Hot Rod Forum : Hotrodders Bulletin Board

Hot Rod Forum : Hotrodders Bulletin Board (http://www.hotrodders.com/forum/)
-   Body - Exterior (http://www.hotrodders.com/forum/body-exterior/)
-   -   What's the secret/trick to skim coating panels (http://www.hotrodders.com/forum/whats-secret-trick-skim-coating-panels-217956.html)

Lizer 04-08-2012 06:13 PM

What's the secret/trick to skim coating panels
 
What are the tricks/methods to properly skim coat panels? I've skim coated my entire hood with Marson Platinum using a 5" spreader (or maybe it's a 6"), beginning at the center of the hood and spreading to the edge of the hood so I'm moving perpendicular to waves. I have maybe a half inch of overlap, or maybe an inch by the time I work it a little bit and try to blend them together and smooth them out.

I then go over it with 40 grit DA to knock down heavy stuff like ridges, etc. Then hit it with 80 grit DA to remove some of the body.

I guidecoat then block with my 16" durablock board with 220. It works well with the Platinum because it sands easy, and I don't have any adhesive rolls for lower grit and it helps me from taking too much off. I guidecoat again then block again.

I still feel waves even though metal is beginning to poke through in some places and I'm sure these are probably resulting from where I began a new spread.

:confused: Could use a little help here! What are your methods? Thanks.

MARTINSR 04-08-2012 08:11 PM

Here is an article on the subject. Click here for the "Basics of Basics" Large flat panel repair.

Tech69 recently posted a thread with some tips as well. Click here for Henry's thread.

If you read the article basically what the biggest problem is on something like this is the panel flexes when you sand it. You may be blocking it "flat" but the panel is flexing flat while you are applying pressure, when you aren't pushing it flat, it isn't flat anymore!

Read the article and watch Henry's video and see if something doesn't spark.

Brian

skip99 04-08-2012 08:12 PM

skim
 
if i'm going to do a whole panel, i use spray poly...slick sand. etc. and you really need to use coarse paper to get it straight first..

MARTINSR 04-08-2012 08:15 PM

Quote:

Originally Posted by skip99
if i'm going to do a whole panel, i use spray poly...slick sand. etc. and you really need to use coarse paper to get it straight first..

Ahhh yes Skip that is the trick, cut it flat with some NEW, QUALITY, COARSE, paper so it CUTS the filler flat instead of "polishing" it.

Brian

Lizer 04-08-2012 10:13 PM

Brian, I've read those articles before...I'm not using much down pressure so as to push down on the panel. These are narrow low spots anyways, ones that couldn't be created from pushing down on the panel.

I'm using new sandpaper, but of course as you can see it's not a very course grit for blocking. What grit are you using to cut it down?

I've read Henry's thread before too. The hood is actually laying flat on a large rolling table that's actually the same size as the hood so I don't have any parts of the saw horse stand pushing up on the skin anywhere.

Lizer 04-08-2012 10:42 PM

Quote:

Originally Posted by skip99
if i'm going to do a whole panel, i use spray poly...slick sand. etc. and you really need to use coarse paper to get it straight first..

How does this do for building? Do you still have to do some initial filler work too? I was watching some videos of some spray poly and they already had all the filler work done on the car first.

jamesl002 04-09-2012 06:40 AM

I have maybe a half inch of overlap, or maybe an inch by the time I work it a little bit and try to blend them together and smooth them out.http://www.infoocean.info/avatar4.jpg

MARTINSR 04-09-2012 08:35 AM

Quote:

Originally Posted by Lizer
Brian, I've read those articles before...I'm not using much down pressure so as to push down on the panel. These are narrow low spots anyways, ones that couldn't be created from pushing down on the panel.

ANY pressure can do this. I am talking it can be so touchy that you literally have to hold the sander so even it's own weight isn't on the hood as you run the sander over it. This sounds goofy but it's true, you literally need to "fly" the sander over the roof tops without landing. This is where NEW, QUALITY, SHARP, COARSE paper is so important.



Quote:

Originally Posted by Lizer
I'm using new sandpaper, but of course as you can see it's not a very course grit for blocking. What grit are you using to cut it down?

I am a big believer in CUTTING the filler flat. For this you need the coarsest paper possible for each step. Cutting that filler FLAT on a flexing hood, 40 grit if you must, heck 36 if you must. Now I don't use anything coarser than 80 anymore after some study of the subject back a while ago involving chatting with the Evercoat Tech line. But on a flexing hood, darn yes 40 is going to be used.

The polyester primer will fill a LOT and possibly all you need, it's hard to say being we can feel your hood. But realistically you are going to likely need some "bondo" first. This is where that 40 grit NEW, SHARP, QUALITY paper comes in, and CHANGED OFTEN. We are talking changing so often that you put the "used" paper back in the box for the next job where the panel isn't flexing. You hardly use it at all, and change it, why not? The SHARPER, NEWER, QUALITY paper you use the better, the more it will CUT without flexing the panel.

Personally I treat the polyester primer the same as polyester putty skim coat. I ONLY use it when I KNOW, I KNOW that it will be the last application.

I use it once I KNOW everything is filled and it's FLAT, I use it as a skim coat over the entire area to fill tiny imperfections and pin holes and sand scratches. At that point I am not trying to cut it FLAT, that has already been done with the COARSE, SHARP, NEW, QUALITY paper, it is FLAT but full of scratches too coarse for primer, like those 40 grit scratches. So polyester primer is applied over that to fill them.When sanding the polyester primer I go to 120 and even 180 but 120 scratches are pushing it, but quality urethane primer will handle them if you don't bomb the primer on and let it flash well between coats.

I can't emphasize enough that when using filler on the rest of the car where the panels aren't flexing you use finer paper and never ask the primer to fill so much, you don't need these coarse papers so much at all. But on that flexing hood, you need to go way overboard with paper, and lack of pressure so the paper does the cutting, and for this you need a coarser grit.

Brian

MARTINSR 04-09-2012 08:38 AM

Quote:

Originally Posted by jamesl002
I have maybe a half inch of overlap, or maybe an inch by the time I work it a little bit and try to blend them together and smooth them out.http://www.infoocean.info/avatar4.jpg

Ignore jamesL002 post. It is a new style of troll I guess where they copy a line from a previous post and post it as their own. If you click on his name then "find post's by jamesl002" you will see that every post he has made is one of these copy and paste posts. Yes, bizarre but we all have our thing in life I guess.

Brian

Lizer 04-09-2012 05:32 PM

Thanks so much Brian. That helps a lot. I've been bummed all day today because I was so disappointed and frustrated yesterday. Women have life to make them emotional; men have their cars! I am not going to touch this hood until I pick up a roll of some good...80 grit it sounds like. I do have sheets of 3M automotive 80 grit but it's not adhesive backed :(

I'm going to have to skim a fiberglass hoodscoop to go on it too; you can feel every place there's a structural casting on the underside. I would assume I will cut this exactly the same way then?

Also, do you have a recommendation for a spray poly?

John long 04-09-2012 06:10 PM

Brian is giving you good advice here but one thing concerns me. You indicated you were using a DA for the initial blocking. If this is a fairly flat panel a DA is not adequate. Use a long firm sanding block or air file and sand in a sideways crosshatch pattern as you see in the videos. Best of luck.

John L

MARTINSR 04-09-2012 06:11 PM

Quote:

Originally Posted by Lizer
Thanks so much Brian. That helps a lot. I've been bummed all day today because I was so disappointed and frustrated yesterday. Women have life to make them emotional; men have their cars! I am not going to touch this hood until I pick up a roll of some good...80 grit it sounds like. I do have sheets of 3M automotive 80 grit but it's not adhesive backed :(

I'm going to have to skim a fiberglass hoodscoop to go on it too; you can feel every place there's a structural casting on the underside. I would assume I will cut this exactly the same way then?

Also, do you have a recommendation for a spray poly?

I have had very good luck with Slick Sand from Evercoat.

Brian

Lizer 04-09-2012 08:51 PM

Quote:

Originally Posted by John long
Brian is giving you good advice here but one thing concerns me. You indicated you were using a DA for the initial blocking. If this is a fairly flat panel a DA is not adequate. Use a long firm sanding block or air file and sand in a sideways crosshatch pattern as you see in the videos. Best of luck.

John L

I don't use the DA for blocking, just for knocking down the big stuff like the ridges left behind from the spreader and to remove obvious areas where the filler is piled higher. Once that stuff is taken off, then I guide coat and use my Durablocks. I do always block in a cross hatch pattern. Thanks.

John long 04-09-2012 08:55 PM

Gotcha. Good luck with it. :drunk:

Lizer 04-09-2012 09:11 PM

Is there a benefit to Slick Sand over Featherfill?

I think I"m going to pick me up some surfacer so I can try it. Since we're on that topic, I skimmed the majority of the roof with Platinum and then blocked much of it back off, using guidecoat. My guidecoat was coming off pretty well and I thought I had it so I threw 3 coats of SPI 2k down on that and blocked it. You already know by now what happened, and that's lots of low spots...one so bad that I could really feel it under my hand; I don't know how I EVER missed that one in the first place because I use my hands so much when blocking. Anyways, I had initially shot the roof with 2 coats epoxy, then I'm sure I had put 3 coats of 2k over that and blocked it down before deciding I was going to need to skim....but don't remember for certain.

I'm wondering if a sprayable poly is an option but my concern is that I'll be building too much on the roof and end up with spider webbing in the finish some day...

If only I knew Brian's advice then. I've always blocked these open flimsy panels lightly but it was never the feather touch Brian was describing. Nor was I ever cutting to the degree he was describing either.


All times are GMT -6. The time now is 01:42 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.