Underbody protection

Woody928

Events Officer
Staff member
Club Member
Hi All,

I'm after some opinions from these who have been here before, what are my options to underseal/wax/protect the underside of my 240Z against corosion, road grimme etc in at DIY sense at home with no ramp access?

I'm thinking of cleaning up the underside of my car and adding a fresh layer of protection however there seem to be loads of choices out there. I'm fairly sure theres lots of pros and cons to different options, I've come across the following three as fairly obvious and well trodden paths however not really overly sure what might be the best course of action?

Dinatrol:
https://www.ebay.co.uk/itm/Dinitrol...751995?hash=item287bfb32fb:g:7lMAAOSwCR9cuugg

POR15
https://www.ebay.co.uk/itm/POR15-Gl...m212daae402:g:A7kAAOSwubRXMbt7&frcectupt=true

Waxoil
https://www.ebay.co.uk/itm/Waxoyl-B...230980?hash=item442e47c2c4:g:iA8AAOSwWqpazSXj

Should I be steam cleaning the underside of the car first, how much old material should I be taking off? Just go at it with a wire brush to remove the loose debris then coat on top of everything else?

The car is very solid with some very minor surface rust starting to occur in a couple of places howeverI want to get ahead of the curve before it becomes an actual problem in several years time.

Any thoughts and input gratefully recieved, there doesnt appear to be much in the way of the archieves on here....
 

johnymd

Club Member
On my cars I tend to get the car up in the air and spend a couple of hours cleaning every part of the underside. Start with a pressure washer to get the worst off and loosen up what's left. Then with a garden sprayer I spray everything with truck wash or TFR. Leave it to soak in for 20 mins then hit it again with the pressure washer. Then inspect to make sure I've not missed anything. Follow this by checking for loose stuff and rust converting any areas of rust I can see. Once dry (day or so) I'll then recoat over the whole lot with Dinatrol underbody coating. After that I'll flood all cavities and corners with a runny cavity oil. I then redo the oil (including sills) every year. I've also tried ACL90 on lots of the nuts/bolts under the car. After all this you should be safe to use the car in most weathers. It wont be a show queen underneath but the oily cavity stuff will protect everything.
 

Farmer42

Club Member
I had mine professionally Waxoyled a couple of years ago. It seems to protect the underside ok but the stuff is a nightmare.
It clogs everything and is really difficult to get off stuff like wires, cables etc and especially nuts & bolts when you are trying to work on them. The added issue I had was that the numpty that sprayed mine didn't cover the rest of the car and I got overspray all over my paintwork. You can only remove it with white spirit and a lot of elbow grease! Didn't do much for the paint but luckily it was before I had it resprayed which I had already planned.
 

Paul_S

Club Member
I read it was a bad idea to steam clean the underside because you're forcing moisture into all the crevasses and the chances are you'll trap water in when you seal over the top.

I'm torn with Waxoyl as I'm led to believe is still one of the best products to use when it comes to protecting your car but, as said above, is a mare to live with.
 

Turn & Burn

Club Member
If it’s ur pride n joy it may be worth letting the professionals at it. I do nearly everything myself, but I reckon this is a job that’s worth getting done. These guys seem to feature in Practical Classics a lot an will sell the product or do it for u.
https://www.rust.co.uk/
 

toopy

Club Member
I read it was a bad idea to steam clean the underside because you're forcing moisture into all the crevasses and the chances are you'll trap water in when you seal over the top.

I'm torn with Waxoyl as I'm led to believe is still one of the best products to use when it comes to protecting your car but, as said above, is a mare to live with.


Waxoyl has been out of favor for quite a few years, i remember a test conducted by practical classics had it well down the top 10

Dinatrol or Bilt Hamber stuff are the go to products these days https://www.bilthamber.com/corrosion-protection-and-rust-treatments/

The Techshield stuff and Corrolan from Rustbuster are also worth considering
 

Huw

Club Member
POR 15 is only good if you put a top coat on it after. Recommends to do it on the tin but a lot of people I know don’t. POR 15 degrades when exposed to UV that’s why they recommend a top coat of your choice.
 

Woody928

Events Officer
Staff member
Club Member
On my cars I tend to get the car up in the air and spend a couple of hours cleaning every part of the underside. Start with a pressure washer to get the worst off and loosen up what's left. Then with a garden sprayer I spray everything with truck wash or TFR. Leave it to soak in for 20 mins then hit it again with the pressure washer. Then inspect to make sure I've not missed anything. Follow this by checking for loose stuff and rust converting any areas of rust I can see. Once dry (day or so) I'll then recoat over the whole lot with Dinatrol underbody coating. After that I'll flood all cavities and corners with a runny cavity oil. I then redo the oil (including sills) every year. I've also tried ACL90 on lots of the nuts/bolts under the car. After all this you should be safe to use the car in most weathers. It wont be a show queen underneath but the oily cavity stuff will protect everything.

Thats sounds like really sound advice, thanks John! Not looking for a show queen underneath, I just want to be able to use and enjoy it, I've found ACF50 works wonders on any working parts that need a little protection like my suspension control arms.

I had mine professionally Waxoyled a couple of years ago. It seems to protect the underside ok but the stuff is a nightmare.
It clogs everything and is really difficult to get off stuff like wires, cables etc and especially nuts & bolts when you are trying to work on them. The added issue I had was that the numpty that sprayed mine didn't cover the rest of the car and I got overspray all over my paintwork. You can only remove it with white spirit and a lot of elbow grease! Didn't do much for the paint but luckily it was before I had it resprayed which I had already planned.

Cheers for the warning Paul, I was under the impression that wax oil wasn't really the thing any more and it sounds like for good reason when it comes to any maintenance and accessing any area or nuts and bolts on the car.

I read it was a bad idea to steam clean the underside because you're forcing moisture into all the crevasses and the chances are you'll trap water in when you seal over the top.

I'm torn with Waxoyl as I'm led to believe is still one of the best products to use when it comes to protecting your car but, as said above, is a mare to live with.

Very true, either just leave it a long time on a hot day or just attack the area with a metal brush maybe, I share your reservations!

If it’s ur pride n joy it may be worth letting the professionals at it. I do nearly everything myself, but I reckon this is a job that’s worth getting done. These guys seem to feature in Practical Classics a lot an will sell the product or do it for u.
https://www.rust.co.uk/

I've considered this several times however there doesn't appear to be anyone more local (Surrey or SE). Given the car needs to be left there I'm less keen unless I know the place has an impeccable reputation. I know at home it will potentially be very messy and awkward though...

I've heard good and bad things about the POR 15 paint, epoxy mastic would be my choice https://www.rust.co.uk/product/em121-epoxy-rust-proofing-paint-black-1

How long does that stuff last if you paint it all on dude?
 

johnymd

Club Member
Just to add. The cavity wax I spray in all the box sections and crevices is very runny and doesn’t appear to turn into a wax at all. It is thin and runny enough to swap into all the joints between panels and leaves an oily film over everything. It came I’m a gallon container and with a metal spray gun for the compressor. I will try and find the name.

I remember over 40 years ago when my dad had a Mk 1 cortina. Every year when he changed the engine oil he would mix it with some parafin and spray it all over the underneath of the car. The car was used every day and in all weathers but was immaculate when he eventually sold it.
 

toopy

Club Member
How long does that stuff last if you paint it all on dude?

From what i've read it is very durable, and many people now prefer to use it instead of powder coating, as it's far less likely to chip, it can also be painted over stuff with no primer needed and even over light rust, although the surface needs to be clean, no grease etc.
If you read the bumpf about it, on a molecular level it gets into the surface pores, as opposed to just covering them as many other paints do in reality.
 

Matt Berry

Club Member
I’ve not long finished removing all the underseal and the best way I found was to spray it with plumbers pipe freeze and then use a blunt blade on a oscillating tool, that is if you’re taking it off. After the epoxy primer has gone on I’ll be going over it with Gravitex. From what I’ve read Gravitex will adhere to existing underseal as well so would be good for patching in gaps if you’re only removing what’s loose. It can also be painted over if you decide to. One of my friends uses it on his rally cars so it can withstand a good battering!
 

Woody928

Events Officer
Staff member
Club Member
From what i've read it is very durable, and many people now prefer to use it instead of powder coating, as it's far less likely to chip, it can also be painted over stuff with no primer needed and even over light rust, although the surface needs to be clean, no grease etc.
If you read the bumpf about it, on a molecular level it gets into the surface pores, as opposed to just covering them as many other paints do in reality.

Sounds like the kind of product I'm after, thanks chap!

I’ve not long finished removing all the underseal and the best way I found was to spray it with plumbers pipe freeze and then use a blunt blade on a oscillating tool, that is if you’re taking it off. After the epoxy primer has gone on I’ll be going over it with Gravitex. From what I’ve read Gravitex will adhere to existing underseal as well so would be good for patching in gaps if you’re only removing what’s loose. It can also be painted over if you decide to. One of my friends uses it on his rally cars so it can withstand a good battering!

Cheers dude, sounds like really good stuff and must be durable if its going on rally cars! I'm thinking a combo of these two may just be the ticket.
 

Graeme - CZ

Club Member
For me, it’s Tetrosyl Stone Chip. Used Waxoil only on the cavities. Like you, I’ll just be jacking the car up, so a clean by hand. I’ll use a friends compressor for the Stone Chip application. Not done it yet.


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