Paint Prep

[Autobahn]

Our audience here is the diy enthusiast and as such the advise given is aimed at them. They are more likely not to consider or even know about the absorption of moisture into the filler and more likely to leave covering the filler with a coat of paint for a while after application. Provided the base the filler is applied to is sound and keyed there should be no problem. Out of the two options for applying filler this is the best for the amateur that does not know all the in's and out's of body prep (which is the target audience). Thanks for the post Redmoggy it will help others.

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So you believe the DIY restorer should not understand body filler is porous?

Guess being ignorant of it's properties is why so many DIY repairs over rust blow out again in a matter of weeks

[amgrave]

Well my last post on this subject was misunderstood so everyone please ignore it and I will leave this subject.

[Redmoggy]

Autobahn. It's one thing to stick to your gun on a subject and another to just start making stuff up. No one has at any point recommended the application of any refinishing product over rust, loose, cracked, chipped or poorly prepared paint. My original recommendation to apply body filler over a keyed etch primer came from one of the worlds largest refinishing companies. I understand that you disagree and have no intention of trying to change your mind so would rather we just agree to disagree?

Regards
Rod

[Autobahn]

Autobahn. It's one thing to stick to your gun on a subject and another to just start making stuff up. No one has at any point recommended the application of any refinishing product over rust, loose, cracked, chipped or poorly prepared paint. My original recommendation to apply body filler over a keyed etch primer came from one of the worlds largest refinishing companies. I understand that you disagree and have no intention of trying to change your mind so would rather we just agree to disagree?

Regards
Rod

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It appears you are confused, my last comment was in direct reply to someone else, not any comments or views you have made.

It was suggested an amateur DIY did not need to know that filler was porous etc, this was clearly quoted above my comment in my reply you appear to have taken exception to.

We both appreciate body filler is porous, that is also an important fact any DIY repairer should be aware off, I made the point that if they are not aware of this fact then like many they fall into the trap of doing a repair over perforated metal then finding it blows out as soon as damp gets into the filler.

On the subject of filling over bare metal or primer.
I spoke to two different body shop managers today ( both in their 30s), they only fill onto bare metal so try as I might I have yet to find someone who fills onto etch primer.
I also think it strange that the hazards of 2k primer are mentioned yet etching primer is about the most evil stuff to use in my experience.

I think we must agree to disagree as you have suggested.

[les]

Now let me think---- what shall I do? I know, I'll leave the dent in.

[Redmoggy]

Yes it seems i grabbed the wrong end of the stick and ran with. I apologize.

We'll leave it alone and allow the individual to make a choice based on their own preference.

Regards
Rod

[amgrave]

Autobahn. Re-read my post please. I am suggesting the "amateur" might not know that filler is hygroscopic not they should not know. I am surprised you read that into it as I have read my post over and over again and cannot find any reference to "should not know".

[Autobahn]

Autobahn. Re-read my post please. I am suggesting the "amateur" might not know that filler is hygroscopic not they should not know. I am surprised you read that into it as I have read my post over and over again and cannot find any reference to "should not know".

You wrote: Our audience here is the diy enthusiast and as such the advise given is aimed at them. They are more likely not to consider or even know about the absorption of moisture into the filler and more likely to leave covering the filler with a coat of paint for a while after application. Provided the base the filler is applied to is sound and keyed there should be no problem. Out of the two options for applying filler this is the best for the amateur that does not know all the in's and out's of body prep (which is the target audience). Thanks for the post Redmoggy it will help others.

I certainly read that you felt advice regarding problems with filler and moisture were not considered a problem the diy repairer needed to know about.
Clearly stating diy enthusiasts would likely not consider or know about the absorption properties of body filler anyway.
You then go on to state the filler might be left unpainted for a while, (again allowing the potential for moisture absorption).
However you then go on to state that as long as it has been applied to a keyed area 'there should be no problem'

OK... I give up.

[Redmoggy]

Ok, to get back on subject.

As I said I'm fairly happy with the roughed out shape, it's now time to straighten it out. Which ever way you choose to apply it you will need a coat of etch primer over the bare steel which should be keyed when properly dry. I've used a course Scotch Brite pad again on a block.

I'm using an acrylic 1K high build primer and am going to apply a few sacrificial coats which will be sanded to lift any low spots. This stuff is still pretty nasty but does not contain isocyanate. A suitable mask is still required.





I've applied 4 coats mixed 4-1, the finish is about as dry as a nursing home honeymoon but that’s not to important right now. If you look at the second picture you may be able to make out a high spot just below the top of the knee pad curve. I would like to say I missed this intentionally for demonstration purposes, but i cocked up!

This is followed by a dusting of black as a guide coat. Any contrasting colour will do, I just had a little black in the bottom of a tin.


Difficult to describe how much easier a guide coat will make the job. It's purpose is to high light any low spots in the surface, not just in the repairs but in any stretch marks in the steel.

I'll start with that bit I cocked up. Some 120 grit on a block and a quick light sand shows up the problem areas.

[Redmoggy]

Continue sanding the guide coat the theory being that once it is gone the surface is flat. The black etch primer shows when the high build is getting thin. The primer has done a good job of lifting the low spots here and has some what levelled the high spots.



I did the same for the rest of the tank. A quick sand to high light



Followed by more blocking



This leaves me ready for more high build primer. However fist I'll touch in the bare spots with some etch.

Rod

[Redmoggy]

So, four more coats of high build, this time mixed 2-1 to give a smoother surface followed by a guide coat. Keep in mind the first primer coats were to finish of the repairs and straighten out any stretch marks in the metal. These primer coats are to fill the dry sanding marks and to finish of the straightening process. If while sanding this coat we break through to bare steel we have a high spot that will require attention. A few taps with a shrinking hammer followed by more primer will usually sort it, unless it's excessive.



Since I dont want any more deep sanding marks I have switched to 800 wet and dry used with lots of soapy water again on a block.



You can clearly the 120 grit sanding marks hi lighted by the guide coat. Also that lingering high spot along the top (no guide coat). This round of blocking sorted all the issues with just a few thin spots but nothing breaking through.





After touching in the thin bits and another light sand I applied a few coats of black base coat to get an idea of the finished product.





Thats it one prepped part ready for paint that wont show repair shadows, sanding marks or ripples in the paint surface.

Yes you can speed the whole process up with 2K primers but that wasn’t the idea of this post.

Regards
Rod

[panky]

Thanks for all this Rod. One problem I've encountered using high build is cracks appearing through the top coat, I did the door bottoms on my camper, and was quite pleased with the results, but a couple of days later these straight little crevices appeared about four inches long and in random directions - as if the top coat had shrunk back. Any thoughts.

[Redmoggy]

I'd say a little to much paint and not enough drying time between coats. If the solvents don't get a chance to flash off they will build up and get trapped under the top coat. I try and leave any primer coats over night if I've tried to build them up.

Rod

[panky]

Ah, I do get a little impatient

[tysonn]

That's why I use 2k.Chemical reaction over air drying.No contest.If it had been available back in the day they would have used it.
Mick

[Redmoggy]

Somewhat missing the point of the post though, Mick. I know how good 2K primers and paints are and how much time they can save. Every time I have read a paint related post (both here and other forums) 2K is the first thing recommended followed by an avalanche of warnings about cyanide and immanent death. Not everyone feels comfortable spraying this stuff around the Wife, Kids, Neighbours, family dog etc. My intention was to show that the same results can be achieved using simple 1K primers that are not quite so scary for the hobbyist.

Regards
Rod

[tysonn]

My post was in reply to the question about the primer cracking not the general thread.
Mick