrylic for that matter) that wouldn't chemically bond with the epoxy if done within the appropriate window. I would like to think that some type of chemical bond would be obtained between the epoxy and most topcoats, even lacquers, if applied within the window - but I could be wrong. I have never heard the term "chemical bonding" used in reference to non-automotive paints. While I am a purist about not mixing and matching ingredients such as reducers or hardeners, I am less of a purist about layering products between manufacturers, especially regarding the epoxy which I think can be used pretty much universally - but I haven't personally done so to any great extent. I have never heard of a compatibility problem between either DPLF or MP170 with any paint. Indeed, I've used PPG's DPLF under DuPont's Centari (and DuPont's lacquer primer-surfacer, 131S) for years very successfully, always careful to follow the time window for no sanding. PPG has always favored epoxy and DuPont has always favored etch primers - at least that's been my impression. And since I favored PPG at first, I got started down the PPG epoxy road and have never left that direction, even when using a DuPont topcoat. Still, mixing layers between manufacturers can be risky and one shouldn't do it without some reasonable assurance of success - notably finding someone else who has done the exact same thing w/o a problem developing - or taking the responsibility personally if things turn to mud. That was my problem in my post below about the Permatex Rust Treatment and the DuPont surfacer. I certainly do not blame Permatex for not having tested such a combination and addressing it in their instructions. And I don't blame DuPont either. Those are two very different products, sold for totally different purposes by different manufacturers to different markets. I took a calulated risk and lost. I have nobody to blame but myself. I agree that the cheap paints have the least detailed instructions and sometimes poor (if not inadequate) safety recommendations. There was a discussion last year in this forum about Valspar's generic alkyd enamel hardener and their safety instructions. Once the label instructions and the MSDS were made known, it was clear the two did not agree regarding the exact same product. I have never seen such a confusing and inadequate statement of safety recommendations as that MSDS. It was not possible for any reasonable person to come to a conclusion as to what was considered appropriate breathing protection when using that product. The difference between that and the very clear statements from either DuPont or PPG is like night and day. I have to think that legal liability concerns have something to do with the weasel words from Valspar regarding respiratory safety. Simply stating that a respirator must meet NIOSH approval doesn't mean squat as far as I am concerned. It sounds good but doesn't mean anything since NIOSH doesn't "approve" anything but supplied air when isocyanates are involved, no matter the air concentration. I suppose that lets Valspar off the legal hook by not being more specific in that regard but the vast majority of users of that product most likely do not know that and do not have the inclination to do the research digging necessary to find it out. As far as Brandon's problem goes, I really don't know if he should have sanded the primer. My tendency would be to say that yes, he should have - if the primer was "dry" - but I don't know. He doesn't indicate what materials he was using or what the label instructions are for each product. Paints are different, sometimes very different and it is not possible for anyone to be familiar enough with them all to adequately answer questions like "what am I doing wrong?", especially w/o knowing all the nasty details. One can generalize but that can be risky. For example, I have a can of Benjamin Moore "Impervo" High Gloss Alkyd Enamel (hardware store paint). It is intended for brush application and says so. There are no recommended additives. Certainly no hardeners. It indicates dry to the touch in 3-4 hours and "if a second coat is required, allow an overnight dry, lightly sanding between coats". Such a practice is unheard of in the automotive paint world where time between coats is on the order of 10 minutes and there is no such thing as sanding between them. The terminology is also different, where applying more of the same material after drying is referred to as "recoating" with automotive paints. This difference in terminology can be confusing if one is not familiar with it. And it can lead to misunderstandings and improper application. In the end, when people have problems with painting, I believe it is far more likely that the problem is with them and not with the paint. They need to carefully go back over whatever instructions exist for each product and try to determine what they did or didn't do that might be the cause. That includes a careful review of spray gun adjustments as called for by the gun manufacturer. It would be helpful if anyone seeking assistance for a problem would take the time to list each of the specific products they used along with the appropriate label instructions of each so that any attempt at an answer could be more worthwhile. Otherwise, unless someone has had the exact same problem with the exact same materials and methods and found a solution to it, answers are nothing more than a stab in the dark. Which may be less than helpful. Discouraging even. My long winded 2¢ of comment. Rod
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