Hey everyone. Recently I’ve been on the lookout for a new dash for the monte carlo and I was finally able to snag one after the junkyard got a new monte carlo. I noticed that the one I got has a couple cracks on the dash, but they all seem easily repairable. Anyone have any advice on how to get this done and prevent further cracks going forth? Let me know!

 

The problem with fixing cracks in dashes and such is usually the texture. Repairing the crack is easy - using an epoxy made for that type of plastic along with some simple reinforcement on the backside you can easily get it back to one piece again. If the crack hasn't made it all the way through the part yet, then make sure to drill a hole at the end of the crack first so it can't continue to spread. But matching the texture on the top side is nearly impossible.

What we used to do back when I worked at a car audio shop was to wrap the repaired plastic with fabric/material (secured down with spray glue). We used a lot of fake leather type products in black or gray for this purpose as they gave a texture fairly similar to the stock plastic - but obviously each type and brand has its own level of smoothness. You do have to make sure to clean the underlying plastic well though- some people put oil based shine enhancers on their plastic that inhibit bonding.

They also sell stuff with a built in foam backing (fairly thin), that gives the material a nice soft touch / expensive feel - but you've got to be careful on panels where you need a tight edge wrap as sometimes you've only got just enough space for the material alone.

Some plastic just gets super brittle with age, so there were some where we'd attach the plastic chunks to a wood backer, then create a fiberglass mold off of it and subsequently a fiberglass or carbon fiber part off of that - but that's pretty expensive / labor intensive.

 

Seems like a pretty labor intensive process all around. If I repaired the plastic and reinforced it, could I scuff the top down and paint it instead of wrapping it with some other material like you said? Getting the texture to absolute perfectness isn't a need by me, I just don't want to keep staring at my ugly dashless interior.

 

Personally, I'd probably bond it back together and wipe the visible side flush to just see how that looks to you first. As long as no chunks broke free / the panel didn't warp, the cracked edges usually mate back together pretty cleanly. This might be good enough for you, at least from the driver's seat.

Sanding / painting can be tough and can make the repair more obvious if not done right. Just sanding the cracked area will make it more obvious as you'll have a much wider strip with a visual difference (a couple inch wide smooth patch that reflects light differently). You could sand the whole panel down at the same time to get it all smooth, but the repair area may still look a little goofy if its not blended right. Its like doing body work on a car exterior almost. That's why I think stopping to at least set it in place after just bonding it back together would be my first stopping point as the level of effort starts climbing quickly from there.


The techniques Id mentioned were from working at a professional business on paying customer cars. The customer expectation was OEM level of quality or better - so we never had the latitude to call a repair good enough. Often it was part of a larger scope of work anyways while the panel was apart - adding speakers, tvs, guages, etc depending on the panel, so it wasn't really an option for us not to refinish it 100%.

 

A few other repair tips:

-Id try to identify the plastic type as best you can. Sometimes they say on them, sometimes you can do simple tests found on Google to ID them (common for bumper welding). Some types of plastic are thermoset and can be melted back together, others get destroyed /charred by heat.

-If doing epoxy, ensure its compatible with the plastic you're fixing. There are a lot of types of plastic and some combinations will have very poor bond. Be wary of catch all epoxy that doesn't specify at all: 'bonds almost all materials'.

-On the reverse side of the panel, I'd heavily abrade an inch or so on both sides of the crack. While good epoxy has a strong bond even against flat surfaces, the bond strength goes up substantially if you increase the surface area / give it something to bite into. Could be ultra rough sand paper (like 25 grit) or even just taking a razor blade and making a bunch of shallow cuts.

-Id also probably scuff clean the bond area (again on the reverse side) prior to starting to give you a fresh surface. Some plastics can form surface oxides that can negatively impact bonding (think Bondo over rust, but on a microscopic level). It's not catastrophic, but you want to give it the best chance of sticking that you can.

-If its a long crack, I'd embed some kind of reinforcement into your epoxy layer at regular spacing intervals. This will help spread the shear stress off of the the cracked area. Doesnt have to be super strong - even something like some little 1" nails bent into a V shape would be fine (so its strong in shear and tension).

 

On the back of the dash near one of the air vents, there's a "PC-ABS" mark. Seems pretty straightforward as to what sort of plastic it is. This plastic is repaired by using acetone on the surface? It seems that by research, acetone is reactive with ABS plastics and will melt off the top layer when applied to it. If so, would you still recommend I abrade both sides of the crack by a lot or would a simple wipe down with some isopropyl alcohol and then going to town with acetone be good? I'll still reinforce it with something, just to be sure. I also think the dash will look pretty good as the crack happened when I was (carefully) taking the dash out of the old Monte Carlo. That's just what intense New Mexico UV does over time lol.

 

Sorry, I've never done that before so I can't be of help on that. I've only repaired plastic with heat or epoxy.

If this just re-melts it back together then there shouldn't be a need to abrade at all, as it'll just dissolve that anyways.

I probably should've mentioned before by abrading both sides for epoxy repair, I'd just meant the left and right of the crack from the non visible side. The less you need to mess with the visible side, the better.