C3:Spraying inside frame

[Steve L.]

I tried out the 3M Spray wand 8998 to do the inside of the frame.

This wand is about a 4 ft stiff plastic house with a nozzle on the end that sprays forwards and to both sides. It has a plastic fitting on the other end to attach to a Shultz underbody oil gun for rust proofing.

In general it did a nice job with POR15 but it doesn't work without the following modifications:

Turn up the pressure a lot - the wand says max 45psi, but I ran it at 100psi at the tank with a 20 ft hose, so it lost pressure along the way but I don't know what it was at the wand.

Cut the wand length in half, and discard the threaded end. Re-insert the threaded adapter.

Thin down the POR15 a lot. POR15 site says a max thinning of 5%, but I had to thin it down way more than that. I don't know what thinning more than 5% actually does?

That got it going decently.

As will as the Shultz gun, I also had to buy a can of what looks like auto transmission underspray, just to get the can.

The wand is about $13

Steve L.
73 coupe since new

[Chuck S.]

Re: C3:Spraying inside frame

Steve, I had similar results using clear vinyl tubing from Home Depot.

I first tried smaller diameter tubing with the Schutz nozzle, then an improvised brass tube nozzle with drilled holes. Like you, I eventually increased the pressure to about 90-100 psi; Frustration and impatience can make one ignore common sense...that pressure level is probably NOT A GOOD IDEA with the Schutz gun "tin-can" screw-on reservoir.

I then tried larger diameter tubing (3/8") with a nozzle, then reduced the length by about half, and still found the pressure drop in each case was just too much to develop any kind of spray.

I then tried reducing the POR15 to improve the spray...I found it required about 100% reduction to get any kind of result, and that after discarding the nozzle entirely. The spray was a loose random "splatter" pattern from the tube end produced by discrete droplets of POR15 blown off the walls of the tube. With enough dwell time, you could probably get 100% coverage.

I decided that POR15 reduced 100% was better than nothing, but I wonder if it's not little more than a black stain.

[Steve L.]

Re: C3:Spraying inside frame

Chuck,
I put together a cardboard tube about 2 ft long and about the tube size of the frame and sprayed inside that to see what coverage I'm getting. I need about a 10 second dwell time. With that it covers fairly well.

Although the tank pressure is 100psi, I must be losing about 20 psi in the hose.

I can tell if the POR15 is too thick because I can feel and hear it bubbling in the Shutz tank.

The 3M wand doesn't have small round holes as you may have made with your improvised brass nozzle. It has 2 large slots on the sides and a large hole at the tip facing forwards.

I can tell if the spraying is decent because there is all kinds of spray coming out of the frame holes to the point that I wear a paint mask.

Any idea why POR15 web sites says you can reduce by only 5%?

Steve L.
73 coupe since new

[Chuck S.]

Re: C3:Spraying inside frame

The reason for the bubbling is the Schutz gun doesn't develop enough siphon force to pull the viscous material up the feed tube...the material is constantly breaking the suction and falling back down the tube.

If you've ever tried spraying oil based house paint with an automotive spray gun, it's a similar deal...you have to reduce the paint until it will barely cover, and then you waste most of it in overspray. If the Schutz gun were gravity fed, it would probably work...maybe one of those throwaway gravity fed Chinese paint guns would work better.

The reason they don't want you reducing it is to avoid compromising its corrosion resistant qualities...it's really designed to be brushed on. They intend for it to go on heavy-bodied, and cure hard and glossy. If you've ever dripped or spilled POR15 where you didn't want it, you know that once it cures, it is virtually impossible to remove...POR15's adhesion ranks right up there with powdercoat IMO. At 100% reduction, I expect it has lost most of it's legendary corrosion resistance, but I suppose it may still be better than nothing.

[Alan S.]

Re: C3:Spraying inside frame

Steve and Chuck,
On a 68-72 type frame that was in very good condition and was NOT dipped to remove the surface rust, how important is it to treat the inside? Thanks!
Regards,
Alan

[Chuck S.]

Re: C3:Spraying inside frame

Steve and Chuck,
On a 68-72 type frame that was in very good condition and was NOT dipped to remove the surface rust, how important is it to treat the inside? Thanks!
Regards,
Alan

I personally wouldn't dip a frame for that reason. Dipping a frame insures that ALL the protective coating and rust is removed...the bad news is you are left with a virgin steel surface, ready to rust both inside and out. The interior of the frame will be more vulnerable to rust than at any time in it's life. If you dip a frame, you have no alternative but to coat the interior, and confirm that you have 100% coverage inside.

As for attempting to coat the interior of a "no-rust" frame after sand blasting, I believe that falls into the category of "warm feeling" unless you have some kind of fiberoptic equipment to inspect and confirm coverage. You can design a technique that would seem to give full coverage, but you can never be sure without visual inspection.

It appears to me that the real destructive frame rust occurs at the kickup area by rusting from the inside out. Even with a frame that has no indicated rust damage, you may have rust in that area that is progressing much slower that it does in the east and midwest...an attempt at coating the interior is worthwhile in my opinion.

I instructed the individual sand blasting my frame to get as far into the interior of the frame as far as he could, knowing that he wasn't going to get very far. Even so, I thought I could devise a pretty good method for interior coverage, and made the effort to coat the interior. I didn't use the vinyl tubing described above for that job...as I remember, it was some combination of the wand sections supplied with the Schutz gun. I recently used vinyl tubing in an attempt to "rust-proof" my original radiator support.

[Steve L.]

Re: C3:Spraying inside frame

There was absolutely nothing left of any protective coating on my 73 frame. On some of the pieces I cut out, it rusted almost as much from the inside as it did from the outside.

I think it's necessary to attempt to get at the inside of the frame.

Chuck is right, there is no way of actually confirming that everything inside a frame is covered unless you get a fiberoptic viewer or one of those Home Depot Snake cameras(around $200) to really check it out.

BTW, I tried other ways of painting the inside of the frame... brushes on end of sticks, or flexable drain snake cleaners and various shapes of sponges home made and from paint supplies. Nothing works very well except the Schutz gun.

Also, the metal on these 30 yr frames doesn't have the same firmness as new metal. I noticed that I have to back off on the welder with the original frame or I'll blow right thru' it where as with new pieces, I can crank it up.

Steve L.
73 coupe since new

[Michael L.]

Re: C3:Spraying inside frame

Hi All
I have heard that there is a place in Texas that can dip your frame then dip it in a primer bath. I think it is in the Houston area I will try to find out if anyone has any interest
Michael

[John H.]

Re: C3:Spraying inside frame

When I did my '57 twelve years ago, I took the frame to an outfit in Romulus, Michigan that acid-dipped it, rinsed it, hot-phosphated it, then E-coated it (electrophoretic dip-prime) and baked it (the ultimate anti-corrosion paint system). I think they went out of business about five years ago.

[Stephen L.]

Re: C3:Spraying inside frame

for other types of car where original appearance is less critical, folks hot dip galvanize the frame after dipping to strip everything - I have asked before and have been told that for NCRS purposes that would leave the frame surface different than when it left the factory (smoother?) - and with a thicker surface - is that the pervailing view? - other than thickness, would a paint application over the galvanization (word?) give you the correct "texture" for the frame? - thanks, stephen