Repairing plastic panels? (interior)

[SteveInOakland]

Several of mine have cracks that are inconspicuous when the panel is not bent; maybe even invisible. But I haven't had much luck in getting a repair to stick to the back side.

Ideally I'd just be applying some thin material across the back that would keep the panel from flexing at the crack, and discourage spreading.

Scratching up the back of the panel with sandpaper and then applying epoxy and a patch -- the patch came off. Shoe/upholstery-type stuff (rubber-cement-style) didn't work well either.

Would appreciate suggestions on both an adhesive and a material to use as a patch.

Duct tape is the best I've done so far.

Fiberglass???

Many thanks,

Steve.

[ktm]

Fiberglas will work. Two of my large side panels were repaired this way by a previous owner sometime ago. You can not tell from the front that they are cracked unless you get up close and know where to look.

I did not know they were patched until I took all of the panels off while cleaning the car after purchasing it. They held up fine to the slight tugging that ensued trying to get them free.

[LEB]

I've been using 5 minute epoxy and glass cloth. Seems to work.

Larry

[BD240Z]

I have a number of small cracks around the mounting holes on mine as well. I've used JB Weld in the past on similiar panels with sucess and it's my plan to repair the 240Z panels the same way. I'll do just like you've said, scuff the backside of the panel with some 60 grit sandpaper then apply the JB Weld.

I think fibreglass resin with some mat or cloth would definately be strong enough, getting it to stick to the plastic might be the challenge.

Maybe someone else has a slick method they've been sucessful with.

Good luck with your car!

Bruce

[EScanlon]

JB Weld with either Cheese cloth, or steal one of your wife's knee-highs and use that. The key being to use a porous enough cloth that the JBW will flow through the strand, but not so porous that you don't benefit from the cloth. T-Shirt material is almost too tight a weave, but if you stretch it out, might work if you thoroughly saturate it with the JBW.

I've even replaced missing chunks out of the corners and area surrounding the rivet holes using this technique.

But the big trick isn't in SANDING the back of the plastic, but rather GOUGING it.

You literally want individual and deep scratches that you then pressure squeeze the JB Weld into, so that it gets down to the bottom of the scratch. I've even gone so far as to take a razor blade and cut into the plastic at opposite angles to each cut on opposite sides of the repair to ensure that the JBW will not crack off. You're not looking to cut through the plastic, you just want a deep enough scratch that the JBW will have both depth and thickness within the scratch.

Fiberglass and fiberglass resin will work, but can be a bear to get it bubble free and to stick properly. Also, if you're not careful, the heat of the reaction can cause problems if you over-catalyze.

I've tried heat welding the plastic as well, but by the time you've heated it enough to accept the repair material, you have it hot enough for it to lose the grain on the visible side.

E¢

[madkaw]

I covered the Back of all my panels with fiberglass cloth and resin.I sanded the back of the panels to roughen it up and then cleaned the panels squeaky clean.I wiped down the panels with a wax and grease prep and let dry thoroughly then applied the fiberglass. It seemed to stick well and I the panel feels indestructable but flexable. I intend on fabric covering the panel so I wanted something substantial to stretch material over but the fiberglass will make a great fix.

[SteveInOakland]

Appreciate all the excellent suggestions. This group never ceases to amaze me, both the knowledge and the generosity in sharing it.

Enrique, are you opposed to using fiberglass cloth with JB Weld? Somehow it seems like cheesecloth would have too much give in it? If not fiberglass cloth, what about some of that non-metallic, nylon-type screen mesh used for window screens?

Thanks again,

Steve

[Jackhammer]

Use Dyna Mat, Fat Mat, R-Blox, any of the foil backed sound deadening material that is self adhesive. It can be easily cut with a razor knife, molds /conforms to the back of the panel. It will strengthen, keep the panel from cracking further not to mention the sound deadening properties.

I have used it throughout my interior and will be doing it to the interior panels this coming week when the rest of the interior goes in.

My .02

[EScanlon]

Use Dyna Mat, Fat Mat, R-Blox, any of the foil backed sound deadening material that is self adhesive. It can be easily cut with a razor knife, molds /conforms to the back of the panel. It will strengthen, keep the panel from cracking further not to mention the sound deadening properties.

I have used it throughout my interior and will be doing it to the interior panels this coming week when the rest of the interior goes in.

My .02

One thing to be real careful of though, you've not REPAIRED the panel, you just used a different type of duct tape, but don't be fooled, it is in fact, just DUCT TAPE.

Not trying to jump on you, but once the plastic has lost that strength it has from the way it was molded, and you have a crack....in my experience in plastics (+15 years) that crack is just going to continue to grow and grow...until you mend it. The tape on the back, may prolong the need to replace it, but if there is ANY type of vibration, and you've not glued the edges to each other, they'll chafe. Chafing will result in the plastic literally sanding itself more.

You need to at least put some sort of glue in that crack. It is difficult to find a glue that works, that's the main reason for this post being such a lively re-ocurring topic, as technologies change and grow, but the tape idea won't cut it.

Also don't forget that the foil backed sound deadening panels require a minimum thickness to work properly. As a result, you'll need to ensure that you don't inadvertenly put some on the back of the plastic at a point that it will be actually causing stress on the rivet holes by pressing up against the steel supports.

It CAN be done, and done well it is an excellent idea...but it isn't a fix all for broken / cracked plastic.

Just my 2¢

E

[EScanlon]

...snip...are you opposed to using fiberglass cloth with JB Weld? Somehow it seems like cheesecloth would have too much give in it? If not fiberglass cloth, what about some of that non-metallic, nylon-type screen mesh used for window screens?

Thanks again,

Steve

If it didn't take so much JBW to saturate the Fiberglass cloth / strand mat, it would be ideal. But that's the main problem. Fiberglass whether in cloth or mat, requires that it be thorougly satureated...as in NO air pockets....in order to achieve it's best strength. Otherwise the strands WILL shift, and will break...they ARE glass. They function very much like re-bar in concrete...they strengthen, but aren't the main source of strength for the slab.

By the time you mix enough JBW and squish it into the fiberglass....it's damn near SET...not a good way to start.

Now the screen suggestion is very good and I have used that and it does work very nicely. Biggest problem with that, is that you absolutely MUST gouge the plastic to give it a good grip onto the back, and you must use enough JBW to thoroughly coat the screen.

Another real good source of thin fiberglass...is the cloth from the POR folks that they use to bond with their paint for minor surface repair. I've even used some of the fabric used to limit silt seepage into lawn drains...it's a very close match to a single layer fiberglass mat.

The main key with any of these repairs is that the backing material needs to be STIFF enough to truly reinforce the plastic as well as bond it together.

By saturating cheesecloth, nylon screen (even metal), or silt sock material, you give the JB Weld / Fiberglass Resin / POR / paint the strength to resist cracking from flexing which in turn strengthens the plastic. Additionally, the JB acts as a glue to limit the continuation of the crack.

You still have to be careful as far as the thickness of the repair, but if you're careful, you can even rebuild missing pieces of plastic.

I used this technique (JB with a bit of silt screen) to re-build the reclining seat covers for my car. The tangs where the screws go through were missing entirely, but I had one piece with ONE tang. I copied that one tang with mold making material and then applied it to the missing tangs. Formed my reinforcement mesh, and the part to go on the main body, mixed the JB Weld, and here I am 5 years later with it still on the car.

I also repaired a corner of one of the plastic pieces and even matched the grain so you can't see it if I don't point it out to you. (The pieces have been painted to blend.)

Once you've repaired the piece, it is an excellent idea to THEN use the Dynamat, Brown Bread...etc, on the back...for sound abatement and not to rein-force the panel.

E

[SteveInOakland]

I've even used some of the fabric used to limit silt seepage into lawn drains...it's a very close match to a single layer fiberglass mat. [...]

By saturating cheesecloth, nylon screen (even metal), or silt sock material, you give the JB Weld / Fiberglass Resin / POR / paint the strength to resist cracking from flexing which in turn strengthens the plastic. Additionally, the JB acts as a glue to limit the continuation of the crack.

Meant to ask -- which JB Weld do you suggest? I take it the standard, slow set, versus the Kwik?

Also -- any more detail on that lawn material, the anti-seepage stuff? Is there a name? Is it sold in big yardage or is it in strips or little squares??

And as long as you're here -- can I ask what you suggest for repairing soft vinyl? Specifically, a few slits of an inch or so in a headliner or similar? (I.e. there's no missing material.)

Thanks for your time,

Steve.

[Zs-ondabrain]

I did'nt read the whole forum but keep this in mind. All these are great ideas but just remember that what ever you decide on should be flexible because in my experience, you usually have to bend the panel a bit to get it back into place.

If the material you choose is not flexible, your rigid fix my snap the panel worse than it was.

I personally used a thin layer of black hot glue on a well scratched up surface. The glue is flexible and pretty easy to fix if you goof.