Underseal questions

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Speedy88
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Joined: 04 May 2009 11:52 pm
Location: Bristol

Underseal questions

Post by Speedy88 » 03 Oct 2010 01:27 pm

Here comes the short journey to get a new MOT and for part of protecting my car further I'm going to under-seal the bottom. There are some areas that are exposed down to the metal and have a slight surface rust on them. Would I be safe to sand these areas down a little, and seal straight over? Or should I apply some paint first to give it a guaranteed layer?

Also, what sort of brand should I go for? Is anything not good?

Last question; is mr MOT man going to be unhappy with the underseal?
'88 340 Williams (Sold)
'85 360 GLS - Drift project (Sold)
'77 Colt Sigma
'96 940 Drift project

Ride_on
Posts: 2262
Joined: 26 May 2009 05:34 pm
Location: Belfast, N. Ireland

Re: Underseal questions

Post by Ride_on » 03 Oct 2010 02:31 pm

I have been looking at this lately and mentioned this in the thread below which got no comments.

http://www.volvo300mania.com/forum-uk/v ... =5&t=10632

Normal underseal is not much good on old repairs as its virtually impossible to get rid of all the rust, you need something with a converter or zinc in it to reduce spread from rust+moisture in the pits.

If you want a quick and dirty repair, anything will prevent serious rust for a few years, probably best used with a rust converter. The main problem is removing layered rust trapping moisture, A drill with a rotary wire brush will not do it, you need an angle grinder or flappy disk. Wire brush on the drill is of some use to remove rust from pits.

The best solution I can see so far is Rustbuster Epoxy mastic 121, followed by a rubberised underseal (eg Dinitrol 447). Another product I have used is Rust bullet, which is a moisture curing paint that sucks out the moisture from the rust, it is guaranteed for 10 years but quite hard to paint over, although like the epoxy cures very hard. Zinga (zinc paint) is also an interesting product, but again hard to paint over and maybe doesn't adhere aswell as they claim.

Treating rust in a lasting way is quite hard I have been doing for 20+ years, most of the commonly available stuff doesn't work. I had the best success with zinc products in the early days, but quite hard to get and I want something better.
1980 345 DL_______1987 360 GLE (project car restored to GLT spec and B230FT'd)
1984 360 GLT______1987 360 GLT
1983 360 GLS______1989 360 GLE
1985 340 GL_______1986 340 1.4
1985 360 GLS______1995 940 SE 2.3 Turbo Estate (daily)
1987 340 GL 1.7

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Speedy88
Posts: 4057
Joined: 04 May 2009 11:52 pm
Location: Bristol

Re: Underseal questions

Post by Speedy88 » 03 Oct 2010 03:35 pm

Cool, so from what I gather the 121 is actually a spray?
'88 340 Williams (Sold)
'85 360 GLS - Drift project (Sold)
'77 Colt Sigma
'96 940 Drift project

Ride_on
Posts: 2262
Joined: 26 May 2009 05:34 pm
Location: Belfast, N. Ireland

Re: Underseal questions

Post by Ride_on » 04 Oct 2010 06:20 pm

No you can brush it, its actually a 2 part material you have to mix so impossible for an aerosol spray can. Its not got isocyanates so you can use it at home. Just got my first delivery of it today.
1980 345 DL_______1987 360 GLE (project car restored to GLT spec and B230FT'd)
1984 360 GLT______1987 360 GLT
1983 360 GLS______1989 360 GLE
1985 340 GL_______1986 340 1.4
1985 360 GLS______1995 940 SE 2.3 Turbo Estate (daily)
1987 340 GL 1.7

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