Undercoating Need Help

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Well-known member
Nov 18, 2006
New Hampshire
Hi all

Need opinions, on what kind of undercoating to use. I am starting to remove rust from the underside of the coach and would like to undercoat it with something that works well. I have to remove all of the storage boxes and replace some supports and then I will do some sand blasting and undercoat the underside and the frame. The last owner did not do any maintenance to the under side of the coach. I would like to only do this one time. I did read the other posts on the subject but did not know if anyone had any updated info.

Has anyone tried www.rustbullet.com
Haven't tried Rust Bullet or even heard of it before. Sounds like it is trying to outdo the original Rustoleum claims and maybe it does, but its still  appears to be a paint and paint can only do so much.

The Rhino bedliner people advertise a professional undercoating service - the rubber based stuff that vehicel manufacturers (those that actually do undercoating) use.
Eurothane is the best but is awfull exspensive.  Same basic material as the bedliner stuff but without the texture.  You can put on multiple coats for best results.  I use Eurothane paint to waterproof the undersides of campers when I have to replace wood panels in them.  Works good for that but you'll need the real stuff.

I have undercoated 3 vehicles and here is my take on your job. 

First get a GOOD mask to protect your lungs and good goggles to protect your eyes.  Cover your ears and hair.  This is VERY important because it is best to spray the undercoating on, not brush it.  Believe me, you'll throw away the clothes you wore when you're done.  Jack up the MH and put jack stands in each corner.  It helps a lot.

In your case clean it up as best as you can by sand blasting and wire brushing or what ever.  It is not important that you remove ALL the rust only the big chunks that are about to fall off.

Put masking tape over important electrical connectors and so forth in case you need to get to them in the future.  A litte grease wiped on zirk fittings is a good idea too.

Then get either spray cans of rusty primer paint or a spray unit to spray to spray on the rusty primer paint.  You'll never get all the rust off, only the big chunks, and this paint will adhere to rusty metal. 

Finally, get spray cans of black undercoating paint (it's somewhat flexible after it drys) or a spray unit  to spray the black undercoating paint.  Some of the Rhino coatings MAY hinder ball joints and other mechanical things. 

Best of luck.  It's a difficult and dirty job.

Make sure you mask off the Drive shafts  If you don't, they will become unbalanced and shake you out of the coach.  Been there done that
I was gassing up last month and this 36' MH pulled up along side.  I noticed that the front had something on it similar to those snap on vinyl covers.  As I looked closer I noticed that it was Rhino Liner.  I got to talking to the owner and he told me it was the best thing he ever did after going through the chipped paint, torn covers, etc.  His coating was tinted to match the paint of the MH.  He told me it's been on three years with never a problem.  It was a much thinner coating than the bed liners and blended in nicely.  Even though it didn't have the Shiny polished look of paint, it didn't detract from the overall look.
I've seen it on roofs of a couple of home done bus conversions.  There was a seller at the Portland RV Show a few years ago that was selling it for roofs.  He had some neat pictures if jobs that were really good looking.
Zinc is the material in good undercoat paints that does the work of combating rust.  It combines with water somehow and does the job.  Boats use or did use a bronze based paint for the hull.  There was a red lead paint that boats also used but it was not as good.
You might also try going to www.eastwood.com  They make all the great stuff of rust removing, washing it afterwards and undercoating. They sell good productsd. I restore cars and have used a lot of their stuff and have very satisfied. Good Luck. BnA


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