Thread: Filling Grinder Scratches

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Hello,
Got a new project,the metal is bare but it looks like they stripped the paint with a grinder. Is there a way to level this out with a primer ? I tried using a DA. sander on it and some of the marks came out but not all of them. I usually use the ppg DPLF primer. Any suggestions?
Thanks

when i did my 66 i had used a little 60 grit fex grinder wheel to take the paint off the lower 1/2 of the car . far too agressive but i couldnt get the paint off i used a 6 in oscilating wheel for the flat uppers and upper sides. the lowers came off fast ,the uppers took days of work i looked like a smurf at the end of the day(blue 35 year old paint)
for your question 1 coat of high build pimer on the top was good but the lowers took 2 coats anf then sanded and 1 coat more. metal had lots of bite shouldnt come off.
for a example i am planning on 2 coats of high build on my t bucket over the sealer on it now and then wet sand before paint. the body is already pretty smooth but it will give it a better final finish .
i am in no way a bodyman or painter just telling what has worked and what i am doing.

If you are using a catlyzed primer, always use two coats minimum or the hardener might not work. I use 2 coats for a smooth, straight surface, and 3-6 coats over rough surfaces, and body work, depending on how bad.

your right when i think about it, we rolled the car into the booth and applied primer for quite a while , i would assume that we put more than 1 coat on the panels in the procees, i know we mixed a lot of primer . we had rolled it back out after for me to start wet sanding and rolled it right back in and hammered the lower sides again as scratches were still showing through.

toolow,
DPLF is not a filling primer its a sealer , its reccomended for an excellent base between bare metal , and your primer filler ( which is for sand scratches and minor imperfections ) .
Depending on how deep the scratches are you may have to use the step down method to eleveate the deep scratches, start with 80 grit on a DA , then 150 , then 220 , depending on how smooth you want the metal ( smoother the better ) , This also helps on not having to spray so much primer filler later !
I will also say this , ALL Products shrink ( caused by evaporation of reducers and catylists/hardners ) in time , and may show those deep scratches later in the final finish , So try and get it ( the metal ) as smooth as possiable .

Spray

i would remove the scratches, not fill them. go to a welding shop and get some disc for working metal. 80,to 180. i've told people for years " whats there when you start, will be there when you finished " nothing worse than finishing the clear coat and having stuff swell up the next day. primers and bondo are not fix alls. a few hrs metal finishing will prevent a disaster down the road.

Stripping with a DA sander on grind with 36 grit has been an old standard in the body shop. 80 grit da as many scratches out as possible, Use what ever epoxy primmer you are use to for good adhesion, followed by a good 2K urethane primmer. 2 coats should be cool. Wait 3or4 days long board with 180 and reprime with the same 2K primmer 2coats. This is guaranteed to give you a quality surface for whatever you wish to use as a top coat. I've used this method on 100s of vehicles and never had a sanding scratch or grinder mark return.

M falconstein, I agree. Same process serves me well every time. The new urethane primers are pretty foolproof.

What is a good PPG filling primer ?

K-36 is good , I use NCP -271 Corrosion Resistant Primer for the past 5 years , Make damn sure you use a charcoal respirator as this stuff is BAD !
Both Sand easy, Both have excellet fast build qualities. can be water sanded .
Needs a gun with a big nozzle for better spray out.
NCP 271 mixes 3 parts product to 1 part catylist , can be reduced with DT reducers up to 10% for slower drying , as every 10 deg. over 78* lessens the pot life buy 10-20 minutes .

Spray

Spraytech,
I use the DPLF then the k36 or what order ?
Thanks

Yes toolow,
The DPFL is an Excellent foundation on which to spray your K-36 or NCP 271 ( both good products )

On a side note : you can scuff sand ( 150-220 grit) the DPLF after overnight dry and apply your body filler right over the top , as reccomended by PPG .
Then you can spray your K-36 over that too .
I make my body men send me their palstic work in 180 as this helps in not having to spray as many coats of primer (NCP-271) over the work , and it blocks quicker and easier . Plus most OEM paint manufacturers are now recommending finer grits on finish work !
Spray

PPGs Omni has a very good 2K primer, Dupont"s Nason 2K primer are very affordable and do not need reduced to be sprayed with HVLP 1.4 fluid tip. Make sure surface prep is good and you use a quality epoxy or wash primer basecoat under your primer surfacer. This stuff has very little pot life so be ready to spray before mixing and follow the direction. Some coatings don't have instructions on the product can themselves, so ask for product instructions. Good luck with your project, this stuff is easy to use and is very forgiving.

I watched a cabinet maker refinish old furniture. I tried his technique and it works. I used a good 4 inch putty or drywall knife and sharpened it razor sharp on a belt sander then finish it with 220 paper on the cast iron top of my table saw. I hold the knife about 90 degrees to the surface and scrape. adjust the angle and presssure until it flakes off as you scrape. three layers came off easy. be careful with the sharp corners of the knife. mabe round them a bit. when 95 % of the paint is off i used aircraft stripper then washed it off with my 3500-psi pressure washer. sanding was minimal.

dont kid your self you can t hide36to 60 grit scratches for very long i like to go to 80 on steel with a d.a and filler 180 to220 this will work i have seen all the hi fill primers will sink put some in a glass jar and see what happens when it drys the less marks the better the old way to strip paint off was to rip the paint off with 36 on a sander if you stop be for you hit the steel you still will have some scratch and this will now be a low spot i have done a lot of older car that where strip like this and the steel ends up beening rip up from running 36 on the steel you can try to sand it down with 80 on d.a .i go over it with a body file to get it straight and use lite coat of black paint is makes the scratches jump out and you can see the low spots along block with 80 on it can help to if you can not get it back you will have to put a thin coat of filler on it .this is much better then pling primer on it when it need to be filled in the fist places .I do not use any thing to strip a car with that will hurt the metal .steel scrapers knives.a hatchet razor blades. plastic filler spreaders i use when using air crarft type stripers and some thinner and a some red scotch-brite hand pads i have strip cars this way and it work very good