mgs
[Top] [All Lists]

Paint misconceptions

To: mgs@autox.team.net
Subject: Paint misconceptions
From: Mike Duvall <duvallcom@sbcglobal.net>
Date: Fri, 14 Nov 2003 15:18:11 -0600
On Nov 14, 2003, at 1:04 PM, owner-mgs-digest@autox.team.net () wrote:

> I was told that the paint was dry enough to shoot over within 
> 15minutes.
> For the best possible finish you need to spray a coat, wet sand, and 
> repeat
> for both color and clear.  This will take days, and is probably over 
> the top
> for your needs.  After you finish you need to wait 30 days or more 
> before
> waxing or using pressurized car washes.  I read once that if one coat 
> of
> paint takes an hour to cure, two coats will take 100 hours since the 
> bottom
> coat is not open to fresh air.

this advice is outdated.  Modern paints don't need sanding between 
coats and never, never sand the color coat of a two stage system. You 
can sand a clear coat but you do not need to unless you have a problem 
to fix. Modern paints dry with chemical additives and are designed to 
be much simpler to apply and require much less sanding which is why 
shops put up with the safety issues. Only sand lacquers between  coats, 
sometimes urethane and never sand enamels.

PPG has all the documentation for each product they sell (I'm sure 
other brands work well but I'm not familiar with them. Napa sells a 
name brand which escapes me at the moment, and I learned on Dupont but 
they are not very big around here anymore).  It is great information 
and includes mixing, drying times, what you can spray over and so on.
http://www.ppg.com/cr-refinish/phase1/frmProductInfo.asp  will take you 
to all the info you need. (there site is a little frustrating because 
you need to be familiar with the products lines)   for the actual page 
of product spec sheets go to 
http://www.ppg.com/cr-refinish/phase1/frmFindProduct.asp

Under product information you can find a drop down menu of paint lines. 
You will want to find what line a local shop carries. If you want to 
easy repair look at single stage and don't clear coat - clear coating 
means any sprayed touch up will likely demand the entire panel be 
cleared again.  Omni AU MTK is a "value line" single stage urethane 2K 
(high gloss and build). Omni AE line has and acrylic enamel single 
stage called MAE that is an economical. urethane will give a slightly 
better look. It is nastier than enamel but both use hardners so you 
need a 3M vapor eye protection/vapor mask (particle masks are not good 
enough) or fresh air.  Omni also has 2 stage paints as well.

Chemically dried paints do not have the same problems with air drying. 
You can spray MTK acrylic urethane and wait "16 hours hours at 70 
degrees to polish and put in service"  It "flashes off" for a second 
coat after 10 minutes.  You can clear coat a single stage paint after 4 
hours.

These new paints demand a clean undersurface. Use ammonia in the 
sanding water and wipe every nook and cranny with a wax and grease 
remover ( Keystone sells cheaper cleaners and primers and the local 
keystone dealer sells PPG). The trouble with sealers is they have poor 
adhesion and your surface chips easily. Without a sealer, any recent 
paints, especially lacquers bubbles the paint. I had this trouble with 
an MGA. I just used a pin to pop the bubble and it would shrink right 
down and you would never see it.

Sand the car and sand & repair any damage. For repairs on bare metal, 
spray with Omni MP 170 Epoxy primer and then use 2K (high build) 
urethane primer to fill the scratches. the new urethane primers can use 
a hardener and dry very quickly. (you can sand with 150 and then 
followup with 220 to get a great surface) Spray the entire car with 
epoxy primer to fill any sanding marks and ensure good adhesion. then 
use MP 213 sealer if you want. Finally spray the whole car. Here is the 
great thing. no sanding is needed and you can let epoxy primer dry for 
30 minutes then add the next coat of sealer or finish. Sealer can be 
topcoated after 15 minutes with no sanding. The bad part is epoxy 
primer must be coated within 3 days and sealer must be topcoated within 
24 hours. If you wait, the topcoat won't adhere. If you wait over the 
time, you must scuff and recoat which costs you money.  After your all 
done, you can sand urethane with 800 to 2000 paper and then Maguires 
polish for a really great polished finish. You can't sand enamels.

Mike




<Prev in Thread] Current Thread [Next in Thread>
  • Paint misconceptions, Mike Duvall <=