Hot Rod Forum : Hotrodders Bulletin Board

Hot Rod Forum : Hotrodders Bulletin Board (
-   Body - Exterior (
-   -   Fiberglass hood blocking (

abarli65 01-05-2013 09:51 PM

Fiberglass hood blocking
I have spent way too many hours on this dang hood.

I am not looking to make career out of this... turning out one restoration every 5 years is not a good business plan.

65 mustang fiberglass 'shelby' hood with the steel bracing. Picked it up from Dallas Mustang. Cosmetically it was in decent shape. I scuffed with a red pad / epoxy primer / 3 coats of SPI regular 2k primer / blocked / filled low spots with poly putty / 3 more coats of SPI 2k.

I had this thing blocked out so nice... BUT, I made a rookie mistake and although I blocked it parallel to the front up to the hood scoop, I had the block parallel to the side between the side and hood scoop.

Evidently, there is a nice big dip in that area that blocked out nicely this way, but I don't think it would look good. So I spent another full day today filling and blocking. Also, you will see in the pictures that there is a little dip on either side of the scoop.

I don't know if I have a question, am just looking for constructive criticism, or just some reassurance that I am on the right track and to keep at it because one day I will be able to actually paint some color on this car. I am 4 years in... granted, I have had a child and started a new job since then... and now that I have a second boy due in April, I am feeling the pressure to get this mustang painted or I may never finish it.

tech69 01-05-2013 11:09 PM

looks like low spots. Just skim it past the lows and once it's good do a final skim coat on that plane to make sure. Guide coat and hand feel will tell you. When mixing use a figure 8 motion and it's the same motion they use to make taffy...and there's a reason for it. Then spread it out on your mixing board tightly so you squeeze out the rest of the bubbles. Then skim it tight and once you do it tight go back over it lightly to soften your spreader marks. This will make the sanding less tendious, which will give you the patience to make it nice and straight. for the area next to the raised area in the middle spread it and then use the corner of your spreader( a flexible one I hope) to feather the edge of your filler. Don't be afraid to spread your second skim across the whole plane. If you spread it right there won't be much sanding and it won't be such a hassle.The lows shouldn't be that bad at this point given it's fiberglass and you already added materials to it.

MARTINSR 01-05-2013 11:13 PM

Henry, how about a few good coats of polyester primer? I am thinking when it's that close, go for the polyester.


tech69 01-05-2013 11:26 PM

I don't really use poly primers to do that. In my experience, you will always be left with something if you do that, whether it be a tweak of a reflection or a low. I have learned if you skim it really tight with a clean spread it's not so tedious and then you can save that primer to help it give you a lazer sharp look. Just my opinion and I haven't used slicksnot or slick sand or whatever you call it.

Maybe inbetween is what's best... Just do one small skim past the lows and not two skims that I suggested and THEN hit it with the poly. Win win to me. :)

MARTINSR 01-06-2013 09:07 AM

Yeah, it really depends on how much you are filling, if those are real low spots you are dead on, I don't mean to use the poly primer as a "filler", that is for the bondo to do. But when you are close, to spread out filler flat enough all over that hood takes a bunch of skills where poly primer would make it very easy, IF you weren't trying to fill much.


69 widetrack 01-06-2013 09:29 AM

Just a few questions...What grit of paper are you using to block the hood out with?

The reason I ask is because it looks real smooth and using a fine grit paper makes blocking to get a large panel straight very difficult.

Another question, what type of block are you using and how much pressure are you putting on the block?

If your using a small small block on a large area it can take for ever to straighten a large panel if you can get it totally straight at all...I see your using guide coat and that's excellent, when you block a panel, there should be minimal pressure put on the block, let the paper do the work. If you apply a lot of pressure, you are actually digging out the substrate, and effectively turning your block into an eraser to remove the guide coat.

From what I've read on your posts you have applied 1 coat of epoxy, putty, and 6 coats of 2K primer...that is a lot of material and just thinking about your blocking methods.


MARTINSR 01-06-2013 09:46 AM

Right on the money Ray, good point you bring up.

Yep, coarser paper like 120 or even courser with the filler of course, using NEW, SHARP, QUALITY paper and changing it OFTEN is the key to what Ray is talking about.

You need to CUT the tops of the high spots off with NEW, SHARP, QUALITY paper. Not using NEW, SHARP, QUALITY paper a lot of times you "polish" the surface instead of CUTTING it flat. The sharper the paper the less pressure you have to apply. This eliminates pushing the panel down "flattening" it out as you sand. I have blocked stuff like a flexing hood where I literally hold the board off the surface so as to not apply any pressure to flex the panel.


69 widetrack 01-06-2013 10:17 AM

Thanks for the affirmation Brian and I agree, keeping paper sharp is one of the keys to getting a panel even and straight. When you block on filler or 2 part putty on a panel this size you can start with a paper as course as 80 grit. Use guide coat on your filler and or putty as well. With minimal pressure on a block (I would use a long board, 16 1/2 X 2 3/4 and gently start sanding. Once the panel is relatively straight, re guide coat the panel and move up to 180 grit on the long board. Never jump more than 100 grit on body work when moving to a finer paper or the foot print left by the coarser paper will still be there. Feel the panel with the palm of your hand to ensure that it is straight (a little trick that works for me is to turn your eyes away from the panel...if you look at it when your checking, often your eyes will lie to you and tell your hand that the panel is straight). After 180 grit, I would guide coat again, I like to move to an even finer grit like 280 grit...or in some cases even with 320 grit for my body work, finish block sanding. The reason is that when I put my primer over top of 280 grit or 320 grit it has less chance of sinking into the scratches compared to 180 grit. Prime the panel allowing proper flash times between coats and give the panel 2 to 3 medium wet coats of primer. Let the primer cure properly, guide coat again, get your long block out and gently block the panel with 400 or 600 grit paper. If you have any low spots seen by the guide coat, you could possibly fill them by spot priming (depending on how deep they are) or put on a light skin of 2 part putty and re-spot prime...block out again with 400 or 600 grit...clean it up and paint it.

Damn that sound's not, it takes patience and practice...the good news is that with experience it does get easier.

Hope this helps.


abarli65 01-06-2013 10:56 AM

Thanks for all of this info...

Re: sprayable poly... I almost bought some when I did my trunk lid. that thing had so many undulations from the steel bracing. That was a year or two ago and I did use too much pressure when I started that. I stuck with it and got it pretty flat after getting help from this forum.
I am not opposed to using spray poly, but I there have been a few 'puruists' out there that talked me in to sticking with spreadable. Also, I have seen some cars that have nice chips due to too much of it, so I am weary of doing it. It does sound so nice to be able to spray on a nice flat coat to sand off.

I finished filling all those areas that I have circled. I have not done a reflection check yet, but it does block out the guide coat now. I am afraid of that right side... it has some waves that seem to block out nice... I am attaching a video clip of the reflection prior to filling.

As far as my grits and blocks...
I am knocking down the poly putty with 180, then switching to 220 once it starts to feather. I will finish with 320 and 400 before the sealer coat.
I use Durablock. I have been using the full size 16" and the standard 11". I have done the flat surface sanding on them, so they are pretty flat. As far as pressure, I like to think that I am not putting too much pressure on the blocks. I try to put just enough to keep a good hold of it and to keep it flat against the surface. I keep my hands and fingers spread out across the block so that I do not apply too much pressure to any specific spot. And I do change the paper regularly to keep it cutting.

Here is the video.. I will do this again at some point today to see where I am now.

swvalcon 01-06-2013 10:58 AM

How bad is it. One way to tell is wet it good with wax and grease and sight down it. The thing with fiberglass is it's almost never straight and even if you get it there it doesn't like to stay that way. Two years from now it will be wavy again.

MARTINSR 01-06-2013 11:06 AM

That may be a little too fine a paper. When blocking something like this it is very important to CUT it flat, too fine of paper isn't going to do that. That poly putty I am assuming you mean something like "Metal Glaze" or "Glaze coat" by evercoat, a polyester putty. It really is basically regular filler that has had the talc ground finer. So sanding it with the same paper you would a regular filler is fine, so cutting it with 80 is perfectly ok. The thing is you don't want to ask urethane ("filler" primer) primer to do too much. You DO NOT want to ask urethane primer to fill 80 grit scratches. So blocking the poly putty with with 80 is ok as long as you go over it with another coat and then block that with 120 then 180 before you prime. You can prime over the 120 though we have learned in the industry that is pushing it a little. If you apply the primer in thin coats and don't bomb it on it isn't a big issue. But if you apply too heavy a coat it is all full of solvent and will shrink into the 120 scratches later.

But if you block that putty with 80 then apply a few coats of polyester primer then block that down with 120 and 180 before applying a urethane primer over that, it's basically the same as if you had primed right over poly putty, the poly primer really is about the same.

But getting back to the paper grit, doing something like that hood using a little coarser than you would typically use on a filler and first coats of primer is often needed. Because the panel flexes using a paper to CUT it flat is very important.


abarli65 01-06-2013 11:08 AM


Originally Posted by swvalcon (Post 1631307)
How bad is it. One way to tell is wet it good with wax and grease and sight down it. The thing with fiberglass is it's almost never straight and even if you get it there it doesn't like to stay that way. Two years from now it will be wavy again.

Yeah, that is a great trick I picked up along this journey.

It is not crazy bad, and that was another thought... At what point am I beating a dead horse? This is no show car, but I am the one doing the work, so I want it to look great. I have been trying to find pictures online of this hood to see if it has waves... I would venture to guess they all do?

MARTINSR 01-06-2013 11:36 AM

However, getting filler wet with wax and grease remover isn't a good idea. That filler can soak up a bunch of it, do a test. Put some wax and grease remover over a panel with a spot of filler and look at it. Let it set a bit and the filler won't remain "wet" with the wax and grease remover on the surrounding metal will. It didn't evaporate off the filler, the filler absorbed it, that is not a good thing.

I don't like the idea and personally never use it like that. No offense to you swvalon, it's just how I see it. There is nothing that causes paint product problems more than trapped solvents. Trapped solvents kicks every other cause in the butt when it comes to out and out causes for failure. So I treat solvents very seriously and letting the filler soak a little up, if only a little, is not something I am going to do. That is an old "trick" that has been going on for ever and many people do it, I just don't see a need in it.

Wax and grease remover should be wiped on wet and wiped off quickly to remove contaminates as they are suspended up in the wax and grease remover, that is how it is used.

I feel that if you can see a flaw, you can feel it. If after you block it and it feels good, apply primer, NOW you can see if there is a high or low. You don't want to do this every time, it isn't like you want to have layers of primer and filler like an autobody lasagna. :rolleyes: But the point is if you do your filler work until it feels good and apply primer, you WILL learn more and more as you go as to how to feel properly so you don't make the mistake of priming before it's ready. When you prime it, guide coat and block and when there are highs and lows that the primer can't take care of, feel it, learn to feel what these flaws feel like so next time you will feel them in the filler BEFORE you apply the primer so you can correct it before the primer is applied.


MARTINSR 01-06-2013 11:38 AM


Originally Posted by abarli65 (Post 1631316)
Yeah, that is a great trick I picked up along this journey.

It is not crazy bad, and that was another thought... At what point am I beating a dead horse? This is no show car, but I am the one doing the work, so I want it to look great. I have been trying to find pictures online of this hood to see if it has waves... I would venture to guess they all do?

There really is no way you can see a wave (realistically) in a photo unless the photographer WANTS you to see the wave. If one is caught by accident yes I guess but man, I must capture waves in photos as my job and it is often very difficult.


abarli65 01-06-2013 11:57 AM

Totally makes sense on the solvents... I will heed that warning going forward.

But since I was getting these videos as you were typing that info, I will share.

Looks like I am just about done with the hood.

There is still one last low spot towards the back on the right side. The left side looks great.

Here is better detail of that low spot in the back: At least, I think that is a low spot?

Left side:

I want to thank you fellas again for the information. I am sure I will be back for more lessons later.

All times are GMT -6. The time now is 08:39 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999 - 2012. All Rights Reserved.