I had applied epoxy primer on the entire car about 2 months ago and shot urethane primer surfacer over that, but now have blocked the driver side door with 80 grit on a 16" board sander following a black guide coat (this works great, thanks Eric). I have taken it back down, thru the primer/surfacer and epoxy primer to the original body filler and metal. Do I need to re-apply epoxy primer again or can I just shoot this blocked panel with the Ultra Fill II primer surfacer that I have ? I suspect that since I will obviously be applying a skim coat at least, that I will have to hit it with the epoxy primer again.
PPG DP50LF is what I used originally. ;)

btt :D

It's not a good idea to make "sandwiches" by applying products over and over. It is hard to say because if there is a LOT of metal, I may apply the epoxy over it. But usually, I would say just re-primer the whole panel in urethane.

When blocking the urethane, you want to avoid cutting thru to the metal. If you have a particularly high or low spot you need to address it by pushing it up or tapping it down. If it is a general "wave" sort of minor high or low spot that you wouldn't be trying to "adjust" better, you probably needed more urethane over the entire area.

It is a fine line between using the surfacer primer to fill too much and not asking it to do it's job. You should have the metal straight enough where two or three coats of urethane will be enough and you don't cut thru. At least not much, you are going to cut thru on most any serious blocking. But you need to keep it down to a mininum.

Thanks for the reply Brian. This was the first blocking I have done on this door (or anything for that matter)with a 16" 80 grit and as a result of previous work and my filler and DA shaping, it needed a serious cut with the 80 grit board. After using a guide coat and the 80 grit on a board, I now understand the principle and results of blocking. The door panel feels much straighter. The area of metal showing is approx. 5% of the panel and the rest is filler and primer, so I guess I will go ahead and go over the panel now with a few coats of the 2K urethane primer/surfacer. That's good news as I did not want to buy any more DP50LF if I could avoid it. Thanks again Brian graemlins/waving.gif

Am with Martin, try not to overuse the products.
If the WHOLE door is in bare metal or good chunks of it Id go ahead and reapply some epoxy.

If not just load up the gun with Ultra fill and spray away.

Also Id switch to 180 grit paper when block out that primer, that 80 grit you are using is WAY to coarse.

Also as Martin mentioned you NEED to address any high low spots that you have in the metal. The highs will need to be tapped down VERY lightly, dont just give her a good whacking.

You might find that you have high lows right nest to each other. The proper way to do that IF you have access is use a hammer and dolly to raise the low and lower the high. Place the dolly on the backside of the low and gently apply slight pressure upward. As you apply the pressure on low spot tap the high with your hammer.

A dolly can be anything from a formed piece of steel to a 4x2 piece of wood, what ever it takes to apply pressure on that low spot.

Hi Eric. I have a few spots that are raised bumps and I took care of one by tapping lightly like you said and skimmimng over it with filler which turned out perfect, so I will be addressing the rest the same way. The reason for the 80 grit was for the initial BIG cut to smooth it out, but I will now go with the finer grit after applying a few good coats of the ultra fill like you said.
I think I might be pretty good at this by the time I graduate from "Eric and Brian Tech". It's a heck of fun learning experience and whatever the result, I'll be happy. :D Thanks guys

Texas 70, what is the part number on the Ultra fill II ? Is that the urethane primer surfacer that you used ? I assume in PPG also, correct ? Mark --------------------------------------1968 Chevelle Malibu (Weekend Cruiser) 1969 Chevelle Malibu (Daily Driver)

Originally posted by Bo6869ChevelleMan:
Texas 70, what is the part number on the Ultra fill II ? Is that the urethane primer surfacer that you used ? I assume in PPG also, correct ? Mark --------------------------------------1968 Chevelle Malibu (Weekend Cruiser) 1969 Chevelle Malibu (Daily Driver) No, it is a Sherwin Williams product. I think the part # is P48 and it is a 3k (primer/reducer/hardener)urethane primer surfacer and is called "Ultra Fill II". I am using this product because it is something I bought early on in my project before I bought the paint itself from PPG. It is very good primer by the way.

The primer and hardener are on the bottom in this photo, below the PPG DPLF epoxy primer.

http://users.ev1.net/~jaaustin/chevelle/primer1.jpg