Micro-cracking and plastic repair

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NWMO
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Micro-cracking and plastic repair

Post by NWMO » Thu Dec 26, 2019 12:10 pm

Hey all,

I have the windshield washer fluid/radiator overflow safely removed, but wanted to know if there is some “protection” provided by coating with polyurethane? I’m just looking to support the micro-cracks, not repair anything structural.

There is the lip of a cap that has cracked, I figured to use gorilla glue for the repair.
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rer233
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My tercel:: Multiple

Re: Micro-cracking and plastic repair

Post by rer233 » Fri Dec 27, 2019 7:21 am

I've had good results with Flex Seal (comes in clear.)
if it aint there, there's a good chance it won't break!
83 SR5 Silver/Blue (Snowmobile/work beater)-totaled but drivable
85 SR5 Blue
88 SR5 White (the 'good' one)-not anymore-totaled
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Petros
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My tercel:: '84 Tercel4wd w/extensive mods
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Re: Micro-cracking and plastic repair

Post by Petros » Fri Dec 27, 2019 7:55 pm

there is a fix for that: use a high temp heat gun (porpane torch might work as well), and VERY carfully heat the damage plastic, circling the heat source and waving it back and forth. watch carefully the cracks, when they reach the point about to melt, it will recombine and than disappear. you have to have it right at the point just before it melts, so the danger is with a bit more heat it will melt.

this has the very strange effect of "renewing" the plastic, it chemically recombines. once it cools, it will be like new again, cracking and even the yellowing disappears. I have done this several times, works great. most important thing is to be patient, keep the heat source moving, and keep a careful eye on it. works on most thermoplastics. black abs plastic that has bleached grey-white in the sun, will return to shiny black again. it will make the bone or off white plastic trim that has turned yellow turn back into the original color.

You can even use this method to patch holes in brittle old plastic, not perfect but nearly so: you find a similar type of plastic and melt it over the spot. use a clean putty knife to blend and shape the new plastic into the old, getting it smooth and the texture to approximate the surface, and than let it cool. Done.

I fixed a black ABS plastic bumper cover on my dad's Volvo. it was all uneven gray-whitish and charcoal colored, with a few dents and cracks. it has kind of pebble grain finish on the surface. all the gray color gone as I went over the whole bumper, most of the dents came back up to profile, and the lone large crack I melted back together and smoothed with a putty knife and than used a rough piece of fabric to press a texture into the repaired surface. it nearly made the damage disappear.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
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garyfish
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My tercel:: 1985 Tercel SR5, stock; 1987 T4WD DLX wagon, manual tranny
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Re: Micro-cracking and plastic repair

Post by garyfish » Mon Dec 30, 2019 8:17 pm

I did a Search here on the Forum, and came up with a few relevant links on this topic:

viewtopic.php?f=7&t=8109

viewtopic.php?f=10&t=11235

viewtopic.php?f=9&t=13134&p=101203
1985 Tercel SR5 4WD wagon, 300K
1987 Tercel DLX 4WD wagon, 6-speed manual, 260K -- got this one running Jan. 2015 (had been sitting for 2 years); this has been my daily driver since 2016

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