Thinking about repainting my 914 and an interesting question was brought up by a friend of mine that has some paint and body experience.

Do you use sealer when painting over the original paint on the 914?

He said to always use sealer, but I was under the impression that if your original paint is good (just faded) you can spray over it with a sand down. Now there may be a few spots that I will take down to bare metal (a spot below the front window has a small bubble).

I usually use sealer. If there's some invisible problems with the substrate they will show up when you spray $30.00 worth of sealer, before you catalyze $500.00 worth of paint.
Sometimes on a small spot repair when I'm blending the color I'll skip the sealer and use blending clear instead to save some room to blend the color before I get to the edge of the panel so that the color looks good between panels. Use the sealer that the paint manufacturer recommends.

Two quick comments on using a sealer (like PPG's "DP").

It prevents any chemical reaction with prior paint on the car.

It also provides a uniform surface for the new paint, giving a more consistant result.

Wes

ALWAYS It's my living. If you don't you're asking fer trouble. May not go bad but you're much better off using a sealer coat. For best results seal, guide coat let dry for a day or 2 then wet block the selaer until you guide coat is gonw or you get totally disgusted with how wavy the car really is

Another PPG DP user.

Do you use the sealer before you apply your primer and then again after the car has been blocked and ready for color and clear?...or do use the sealer after the car has been primed, blocked and is ready for color?

My buddy doing show winning hot rods and customs always does.

Unless you have history with the previous paint job...even then, use sealer--it'not worth the risk. Paints and prep materials react differently with each other. As many have already stated, sealer provides a nice consistent surface to work with. If you have ever seen a cheap paint job by a shop...it may look OK at first, but as time passes you can often get shrinkage and then you begin to see all the swirls, sand marks, chips etc. Seal it.

I don't know what kind of finish you want but my suggestion would to be :

1: find out how many layers of paint are on the car. If the car has been painted more than 2 times I would block the whole car down to the first paint job, seal, do any body werk. ( by blocking the paint off you will be flattening your panels and also revealing high/low spots)

sand out to no less than 180 grit and re-seal, guide coat 2-3 coats of sealer, let flash between coats, and wet sand with no less than 400 grit. If you are shooting a metallic wet sand to 600 grit. The farther yo wet sand the better the results but 400 minimum for solids and 600 min. for metallics.

This is a fairly quick way that will give most people a good result. What I do at work is a completely different animal. I have been known to seal, block reseal a car as many as 6 times, blocking with finer grit each time and letting the car sit for months in btween layers to minimize shrinking. Final coat would sit for several months then be wet sanded one last time prior to base coat. Base, clear (2-3 coats), block clear with 1000 grit, RE-clear ( 2-3 MORE coats ) and wet sand that out to 3000 grit then buff. Ask me why our paint jobs cost so much............

When you say seal, sand, re-seal, etc are you using sealer only and not a primer (ie polyprime). Or do I seal then use a primer as my sanding coat?

Typically ( for me at least) a "primer" is the same as my sealer. I use Spies Hecker and the primer of theirs called Vario, can be shot as a "high build" by mixing it unreduced or it can be reduced and shot as a sealer. Usually a "sealer" coat is a thin coat used to seperate 2 layers of paint, however many companies "sealer" is good as a mild build primer to be wet sanded. Talk to the paint shop that sells the product you will be using. I am familiar with Spies, Dupont ( to some extent )and U-tech which is a very good low cost undercoat. I would still use Spies or Dupont as my color and clear over the lesser brands. PPG is good stuff to. Also know that a etch primer for bare metal is not to be sanded, only scuffed with a scotch brite pad if it sits for a while, etching primers have almost no build to them. There are exceptions to this as well. U-tech makes a "etching" primer ( E-380 )I have used that actually has a good build to it, but I have yet to see that paint after more than a year or two to know that it held up.

From bare metal :

1- etching primer
2- high build sealer
3- guide coat
4- block with 80-120 grit
5- work high/low spots
6- spot guide coat and reblock/rework until satisfied
7- RE-seal/ prime 2-3 coats
8- block out to desired grit or keep blocking and re prime-ing up in grit if you want an optimal finish
9- base
10- clear
11- block clear and buff

Again, keep in mind this is kind of a basic of the process for a nice but not high end finish. If starting with existing paint and not stripping bare skip the etching primer, it is not necessary unless you have a large area that is bare. Most primers ( non etching) will be fine on small ( fist sized) bare metal spots. Anything over fist sized I always spot etch first.

I think from what you have said you will want to take off a layer or 2 of paint, using a high build sealer coat the car 2-3 coats then block it. Again U-tech has a K2 sealer that has a very high build, and is great for seperating layers as well as having something to block afterwards.

Great information...thanks alot!