plug welding floor pans (and other floor questions)

when plug welding (rosette welding) floor pan patches into place how big should the holes be, how for in from the edge and how far apart?
I made some patches today for the front floor and toe kick in the shoebox using the HF bead roller and a piece of angle iron for a break and I think they came out pretty good, I'll try and post some pics tomorrow.
I plan on using Rust Bullet or POR 15 or something like that. Does the seam sealer go under or on top of that stuff? I hear talk of two part seam sealer being best, what is it called and where do I get it? I want to take the firewall insulation out when welding and to smooth the firewall, can I just replace it with dynamat, or what is good stuff to use for floor and firewall insulation?

 

I like 5/16" holes for plugs. Far enough off the edges so that your heat mark(the blue circle) doesn't go all the way to the edge. I usually space the welds at 1&1/2" Again, as long as the heat markes don't over lap your good to go. Duramix & Fusor are two brands of two part seam sealer that I like. You can get them at any automotive paint store. The last Duramix rep I talked to said to go directly over bare metal, but the package, and everything else I've read says to use epoxy primer first. Don't use them directly over self etch prime, aparently they don't like the acid in the etch prime.
I don't use por 15 or rust bullet, so your on your own there. I usally shoot floors & the inside of firewalls with Morton pick up bed linner, over epoxy. (been using self etch, then epoxy lately, with good results) I've used Q pads(same as dynamat?) on the firewall, as well as several types of insulation.

 

5/16, one inch apart. I'd put down the seam sealer first, then whatever else over that.

 

I usually go with 5/16", two or three inches apart, with about a 1/4" inch from the edge of the hole to the edge of the panel. Etch, primer, then seam-sealer. I use the IES and SIM two-part self-leveling, or IES inter-gray(I think is the name) seam-sealer. Then under-coat it with a rubberized under-coating, also IES. POR-15 over rust also works great. Dyna-mat is good, but there are tons of similar, less expensive insulation mats out there.

 

Good advice so far. One thing you want to be sure to do is de-burr the holes befor you clamp in place. You want a no gap fit befor welding. It keeps the wrinkles out.
The Wizzard

 

Dan, two things I forgot in my first post.
Spaceing from the edge; Center your line of holes in the overlap (1&1/2" overlap=holes centered 3/4" in from edge. 1" overlap= holes centered 1/2" in from edge.)
Also use weld thru primer on the lap(inbetween the two pieces of metal)