what about undercoating?

[Lonnie]

I've about got the undercarriage scraped off. What have youse guys used to repaint the undercarriage? I'd like to go with some sound deadening, but is it necessary?

Lonnie

 

[Steve_S]

Some use undercoating, some don't. It works great until it gets really old at which point it cracks and lets water between it and the metal. Bad news. In California you really don't need it. My B has been driving California roads it's entire life and the chassis is rust-free, no undercoat, no restoration performed.

 

[703MGB]

I am in Montreal Canada so undercoating is always a good idea even if the car is never seeing snow.

The biggest improvement I made to my B was sound deadening material but it goes inside the car not under.

Here the link to the company that I bought it from.

https://www.b-quiet.com/

You may also want to look at the picture I am attaching which shows the results.

The noise level in the car really went down alot.

 

[Lonnie]

Steve,
Did you paint?
Lonnie

 

[703MGB]

The floors were already repainted (my car was totally rebuilt which included new floors). You need to apply this stuff on painted surfaces. You may also paint it but I do not see the value since the carpet goes over it.
One thing for sure now the steel floor is totally isolated from moisture (you need to apply it when the car is totally dry and in warm weather.

 

[Banjo]

Undercoat is only going to work if it is applied over top a good, solid, clean ,paint job. It really acts more as a chip guard. stopping stones and debris from breeching the paint.undercoat itsself does not prevent or stop rust, it will actually do more to hold any moisture agenst the metal. If you spray it over bare metal or rust you're asking for toruble. It's only going to mask problems for a short while. I would prep the bottom of the car as if you were planning to leave it in paint and then you can add the undercoat if you want to.
That's my take anyway

 

[Steve_S]

I've never painted the underside of my car, it's all original including thick layers of road scum. But no rust other than the usual surface rust here and there, such as battery boxes. If you're in Northern California where it rains and snows a lot or if you live by the ocean then some form of rust protection other than paint may be a good idea. I live inland, about 15 miles from the ocean so I don't see any salt air at my house.

 

[John Moore]

I'm in the process of re-doing the bottom of my car, I've check alot of options. I think I'm going to paint mine with POR-15 sealer, then POR-15 top coat, then paint body color. Another option is to go with truck bed liner. It does have some sound deadening qualities. Some truck bed liner is also tintable. But I those have to be professionally sprayed. But there are some truck bed liners the DIY'r can brush on. Rhinoliner comes to mind.

 

[aeronca65t]

If I were to undercoat a car nowadays, I'd use some of the cold galvanizing paints. These products really cut down on creeeping rust.

https://www.alvinproducts.com/Products/Products.asp?ID=4


As stated, the "thick" style undercoatings may only hide and trap moisture. POR-15 is a good product in terms of sealing, but the surface must be *absolutely* dry....I wouldn't even apply it on a humid day (for what it's worth, it's made within walking distance of our house).
I recall that in the old days, people would have their cars "undercoated" with used motor oil once a year (the local gas stations would do it). Not a great idea environmentally, and I'm not sure if it worked that well anyway.

 

[Steve_S]

I almost bought an MGC from a guy who sprayed underneath once per year with diesel fuel! To my suprise it was the most rust-free underbody I've ever seen.