Underbody protection

[steve]

My sons mk6 golf had an advisory for corrosion on the last mot. Seems to be very light surface rust at the moment so looking for advice & opinions.
 I once had a Nissan Terrano which had surface rust on the chassis, I shot blasted it back to bare metal then primed it and painted it then coated it with Dinitrol on the outside & used the dinitrol cavity wax on the inside. This prolonged the life of the Terrano but it still rusted in areas where the chassis was double skinned, like around tow bar mounting. Double skinned areas obviously holding moisture & can’t be accessed to be treated.
Still hoping to be able to protect the golf for a bit longer, what products do you prefer or are there any we should avoid?

[chippie]

I’ve used waxoyl in the past….

My 63 plate Fiesta is going to get treatment soon, once the weather picks up….Clean front cross member, back to bare metal and repaint…then waxoyl

[valhalla]

It isn't the best time of the year for this work; you want the protective waxes to flow inbetween the sections and seams.

If you really have to do this job right now, then there are two products that will protect any metalwork properly, without a heated workshop;

The Bilt Hamber Dynax S50 wax (aerosol or big drum for pressure-spraying) is thin enough to flow into the nooks and crannies, but is best applied in slightly warmer weather (15c is good)

Even better, and a product I'm testing right now, is Lanoguard oil-film, which is applied out of a trigger bottle (you can fit a mini-lance to the bottles) and is runny-enough to flow into the welded joints, without just disappearing onto the floor. I am using this stuff down to 5c ambient temps, but I would recommend smearing the equivalent Lanoguard Grease over exposed areas near wheelarches and in direct line-of-fire.

[steve]

Thanks for your help. We wouldn’t be doing it until the summer, I will try to remember to post on here again when we do the work.

[rhyds]

Bit of a thread revival but I'm looking to give my 12yo Focus a bit of a helping hand to keep the rust at bay.

While I understand its much easier and more sensible to rustproof cars in the summer I'd like to start getting my plan and materials together now, so thought I'd best ask the stupid questions early

First off, if I'm using something like the Bilt Hamber S50 do I need to wire brush and/or paint the underside of the car first? Or just get the loose rust off?

Secondly, I assume there's no real problem with spraying said protectant on suspension bits as long as I keep it off any sensors and brake surfaces?

And thirdly, for areas that are protected by plastic undertrays and liners (e.g. inside wheelarches) is it better to take them out, spray behind them and then put them back on?

[chippie]

Any decent rust prevention is best applied when the car is driest so you don’t trap any moisture…….So a warm sunny Summers day ( rare these days….😂 )

As to where to apply, I would remove any flakes and apply to good sound areas…..going back to bare metal and painting is a bit overkill..where do you stop?

Any areas not directly exposed to water are just as important in my book, moisture can form due to condensation…

In the past I’ve applied Waxoyl to all surfaces, nuts and bolts and just about anything but avoid friction areas like brakes and any sensors…
Engine under trays are best removed as are wheel liners for access to indirect areas, but again I think it’s personal preference..

[valhalla]

Mar 8, 2022 23:56:33 GMT 1 rhyds said:

And thirdly, for areas that are protected by plastic undertrays and liners (e.g. inside wheelarches) is it better to take them out, spray behind them and then put them back on?

Definitely. It will give you the chance to clean and dry the surfaces under the liners. As Chippie says, you want to make sure the surface is dry first. If you have an air-line to hand, then I would recommend sweeping-out any loose mud and sand that has accumulated behind the liner, then blow it all down with a decent blast of air, then leave the wheelarch to dry in a garage overnight before spraying - preferably warming the surface before leaving it, so that any condensed moisture can dissipate.

S50 is brilliant stuff, but you need to be careful about it all just running back off the surface before it has had a chance to dry a little. My own experience of this was decades ago (around 2004) when I sprayed all the internal voids on my (relatively new) Defender bulkhead as a trial. It still does its job 18years on, but the voids are not in line-of-fire from roadspray, etc. I think this stuff needs protecting from impact and abrasion, so behind liners and inside box-sections is its best use.