K36 Question

You should ask. That's one way of finding out things. Unfortunately, in the painting area you can ask 10 different people, even experienced people, and get 10 different answers. It's very easy to get confused with a mulitude of different products from different manufacturers used by different people.

Just because the pro body shops are using something doesn't necessarily mean that it is the best choice for a part time home user. There are a number of things to consider. In current pro circles you will likely find K36 used a lot...or a similar two component surfacer from another manufacturer. Unfortunately for the DIY, it requires a catalyst (read hardener) that contains isocyanates. If you are new to this stuff, isocyanates are extremely nasty chemicals that require special respiratory equipment to use safely. I won't give my standard lecture here but check out the MSDS (manufacturers safety data sheet) for K201, the catalyst for the K36. You'll see that a positive pressure supplied air respirator is required. That's a piece of gear that runs about $400 minimum. Unless you are willing to invest in such equipment (or play fast and loose with your health), I'd recommend staying away from the K36 and most two part products. That would include the OMNI MP182 which also requires an iso-containing hardener. Do a search in this forum on "isocyanates" or "isos" and see what I am talking about. You could also do a net search on it. Fortunately for the the DIY, the best bare metal primer (IMO) is epoxy and most epoxies, while they are two-part, do not contain isos in the catalyst.

Perhaps your ex bodyshop owner goes back to the days before urethanes and isocyanates became standard, common-use materials. The "sand and fill" that you mention is actually DuPont 131S, Fill & Sand. It is an acrylic primer surfacer (lacquer based) that was very popular years ago. I've used it successfully in the past. It has its' limitations for most current pro bodyshops. More modern two-part urethanes have essentially replaced it. It is still a good choice though for the DIY that doesn't have proper breathing equipment to deal with isos. The 131S is a single component product that does not require any iso-containing additives. A similar product from PPG would be the OMNI MP181 (not the MP182). Neither of these products are recommended to be applied to bare "untreated" steel however, just like the K36 is not.

Yes, if want to avoid the isos, the 131S would be a good choice in the DuPont line or the similar MP181 in the PPG OMNI line. That is if you really need a surfacer at all. You realize with any surfacer that you will likely wind up sanding everything again with 400 or so grit after applying the surfacer? A surfacer is intended to be applied in multiple coats and then sanded - the purpose being to fill in and smooth out sandscratches. I would try to avoid a surfacer altogether unless you are trying to fill sandscratches coarser than 400 grit. If your existing paint is sound and you sand all over with 400 grit and nothing coarser is needed, then I would forget the surfacer. Here's what I would do:

1. Sand everything with 400 grit, after cleaning with something like PPG DX330.

2. Sand any bare metal areas with with 180 or 220 grit. Make sure there is no visable rust left. Clean with DX330.

3. Spot prime all bare metal areas with two coats of epoxy primer such as PPG OMNI MP170. DuPont has an equivalent epoxy but I have never used it. Carry the spot prime well onto the surrounding area.

4. Sand the epoxy with 400 grit. It doesn't sand as easily as a surfacer but you can sand it. If you still see sandscratches coarser than the 400, give it another spot coat of epoxy. Make sure you extend the sanding onto the surrounding existing painted areas.

5. If everything looks good at this point then I would clean again with the DX330 and shoot the whole thing with one coat of the epoxy primer. You can even thin it slightly to promote good flowout although I haven't found that to be necessary. If you use the MP170, up to 10% acetone can be used for any thinning. I don't know what the direct-to-metal DuPont epoxy says about doing that. What you want is a step similar to a sealer...something that flows out well and doesn't have to be sanded again. You shouldn't need a sealer here but I always like to have a uniform color shade as a base for the color coat. This step provides that. You can then proceed to your topcoat being aware of the time window appropriate for the particular epoxy you use (3 days max for the MP170 - others are different).

6. In staying away from isos you are also limited in topcoat choices. But no, you would not be limited to a lacquer. There's PPG OMNI MAE acrylic enamel used w/o hardener. In the DuPont line, Centari acrylic enamel would be an excellant choice although more on the pricey side nowadays. Centari is still available as a non-iso field mix, at least in my area. It is known as Centari with Ultra 1K Pac. There are similar choices in other paint lines but I am not familiar with them. DuPonts' NASON FastDry is one but I don't know if it is available in the color you want.

If you have some old sheet metal, you might want to try at least one test sprayout using the above to see if the appearance you get with no surfacer meets your expectations. If not, you can always replace the overall epoxy "sealer" above with a surfacer and then sand all over again. Be aware that many automotive topcoat enamels used w/o hardeners can be troublesome in trying to repair any screwups like runs or excessive orange peel. The OMNI MAE doesn't have a safe recoat period (per PPG but not noted on the tech sheet) so what you see after the last coat is down is basically what you get - no going back, sanding out the runs or peel and recoating. There is a risk of lifting the paint film because of solvents in the fresh coat. The Centari 1K tech sheet says it can be recoated after 4 hrs but I have never confirmed that. You couldn't do it years ago but things have changed now with newer, different solvents. Whatever you wind up deciding on for products, make sure you get the manufacturer's tech sheets for each of them since the usage differs between manufacturers, even for very similar products.

This is not to say that other methods with different materials cannot also produce good results while at the same time avoiding the isos. It's just how I would approach your situation.

Thanks,
Tim

I have never used any K36 but I'll offer some comments. Make sure you are using the latest tech sheet for the product. I have noticed recently that the links at TriCityPaint do not always yield the latest version, even though they link back to PPG. The latest versions are obrtained by going directly to the PPG site. For example, the tech sheet for K36 at TriCityPaint is dated 3/1998. The one you get if you go directly through PPG is dated 8/2002.

Why do you suspect there might be a problem over existing OEM paint if sanded per the tech sheet? I certainly would not expect there would be a problem, since that is stated as a suitable substrate. More importantly however, make sure you carefully read the prep for bare steel. IMO the current use of the term "primer-surfacer" is somewhat of a misnomer since it implies that the product is a real "primer" when it is not. Note the term "treated" when used for bare steel. That usually means 1) a 2-step phosphoric acid pre-treatment or 2) a "pre-prime" using an etching primer, or 3) a real "direct-to-metal" primer such as an epoxy. For your bare metal areas, I recommend you spot prime with an epoxy (it's on the tech sheet), assuming there is no visable rust after you sand those areas.

Personally, I think you would find the OMNI line to be very acceptable, especially if you are are doing an overall and not trying to perfectly panel-match an existing OEM color. I believe it provides good value for the money spent and doesn't break your bank account for a "decent" paint job. The reason I haven't used any K36 is that it has a higher price than I am willing to pay for such a product line. I find the OMNI MP182 urethane surfacer (and the entire OMNI line) does a great job at less cost. Since I do work only for myself and am not into high end jobs, the cost of the materials are an important consideration. If I were panel-matching a relatively new OEM paint, I would go for the higher end materials. I have found in the past that the color match is a little better with them and makes the higher cost worthwhile.

BTW, I hope your "early 80's" PU is not a GM product. I have an '83 Chev PU that had the worst OEM paint job that I have ever seen. Within 4-5 years the paint began peeling away from the primer. I think that was back when GM was "experimenting" with waterborne enamels to meet air emission regulations. If you have any noticeable peeling, I suggest you strip the OEM topcoat altogether and start from a better base. One test you might do if you are not sure is too put on a length of real sticky tape (duct tape would work good) and pull it off fast. If some color peels off with it, that color is not suitable for a base for new paint, even if sanded w/400. That's how I stripped a good portion of the color from my truck - simple masking tape - it was in that poor a condition. Thank you GM :o).

Rod