The 5 litre tubs offer much better value but you can only use them if you have an air compressor and spray gun in which case you can dilute it with 500ml/750ml of white spirit because Dynax in tubs is much thicker then the aerosol version.   I do not get a commission by the way its just the best product according to our research and own tests, Go to this page to see compilation of test videos of different products from around the world. 

• dries to a semi hard wax which looks amazing.
• Lanoguard stays wet looking and sticky attracting dirt.
• Dynax will last 3 years or more without needing a recoating.
• Lanoguard must be applied every year. 
• Dynax comes in an easy use spray can.
• Lanogaurd is applied from a manual trigger spray bottle.
• Lanoguard has a pungent smell of sheep Dynax does not.
• All clear coats like lanoguard lend themselves to inconsistent finish because you cannot gage the evenness and thickness of the liquid applied.

In the list above I have suggested 6 cans of Bilt Hamber Dynax for car which are £17 each. With an air compressor you can buy the 5 liter (£50) can and dilute it with 500ML of white spirit because it is rather thick for most spray guns. 5 liters would be ample for 1 car but that is coating every square inch metal and non metal and also coating the wheel suspension and inner arch. You could use a lot less cans if you simply covered metal. I however normally put a thick even coat all the way round for aesthetics as well as rust prevention. Lanoguard per liter is around the double the price of Bilt Hamber Dynax the company suggest you only need a small amount but that is by using a thin uneven coating which is not ideal and could be achieved with any undercoating. Also lanogaurd is simply not as good as Dynax and must be applied every year compared to every 3 years for Dynax.

• First start by removing loose and crusty rust. Its impossible to reach every part but remove what you can with you wire brush using sweeping motion back and forth until no rust or debris is loose. 
• The hammer and screwdriver can be used for heavy scaly rust. 
• Ask yourself is the surface solid without flaking? There is a common misconception that to stop ongoing rust that you must remove all rust. That is NOT the case the underseal is designed to adhere to stable surface rust and displace moisture so it stops ongoing rust (removing all existing rust is not necessary to stop more rust forming). 
• Check spots of rust in some cases spots of rust can work there way under factory rubber underseal or paint so you need to peel away surface around the spot. 
• When you have finished removing loose rust move onto general cleaning. 
• I will assume the car is bone dry if not you can put a cover over the vehicle if it is raining otherwise there will be water leaks in some places.
• Not having an air gun is a major disadvantage which I would normally use with a brush to remove a lot of mud a debris. However you can try a hoover or air can. 
• Now use the 2 brushes: dustpan and longer brush and cleaning wipes if obvious dirt on surfaces needs to be removed but generally speaking the idea here is to brush away loose mess so the surface is solid and stable.
• It is physically impossible to remove some marks and serves no purpose whatsoever. Remember you are not painting the underside you are applying a heavy waxy product which will displace moisture as long as the surface is not sopping wet or caked in mud it will adhere and form a barrier to moisture and oxygen.
• Some people will insist on a Jet Wash and can often be heard mumbling “its all in the prep” and “a fair days pay for a fair days work” and “Never put off until tomorrow what you can do today” These are often the same people using Lanoguard which is very poor product.
•  You can jet wash a car but NEVER do it first which most garages do. Why because if salt irons are present they will be under the rust you remove and under the debris.  So its always best to remove most of the debris by hand. However be aware a jet wash is very limited. I remember once undersealing a Toyota 4×4 the owner told me he had washed the vehicle twice and yet it was caked in muck. A dirty car can never really be washed with a a hands free car wash and the dirt under a car is ALOT heavier. 
• If you do wash a vehicle use AUTO WASH from Bilt Hamber as the main cleaning agent this has anti corrosion properties and as a rinse use Atom Mac also by Bilt Hamber diluted in distilled water as a rinse. Leave everything a few days to dry and do this all in the summer.
• Many vehicles will have mud in the chassis and in the sills washing with normal water will make the mud soggy and repel the underseal. 
• Bilt Hamber will work brilliantly on a stable surface a small amount of adhered dirt WILL NOT stop it working in the same way dirt in surface rust does not stop Bilt Hamber working. No matter how much you try unless you remove all parts from a vehicle and use a dry ice blaster your car will always have dirt you cant reach.
• The main thing to avoid is loose up mud or wet surface. Mud can often be found at the end of the sills near the wheels if you pry back the plastic trim.

When I prepare a vehicle at someone’s home I have an advantage of a 50 Liter air compressor. This allows me the benefit of a needle gun which is great for reaching into tight spots and removing heavy rusted scale.

Other tools I will sometimes use is an angle grinder with wire brush attachment, this is only really good for larger flat areas like the frame of a motorhome or van more so then a car.

The single most important benefit of the compressor is for a high pressure air gun as used by professional car cleaning (detailers) The gun removes a huge amount of debris and mud from the inner chassis by pointing the gun tip near open holes.

So with this in mind investing in a air can “might” serve a similar function. I remove a huge amount with the air gun so it is a big loss to a home DIY set up. Although some hoovers or a leaf blower might be able to do the similar. 

You will not be able to do a perfect job without an air compressor and you can’t use the most efficient tools. That said you can still a very good job and put a coating on to displace moisture and oxygen. Bilt Hamber Dynax is so much more forgiving then other Lanoline products because it adheres to the surface and dries. Other Lanoline products like Fluid Film, Woolwax and Lanoguard stay much more wet in consistency and loosen the surface they  are also sticky which attracts dirt. Professionals will simply do a quicker more efficient job this is not rocket science. Apply a Bilt Hamber Dynax to a stable surface and your novice job will be superior to any professional applying Lanoguard.