On 01/20/98 Mike Robson wrote:
<<<<<I tend to agree that 80 grit is too coarse for the final sanding before
paint but something rougher than 400 is needed for an initial sanding
when youre cutting through 2-3 layers of paint, surface rust, bondo,
birdshit ,snot and the like
When my 72 got paint (shitty maaco paint FWIW) a couple of years ago i
made the mistake of only going with 400, the result was ok but my GT
finished with 600 is a lot better!
I wondered if anyone in the know could review what im doing now and let
me know if im headed for a major cock up.
At present the 69 is getting its first (dry) sanding (of all the
aforementioned substances) im using very common or garden "medium" emery
cloth from Sears which is cheap and great for this purpose - provided
there is no metalwork needed (which i cant do- i failed metalwork at
school for making a bent screwdriver) i will skim bondo and spot prime
where needed and do another medium run - then 320, then 400. with odd
spot primes as necessary - I figure to get the car fully primed
professionally (for my spraying ability - see "metalwork" above) then let
the pro sand the primer with 600 and shoot the topcoats (id be letting
him do the sanding cos i doubt he wants me sanding the thing in his shop-
plus hes only open when im at work!)
My aim is to have a decent, not concours finish - its not a ground-up
rebuild but a car that will get a lot of daily use - hence my sudden
uncertainty - hehe
mike robson>>>>>>>>>
Mike,
You're right, your initial sanding of the car should be a coarse grit like 80
to 120 grit to remove the unwanted surface quickly. Once you have removed
the ugly stuff, you then take care of the dings and blemishes, or in some
cases dents and rust holes. Most paint systems use a sealer prior to this.
Use a polyester filler like Bondo because it will not shrink like a laquer
filler. Laquer filler is okay for minute scratches and dings. You can then
block sand the filler with a coarse sandpaper to start, then go to a finer
grit like maybe 240 to smooth, feather and shape.
Once you are ready for the sandable primer you will want to use a grit in the
240 range, using a guide coat (usually a contrasting color-check Eastwood) to
ensure that your surface is free of defects. Once you feel certain that you
have repaired
all the defects then you can spray your last coat of sandable primer and
finish by wet sanding with 400 grit. I use a guide coat just prior to the
finish sanding also because there are always more small defects that will show
up, and believe me, they will show up after you paint.
I did the finish sanding on my MGA with 400 grit because that is what PPG
recommended. Anything finer that 400 grit can cause poor adhesion so you need
to be careful. I was real happy with the results without going any finer than
400 grit and you won't find any sanding scratches on my car. As always talk
to your paint rep. A lot of times when you see sanding marks after a finished
paint job, it is because the final sanding job was not carried out properly
and the sandpaper marks from the earlier stages have not been removed
sufficiently.
For an older car with small dings and imperfections on the surface you might
want to use a high build sandable primer. These primers spray on thicker and
fill in the dings and scratches so when you remove the build up, the
imperfections are filled in.
These are just some of the things I've learned by doing my own
cars....sometimes the hard way!!
Scott Helms
http://members.aol.com/Trmgafun/index.html
1958 MGA
1957 BN4
Be sure to visit the British Car Week page at:
http://members.aol.com/Trmgafun/britishcarweek.html
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