Time For Some Under-seal!

With winter on the way and the salt and grit and bad weather, this weekend could be the last chance you get to under-seal under you 4×4 or car, as you don’t want it rusting away and you don’t really want to try to user seal in cold wet weather.

How To Under-seal your vehicle


Many people do this different ways, some use paint brushes and a can of undercoat like waxoyl, some use spray can of waxoyl, I personally like and use the Waxoyl Pressure Can and sprayer as it gives a good coverage and is easy and fast to do. I can normally spray under my land rover in about 1-2 hours, but this doesn’t take into hand the cleaning time. I also use the BLACK Waxoyl not the clean as I feel the black looks better on an older chassis.

What you will need:

Waxoyl Pressure Can
Waxoyl sprayer
Cheap Paintbrush about 2″ will do.
Terps / thinners, only a small amount for cleaning the sprayer once done
A Bucket
Wire Brush
Hose Pipe & Pressure Washer
Ramps (optional but handy)
Bottle Corks (optional but handy)
Dirty Clothes
Goggles and Mask
Old / Used engine oil

Step one: Cleaning

Before you start to underseal you vehicle, you will need to give the underside a good clean, I normally go down to my local car wash first / Jet wash and using a set of ramp drive the front or back end up on the ramps and power wash the userside and chassis. Get as much off as you can and get build ups off areas like the out riggers and petrol tank etc.

Once the underside is clean I Personally like clean out the inside of my chassis due to offroading. To do this i plug the drain holes on my chassis bottom with bottle / wine corks (my need a little cutting down)  and using a hole higher up (behind the springs on my landy) put some washing up liquid and water into the chassis using a hose pipe. I then go for a drive over a bump road (not offroad other wise you need to clean underneath again) to wash around the water inside. Once happy remove the corks and watch the dirty water come out. Another drive is also good to make sure all the water is out.

Step two: Scrub

Using a wire brush give the chassis a good scrub / rub down and get as much surface rust off as possible and check for areas of bad rust. If you do find areas please have these repaired before going any further.

Step three: Underseal

If like me you are using the Waxoyl Pressure Can and sprayer you will find that it works better when the waxoyl is runny. Some people say add thinners but I would not recommend this as you are just thinning the protection. The way I make the waxoyl spary nice is by heating it. I found that putting the tin in a buckets and poring boiling water over it and letting it stand in the water keep the waxoyl hot and nice to spray.

Once you have heated your waxoyl, pump the waxoyl can to pressure. Now wearing your Goggles and Mask (don’t really need a mask as there no CFC gasses in the pressure can as you using air pressure, but the wax oil not nice if you get a blow back) start at the spray the chassis of your vehicle. I like to start from the inside from under the vehicle and then do the outside, otherwise you under can run on just sprayed waxoyl when climbing under the vehicle and get covered. once the chassis is covered give the petrol tank a coat as these also rust and can be an MOT failure.

For the fiddly bit use the paint brush. Spray the paintbrush and apply.

Once the chassis is done you can also spray your axles and A frame. Try not to get any on your brakes. Buy this time you will be a dab hand with the sprayer and find it easy not to cover part you don’t wish. If you have any left in the pressure can you can spray this inside the chassis through the holes you used and plugged before or spray the underside of the body, but save some for inside the chassis.

Step four:  Cleaning / Inner seal

You now need clean the sprayer. Release the pressure from the pressure can via the valve and remove the sprayer. Add some thinners to the pressure can and remaining waxoyl.

Plug the chassis once more, now using the sprayer, spray the thinned waxoyl into the chassis. this will cover the inside of the chassis and clean out the sprayer for next use. You may wish to mix more if you have a refill can
. If not don’t worry. Now clean the spray gun its self with thinners so its ready for the next time you need it.

While your chassis is still plugged, use a funnel and hose pipe and pore used engine oil into the chassis, but watch for leaks so you don’t mess up your drive or the road. Now take you vehicle for a drive so the oil moves around the chassis. This acts as protection. return home and remove the cork plugs and drain the oil and discard. Please try to keep oil off main roads. This method is a very OLD SCHOOL method but does protect the inside of your chassis.

The CORRECT way is to use the Waxoyl Extension Probe which connects to the sprayer and allows you you push it inside the chassis and spray, how ever this requires you to use Waxoyl Clear as the black blocks the extension pipe. You may be able to use with thinned black, but I have not had any success with this.

Small clear Waxoyl refill cans are available and you may wish to invest in one of if you intend to use the  Extension Probe.


This will protect you chassis for years, but if you do alot of offroading and wading, I would underseal every year or every other year. the pressure can will save you time and money compared to the £300 plus a garange will charge for undersealing…. and you will still have to do the cleaning the scrubbing stage.

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