under body treatment (what shall i do)

[chipmonster]

Just got myself a datsun.

Need protectecting and rust proofing underneath. Not sure what to do, new to classics?

[Onne]

I'd say find/fix rust issues, remove all loose existing underseal and use a good wax oil.

[akku]

I hate thick underseal type products. As Onne says you need to find and fix whats up first, then treat it with something to kill it in box sections and so on. For the floor and bits you can get to I like a chassis black or synthetic floor paint type product. Something which is tough enough not to chip but not brittle so it comes off in chunks if it does get damaged. There have been a few recommended in this section of late - some form of brushable epoxy primer followed by Chassis Black of some sort would be the winner from what has been said so far.

Anything that looks like roofing tar should be avoided!

[br1gg5y]

Ah the pictures help. you need to get rid of any loose under seal and rust, a wire brush or a knot wheel on a grinder will help greatly, wear goggles, and a mask for all the dust, snot and grot. Then treat any rust.
Where you have bear metal showing I would personally use underseal paint, put in the house or in a hot tub of water to help it flow, if all else fails add touch of white spirits. Then over the top metal paint, it adds a layer of protection.
For the sills and areas that will get debris flicked onto it by the wheels add stone chip, it can be painted over to suit your taste.
waxoyl is good, but is a curse word to use, and there can be a lot of wastage.
Personally I apply underseal with a brush, there is less mess and wastage. I then spray waxoyl where I cannot get a brush to. Do remember waxoyl does burn, so any welding might well set the waxoyl "sayin your sills" a flame in the future if any welding is needed in the future.

[ejenner]

I tend to leave the old rust protection in place where it is good and where there is no rust. Manufactures didn't mess about when it came to quailty underseal products. Some better than others... but I work on Saab's mostly and they have excellent underseal.

If you have to fix some rust get it back to bare metal and then you must use etch primer. It bites into the metal. You can't get a better start than that. Then some normal paint, I use a proper car paint with a hardner if I have some. I don't really like cellouse as it's a bit weak, other paint or oil will break it down. Then go for chassis paint. For my car I have done recently I've been using 3m stonechip followed by 3m waxoil type product. Doing it this way covers all the bases.

If you want to use seam sealer over some welds or anywhere else then I would recommend applying the etch primer first, then the seam sealer, then other paints or coatings. This way the etch primer protects the metal at the basic level.

[ejenner]

The top photo has the waxoil product. The bottom photo is just stonechip. I actually forgot to apply the waxoil stuff while it was all masked up so I'll just go over it with a spray-can in some sensitive areas later.

[fred]

Not sure if Datsun at the time did rustproofing, but like the above threads, wire brush all the loose rust off. (horrible process), try and get it back to bare metal if you can, I used a huge can of hammerite smooth rite paint on my old Ventora, and it lasted perfectly for 6 years and above, sold it solid, but the by word is preparation, better job you can get before you apply whatever you want to apply the better, and yes wax oil is excellent for the box sections and sills

[Jizmondo Scrotmondo]

I used smooth black Hammerite (painted on with a brush) on the underside and arches of my old Bug. As above, the worst bit is getting it ready for the new paint/underseal etc, in fact it can be horrible. Your Datsun doesn't look bad at all, I've seen worse on 10 year-old cars.

Get under it with a wire wheel and start cleaning the grot off.

[joda]

Get the old underseal off, if it is left on it will trap moisture and make things worse than better!

Bonda primer the bare metal, over this put some stone chip, then over this a primer/top coat of your choice!

[chipmonster]

How do I take old under seal off. I tried but it would not come off

[fred]

Paint scraper and loads of elbow!! if the underseal is solid, best leave it its doing its job, concentrate on the flakey stuff, and the rusty bits, any corrosion give it a good poke, if it doesnt give way leave it. once all the flakey stuff is gone and if you havent found anything which needs a patch of weld. whack it with hammerite, and a brush, leave no stone unturned !! nasty job, but it will keep the old girl going for years to come, best of luck mate

[fred]

To be fair the pics you put up, your motor doesnt look that bad

[will930]

may i hijack quickly and run theough my plan/idea

simply remove any loose stuff/remove worse of solid stuff to ensure no hidden nasties
treat (not sure what you use) and seam seal any iffy bits of rust
either etch primer or red oxide entire underbody
smooth black hammerite
anything to add to that?

then obviously the oblitery blasting of everything hidden with waxoyl

[chipmonster]

Been at it for two days now, on and off.

Used a wire brush on the drill and took off all the old under seal. The centre bit was solid so left on.

I got bilt hamber electrox and put on all four arches and on the sils. Expensive stuff 30 a litre so only bought one litre and used it all.

This morning put on bilt hamber dynax ub and completed half the car, used a litre of dynax ub. Going to complete the full car tonight, after 5.

Tomorrow, will do 2nd coat of dynax ub.

Will post pictures once complete.

Lesson learned on my project.

Don't wear a t shirt, full sleeves is essential and overalls even better. I spent 1 hour scrubbing myself in the bath, not pleasant.

Use a barrier cream or Vaseline if u don't have barrier cream. Dab as much as u can, it acts like barrier cream.

Finally, also wear a hat, the gunge is not very good on your head.

Even better is a balaclava, keep your self covered as much as possible.

These are my thoughts!

[fred]

chipmonster

sorry mate I should have said that, last time I did what you did, took me ages to get the wibblepoo off me, it was july, and I blasted ground and scraped it off in shorts and t shirt, looked like a bloody miner when I'd finished LOL

[75nut]

Just done this on my Alfa 75 underside. Although the factory underseal was good in places and very thick on certain areas it had lifted and allowed rust to build.

Top tip for removing thick underseal without power tools is a wood chisel, its sharp and will scrape even the thickest stuff off without to much effort.

I forcus on removing only the lifting areas with the chisel, then wire brush to remove loose rust, then kurust to kill the rust then hammerite and waxoyl after.

[dooh]

Just to say ... an old trick i was told by a classic car restoration garage was to mix under seal ''the thick stuff'' with waxoil. Under seal just gets hard and crumbles off after time as i found out but with the waxoil stays subtle for the under body etc and the both together don't leave it too tacky. I also ... like suggested cleaned loose debris etc with a wire brush drill pieces ''cheap at screw fix - eBay '' etc. Then hammerited certain areas. Only thing i found was i was walking round like a porcupine for days finding wire brush bits in my clothes and carpet OUCH!! ...

[madmog]

Something I did that lasted well but by all accounts shouldn't do.. after getting to good metal and repairing anythong that needs repairing, primer, then hammerite - 2 coats, then cheapo underseal 2 or three coats then two more coats of hammerite. From memory one of these didn't like being painted on the other but did stick well when dry. The first layer of hammerite seals the metal against moisture, the underseal then acts like a stonechip protect protecting against stones chipping the paint and the hammertite on top of that stops the underseal drying out and falling off. and is a cleaner suface that curse word tends not to stick to.

This tactic was based on getting large tins of discontinued or garish coloured hammerite very cheaply.

[panelbeaterpeter]

the best method is kinda dependant on how fussy you are being, whether you want rid of 100% of the rust and to get it concourse, or just kill the worst of the rust and seal it from the elements. I generally do the latter. Last time I did the underside of a car like that, I jacked it up high, hot pressure washed off the worst of the loose stuff with chemical, let it dry completely, removed any remaining loose stuff with a scraper, sprayed on Wurth rust converter with a spray bottle, then gave it a very thorough coat of black waxoyl. Did the job with not very much grovelling about.