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I thought I'd show the results of using Plastex to make a simple grill repair. Sorry it isn't something fancy like a Charger or road runner...but my road runner grill doesn't need fixing. 
So for the purpose of this exercise, I'm using a broken grill from my beater Pontiac Montana. If you don't know, Plastex is one of a variety of brands out there that use a powdered plastic substrate that you add a solvent to in order to melt it into one piece. Plastex Repair Kit - Plastic/Fiberglass Repair Kit - Master Tech Kit Size - 2006 | eBay
You can see here that a hole is in the hexagon grill, that piece was missing when I got the van so I didn't have it available to glue back in. So instead, I'll have to recreate it. The plan was to make a mould of the pattern in the good area and then move the mould over to fill with Plastex and repair the missing part.
This is the back side, the grill insert has a flat back so taping it up was easy.
The Plastex kit actually comes with some blocks of moulding plastic that you're supposed to heat up (around 140 f) so that it softens and you can get an impression into it from the original material, but while it works well with flat pieces such as a missing tab, it wouldn't do the job for a deeply inset area like I was working on. I needed something else.
My first thought was that I could use a plaster based moulding compound, similar to Plaster of Paris but much stronger and specifically made for moulds. I sealed the bottom with tape and made my mould. I had read that coating the plastic with dish detergent would enable it to freely separate after curing. It didn't work out. After it had hardened, I found that it was firmly stuck to my grill and couldn't be detached at all. I ended up chiselling it off in small chunks and had to sand the remainder from the plastic. Its possible that if I had used a PVA mould release it would have separated, but I thought I'd try a different approach.
Next attempt was to make a silicone mould. Using two part silicone made for moulding, I again taped up the bottom and also made a dam to keep the liquid in place as it hardened. This took all day, it was at least an eight hour cure but I let it go for 24 hours to be sure before seeing if it would release. And it worked, peeling away easily, not sticking at all like the plaster did.
You can see that the impression is a perfect mirror image of the original part. So after a bit of trimming with scissors to better fit the edges, I put it in place, firmly backed with a piece of plywood to prevent it from sagging. Had I known better, I would have put a plywood backing right into the liquid silicone and let it harden in place to retain the original curvature of the grill; this stuff is fairly floppy and wants to sag easily without reinforcement.
Anyway, once in place, I started to fill the empty grooves of the mould with plastic powder. The kit I have has three different choices; black, white and clear. I used the black powder, after which I dripped the solvent from a small squeeze bottle a drop at a time until it was all saturated. This is a very strong, pungent smelling solvent and I wouldn't recommend doing it indoors, however it does evaporate fairly quickly so if you work on it outside you can still bring it in after ten or fifteen minutes and most of the smell will have dissipated.
I don't know just how long it takes to set up, I went to work while it cured. But when I returned to it, the new plastic was quite hard so I went to see if I could remove my silicone mould. What a relief to see that it easily separated and popped right off. And I was happy to see that it had re-created the missing area of the grill quite well. Well, for information purposes of this tutorial, that's how it went. In reality the mould was a little smaller than the repair area so I did it in two steps; making a partial repair and then moving the mould over to finish it off. While I was at it, to satisfy myself that it was going to have the needed strength to really work, I took some cutting pliers and snipped off some of the new area (since I was going to be adding more anyway) and found it to be every bit as sturdy as the original plastic. Here's how it looked when the silicone was peeled away.
After trimming off the bits of flashing and a light sanding, I masked off and sprayed the grill with semi-gloss grill paint. But first, since I already had the products, I cleaned and prepped with SEM plastic and leather cleaner and a second coat of SEM plastic primer cleaner. I think the grill was probably painted silver originally but as you see it had all worn off to the base yellowish plastic. Since the whole van is black, I went with black semi-gloss for the grill.
And there you have it, back in place and if you didn't know that it was previously broken, you'd never even suspect. The only way to tell is by looking at it from behind.
At the end of it all, I still have most of the Plastex material left, plenty for other projects so the end result cost far less than buying a new grill for $180. For older grills that aren't available, this could be a lifesaver.
And if you don't have missing pieces, but your plastic is cracked or broken, this stuff makes great repairs for that as well. Just vee out the crack, back up with tape if needed and go to work on it.
So for the purpose of this exercise, I'm using a broken grill from my beater Pontiac Montana. If you don't know, Plastex is one of a variety of brands out there that use a powdered plastic substrate that you add a solvent to in order to melt it into one piece. Plastex Repair Kit - Plastic/Fiberglass Repair Kit - Master Tech Kit Size - 2006 | eBayYou can see here that a hole is in the hexagon grill, that piece was missing when I got the van so I didn't have it available to glue back in. So instead, I'll have to recreate it. The plan was to make a mould of the pattern in the good area and then move the mould over to fill with Plastex and repair the missing part.
This is the back side, the grill insert has a flat back so taping it up was easy.
The Plastex kit actually comes with some blocks of moulding plastic that you're supposed to heat up (around 140 f) so that it softens and you can get an impression into it from the original material, but while it works well with flat pieces such as a missing tab, it wouldn't do the job for a deeply inset area like I was working on. I needed something else.
My first thought was that I could use a plaster based moulding compound, similar to Plaster of Paris but much stronger and specifically made for moulds. I sealed the bottom with tape and made my mould. I had read that coating the plastic with dish detergent would enable it to freely separate after curing. It didn't work out. After it had hardened, I found that it was firmly stuck to my grill and couldn't be detached at all. I ended up chiselling it off in small chunks and had to sand the remainder from the plastic. Its possible that if I had used a PVA mould release it would have separated, but I thought I'd try a different approach.
Next attempt was to make a silicone mould. Using two part silicone made for moulding, I again taped up the bottom and also made a dam to keep the liquid in place as it hardened. This took all day, it was at least an eight hour cure but I let it go for 24 hours to be sure before seeing if it would release. And it worked, peeling away easily, not sticking at all like the plaster did.
You can see that the impression is a perfect mirror image of the original part. So after a bit of trimming with scissors to better fit the edges, I put it in place, firmly backed with a piece of plywood to prevent it from sagging. Had I known better, I would have put a plywood backing right into the liquid silicone and let it harden in place to retain the original curvature of the grill; this stuff is fairly floppy and wants to sag easily without reinforcement.
Anyway, once in place, I started to fill the empty grooves of the mould with plastic powder. The kit I have has three different choices; black, white and clear. I used the black powder, after which I dripped the solvent from a small squeeze bottle a drop at a time until it was all saturated. This is a very strong, pungent smelling solvent and I wouldn't recommend doing it indoors, however it does evaporate fairly quickly so if you work on it outside you can still bring it in after ten or fifteen minutes and most of the smell will have dissipated.
I don't know just how long it takes to set up, I went to work while it cured. But when I returned to it, the new plastic was quite hard so I went to see if I could remove my silicone mould. What a relief to see that it easily separated and popped right off. And I was happy to see that it had re-created the missing area of the grill quite well. Well, for information purposes of this tutorial, that's how it went. In reality the mould was a little smaller than the repair area so I did it in two steps; making a partial repair and then moving the mould over to finish it off. While I was at it, to satisfy myself that it was going to have the needed strength to really work, I took some cutting pliers and snipped off some of the new area (since I was going to be adding more anyway) and found it to be every bit as sturdy as the original plastic. Here's how it looked when the silicone was peeled away.
After trimming off the bits of flashing and a light sanding, I masked off and sprayed the grill with semi-gloss grill paint. But first, since I already had the products, I cleaned and prepped with SEM plastic and leather cleaner and a second coat of SEM plastic primer cleaner. I think the grill was probably painted silver originally but as you see it had all worn off to the base yellowish plastic. Since the whole van is black, I went with black semi-gloss for the grill.
And there you have it, back in place and if you didn't know that it was previously broken, you'd never even suspect. The only way to tell is by looking at it from behind.
At the end of it all, I still have most of the Plastex material left, plenty for other projects so the end result cost far less than buying a new grill for $180. For older grills that aren't available, this could be a lifesaver.
And if you don't have missing pieces, but your plastic is cracked or broken, this stuff makes great repairs for that as well. Just vee out the crack, back up with tape if needed and go to work on it.
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