my 34 is in laquer primer, decided to knock down and spray with an epoxy primer. just how far down should i take the old primer down to get good bite with DP 40. some say must take all off others say not. what are the pro's and con's thanks for input
Most likely the primer isnt going to be in workable condition due to all the stuff that could contaminate it and whatever you put over could fish eye and such. I would start with bare so you know what your dealing with in the long run.
As said bare metal,your doing it right and that primer is pricey but top of the line stuff.I have swithed to valspar it is a little cheaper but comparable in quality.Make damn sure you wear a mask when spraying it.
If I knew for sure that the original primer was in good condition, that it was a good quality product, and it was properly applied over a correctly prepared surface, I wouldn't feel it was essential to strip to bare metal. But, if the paint job was going to be anything more than a "regular" paint job I would strip to bare metal just as insurance against future problems.
"A chain is only as strong as its weakest link"...the old lacquer primer would be the weakest link if you want to put DP40 over the top of it. R-
I second that....bare metal.....be sure to wear a respirator....not just a mask! The epoxy is not good at all to breathe. Some people have reactions to it on their eyeballs...I would wear eye protection also. The other thing is the epoxy will land on everything that is not masked and you will NOT wipe it off with lacquer thinner! Ask me how I know!
DP 40 is metal etching epoxy primer. DESIGNED to be sprayed on bare metal. It contains lead. If you don't want the lead, which is a little scary to sand because it will create lead dust, use DP 40LF. The LF means lead free. Both are very durable products but I wouldn't bother if not spraying on bare metal. Get a primer meant for spraying on primer if you decide that you really aren't going to strip or sand the old paint off to bare metal. Talk to the PPG retailer, they should be able to recommend a product and give you all the right stuff to use with it. If they don't tell you the same thing everyone else here is telling you they probably don't know what they are talking about. Once you decide to use a brand, use all their thinners and hardeners that are supposed to go with what you are spraying. Get a paper suit either way and an organic vapor respirator, those two things should be about 30 bucks. Both DP 40 & DP 40LF are very toxic. take out the respirator cartriges and put them in a ziplock, you can get about 4 hours if you keep them clean, longer if you dare. But don't leave them in the mask w the prefilters because they will continue to absorb fumes off the overspray, must take them out. You can reuse the paper suit as well if careful. If you are going to take the chance and spray over old primer/paint then try to get the same primer used before. Talk to the paint shop. A guy I knew once was given about 100-200 gallons of old automotive laquer products from the shop of an old time motorcycle custom shop who's owner had passed. He mixed and matched that stuff and oh boy what a big mess he made out of a lot of neighborhood cars. I couldn't believe it, he just kept trying, and everyone kept coming looking for a deal. At least in California, the paints are constantly changing. Dupont, PPG, etc, they all have their own brands and product lines and they are designed to work together and I have seen many guys even at professional paint shops get burned by trying to mix and match. It just isn't worth it for all the work even involved in a quick prime job. Bla bla bla, rant over
What is under the lacquer primer? If it's bare metal the you definitely need to go to bare metal. Lacquer primer is porous and moisture can seep thru it starting the metal under to rust. We use to have problems with that back in the day here, can't imagine lacquer primer over bare metal in Michigan!
Sounds good to me. I just can't imagine what you would want to spray it over in terms of a paint, but if you mean plastic body parts etc.? I guess I should shut up and read the data! Interesting stuff
DP is an excellent primer, but it is not an etching primer. My understanding is that only LF is presently available in the U.S. Being near the Canadian border, at one time some from my area were buying lead containing DP in Canada(illegally?) and bringing it here. They were doing that because the LF series doesn't spray as well, isn't as protective, and is better overall than the "improved" LF replacement. Adding some lacquer thinner to LF improves how it sprays, but that degrades the product a little and increases shrinkage.
Llacquer primer primer must be removed if you are going to use any catilized paint. The lacquer primer will soften in the sun and move around a bit and WILL crack any top coat!
remove all the mystery (old paint) and prep your metal accordingly. DP primers like sandblasted surfaces best. wipe down with acetone after blasting, and prime asap so there are no contamination issues. i usually follow the dp primer with K-38 high build epoxy primer to give you some blocking ability, as the dp has no real build. i also put 1 part acetone in the DP mix to help it layout nice. my 2cents.
The biggest issue that you would likely face is adhesion in the current lacquer. I would visually inspect the current coating and make sure that there aren't obvious places where the primer is bad (cracking, bubbling, etc), then I would snad through the primer in a couple of places to see how well it is adhering to the metal...if the primer has a nice featheredge then the initial bond is good. Assuming a good bond and no obvious issues with the existing primer coat I would sand and recoat without going down to metal. I assume that since you asked this question that you are not an expert in paint and are more than likely looking to gain a servicable paint job as opposed to a show car finish. If this is not the case then stripping the old finish is the only way to be certain that you have a pristine foundation on which to build your finish coat. As for primers...I use SEM Metalock, it is easy to spray and sand and it is a DTM product.
I get a splitting headache at just the mention of DP40 primer. I don't know why, but one whiff of it gives me a headache.
Just a note, if you find a PPG jobber that carries commercial paint or the CPC line of PPG products ask if they have EPX primer. It is the OG DP that PPG moved over to the CPC line once DPLF was introduced. I sell a two gallon kit of EPX primer with catalyst for about $110
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