lewisdj

Looking to get the underside of my Hawk STI professionally undersealed. The car has been garage kept for the last 8 years of ownership and hasn't seen the rain for years so the underside is relatively tidy, but i'd like to get it sealed as a preventative measure.

Anyone know a company that can carry this out in the South Wales area?

Cheers

lewisdj

Or has anyone done this themselves? Any links to any guides?

ST-X

It depends how far you want to go but avoid the non-setting black Schultz or wax oil as they allow moisture to creep underneath, sit and then cause more rust than they prevent. The absolute best way is to remove parts and paint them as that's the best form of protection, followed by underseal wax, but it's a lot of effort so a combination of removing any loose areas of surface rust and painting with an epoxy mastic, followed by a wax is a good second. There are multiple different sprays; some are thick stone chip like products but IMO these are not the way to go and instead using something like Bilt Hamber Dynax or an equivalent is going to be the best from a DIY perspective. It'll probably need annual top ups in high wear areas but I generally think most of the professional coatings will need similar anyway, albeit at a higher cost. If you're comfortable with getting the car up on high stands then aerosols or a Schultz gun and compressor to apply the stuff copiously shouldn't be too onerous and give you a good finish. The key is prep though so lots of degreaser and ideally a hot wash or steam clean, followed by time to dry is critical. An angled jet wash head will help with getting into corners. I'd spray with a water dispersant like BH Ferrosol followed by the wax, and make sure to bag/mask off the exhaust/headers and the brakes with all the wheels off so you can get into all the areas. Make sure you take off all the plastic under trays and the side skirts and flaps too, as well as the arch liners (the front ones hold mud against the inside of the wings and cause bad corrosion in my experience). Make sure to well protect the rear arches, particularly the back corner where you normally see bubbling on the outside, as well as up inside the turret. I don't think it's possible to apply too many layers in these areas. The outer portion of the inner rear arch is bad too as it isn't protected with stone chip. Clear wax (Dynax UC) is obviously better visually but the UB which dries a dark brown is longer lasting. You pays your money etc etc. I'd make sure you use a good cavity wax too, I like Dynax S50, and go copiously into all channels, sills and subframe cavities to the point where it's dripping out of all the seams. I do think a thin spray grease can be better for creeping into seams but the S50 does seem to be pretty decent as it comes out very thin. A heated garage and warming the cans in hot water first will help give the wax longer to creep into joins better before it starts to solidify.

Hauntednsk

Check this: and after - this and this
I just used CRC 06026 Corrosion inhibitor to seal and protect for the season. Used 5 cans for SG5. Almost no dripping, sticks great.

lewisdj

Thankyou for the comprehensive guide there, appreciate that. I think I will attempt to do it myself, will be a nice project for me to carry out over the next few weeks.

I don't think id remove each part under the car and paint them as its reasonably tidy under there

As for the prep, i don't have access to steam but i do have a jet wash and degreaser, was thinking of saturating the underneath with degreaser and giving it u good scrub and jet wash down from prep, would this be sufficient?

How many of the spray cans (Dynax-s50 and Dynax-UC) would i need to carry out the job?

lewisdj

That first video is terrifying!!

Second video was very useful in comparing the different brands of spray, that CRC 06026 looks like some excellent stuff, how did you prep before using this?

ST-X

There are ideal ways and there are the ways you have open to you; do the best you can, scrub stuff as much as possible, and then make sure its dry before you spray the wax. I'd go on three or four cans of UB/UC and then a full can of S50 to do all the cavities, but would maybe order two to be safe, especially as you're saving money by doing it yourself and it's always better to use too much (no such thing) than too little.

If you're not removing stuff then that's fine, it's a massive rabbit hole, but I would still aim to remove the plastic panels under your sills, the skirts and the front wheel arch liners. This is where a lot of mud and moisture gets trapped and that's the bits where the rust gets a stronghold and starts eating away at the metalwork.

Hauntednsk

Nothing special. Just used to spray some engine degreaser spray underneath where I could reach and they washed underneath at the car wash - that is it.
My Forester was just imported from Tokyo in May and it was so clean underneath, so basically I just washed it with a high-pressure washer.

CRC 96926 is sticky and sticks to any surface perfectly, even if there is some dust on it. It penetrates and makes a kind of fluid thick film. I used it the first time and looking forward to applying it every 2 years.

lewisdj

Have ordered 5 cans of Dynax UC, a couple of cans of S-50 and a load of degreaser.

Will look to start the job in a couple of weeks.

Thanks for your input and advice gents much appreciated

hedgecutter

iTrader: (5)

UC is good but not hard wearing. Just use it on the fancy coloured parts you wish to see.

jaygsi

iTrader: (46)

Mine was undearsealed from new and the bodywork is mint under the underseal. Looks like standard waxoil, but the original owner paid loads to have in=t done by Subaru.