how many times is the norm. to prime and block sand.I've primed and block sanded and reprimed.what do you think,block and shoot color or block and prime again then shoot color.Mike

Prime and block sand until you are happy with it. Sometimes you have to do it over and over and over, well you get the picture.

You have to shoot the colour after block sanding, not after priming. You want to block until the surfaces are flat enough that you are happy with them. Just remember that the colour will have the same surface as the blocked primer.

Peter

You might be at it a while. Usually when you are all "done" you find something else that isn't quite right. I thought that I was done two different weekends before the weekend that I painted my buddies Bronco. But the results were worth it.

Mike

You can use a lightly fogged guide coat to show high and low spots. Or wet the surface with a rag and sight along it with the light at the right angle. I found out after blocking and priming my front fenders 5 times that I wasn't using a thick enough primer-surfacer or a big enough oriface in the gun. Dupont Europrime is thick enough to block to a smooth finish. Be sure to use a long board (sanding block about a foot long) as much as possible. After the Europrime is glass smooth, shoot a coat of paint-brand compatible primer over that.

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von '69 300 Dlx SS TC #15 ACES #1575

131s here by dupont,i think it builds guite nicely and sandes with little effort.as far as highs and lows i just spray it real wet and take a look.mike

I don't think that you can quote a number of times that you have to block sand.

My guide lines would be to "keep doing it over and over again until you can't stand it anymore"!


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Wes. Vann
Technical Reference section
Gold Member #5

good point Wes so i went and spent another 90.00 on a gallon of primer and here i go again.man is this fun or what.mike

The idea of applying primer over and over again is a myth. You need to do it over and over because you are learning. If a pro had to do this he would go broke.
There is no reason that you can't apply one application of primer, block and paint.
Let me tell a few reasons that you would be doing it over and over.
1. The body work is not done correctly.
Primer can't make up for poor repairs (well, sometimes it can) If you leave coarse scratches to fill in the bondo, (I hate calling plastic filer bondo but for sake of explaination I will). You should be finishing all bondo in a minimum of 80 grit and leaving it in 100 or 120 is much better. The finer finish will also allow you to feel imperfections easier. The most common mistake in learning body repair is not giving the size of the dent the respect it deserves. If you have a 5" dent take the paint off four of five inches around the dent, and apply the bondo well past the dent, feathering it out to a thin skin at the end. Most people don't do this and they never really fill the dent but only the center of it, then try to make up for this with primer. If you have a lot of small dents like on the side of a door, remove ALL the paint and treat it like one big dent. This way you won't be trying to feather out each dent, and if there is a skin coat of bondo between them, who cares, getting the panel flat ALL the way across is what you are after right?
2. Improper primer choice. If you are using Lacquer primer, forget it. Lacquer primer has about 22% solids. Even first generation urethanes have 30 to 40%, and some newer products have up to 70! Solids=filling power, the more solids the less shrinkage. Lacquer primer pilled on wet could give you about 4 mils of primer...when it dries (not cures, but dries like house paint) you are left with 1.5 to 2 mil if you are lucky. A few coats of a high solids urethane can LEAVE you 3 or 4 mils after it has cured (not dried, but cured). A polyester primer can give you 4 or 5 mils PER COAT or more! That is right, I have a test panel where I applyed 21 mils with THREE COATS! Now this is abusing product, but it is possible. If you will notice the name "polyester" it's just like the bondo you are filling the dent, just less solids. It sprays like crap, and is harder to sand so it's uses are limited, but when you need it you REALLY need it. A good urethane should be the primer of choice for 90% of your work. By the way, the name "primer" implies application over bare metal, but not all primers are "surfacers". Some have very little solids and are made to prime bare metal for paint, with no sanding needed.
3. Improper application of the primer. Urethane primer needs at least 55 degrees to cure at the very minimum! You really want 60 and up. If it doesn't cure, it may feel hard and even sand, but it is not insoluble. When this happens it will continue shrinking and you could block it...reprime it, and soften it with the solvents frome the second application. Now it will again shrink, and there goes your flat surface you just blocked! Also, even if you have the temp, you could be "loading" it up or "bombing" it on to the point that solvents are getting trapped and this will slow the cure and cause shrinking.
The trick is to apply three or four medium coats, allowing PLENTY of time to "flash" depending on the product, and temp this could range from 5 minutes to 30 minutes between coats. Prime like you are painting a metallic enamel paint job, being careful not to model the flake. READ THE TECH SHEET! All the major manufactures have a web site with all the product data at your finger tips.
To give an example of the "loading" problem:
I had a customer (forgive me if you have read this before, I repeat it often) who was complaining about a primer he bought from me, saying it was taking too long to dry and it was soft even then. I explained what I have told you here, he took his gun which had a 1.5 tip (gravity feed) and primed a bondo spot on a car in the shop, even after my "lecture" he was really laoding it up(I can only imagine how bad he was doing it before I got there.)I only had my Clear coat gun with me, a Sharpe Platinum with a 1.3 tip, far from your usual primer gun! I applyed three coats on another spot, as did he on his. I also took a bare piece of metal to check mil thickness, he primed on half, I primed the other. I then took off for lunch. In about an hour I returned and the spot he primed was still soft and far from sandable, mine easily sanded. Now this is still pushing it because it will shrink more over the next few hours but it was sandable. (if after you prime and it is dring, take a piece of 220 or so and scuff it off, this will allow the solvents to excape easier.) Then at the end of the day I checked the bare metal piece with the digital mil gauge. MY side was .1 mil thicker! All the primer he "loaded" on was just full of solvent and when it flashed, it shrunk up. If you will notice, I have not mentioned any product names. I did this because we are talking very similar technology, a urethane primer is a urethane primer no mater whos label is on the can. THIS DOES NOT MEAN THAT YOU SHOULD MIX PRODUCTS! People get all hung up on labels, they all work in "basicly" the same way. Good luck.

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1965 Buick Gran Sport Convertible
1965 Buick Skylark H/T

Jeez after that long post I have to add that it doesn't mean that you NEVER prime and block and prime and block. Sometimes it is necessary to, but only because you slacked on something I mentioned. S**t happens to all of us, I don't mean that if you had to block a few times you are a hack. http://www.chevelles.com/forum/smile.gif

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1965 Buick Gran Sport Convertible
1965 Buick Skylark H/T

MARTINSR;

In regards to a professional doing the work, I agree with what you are saying (I noticed that your profile lists your occupation as "auto paint sales"). However, I have to assume that a person posting a question on this board about this sort of thing is a "hobbiest".

Over the years, I've painted something like 6 cars and have used lacquer, Imron, enamels, and urethanes. I buy top quality material and good equipment.

THAT SAID, I'M STILL JUST A HOBBIEST, and when I say that you should plan on doing body work until you can't stand it anymore, it comes from what I've ended up having to do in the past.

If I was a professional, I'd go broke due to the time I've ended up spending plus the amount of paint material that ends up as dust on the floor.


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Wes. Vann
Technical Reference section
Gold Member #5

Wes, I understand what you are saying. That is why I posted what I posted. The time we spend in our garages is very valuable time, at least to me. I have family, I have a job, and when I get out to the garage to "play" I want my time spent in the most productive way. Plus the products cost a TON of money and I sure don't want to waste. I have been doing body and paint for a living for 20 years, I know how hard the work is. If I can tell someone how to save some time and get a better job to boot I will, just as I hope others will do for me. I have seen many guys study, learn and do some very nice work right away. I myself have done things VERY wrong for years sometimes, then I learn a trick or go to a training center and find out a much better way to do it.
I highly recommend anyone interested in this work as a hobby or trade start by calling the paint manufactures and finding out about their training centers. There are centers all over the country and in a few days you can learn more than in years of trial and error.
If you think that doing it right or learning some technical info on these very technical products you are using is "better left to the pros", I'm sorry I wasted your time.

There is NO difference from a "hobbiest" to a "pro" in the product and the desired outcome. I don't know how one should explain the SAME info to a "Hobbiest" or a "pro", if either asks a question.

I notice you commented on my commentary in the first four sentences of my post. I don't know if you think it is some sort of personal dig or something, I assure you it is not. If I had ment to post some smart a** comments, I sure wouldn't have spent the time to leave such a detailed explaination of how to solve the probelms posted by the originator of the thread.
Forget about my personal comments and read the "facts" about these products, it may come in handy. http://www.chevelles.com/forum/smile.gif


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1965 Buick Gran Sport Convertible
1965 Buick Skylark H/T

ok fellas we are talking about cars not whos the most intellegent here,martin tell me about urethan primers do they sand as easily as what i'm using? yes i'm a rookie and my time is valuble,and as far as my work you all will get to see pictures of my 16 year old sons bb 70 chevelle real soon,paint interior,weather stripping and glass is all thats left now.total frame on reso.started jan 1 2000 and looking at 6 more months.my last project took 2 years and had less body work to boot.yes, wes i too thought he was insulting me but i blew it off. Mike

Man, I am sorry. If I sounded like I was insulting anyone, I didn't mean it.
okc, 131S is a Lacquer and will sand very easy. This tells you how soft it is, and after you do all your blocking, and apply another coat it is getting re-wet and you are taking a step backwards. Urethane primers sand pretty easy as a rule. Different brands and different ones within a brand can be a little different in their sandability (is that a word?) It kind of comes down to brand preference at that point. Of course I use Martin-Senour (available at NAPA stores)and the Tec-Prime #5100 or my favorite Tint-Prime #5103. Duponts Uroprime or PPGs K200 are also very good. Sometimes Urethane primers need to be cut with a little more agressive grit like 120 or 150. Not so much because they are harder to sand but because you want to cut the high spots fast. If you use a finer grit the paper seems to travel in and out of the low spots, never cutting off the high parts. Because they fill so well the 120 is no problem. After you block it once apply a couple more coats and it is ready to final sand and paint. You could on many spots just apply three or four coats, block with 120 or 180 then spray a guide coat and block with 320 or 400 and paint. But I usually am doing one panel at a time on a long project and just block and reprime each panel as I go. That way once the whole car is done, It is ready for a final sand with 400 or 500 and paint. No sealer is required, because the urethane primer is insoluable and a perfect base for the paint.

You will need to protect yourself with a good respirator, which you sould be doing with the lacquer anyway! There is a lot of talk about the ISOs in urethane and the protection you need, but... I can't emphasize enough YOU SHOULD BE USING THE SAME CARE WITH ANY OF THESE PRODUCTS.
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1965 Buick Gran Sport Convertible
1965 Buick Skylark H/T



[This message has been edited by MARTINSR (edited 12-25-2000).]

In hopes of trying to help everyone understand where MartinSr is possibly coming from, and maybe some others, the world of paint and body is full of so-called "VooDoo" products. There are so many products, methods and information, it gets very complicated to the newcomer. In fact, it gets very frustrating for everyone involved at times when discussing the subject. I don't think MatinSr ever tried to insult anybody at all, although it may sound that way at times due to the level of product knowledge he has, and how much needs to be explained. It's hard to understand in a paragraph or two in what he's trying to explain. I can see how it may sound derogatory, but it's not intended that way. As the saying goes, " Life is 20% what happens to you (or what's said to you in this case) and 80% of how you respond to it". I've seen 3 different high end painters do things 3 completely different ways and still come out with an awsome end product. There's 1,000's of ways to do body work and paint work. For the in-experienced, It's best to learn about as many different products and methods as possible. Sticking with 1 manufacturer's products is a good idea. That way you recieve information and procedures from one source, instead of many sources that may not make as much sense to the new-comer. We can ALL learn from one another. That's the idea of this site, right? And, in defense of hobbiest, I can tell you all that I've seen many, many show quality paint jobs that were done by hobbiest. Don't ever under-estimate your abilities until you try. Granted, it takes talent and ALOT of patience, but, YOU can do an awesome paint job. I've seen so-called professionals put out junk paint on what the customer thought would be a really slick, smooth paint job. Most won't take the time to sand & buff to perfection, when the knowlegable hobbiest will. If anyone has a question, please post it. There's alot of experienced people here who are glad to help. We all want every Chevelle out there to look it's best, Aah?
Oh, by the way, use a BIG paint stick, like the ones you get @ Home Depot for stirring 5 gallon cans, cut in a six" long piece to block sand with. Use the sticky backed sand paper on the stick. That's one of my tricks I learned from a 70 year old piano painter. Also, to help guide you as to when you're done block sanding, finish sanding the car with 600 paper ALL OVER when you think everything is straight. Wash it well and squegee it dry. Look down the panals with your eye close to one end looking down the other. Waves and distortion will show up if they are there. This should show how the finished product will look after paint is applied.
OK, I'm done now!

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Triple Black 69 SS 396

WOW! This is more great stuff from Team Chevelle. I read it all and now I am excited about block sanding (and tired from reading). I better get started on my tailgate before I forget it all (if I'm not too scared of priming and sanding by now).
What do you do about the areas you can't block sand like door jams and fire walls. How do you get them smooth and will the paint stick to the unsanded, or lightly sanded, spots?

Bill, who says you can't block the firewall or door jams? http://www.chevelles.com/forum/smile.gif Just use a smaller block. Now whether it worth it to block these areas is another thing, that is up to you. You can get foam blocks that work good for the curves that you find in these areas.
There is even foam that is covered in grit that works good or just use a "scuff pad" Red is great if you are going to apply a primer or sealer, but if you wnat to top coat over it, go with the gray.

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1965 Buick Gran Sport Convertible
1965 Buick Skylark H/T

I forgot one thing that is also good for "scuffing" door jams is Scuff Gel, "Final sand", "Ting" or part #6381 at NAPA stores are a few and is great for scuffing anything. You put a little water on the scuff pad and then scuff away! It helps clean the surface of contaminates and "lubricate" the scuff pad for easier sanding. GREAT STUFF!!

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1965 Buick Gran Sport Convertible
1965 Buick Skylark H/T

I also missed your question on paint sticking to unsanded or lightly sanded areas. Yes and no, epoxy or etching primer will stick remarkably well, but most top coats will not. Use the methods I desribe in my last post.

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1965 Buick Gran Sport Convertible
1965 Buick Skylark H/T