Defroster Grid Repair Weirdness

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   So only one of my grids actually worked. The rest had either small nicks or pretty large pieces missing. Those Permatex repair kits are small and expensive but I seemed to get everything repaired last summer. Went over it with a multimeter and a bright light once I was done and couldn't find any more breaks.

Fast forward to winter and no, there's still non-functioning grids. Worse yet some of the repaired grids are unevenly heating, leaving small bulls-eye hotspots while the rest of the horizontal grid remains cold.

Did I apply an uneven layer of grid repair or are there more breaks I didn't catch?

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MIPS Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Nut Joined: Mar/11/2019 Location: Kamloops, BC Status: Offline Points: 347	Post Options Post Reply Quote MIPS Report Post Thanks(0) Quote Reply Topic: Defroster Grid Repair Weirdness Posted: Jan/14/2021 at 12:28pm
	So only one of my grids actually worked. The rest had either small nicks or pretty large pieces missing. Those Permatex repair kits are small and expensive but I seemed to get everything repaired last summer. Went over it with a multimeter and a bright light once I was done and couldn't find any more breaks. Fast forward to winter and no, there's still non-functioning grids. Worse yet some of the repaired grids are unevenly heating, leaving small bulls-eye hotspots while the rest of the horizontal grid remains cold. Did I apply an uneven layer of grid repair or are there more breaks I didn't catch?

tyrodtom Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Sep/14/2007 Location: Virginia Status: Offline Points: 6214	Post Options Post Reply Quote tyrodtom Report Post Thanks(0) Quote Reply Posted: Jan/14/2021 at 10:14pm
	I've used that kind of repair before. After several tries I found the best way to do it is take the hatch off, and lay it flat on some saw horses. Where it's upside down it doesn't adhere very well, let gravity help you. I've tried it on stationary rear windows and had results about like what you did.
	66 American SW, 66 American 2dr, 82 J10, 70 Hornet, Pound, Va.

tomj Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Jan/27/2010 Location: earth Status: Offline Points: 7555	Post Options Post Reply Quote tomj Report Post Thanks(0) Quote Reply Posted: Jan/14/2021 at 11:10pm
	Is the repair material itself resistive, and therefore heating? Or does it just bridge the gaps, connecting the heating sections? My point is, if the repair stuff is not resistive and heat-producing, you're connecting a number of "heating resistors" together, each strip will have a lower resistance, will draw more current and yes, hot and cold spots. Also if different strips/runs have differing amounts of gaps, and you bridge those gaps, some strips will draw more current than the others, and depending on how it's wired (all in parallel, or series, or combinations of series-parallel) it could make for a very confusing pattern.
	1960 Rambler Super two-door wagon, OHV auto 1961 Roadster American, 195.6 OHV, T5 http://www.ramblerLore.com

MIPS Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Nut Joined: Mar/11/2019 Location: Kamloops, BC Status: Offline Points: 347	Post Options Post Reply Quote MIPS Report Post Thanks(0) Quote Reply Posted: Jan/15/2021 at 3:36am
	The repair paint that Permatex sells is pretty much a mixture of fine metal particles and carbon mixed with an adhesive and what smells like acetone to make it brushable. A tiny bottle about half the size of your pinkie finger costs around $50CAD. I called the auto glass shop and it's the same thing they use so you can't get it in larger bottles. It's designed to replicate the original grid wen brushed on. The documentation does not say anything about thermal hotspots of put on too thick or too thin. The guys over at Cold War Motors recently tried it and seemingly had excellent results. Edited by MIPS - Jan/15/2021 at 3:57am

tyrodtom Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Sep/14/2007 Location: Virginia Status: Offline Points: 6214	Post Options Post Reply Quote tyrodtom Report Post Thanks(0) Quote Reply Posted: Jan/16/2021 at 9:35am
	I've done this 5 or 6 times. Every successful time I had the window either out, of if a hatch off the car, and laying on a set of saw horses. You can control the mixture and thickness better from above and gravity helps level it. I also took a fine 3M pad and lightly went over the 2 areas I was trying to join. Plus when it had dried, If I had any high areas I sanded it down to as close to the same thickness as the original strip as I could. I was going for a undetectable repair from either inside or outside, I got that plus the grid seemed to work evenly. The one that didn't work too well was the first one, a hatch left on the car. I took it off and redone it. But since I couldn't get all my first repair off, the second attempt worked a little better , but still not to my satisfaction. From then on if I couldn't work on the window flat, I didn't even attempt the repair.
	66 American SW, 66 American 2dr, 82 J10, 70 Hornet, Pound, Va.

Heavy 488 Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Apr/27/2019 Location: In the Status: Offline Points: 3557	Post Options Post Reply Quote Heavy 488 Report Post Thanks(0) Quote Reply Posted: Jan/16/2021 at 10:19am
	Peel it all off and replace the grid. Much less cost and labor than trying to duplicate a decal that's microns thick with a brush.

Steve_P Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Charter Member Joined: Jun/28/2007 Status: Offline Points: 3808	Post Options Post Reply Quote Steve_P Report Post Thanks(0) Quote Reply Posted: Jan/16/2021 at 1:47pm
	not that it helps, but the original grid is a very expensive paint containing silver that is silkscreened on and then baked in an oven to dry.

Heavy 488 Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Apr/27/2019 Location: In the Status: Offline Points: 3557	Post Options Post Reply Quote Heavy 488 Report Post Thanks(0) Quote Reply Posted: Jan/16/2021 at 5:36pm
	I've had the grid on an eagle wagon pop in a few places. Blew a hole a few holes in the lines and lifted the edge. Sometimes you have to stop and look objectively at how many patches to realize, yes its junk. Frostfighter.com has grid kits I've used these successfully on a truck cap.

Heavy 488 Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Apr/27/2019 Location: In the Status: Offline Points: 3557	Post Options Post Reply Quote Heavy 488 Report Post Thanks(0) Quote Reply Posted: Jan/16/2021 at 5:43pm
	Whatever you decide, good luck