Block sanding....did you ever have that "I'll never get it" moment

[AmadeusCharger500]

Ok I know Im a complete hack. But if anyone would be kind enough to read my term paper for me I'll listen humbly.

[69 OUR/TEA]

Explain better what you are struggling with.

[69 OUR/TEA]

Show what you are using for blocks,paper.what product is that you are blocking??etc,etc,etc....

[AmadeusCharger500]

Im using a 16 inch dura block with 220 grit on 3 coats of medium build primer. A few questions come to mind as Im blocking. What is the proper angle to hold the block/door. How do you deal with the fact there are almost no flat spots. I tried holding it 45 degree to floor level, moving the block basically sideways instead of length ways, and was getting what I thought were understandable results. i.e. a nice big low spot from below and left of door handle opening about just above the body line. Then I got to the front portion of the door and that angle was producing terrible results. I was getting a low spot pretty much the length of the block, thats what made me shake my head and say I'll never get this

[69 OUR/TEA]

Actually,back up,what was done to the door,stripped to bare metal,or just sand whatever finish was there and prime?
There is alot to know,and we can never go back and forth and get you to "get it" here.Simplified,you basically get a feeling for it.I will try to explain the best I can to put it into perspective as I do it.Be preparred that 17 other people will follow and tell you numerous diff ways,remember there is more than one way to skin a cat.
To start,just one block is not going to do it,you have to have an arsenal of all diff lengths,shapes,firmness,etc.
Every cars body is diff,you have to know the correct way it is supposed to look first off,and then try to follow the pattern.I.E,alot of people making the body line on Chargers razor sharp.Lower body lines being to sharp,and on.
Second,using 220 is useless,you have to be more aggressive with the grit(NOT 36 either !!!!!)If you used a polyester primer (sprayable body filler)you can block that with 80-100 to start.Urethanes 150-180grit.
If you guide coated as it looks in your pics,and have that many low spots that deep,you need to be skimming with plastic(body filler) to bring those up,you will not get them out just by 3 coats of med primer.NTM,it would be better if the door was off the car and on a stand.
Third,stop breaking thru everywhere,not a good thing!Try to keep the diff substrates covered as a whole.Clean up everything you show with 220,make sure you get all that rattle can guide coat out of the low spots,reprime the whole door,let it dry,even stick it outside in the sun for a few days,re-guide coat,block with 150-180(easy) to find your low spots again,and as I said you have some plastic work to do in those(I know easier said than done).
I don't know what you are trying to achieve,but followed by that is the polyester,that you can block the sh$t out of to get panels real straight,then back to a urethane primer,sealer,topcoat.
And especially finish off your sanding and or bodywork to 180-220 before priming(DO NOT LISTEN TO ANYONE THAT TELLS YOU STOP AT 80,120,150 PERIOD!!)
See what I mean,I wrote a short story and there is still lots that you should know.
I find it harder to explain into words vs. doing the bodywork/blocking etc.!!!!
Hope this helps.....

[restoman]

^^^^^^^^^^^^
All good advice. I'll add a little more regarding those pesky low spots - keep blocking until most of them (if not all) disappear or are greatly reduced, then re-prime or glaze with two part filler. I'd use polyester primer as mentioned above - fantastic at filling and blocks out exceptionally well. With very little shrinkage, it will fill some really horrible work with no future concerns. Finish it with 220 or finer (I use 120 grit to level things out and then move to 220 to reduce the 120 grit scratches) before putting any urethane primer on top. Urethanes do shrink, and will later reveal coarse grit scratches if you're not careful.

[elitecustombody]

^^ these guys are right. First ,take the door off, assuming it fits well and all the gaps are proper,we don't know what has been done to that door, but if it's fairly smooth at this point, buy a gallon or two of Evercoat Featherfill G2 primer, it costs around $60,it comes with MEKP hardener. I prefer using  black,because it contains high level of zinc, it sands alot easier than gray,not to say that gray is tough to sand, I've been using gray for years,til I tried black, it's just better for heavy filling/blocking . If the door has low spots of 1/8" or deeper, roughen it up and skim,or straighten the door first,the less material on the panel, the less chances of problems down the road.

[AmadeusCharger500]

To answer the first issue. I basically scuffed the paint from midway up with a 80 grit da and then 6 inch block with 80 then 180 then 220, as it all looked to be in good shape. I know this is not preferred method by many but I am comfortable with it....at least so far!. About midway down I took much of the door down to bare metal. There were several low spots and strange waves I found before doing this and I wanted to know what was going on underneath. There was especially some waves in the door midway vertically and toward the door jam area. I tried to fill these and form them to the best of my ability. I use a 16 flexible sander with 80 grit to follow the curve of the door, and then an 8 inch normal sanding block to smooth every thing. I then applied some more filler on the spots that were uneven, there were no rust holes and very little rust overall. I removed anything I found. When I had everything to what I thought was fairly straight I then scuffed it all with 220 then da with 220 and 320 then sprayed the primer on. My source of headscratching confusion is perhaps related mostly to how to properly fill those low spots as I am not sure I did this correctly in the first stages.

Here are the materials Im using. Maybe that is another issue I could need advice on as these may be the wrong tools.
1 gallon plastic body filler. I used this to fill the low spots and reform the waves to conform to door shape
1 qt polyester glazing putty. I used this to glaze over each area I filled.
1 gallon primer surfacer. This is called 3 in one. and claims it is a high to medium build surfacer when mixed with less ratio paint/urethane thinner, and a sealer when mixed with more thinner.
I've seen guys spread filler on huge areas of panels like maybe the whole rightside of the door. but I have never gotten the trick of spreading that much filler before it hardens so I usually only worked in 10 inch by 10 inch square areas.

Really appreciate the help and Im ready to do exactly what you just told me I also realize you're advising me with me providing very little information or doing this by reading is very difficult. I hope to keep your attention as this is extremely helpful

[AmadeusCharger500]

Ok I've been looking closely at this spot where the door has a weird wavy area. I'm pretty sure the car scraped along something at some point and put a fairly gentle but noticeable flat line into the door at its outer most curve.....about midway down the door. Its about 3 inches top to bottom and runs for about 12 inches from origin spot to the door edge on below the handle area. I've done some more mild block sanding at the top of the door and its all coming out good and flat so at least that's gives me hope as to understanding the block sanding principle.

I think what I'm hearing from everyone is that I need to use a more serious coating of primer surfacer and I need to let it bake on the door longer and put the dang thing on a flat surface to work on it. This all sounds pretty straightforward. I am however still a little fuzzy on skim coating to repair this area and how you sand that coating correctly to the contour of the door. Can someone point me to instructions on this process?