What did you cover when undercoating?

[Mike]

I did it the hard way. I sandblasted everything from underneath, primed it, and then used the rattle-can undercoating.

[Ed]

I think I read somewhere that rattle can undercoating is porous.

[Zs-ondabrain]

I used the spray-on from a can. (Dupli-Color Professional Undercoat & Sound Eliminator) P/N UC102 It's Paintable, Rubberized, Corrosion Proof and Drys quickly. It costs about $6.00 per can and I'm pretty happy with it, for being on a budget.

I used wads of paper to fill all the screw and bolt holes, and strips of tape (to lessen the thickness between the body and the parts to be remounted) where the larger items were to be bolted back up to the body.

Here are a few pics with the parts put back on after undercoating.

[Zs-ondabrain]

I'm still deciding on whether to undercoat the rest of the floor pans until I get rid of a few inward dents. ( I think the P.O. used the car for stump jumping or something) the passenger side has one big lump on the inside floorboard, I think he might have tried to jack the car up from the end of the frame rail (just forward of the seat)

[AChev]

Zsondabrain, I have the same exact thing going on with my car, I have found a few people with very similar dents. A little while back, I think it might have been Ed who gave me some advice. He said he took a 50 lb. dumbell and dropped it on it a few times and it knocked it right back into place! ALthough my dented is rusted, it doesn't have any holes yet, but it has some extreme surface rust goin on, so I might go with new floors, not sure yet.

I had planned on pooring the undercarriage and then using a truck bed liner, although that is starting too look at little bit pricey, although that finish that Ed got is really spectacular, should hold up well too. I haven't ever dealt with truck bed liner, but is there any chance of it detaching from the paint on the undercarriage?

[Zs-ondabrain]

It's been my experience that if you undercoat or use a truck bed coating over paint, the paint can still chip off and take the undercoating with it.

Strangely enough, thats actually how I removed all the old undercoating on the underside of my Z. The P.O. or some one else had sprayed undercoating ontop of the existing paint. When I tapped it with a sharp hammer, bits and chunks came flying off at me.

It was cold in my garage when I did it so keep that in mind if you decide to remove undercoating. If you want to remove dents with out removing undercoating, make sure that the surface of the panel is warm or even hot before you bang on it. I have NO rust in or on my floorboards and plan to keep it that way.

Good luck,

Dave

[xray]

Zs-ondabrain, I think Shevets used "paint" to be synonymous with the POR-15 product that Ed used...if so, POR should have a tough time chipping off, and I would be more concerned about the undercoating separating from the POR...Since the POR is still firmly adherent, it may make some aesthetic difference or possibly some change in level of sound deadening, but shouldn't put the undercarriage at risk for rusting, right? I guess anything's at risk for chipping when hit by rocks at 60+mph though...

[EScanlon]

Couple of fast comments:

You don't want metal to be hot when you start trying to knock out a dent. Not only would it be hard to feel the metal to see if you did remove the dent, but you'd also be BENDING thee dent out, not knocking it out. Be ready for a LOT of warping.

Next, undercoating that has been properly applied and allowed to dry is basically a really THICK gunky tar. It's protection of the metal is in that it absorbs and deflects rock/dirt/pebble impact by deforming. When it's as old as most of our cars are, this stuff turns into a linoleum-like coating. Once you chip past the edge it starts lifting easily. New undercoating is hard enough that you won't be wiping it off easily, but it isn't hard as a rock. Since it's basically like a hard putty (still pliant yet has a definite skin) it will absorb most harmonic vibration in the sheet metal panels and quiet the car's metal from resonating.

Unless you've left a coat of dust on the POR, the undercoating should stick. Remember, this stuff is basically liquid tar mixed with snot, it sticks and stains like silicone on everything except standing water, and even there it will make it's skin.

E¢

[Zs-ondabrain]

Enrique,

No offence given and none taken but DUH! I'm not talking fricken HOT, I'm talking at least room temperature or above. I obviously did'nt look to see where "Schevets" lives or take in to account that he may actually have a "real shop", as compared to mine. But I was thinking about the fact that it is winter around here. My garage when the heater isn't on gets to be about 40 degrees or less. And even NEW undercoating will get brittle as the temperature drops. If any one on this site would have an understanding of how finicky I am or my complex understanding of how things work, especially on a Z, I thought it be you.

As for the POR-15, I still don't quite understand why a lot of you are putting it on, then undercoating. Undercoating, when applied to a clean, bare metal surface will protect the car from rusting. Thats why the factories do it that way. And they don't use POR first. call me silly but it seems to worked for them for the last umpteen decades.

Obviously you guys have a way of doing things that I've yet to understand.

I DO use POR-15 on metal that needs to be protected but will not have undercoating applied such as my control arms and strut assemblies, as you've most likely seen from the pictures I posted the other day.

I think that POR-15 is a great product! Hell, I use it myself. But when you're on a budget as I usually am, You don't think about covering a great product like POR-15 with a cheaper product like undercoating.

Like I said earlier, "no offence taken, none given". We were both obviously looking at different sides of the coin.

[xray]

...As for the POR-15, I still don't quite understand why a lot of you are putting it on, then undercoating. Undercoating, when applied to a clean, bare metal surface will protect the car from rusting. Thats why the factories do it that way. And they don't use POR first. call me silly but it seems to worked for them for the last umpteen decades.

Obviously you guys have a way of doing things that I've yet to understand.

I DO use POR-15 on metal that needs to be protected but will not have undercoating applied such as my control arms and strut assemblies, as you've most likely seen from the pictures I posted the other day.

I think that POR-15 is a great product! Hell, I use it myself. But when you're on a budget as I usually am, You don't think about covering a great product like POR-15 with a cheaper product like undercoating.

Like I said earlier, "no offence taken, none given". We were both obviously looking at different sides of the coin.

Well, the factory undercoating sucked major a$$, which is why a lot of our cars are rusting. So, in an effort to preserve the car in a (hopefully) better way, we add a layer of POR-15, then our primer/undercoat/paint. Maybe it's just a "belt and suspenders" approach, but after dealing with factory undercoating (and the rust which lay beneath) I want my effort to have some impact...we also POR the inside of rocker panels, doors quarter panels and frame rails, so maybe it's an obsession!

POR is UV-sensitive, so it's better to topcoat it with something or it'll degrade over time. Maybe a lot slower on undercarriage parts, but not worth the risk for me.

IMO, the hardened surface of POR is much too glossy to look right, especially on the undercarriage. So we put on some undercoating to give it a more "correct" appearance, while adding some sound/heat insulation.

Steve

[montoya_fan01]

not sure if we are talking 240Zs or another model, but there was NO "factory" undercoating on 240Zs sold in the USA. N O N E ! ! Zip. Nadda.

Painted metal was what you got from the "factory" if you bought one in the USA. DEALERS added undercoating (of varying quality) just like they added many other things like aluminum wheels, vinyl tops, mirrors, stereos, yadda, yadda, yadda to many of the cars before they hit the sales lot.

FWIW, according to the Tech Rep at my regional POR distributor; the POR15 is sensitive to UV in relation to it's appearance and will become mottled over time, but UV has no effect on it's protective capabilities. But, that's enough of a reason for me to topcoat it with POR Chassis-Coat Black.

[Marduke]

I know this topic is a bit old but I was wondering if I could get some new input as this step is exactly where I am at with my Z.

My questions are below but a bit of background first ...

I'll have my Z just about stripped to bare metal underneath by this weekend. I don't have a rotisserie (jack stands) but I found that in my case if I heated the undercoating a bit with a propane torch for a quick second that I could scrape off it and most of the layers of paint underneath in one easy swipe with a sharp putty knife. What I couldn't get off that way, I wire wheeled etc.

Anyway, I noticed that in the areas where the car leaked oil/tranny fluid that the old rubberized undercoating was virtually liquid and I could literally wipe it off with a rag. Underneath those areas I found pits of rust beginning to go to work. So, I'm not convinced of the longevity of the spray can undercoating.

Now for the questions ...

Has anyone put any miles on a car with the herculiner undercoating? How has it withstood the test of time? Any flaking etc? It must be fairly pliable as it obviously works in truck beds but the belly of a Z car I think would be a little more "demanding".

Any input is appreciated.

Thanks,

Scott