Thread: Filling Grinder Scratches

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When prepping cycle tanks the easiest way to remove the old factory paint is a 50 grit grinder disc. Then hit it with a DA and some 80 grit. 3 good coats of a Urethane catalyst filler primer works wonders. Prior to block wet sanding, dust a dark guide coat over the area. If your scarthes are still there the guide coat will show them. I have even wet sanded out a few small dings that required nothing other than the filler primer. If you think the scratches are too deep. Use some 220 on a DA, then re-coat with the 3 and wet sand.

one of the bigger problems here though is shirnking. ya, you might not be able to see the scratches after you prime and wetsand, which is usually the case, but once all the solvents evaporate and that primer settles down into where the solvents used to be, you will be able to see all the scratches through the paint. It is best if you dont have to prime any deep scratches at all.

DITTO !

Like I have said before , the smaller the scratches you have to prime over the less chance of shrinkage .


Spray

yes

Spraying the new primers don't shrink the way the old red oxide primers did. Ifyou used a glazing putty to try to hide your scratches, it may have looked good, but a few months later when the shrinkage occured your job looked like Uncle Earl did it..

Anything is going to shrink, i dont care if it is the most state-of-the-art primer, it will still shirnk if you try to fill big scratches, maybe it won't be as bad, but it will still happen. Glazing putty will also do the same thing if you try covering up some deep scratches. If everything is done properly, there shouldn't be any deep scratches left to fill.

These new products were designed for using finer grit papers , not the old route of 40 grit then 80 grit then prime . Some are even designed over properly preped paint as by BMW and Mercedes recomendation .
They are ment for 80 grit to start with and finished off with 120- 220 grit , then prime , this speeds up the paint process in a shop ( minimal scratches = less material= faster dry times ) , as the paint always took the longest time of the repair side of yesteryear , not so today .
I also have been using the UV primers , 2 minutes on the UV light , and wipe with a special chemical rag , sand and paint . Bad side is its for small repairs 9"X9 " area Max .

I have sanded some of the scratches out but am afraid to sand any more. I don't want thin metal. I bought some K36 primer but I've been hearing alot of bad things about it. I also heard that PPG quit making it. Has anyone else heard this? As far as shrinking goes no matter how I fill the scratches the car will proably sit in primer from fall until spring, and hopefully all the shrimg will have happened by then.

I hate to disagree with anyone, but I do believe in the "test of time".

I've been using urethane primer, and then Fiberglass-Evercoat Euroglaze over 36-40 grit rough prep for over 15 years with no problems. It's been one of those products that I never have to worry about. I do seal before painting, to prevent the porous area from absorbing solvents. That could also cause a shinkage problem.

why so course of grits ?
Technology has advanced and it doesn't require the 24 open coats and the 36 grits.

Thats good that your system works for you , but alot of wasted material for nothing in my honest opinion . Just a few extra minutes with a finer grit will give smoother results , and requiring less material .
But thats just me

I'm not big on anything Evercoat , they recommend trying their Feather Fill Product several years ago on a resto 69 Hemi Charger I was doing , and that crap Blew up before I even got paint on it , it wouldnt even go back over itself ......LOL It even ate the bondo , and blistered it off the metal .

I had their Techs look at it , and they said I water sanded it ......I dry sand most everything , I hate water sanding !!!

this is like beating a dead horse.here it is if you spray it out of a gun you will have to thin it .the primer will shrink .why? it hase been thinned and in till all thinner are out of the primer it is fat and when you sand it is still fat but when the primer set out and the thinnner get out it will start to sink down and pull on the scratches i have done body and paint work for more than 20 years and there is NO way you need 40 grit scratches to hook primer on steel 80 gets the job done and less is better no one make steel that comes out of a can that you can spray on when the steel is to thin you are screwed all the new hi fill primer can be help full but a lot of people use it to fix bad body work and the thicker you pile the crap up ,the more all this stuff will shrink and spot putty is for some asking for it .the fast way to be out the door were i worked was to use spot putty

SprayTech, If I haven't learned anything else on this group, it is that no two painters use the same process.

I use 36 or 40 grit on a vertical sander to strip paint. I can strip a full size car in 3-4 hours, or I can strip a set of bike tin in about 10-20 minutes per piece. no chemical residue, no warped sheet metal, no doing bodywork over, Just metal prep, prime heavy and block with 360. I don't know if you enjoy sanding, but I use the heaviest grit that will not give me problems later.

BTW, I hated Feather Fill too!

Most of what I've learned is self taught over a 40 year career. Classroom theory, and manufacturer's recommendations are fine, but for me, it's a reliable process, and as few hours as are necessary to get the quality I need. I do only custom work, so the standard has to be pretty high. If it didn't work for me every time, I would have already changed my methods!

HRP , I am not trying to knock the way you do things , its why I said if it works for you by all means do it .
There is No argument from me
I Have been painting 30 years and have a excellent rep myself .
Finding a system that works for you and sticking with it , as long as there are no paint problems is what a painter strives for . The switching of this new item , and switching to that new product , a person never finds a system that works and makes you money , or good results .
I have had helpers that always ask me why I dont try some of all these latest new fangeled products , I tell them I have a fool proof method , use less products , and achieve excellent work ! I will switch when I think a product will save me time , not because everyone else is using it !

I just find that the finer the sand scratched the less wear and tear on the old body for blocking
My back , shoulders and hands ( carpel ) have set in . Knees are going now

I can rip the paint off in almost the same amount of time using a MUD HOG with 80 grit , its why I question the grinder and 36 or 40 is all . I will then go over it with 150 on a mud hog , and have a nice smooth surface .

Spray