Any paint gets blasted off. I've used a product called Rust Doctor and have been impressed with it- though not under a deck. It changes the rust into a hard surface- kind of like the Extend stuff you get from the hardware store. I'm lucky as my local hardware also has the rust doctor.
BTW, I've heard where people apply truck bedliner under a deck but haven't seen it until this summer. A guy inherited a tractor that had it done who knows how many years back. It was at least 3 years. The old guy that did it had prepped the bottom of the deck so it was shiny bare metal. We had to remove it as it had shrunk and got damaged and was hitting the blade. This was on an old 46" Sears deck that is pretty shallow. It came off easily though.

If your paint peeled, you didn't prep correctly.

Main thing is to wash under your deck after you mow. Prevention, prevention.

Some spray under the deck with silicone spray to keep sticking down, but there is no way to eliminate sticking grass completely. I have tried that, it helps but doesn't remove the need to clean the deck.

I have found that sanding/sand blasting the underside of the deck, followed by a good soak of "OSPHO" will do wonders to stop rust and help paint stick. I hit all bare metal surfaces with OSPHO before painting. Heating the deck above ambient temps (simply leaving the deck in the sun, under a heat lamp etc) will do wonders to eliminate the moisture that invariably gets between paint and metal. I have learned the hard way living on the coast that when you paint metal, the flashing off of the reducer/paint thinner in the paint can lower temps enough to cause condensation on what you are painting. Any moisture at all between paint and base will destroy adhesion.

Anyone use POR-15? This is supposed to be like no other paint.

http://www.por15.com/

Thanks everyone for the help. I'm going to try your advice/suggestions.

I would not repaint the underside of any deck. Most of the time the build-up can be removed by just running the mower through dry leaves - piles of holly leaves or live oak leaves are perfect, and act similar to walnut tumbling media. You can do it with pine cones or even regular fall leaves. Once it's clean, simply spray a dry-film lubricant like DuPont Multi-Use Dry Lubricant. This goes on wet but quickly dries to leave a light waxy coating for storage. There's really no need to put any lube on it if you're going to keep using it, only for storage. There is essentially no way to keep the inside of a blade housing painted.

ANyone use Fluid Film?

Fluid Film would probably be okay along with a number of other products. If it's still made the same as it was twenty years ago, it's a natural product based on oil from wool or some such. I've used it for a few things over the years.

saxman, I don't have any leaves available in my property. It's a new community.

One thing I learned here and which I wasn't aware of is washing it after usage. I never did that. :(

Not to change the subject. Rust is the main reason I am looking at the Husqvarna WC21 or Toro commercial this time. They both have aluminum deck. My crapy Troybilt mower is only 2 years old to the exact, not only the front wheel is dangling, the under deck all rusted out only one year in. I do not even bother to spray Fluid Film because it is already so bad. Hopefully I'll be buying the new toy in 6 months. I even rule out Snapper, Ariens and even Honda. They all steel deck and I don't need that.

Yungman, be aware that aluminum decks can rot away as well. It tends to be those units that don't get cleaned up after cutting after all those fertilizer applications.

tom hit the nail on the head. Keep the deck clean and store the mower inside and you shouldn't have any rust issues.

Yungman:
If you hit a rock on a steel deck you get a little dent.

If you hit a rock in an aluminum deck, it can fracture the deck and destroy itself over time.

I had a little 20" mower back in the 70's with an aluminum deck. Ran over a stick and it broke a chunk out of the left side -- exposed 4 inches worth of the blade. Pretty cool, I could discharge left and right at the same time, but other than that I wouldn't recommend an aluminum deck.

Back to your concern about rust: Wash out the deck with your garden hose after you're done mowing. Then get some Pam cooking spray and spray the inside of the deck. It will drip for an hour, then dry. Biodegradable. You'll need to do it after each mowing and cleaning, but it will help keep grass from packing up, and help to some degree prevent rust.

Good luck,
James

Zoulas: Yes 15 is a great Product , I have used in on restoration work (frames) on various vehicles .

V1 Any epoxy style paint would suffice for your application , the Bed Liner (Rhino) or other Brands would work also once you have cleaned and prepped to White Metal , a small thin coverage is all that is req'd.

As Metal and Tom have advised cleaning and drying immediately after use is the key.

P.S. Thanx Dude for the Dupont Moylebeum Di-sulphate Dry
Spray heads up , I have a chum who has been going through chains on his enduro and he could not find any form of Product without a oil additive . I advised to check the Industrial Jobbers but no luck , Thanks again..Ty !

Yungman : Have to agree with Tom and James , Aluminium although making the mower lighter , does not in theory preclude Oxidation (Rust) pitting potential , especially if exposed to Harsh Chemicals. I had a Lawnboy for over 30 yrs (Two Stroke Model) great mower , never damaged the Non Ferrous Metal Housing (guess I lucky) but my Son trashed his with numerous rocks and sticks lol . Welding Aluminum was not convenient , so he temporarily Pop Riveted some 12 Ga. metal until he got the mower back from Camp. Then called and asked to borrow mine ...dah ..Don't think So
lol ..Ty .

The answer to all this is the Honda Xenoy (or whatever they're using now) deck. I had one for several years, and it's a great weight off your shoulders knowing it cannot rust, corrode or oxidize. Ever. You still have to maintain it to an extent to keep the film build-up in check because it affects mower performance.

Saxman1: Your the Dude that requires the Cudo's for the Dupont Info...Thanks again Bro ! Back when I was actively Racing Moto & later with my Harleys I used Dry Moly exclusively to increase chain life and reduce stretch due to dust and dirt contamination and cosmetic lubricant fling. As for Fluid Film , who makes it ? also Marvel Mystery Oil Product ? apparently these Magnificent Products are Sold out Prior to being available to us Canuck's within the Great WHite North ...Ty .

P.S. Hell , almost forgot back in my Snowmobile Racing Days (I had a Mis-Spent Youth)I ran a Snow-Jet "Thunder Jet" the Tunnel was Titanium I believe the Metallurgy Tec's said it's twice as light as Alluminium and 3-5 times stronger than Steel of the same Gauge ? I 'am long in the tooth but recall tweaking one and you could not hot stretch it only Cold Form , and even then Stress Cracks normally would develop. They were almost bullet proof , I guess they never made it to Commercial Lawn Mower Decks lol :) .

"If you hit a rock on a steel deck you get a little dent.
If you hit a rock in an aluminum deck, it can fracture the deck and destroy itself over time."

At best those facts are mixed up and the result is incomplete. If you hit either a steel deck or an aluminum desk with a rock you cen get a small dent, or it can puncture the material depending on the size, speed, shape, etc. of the rock.

Road Bike : Tread lightly Dude ! Poor Ole Mr Garfield was just trying to relay that Aluminum has a tendency to chunk out more readily than Steel . It lays somewhere between the Ductility and Malleability Physical Properties . Your are spot on though with the M x S = F Correlation lol . Don't whip the Bro to heavy his intent was Positive .

It's a myth that aluminum mowers are lighter that their steel counterparts. I have seen aluminum deck mowers marketed for areas where salt corrosion is a major problem for steel decks. That isn't the only reason though. Aluminum deck mowers are much stiffer. (MTD made a stainless steel deck mower and it was really floppy and would twist significantly if lifted from the side.) All in all aluminum deck mowers hold up over a long period better than steel.
It's also a myth that titanium is lighter than aluminum. It's not, titanium is heavier than aluminum but lighter than steel. It is true that titanium is stronger than aluminum but it is not stronger than steel. Titanium does however does hold up to corrosion/oxidation better than either steel or aluminum. A titanium deck would be too expensive though.
From the evidence I have seen aluminum decks survive longer than steel ones on average but both have weak points.

Good Post Ray ! I agree 100 % Sorry I had to Bait You again lol . T. is 60 % Densor than A. 85 % Stronger .
T. is 45 % Less Dense than S. camparable
Tensile Strength within same Guage .

Saxman: As far as Lightness , The Honda "X" Composite PBT (Polybutylene) & PC (Poly Carbonate) probably is also at the Top of the List . I'am not sure of the Crack or Fracture Resistance , because I have seen cracked mower decks on Used Hondas (2003 - 2005) within the last few yrs.
But then some people damage Grader Blades lol . Good Posts Guys ! :)

Ok here it is the answer to this is called clean deck graphite. Search it let me know what you think. The lawn shark in south Georgia

One could try the graphite. There is your homework assignment johnhearon. It reminds me of what I always called grease paint. It was used in gravity boxes. My experience with a similar product didn't fair well. I prepped and applied underside of a new aluminum recycler deck and it pretty much got blasted away well within the 1st season. Maybe this is better. People have me put Modeck on , but I'm guessing it is short lived for the average consumer that doesn't keep clean and reapply. Strangely enough the stainless decks don't seem to clean any better that regular ones. That is using the logic that you aren't dealing w/ pitted rusty decks. Honda's plastic is the way to go for non stick as mentioned above. Love those rounded scrapers.