Is there some way besides welding to fill screw holes in the interior?

[Canonman67]

The subject line says it all. I've had some success with patching larger holes with leftover floor pan material overlapping from behind but when I tried to fill a few screw holes I just burned through even though the mig was set at the lowest setting. I also burned through when I attempted to buttweld a patch where the dome light used to be. Any ideas on what I'm doing wrong? I'm new to welding but I have managed to get my floor pans in without too much drama. It's the cab walls that seem to be giving me fits. Here's a shot of the dome light patch.

Any help would be appreciated.

[MAK]

Put a piece of copper behind the hole. You can pound a piece of scrap copper tube flat and it will work great. They also make magnetic copper backers but the magnets don't hold well unless you have a good smooth fault surface. I've found filling holes like this is about the easiest welding I've done and I am far from being an expert welder.
Butt welding thin material is tough, especially if it's already thinner because of rust. Here too, if you can use a copper backer behind the section where the two pieces come together it will make it much easier. Sometimes you can't get a piece positioned there but if you can it will help. Also has the added benefit of helping keep the pieces aligned.

[Canonman67]

I was wondering why the butt weld was so tough. I'm guessing the copper acts as a heat sink? If so that explains why the other patches I've done have worked out.

[1968-f250]

I was wondering why the butt weld was so tough. I'm guessing the copper acts as a heat sink? If so that explains why the other patches I've done have worked out.

From my experience the copper acts as a backer so you can start building up a weld puddle around the edges of the hole and then you can fill the rest in once you have solid metal to build off of. Without the copper there is no place for the weld to start if the metal is very weak so it will keep blowing through. It is definitely easier to butt weld and fill holes with the copper behind.

[tac]

This metal is thinner than the floor pans and requires a little more finesse. Short bursts, just enough to get penetration, let the red almost disappear then hit it again. keep doing this until the hole is filled. I don't see a lot of splatter so I would assume you are using a shielding gas and not using flux core.

[Canonman67]

Yes it is gas shielded. I'm thinking I'll take a small vacation from the welding and finish the floors so I can hang the pedals and put the steering column back in. Any ideas on filling screw holes? A lot of them aren't where I can get behind to back them.

[HIO Silver]

Is the patch the same gauge as the cab? If not, use very short bursts moving from thicker to thinner in quick fashion. Maybe your gaps are too big.

What wire gauge ya using? I use .023/.024 for body panels up to 0.125 thick. Beyond that, .030 wire.... it's nice having two MIG welders.

[zazoos]

How close is your gap on the patch piece. The closer the fit the better, it really makes a big difference. Also the copper backing when you have access is well worth the effort. To answer your initial question you could use fiberglass to fill holes, but welding is better.

[HIO Silver]

An alternative is to prep the hole and use automotive panel adhesive to apply a patch over the back. Then fill with non-shrinking filler.

... but nothing substitutes welding them shut because if done with exacting standards, filler isn't even needed.

[tac]

I have never tried this but I read somewhere that someone used a nail and pulled it through from behind. Hold the nail head up against the hole with pliers and tack around it. One suggestion is to never grind the weld flush until the weld is complete to prevent thinning already thin metal. I tack the perimeter about 1" apart and grind these down with the edge of a 3" cut off wheel just above the parent metal. Tack in between all of these, grind and repeat until there is no more seam. Then finish it off with a 2" or 3" ROLOC type grinding disc to get what is left of the welds flush. Also if the weld doesn't get penetration it will leave a hole when you grind it flush.

[Canonman67]

Since I plan to put a dome light back in I wanted to avoid using a bunch of filler. I plan on putting a cargo light in so I might put backer strips in then OR I'll cut what I've done out and start again. I haven't decided yet.
Before I started where there was a gap it wasn't more than a 1/16, for the most part the seams were tight. For my intial start I was stitching from the patch to the cab metal about 2 inches apart. The wire is .023, I checked when I started having problems.
I've seen the nail trick too, problem is I don't have access behind a lot of the screw holes to put anything back there. I'd like to paint the dash and kick panels before I put the steering column and pedal assembly back in. What about JB weld for the smaller ones? I've never used it so I have no idea if that would be suitable. Can it be painted? I'm thinking of holes no bigger than #10 screws.

[tac]

Epoxies are great but they need some surface area and you need to be down to the metal to get them to stick. Just filling the hole will with it doesn't give you enough surface for it to stick to unless you dimple the metal around the hole, then you have the possibility of rust creeping in but it will take awhile because it doesn't see a lot of moisture there. The best way to glue a patch would be get from the backside. Remove the rust and glue a small patch over the hole using 2 part panel adhesive.

[Canonman67]

Thank you everyone for all the help. I'm officially out of ideas for the holes I can't get behind.
At least the ones on the dash I'll be able to glue.
If anyone else has suggestions for the holes I can't access from behind I'm all ears.
Again, THANK YOU ALL for every suggestion and idea.

[6Delta]

Look into "old School" lead repairs. I have repaired larger holes than you have with an old time soldering iron and blow torch. You get the iron red hot and place it into the hole. Then when everything is the right temp the lead will flow into and over the hole when you twist and pull it away. Old tire weights can be melted down to get the lead from. Do some on-line research and yo should be able to find something.
Good luck.

[Busboy]

At this point I think I would look for a larger dome light from a later model truck that would completely cover the area.