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Old 05-14-2013, 04:36 AM
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Block Sanding question

My question is I have a daily driver truck that needs painting.

I want to block sanding the sides and a few other area's first with 320

Should I do this wet or dry?

The paint on the truck is in very good condition and the only reason I am painting it is to change the color.

The sides of the truck really need to be blocked because of some past bodywork.

A good friend who paints for a living said I should just use 320 wet and block and then prime the entire truck and shoot it with single stage
polyurethane paint.

What do you think? Jimbo

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Old 05-14-2013, 04:51 AM
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320 ain't gonna block nuttin !
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Old 05-14-2013, 04:58 AM
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You need a more coarse grit for blocking if you're trying
to straighten it. I like 150 to 180 for primer.
Or 60 to 80 for body fillers.
320 or 400 is good to remove scratches before painting
but that's not considered "blocking" or straightening.
320 is more for "smoothing"
Hope that makes sense.
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Old 05-14-2013, 05:22 AM
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Old 05-14-2013, 08:16 AM
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Ok, first, is the paint on the rest of the truck in decent shape? If it is DO NOT sand and prime the whole truck. There is NO REASON what so ever to apply primer to anything that doesn't need some sort of "surfacing" (blocking) or covering up some bare metal or something like that. If there is decent paint there, sand that decent paint and apply your new paint over it. If that paint has somehow failed, well then it needs to be removed or sanded real well to remove the failure so your new paint has a good foundation. This "could" require sanding so much that you need to prime over it, but usually this is simply not needed on your typical "repaint". If you are wanting a super nice and straight car then you may want to prime and block that primer to get it super nice before painting. But for you average "repaint", sanding the existing paint and painting over it is just fine and exactly what happens to 99% of the "repaints" every day across the country.

Sometimes this sanded paint gets a sealer shot first, a "wet on wet" sealer that is shot right before you shoot the paint, just to even out the color over primer spots and what not before you paint.

But to "Block" as the others have said you need to go courser as the purpose of blocking is to "CUT" the surface flat. You can't CUT with 320 so to "block" with 320 then prime.....a HUGE waste of time, a HUGE waste of time and primer.

If you want to straighten those sides do to poor body work, block that existing paint with 180 and apply primer over it, block that with primer with 180 again then another application of primer then sand and paint. There are many ways to do it, but for a "repaint" of your average car that is how it would be done 99% of the time across America every day.

Brian
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Old 05-14-2013, 08:25 AM
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I would isolate the wavy areas and hit them with 120-150 then 180. the rest in 180-220. spot priming also an option so that would change my grit options.
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Old 05-14-2013, 10:55 AM
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Quote:
Originally Posted by Jimbo17 View Post
The sides of the truck really need to be blocked because of some past bodywork.
Jimbo
He needs blocking
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Old 05-14-2013, 12:11 PM
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Yeah Jim, I went off on my you don't need to prime where it doesn't need it tangent. But yes, that area needs to be blocked and primed and blocked if that will take care of the problem, it may even need filler or a skim coat of polyester putty. My point was that the upper area of the truck that has no damage there is absolutely no reason to sand and prime it. Sand it with 400 or 600 and paint it for goodness sakes! Nothing coarser than any other prep for paint, 400 or 600 would be fine for a SS polyurethane as he is planning.

Anything coarser than that would require primer and priming over un-damaged paint is a huge waste of time and money if we are looking for a SS paint job on a driver.

Brian
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Old 05-14-2013, 01:16 PM
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I know, and I agree with you completely (as usual)
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Old 05-14-2013, 01:37 PM
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Quote:
Originally Posted by Jimbo17 View Post
My question is I have a daily driver truck that needs painting.

I want to block sanding the sides and a few other area's first with 320

Should I do this wet or dry?

The paint on the truck is in very good condition and the only reason I am painting it is to change the color.

The sides of the truck really need to be blocked because of some past bodywork.

A good friend who paints for a living said I should just use 320 wet and block and then prime the entire truck and shoot it with single stage
polyurethane paint.

What do you think? Jimbo
I have been thinking about your questions and I just wanted to make something clear. We aren't there looking at this truck, we can't see for sure what is needed prior to paint sitting here looking at our computer screens. Your friend who paints for a living may be right in his suggestions and you have lost something in the translation.

If the blocking required isn't very much, say it's sand scratch shrinkage and you can see this body repair because it wasn't properly prepped for paint. You "could" block it with 320 wet using the paint that is there as the filler. You could very well get a lot done doing this, if there was a lot of paint on the truck for instance, it was painted with three or four coats of SS urethane, there is a bunch of material to use as a "surfacer" just like a primer. So you "could" do this.

As far as "priming" the whole car, makes no sense what so ever, but could you have mistaken "priming" for "sealing"? It is very possible he said to do as I just did with blocking the paint with 320 wet then sanding the whole thing with 320 then sealing wet on wet a painting your SS polyurethane paint over the sealer, done deal.

I just wanted to toss that out there, your buddy isn't necessarily wrong because he is there looking at the truck, we aren't.

Brian
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Old 05-14-2013, 01:46 PM
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To make it clear, the sealer is applied and not sanded, thus "wet on wet". The sealer can be allowed to dry to form a better barrier coat and again be painted without sanding it. But commonly it's called "wet on wet" that's why I called it that to emphasize that it's not sanded. You put a coat of sealer over that 320 sanded old paint and then apply your paint right over it without sanding the sealer. The sealer makes a uniform substrate over the truck for your paint so if there are any sand thrus, or primer spots or what ever, it makes it all one color and will fill some minor scratches as well. This is your basic standard practice in "repaints" across America.

Here is a little "Basic of Basics" on terminologies around the paint shop. http://www.autobodystore.com/ms7.shtml Go down to sealers and you will get a good explanation of their use.


Brian
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Old 05-15-2013, 05:03 AM
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I'd like to add that a epoxy primer thinned down per mfg's rec.
makes an excellent sealer.
Along with providing a uniform color to paint over, it fills
sand scratches and will greatly increase adhesion.
I have been using it on all my bumpers now and it's
really reduced the normal road rash.
The one I use allows you to paint over it after only
an hour of cure time when used as a sealer, it also comes in
black and white so I can mix to get a complimentary shade for
the paint to go over.
I recommend using a epoxy sealer just for the adhesion gain.
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Old 05-15-2013, 05:26 AM
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The problem I have with all this is.....If the bodywork is that bad,what else is done halfbaked underneath,,,could be lacquer primer or a host of other stuff that'll give you trouble later.I think I'd get the grinder out...hard to say without actually seeing it...Generally, body guys that do this kind of work use LOTS of primer so putting more on might not get you there...
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Old 05-15-2013, 07:55 AM
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Quote:
Originally Posted by jcclark View Post
I'd like to add that a epoxy primer thinned down per mfg's rec.
makes an excellent sealer.
Along with providing a uniform color to paint over, it fills
sand scratches and will greatly increase adhesion.
I have been using it on all my bumpers now and it's
really reduced the normal road rash.
The one I use allows you to paint over it after only
an hour of cure time when used as a sealer, it also comes in
black and white so I can mix to get a complimentary shade for
the paint to go over.
I recommend using a epoxy sealer just for the adhesion gain.
X2

Brian
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Old 05-15-2013, 07:56 AM
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Quote:
Originally Posted by deadbodyman View Post
The problem I have with all this is.....If the bodywork is that bad,what else is done halfbaked underneath,,,could be lacquer primer or a host of other stuff that'll give you trouble later.I think I'd get the grinder out...hard to say without actually seeing it...Generally, body guys that do this kind of work use LOTS of primer so putting more on might not get you there...
This is a "driver" we are talking about.

Brian
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