A topic done to death... Underseal

  1. My model of MX-5 is: '21 R-Sport
  2. I’m based near: Neath, South Wales
  3. I’m looking for technical help or recommendations on: Undersealing

Hi all, I understand that this is a topic that has been done to death but I’m looking for advice on undersealing my car. I’ve looked at so much stuff - Dinitrol, Lanoguard, Waxoyl etc… I’ve blown my mind. I am not in a position to do it myself as I have no idea of where I can take my car to lift it and clean underneath. I do have a drive but its uneven. In an ideal world, I would like another MX5 club member to help me or even do it for me… but failing that, where can i take my car thats relatively local? I have been quoted £1000 for Dinitrol treatment in a garage near Carmarthen. I have contacted Total MX5 repair who’ve said to recontact when its drier however my car is a daily driver that is left outside on my drive so I’d like it sorted sooner rather than later. Im also unaturally worried now about driving it in rain and am dreading grit. How can I clean the underneath until I get it sealed? Is a hose on sprinkler setting OK?

Any advice most welcome…

Don’t panic… running a 2 year old car through the winter will not cause any significant detriment to carrying out a good underseal job when weather is warmer. Total MX5 are correct, now is not the best time, personally I’d say in the May - Sep timeframe.

I clean my car underneath periodically with an underbody spray attachment for the pressure washer.

My 2019 car is not yet undersealed, I’ll probably do it next year, last underbody inspection in September didn’t highlight anything I wouldn’t expect to see for the age, basically surface rust starting to appear on subframes.

I have done 2 x brand new ND’s and in good conditions and a lift you can do it in 4 - 5 hours if everything is bone dry. Materials wise it is about £150 - £200 using Dinitrol, masking materials etc, labour time is where the cost comes from.

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Probably not a great concern at the moment for you, when you do get it undersealed etc they will wash and treat so “one more winter” shouldn’t be a worry.

In the meantime, a power washer is a good tool to get wheel arches and easy to see places washed down. I bought an angled attachment to get into crevices a bit easier and it attaches to my Karcher washer.

Angled Power Washer attachment for wheel arches

In the meantime, if you are concerned you can get this attachment for a power washer, it may also work with a hose pipe if the pressure is decent (but thats a guess)

Under Car Washer Attachments - Amazon

From quotes I’ve received in the past, as seen in other posts on this subject, range from £200 to £600 for a simple underseal to a full job including cavities although I’ve seen some online estimates in the £1,000 range.

Probably not helpful to you, but a place in Hertfordshire in the link below gives £££ price but plus VAT. Gives a range depending on the service you want. May be useful to you if looking around for price comparisons.

CSK Hertfordshire

Posted about the same time as Ian!


I used these guys in the summer of 2022 and they were very good. Importantly they spray, brush and apply. And the wheel arch covers get taken off to get to the areas beneath. There will be a branch fairly near you I reckon:

Waxoyl Treatment For Land Rover Defender Discovery Jaguar Mercedes

More generally, don’t overthink which product to use, the three you mention are all good enough in their different ways. The key is that a professional job will be in the order of £600 and take a day to do. Anything less in terms of time and money and they probably aren’t doing it sufficiently well.

Of course, it’s possible to take things to the max and get a multi-day job (some members have done this) which removes the bumper, sub-frames etc.

But bear in mind that undersealing MX5s remains a controversy, a bit like the efficacy of regular blood screening in medicine. There are those who would argue that a power hose to the underside of the car every couple of weeks through the winter to get the salt and muck off will suffice, as long as the car is not badly rusted already.

With all that in mind, I steered the middle course - the £600 job.

Other views (many of them!) are of course available…

As noted above your car is relatively new and there’s no real need to rush into a decision. However, if you want some ‘peace of mind’ you could consider a basic Lanoguard treatment. I found a few garages in my area who were ready to wash, dry off, wire brush any obvious surface rust and apply the product for around £250. I believe it will be good for about a year. I had this done in October and depending how it looks next Autumn I’ll either repeat or go for a more comprehensive job. Good luck.

I’m not far from you,in Skewen. You could try the guys at Select accident repair. Theyve just moved into new premises by Zoars Ark

Hi all, thanks for the advice! And thanks to Dave too! I dont have a pressure washer ATM. Is a hose on sprinkler setting ok to clean underneath?

Dont use Lanoguard, it does not last.

For anyone who wants to do it, do it right, that means take all old underseal , treat the rust by removing it then, buzzweld rust enscapulator zinc primer and paint, Buzzweld cavity paint, bilt hamber dynaz s-50.

Do it once, to it right.

Does anyone know where I can get it done like this thats nearby?

Don’t know if you do Facebook but there’s a guy “Anand Viad” based in Iver which is 3 hrs from you who is very good at this work.
He’s closer to 4 hrs from me in Liverpool but I took my NC1 to him last year, kept it for a week and give it the bifters.
He comes well recommended

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I can also recommend him, he knows if stuff

Yes, its been done to death on the Forum.

£1000 incl vat for a thorough Dinitrol treatment doesn’t sound unreasonable. If they do it properly it will take 2 or three days. They’ll remove the wheels and bag the brakes, remove the plastic liners to the wheel arches etc. They’ll then need to prep the car by removing any rust/ scale. The RC 900 rust converter will then be applied and allowed to dry, followed by 4941 underseal with ML injected into to the box sections and cavities, once this is complete the car will then be reassembled. This isn’t something that can be done properly in day.
See if you can get some customer reviews from the garage.
Preparation is key.
I did this myself on my 2009 NC2 a couple of years ago and it took me 3 weeks part time. Removing the rust with a wire brush on my back took ages. The Dintrol DIY comes in aerosol canisters and is the easy bit.
Good luck.

That shouldn’t stop anyone asking a question, local services can change, people can comment on the efficacy of products etc.

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Also the tech and the general consensus evolve…

The trouble with “undersealing” - and any traders calling it that should be treated with scepticism - is that you can’t really see what’s been done. Fly-by-nights will just spray black gunk over the underside of the car, which is next to useless.

The important thing is to clean everything of loose rust, dry it thoroughly and inject all the cavities before even thinking about coating the visible surfaces. Even then, something waxy and self-healing would be better than bitumen underseal, which can trap water underneath if it has any holes in it.

Anand Viad Is your man. Check him out on FB. He goes to the Nth degree by also trimming the plastic arches by a millimetre or 2 to stop them rubbing paint and causing more rust opportunity. He removes all old and full treats bare metal including inside box structures.
Top bloke too if not always out for a ‘little snack’

Avoid Waxoyl, it was a good product in like 1980 but nobody should be using it now, except arguably on classics.

The question is basically, permanent or not. Permanent is obviously better, right? Except, permanent has to be done right. For a rusty car, permanent to mean derusting first and that’s a massive job. For a new car, maybe it doesn’t, but at the very least you’d expect it to be only localised and that’s a big difference.

(exception being cavities- there’s nothing you can do to a car that’s better longterm than a really good cavity and sill treatment, and because you really can’t clean it, anything but a really good treatment is a bad idea. And it’s easy to do well- or, rather, it’s easy to do as well as it cna be done, just because of access. So always go ■■■■■ out for cavity protection)

Impermanent is worse, except, you can do it over rust, you can do it and then do permanent later, so the absolute worst is that it makes things a bit better for a while, you can’t cause harm. That’s where lanoguard shines, you can literally just spray it on everything bar the discs- it’s safe on rubber and shocks, you can just descale any rust scale and otherwise it’s fine to spray over rust, and while it’s not as good it’s still helping. It wants topped up annually but the top-ups are a much smaller, quicker job.

In your case, that’d basically mean not stopping the aging of teh car but slowing it massively. In 5 years time it’ll be in about the same condition as it would be untreated in a year or 2, at very low effort. And it protects shocks and rubber too. Eventually there’s a tipping point where it’d have been better to have gone all in, but, will you even own the car then? Will it even last that long? I’m doing a full permanent derust, epoxy and wax on my NC and there’s basically no way it’ll pay off, the car is pretty much going to be rustproof til I die and what are the odds I keep it that long and don’t loop it on a roundabout or a trackday? I just like doing it right is all.

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How do you expect anyone to take what you say seriously when you start your post with such a comment.

Used correctly there is nothing wrong with Waxoil, yes there are other more ‘contemporary’ products that will also do a great job when applied correctly but please do not be so dogmatic and dismissive when expressing a view.

If anyone wishes to know how Waxoil can protect then I am happy to send you some pictures of our 31 year old mini as actual and factual evidence of its effectiveness.


I have to agree with the other poster waxoyl has had its day, far better products on the market now.

Bilt Hamber is far better in my books

Well, today after work, I drove down to RustOust near Cowbridge. I had a funny feeling about going there. I should have listened to my gut… enroute to the location, a massive Ford Ranger drove past me on the M4 and something fell off the car bounced into my lane where it proptly hit my car and bounced underneath. Im hoping it’s just mud. The B roads leading to the garage were lightly flooded and full of debris, but I persevered on. I got to about 1/4 of a mile away and the ‘road’ leading to the garage was full of potholes. I’ve seen shallower caves, and I had to negotiate a nighmare panicking that I would grind my car to bits. Eventually managed to find the garage and, with no disrespect to the business, it looked pretty ropey however, after driving nearly 30 miles and driving through potholes, I wanted them to have a look. The ramp looked like the car would scrape it if driven up the ramps one of the employees who said that he would have to drive the car onto the ramp said that the car ‘should’ be ok! I told him to leave it and he ended up putting wooden blocks down to help get the car onto the ramp. This was done and he started raising the ramp… it got to about halfway and water came pouring out of the control box for the ramp! Despite this, the ramp was raised to full height. By this time it was getting dark and a different emplyee came over looked underneath and said that they couldn’t see any sign of rust (I’m not surprised as I couldn’t see any detail because of the rapidly fading light). I used the torch on my phone to have a cursory look and could see some small patches of rust, but nothing crazy. I told them that I would think about it and watched them drive my car off the ramp (when it was lowered!). The car almost came off the side of the wooden blocks! I couldn’t wait to get out of there albeit it took me even longer as I couldnt see the potholes clearly. Anyway, long story short, I cannot recommend rustoust and will not be trusting them with my car…

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