Does anyone know what the best thing to put on body filler so it doesnt show through paint?Also what kind of primer should be my last coat primer and does it get wet sanded?

 

I put on a 2k primer once I have sanded down the filler. Then I apply a flat black paint on the primer (just a light coat or mist) and then block sand the area to see if I have any low spots

 

thanks for the info

 

First you need to define "showing thru". Do you mean that you can still see the area where the body filler was applied because of a difference in texture, sanding scratches or the edges not feathering, or do you mean bleed thru where the primer is being discolored?
For the former, the problem is application technique and proper materials.
For the latter it's usually caused by old hardener that has deteriorated. If the hardener is runny, toss it and buy a new tube.
The problem with show thru is improper application/sanding or at the wrong time plus not using a surfacer putty to get an invisible feather edge. First you must carry the putty well beyond the dent (I'll use dent as term for any area you are puttying). Find the edges of the dent with a metal yardstick held on edge against the panel. Find where the yardstick lays against the panel and where it is indented. Mark the edge with a sharpie. If all the paint has alreay been removed you can also find the edge by going over the area with a "longboard" sanding board with 80 grit paper. The low area will be duller than the surrounding shiny sanded metal. Be sure to apply putty at least a couple inches beyond the dent margin for feathering purposes. Use a long board or sanding block that is longer than the longest dimension of the filled area and break down the putty with 40 grit no load paper. The putty should sand to a powder without too much effort. If it clogs the paper, wait until it cures a little longer. If it's hard to sand without pressure on the board (use only enough pressure to hold the paper tight against the panel, DON'T press hard!) you waited a little too long. No harm done, it's just going to take longer to sand down, have patience! Always hold the board parallel to the ground or long dimension of the panel with both hands, but move it in a diagonal direction. Alternate diagonals every few strokes. Only sand with the 40 grit until you have knocked down the high spots and cut thru the skin of the putty. Switch to 80 grit on the longboard and use the same diagonal stokes to shape down the putty until it is level with the surrounding area and you have feathered the edges back to where you had previously located the edges of the dent. There should only be bare metal surrounding the area, and no hard line or edge around the putty. Examine the patch carefully looking for low spots, scrapes or hard edges. Wipe the puttied area with a clean rag wet with denatured alchohol. Mark any defects with the sharpie, and apply another coat of putty to those areas. Press hard a thin coat of putty into the area first to wet the surface to be sure the next coat bonds then apply however much is needed to fix the defect allowing a little for sanding and shaping and carrying it beyond the defect for feathering purposes, try to scrape the edges to a feather with the applicator to give you a nead start. Break down this coat with the 80 grit on the long board, concentrating on the freshly puttied area so as to not oversand the previously coated area. Avoid the temptation to use a small block or paper around your fingers for sanding the putty, You'll surely sand the edges lower than the surrounding metal, which will show thru any finish. After fixing all the defects and blending in the repair, you are ready for the final step, go over the entire patch with a clean rag and alchohol, then apply a skim coat of a catalyzed polyester surfacing putty I use Evercoat Eurosoft in the green can. It a thinner material than the filler putty and will fill any pinholes, sanding scratches and feather all the edges. You only want a very thin coat, this is not for shaping. Let it harden a little longer than the putty then sand the entire area with 100 grit on the long board, just enough to knock down any lumps or ridges from the applicator and give the panel an even sandpaper finish. Wash the panel once more then examine carefully for any defects at all. Holding a strong light so it is close to the surface and skimming it across it will show any defects, Repair any defects with the surfacer putty as before, until you have a perfect repair. NOW you are ready for primer. Use the system of primers recommended by your chosen paint manufacturer. Typically that will be a coat of etching primer then a catalyzied high build primer, or a direct to metal high build primer. The high build primer should be block sanded with the longboard and 240 paper dry using a guide coat to pick out any low spots. Depending on how low they should be filled with the surfacer putty or a couple more spot coats of high build primer. Once you have a perfectly smooth primer coat, shoot a coat of primer sealer and wet sand with 400 paper being careful not to sand thru, wet sanding cuts VERY fast! You are now ready to apply a super paint job!
#1 mistake is to rush thru the putty and sanding. Have patience, the rest of the finish is only as good as the base. #2 is not using a large enough or no sanding block. The larger the block the flatter and smoother the finish will be. The dead givaway of a patch is the ripples left by improper sanding.

 

Wow, Ax! Excellent description!! Exactly how I would do it. Of course, almost all of my body work has been with lead, but I think my leading days are over - plastic for me! But you can't go wrong with your technique. Probably the most important, is "Avoid the temptation to use a small block or paper around your fingers for sanding the putty, You'll surely sand the edges lower than the surrounding metal, which will show thru any finish." I have seen more excellent jobs, ruined because of poor hand-sanding technique, than any other cause. Understanding what you are trying to accomplish, will go a long way towards a great finished product.

My hat's off to you, my man!

R

R

 

Thanks, fortunately for our health, plastic fillers have become as good as or better than lead, and much much safer.

 

thanks for the advise.

 

Not trying to hi-jack but who makes the plastic fillers, I'm guessing that you are not talking about epoxy body filler are you. Do these plastic fillers work as well for filling seams?

I do like the in depth discussion on filler, prep and paint...Thanks Ax I printed it off for later reference.

 

Most body fillers are polyester rather than epoxy. Easy to tell the difference, epoxies need to be mixed resin and hardener in very specific ratios typically 1:1 or 2:1. Hardening time is determined by chemistry. Polyesters come with a big can of resin and a little tube of cream hardener. Mixing instructions are much less precise, typically something like: to a puddle of resin ~4" in diameter add a 1" ribbon of hardener. Hardening time can vary with amount of hardener used, or temperature.
I prefer Evercoat brand products. I use their Rage Gold or Rage Extreme for filler and Eurosoft for surfacer putty, but they have a full line of products (almost too many, hard to pick). Their website
http://www.evercoat.com/productCategory.aspx?cat=2
Has details on everything they make and excellent videos you can watch online or download. Only watch online if you have a very fast connection they are fairly long.
You can buy their fillers at most good body shop supply houses, but it is much more economical to buy online. I buy the filler in gallon size and the surfacer in quarts. It will keep if you keep the resin can sealed and the hardener cool. If the hardener get runny, throw it away and buy another tube, it's inexpensive. You can also mix together the filler putty and surfacer putty to get an inbetween consistency, or add "honey" if the filler starts getting stiff in the can (somehow that doesn't sound quite right...)