Underbelly deterioration on 2013 Mountain Aire

[DRM901]

You really don't need marine plywood. What you need is good quality plywood, then coat all 6 sides with at least 3 coats of 2-part marine epoxy. Ideally, you want to warm the wood up some (if down here in Texas, I just stick it out in the summer sun for a while, but near a heater or a heat gun will work as well), then paint on the epoxy. This gets the wood to stuck in the epoxy a little more.

I've been using West Systems products for 30+ years with great success. Their web site has a lot of good reference material to help you out, including the idea of heating the wood.

If you drill a hole and put in a screw, you need to seal that hole. Just coat the screw with epoxy before you screw it in or squirt some into the hole with a West Systems syringe.

If you have any questions, just contact me.
Dale

[Dav L]

My question is: what is your work surface? It looks like carpet? Doesn't look like concrete from the pics. Just curious

[Firedog3722]

That actually is concrete. When I'm working in the bay I have a few large sections of cardboard from freeze/refrigerator boxes that I move around. They are thin, move easily, and provide just enough softness for my knees and keep the cold surface off my butt.

[Delacroix]

Firedog: I have a large metal fabricator locally. I’m thinking of using some form of metal in place of the aluminum. I was planning on talking to them for recommendations. I wish I knew what type and where to buy automotive grade plastic( some form of polymer) that I could put in place of the aluminum. What adhesive are you planning to use to place the aluminum panels with? Obviously it needs to seal and bond. I was able to order marine grade plywood from my local Home Depot. I have scraped and sanded my steel structure pretty well. I’m planning on using a “rust dissolver” ( basically an acid) on the rust prior to priming. I was planning on using a primer that also was acidic that would help bond to the metal beams better. I was planning on using pull rivets. My handyman skills are pretty decent. No pro by any strech of imagination. I’ve done this kind of stuff all my life learning by trial and error. I worked in coal mines while going to school. I’m a retired dentist. My age is a bit of handicap getting under and crawling around. Just not as fast and strong as when younger. I learned very early in practice that I needed to repair my own equipment or shut down for 2-3 days waiting on repair man. I would greatly appreciate any adhesive and caulking material suggestions. I had just planned on studying on Google to come up with products. With your knowledge of riveting, when I repair the wheel well area, do you think the pull rivet or stainless steel screws would be better?

[Dav L]

Originally Posted by Delacroix

I wish I knew what type and where to buy automotive grade plastic( some form of polymer) that I could put in place of the aluminum. What adhesive are you planning to use to place the aluminum panels with? Obviously it needs to seal and bond. I was able to order marine grade plywood from my local Home Depot.

Home Depot paneling department has FRP (fiberglass reinforced plastic) 4'x8' panels that are perfect for what you are trying to do. cheap, readily available, strong enough, clean, can be glue with FRP glue (same aisle), water proof, no shipping required (just your truck / trailer). About $25 per sheet. White with dimples on one side, flat on the other.

https://www.homedepot.com/p/Glasline...9600/100389836

[Delacroix]

Does anyone know if fiber glass reinforced plastic can be secured to metal by gluing with a long term adhesive to the metal beams under coach.

[Dav L]

Originally Posted by Delacroix

Does anyone know if fiber glass reinforced plastic can be secured to metal by gluing with a long term adhesive to the metal beams under coach.

The general answer is sure.
But what are you really trying to do? Pics please.
Without any details, glue and screw is probably the right answer. Self tappers.

[Delacroix]

I’m still trying to determine what I plan on my first layer. ( area that directly face road). I was in contact in a real round about way today that is mechanical engineer and worked on early space shuttles. Firedog you and he probably have a pretty comparable knowledge in materials. He suggested low density polyethylene and told me of an online site to buy from. Called U.S. Plastics online. It’s not cheap but also not extremely expensive. I also thought about pricing 1mm stainless steel. I have not followed up yet on any insulation properties. Dav L: I promise I will try to post some pictures. Every time I’ve tried to learn I get frustrated and give up. I’ll try to have my 18 yr old daughter help me. My rig is identical to what Firedog posted. Almost ident breakdown of Aluminum on the back wall you see. I have read you can wield this material but I done not know the adhesive properties yet. This will need to bond(adhere) to metal with a sealant.

[Firedog3722]

The first layer I'm going to use is the same stuff Newmar uses. It is a thin aluminum with Styrofoam laminated to the alum. I'm using this for the insulation properties involved. I'm sure you would want to have some type of insulation. What were you planning to use? The wet bay heater is good but if it is really cold outside and you don't have some insulation I think you will have an issue.

The stuff from Newmar is relatively inexpensive, and they pay the shipping. It came freight in a 4x8 wood crate frame with cardboard on the outside. I personally would stay away from something heavy like SS because it will take away from your vehicle weight capacity.

I removed the bad part of wall that sits in front of the rear wheels today (see pictdure below). After a discussion with my aircraft mechanic friends we all decided that pop rivets will be used. The bad wood product on the back wall has also been removed. You can see in the picture what I removed to insure I had good wood. I'll have to cut the replacement in an odd shape to get it back in because of the two longitudinal chassis beams and the sealing they have around those. My plan is to insert the new wall between the remaining alum wall and the remaining wood, rivet the two pieces of alum together, with sealant between the pieces. After the rivets are in then I'll use sealant over each rivet on the outside and inside to cover the heads and hopefully stop any potential water path.

I also removed my water pump that was attached to the wall as well as the auto fill valve. To my surprise those were installed on the wall with screws that whet completely through the back wall and were an avenue for water to penetrate the wall (the screws had nothing on the threads when they were removed). I don't know if the pump was installed by Newmar or not, it did look new.

I'm going to call Newmar tomorrow to see what they use as far as sealants go. There are hundreds of sealants and it depends on who you talk with. I'm going to visit a couple auto collision repair shops to see what they use for metal to metal sealants. Looking at new cars today you can see some of the seams they have sealed and it looks pretty good. Will let you know all the suggestions.

[Delacroix]

Did you order two sheets of the Aluminum-styrofoam from Newmar? I need to do the math still to see what is the minimum needed. I have only taken out about 1/2 as much of the back wall as you have done. My wood is this area appears sound when cutting it. I will use marine plywood here instead of “press board” that newmar used then cover with some metal product. I fear the aluminum-metal reaction reoccurring. I guess if I could find the correct adhesive-sealant I would not have to worry about it. I’m interested in hearing what you find out from newmar. When I started the job the guy on customer service line really was not much into giving info. He wanted me to go to the Newgal owners site. My wood is sound under the final 1/4 under the drivers side where all the water inlets and dump valves are. I was going to try and not take that portion out.
As I’ve looked and studied this I think all my water intrusion has occurred in the wheel well area. I plan to really put in the time and effort to get this area perfect.
My original plan was to place whatever I decide to use against the road then adhere styrofoam insulation they have at HD to that then place my plywood. I really fear the chemical breakdown of the aluminum-metal.
I had no idea of the wheel well breakdown but had been resealing the underbody yearly with spray undercoating. Last year I decided to try and re-glue some of the styrofoam and my glue instantly melted the styrofoam.
How long did you have to wait on the aluminum-styrofoam from Newmar?
I really appreciate you sharing. You are a few steps ahead of me. I wish there was some way to get the word out so others could be proactive.

[Dav L]

Originally Posted by Delacroix

Did you order two sheets of the Aluminum-styrofoam from Newmar? I need to do the math still to see what is the minimum needed. I have only taken out about 1/2 as much of the back wall as you have done. My wood is this area appears sound when cutting it. I will use marine plywood here instead of “press board” that newmar used then cover with some metal product. I fear the aluminum-metal reaction reoccurring. I guess if I could find the correct adhesive-sealant I would not have to worry about it. I’m interested in hearing what you find out from newmar. When I started the job the guy on customer service line really was not much into giving info. He wanted me to go to the Newgal owners site. My wood is sound under the final 1/4 under the drivers side where all the water inlets and dump valves are. I was going to try and not take that portion out.
As I’ve looked and studied this I think all my water intrusion has occurred in the wheel well area. I plan to really put in the time and effort to get this area perfect.
My original plan was to place whatever I decide to use against the road then adhere styrofoam insulation they have at HD to that then place my plywood. I really fear the chemical breakdown of the aluminum-metal.
I had no idea of the wheel well breakdown but had been resealing the underbody yearly with spray undercoating. Last year I decided to try and re-glue some of the styrofoam and my glue instantly melted the styrofoam.
How long did you have to wait on the aluminum-styrofoam from Newmar?
I really appreciate you sharing. You are a few steps ahead of me. I wish there was some way to get the word out so others could be proactive.

Everything you need is at your local Home Depot. The pink foam at HD is higher R value and stronger than the bead foam Newmar uses. The glue is sitting right there next to it. The aluminum sheet can be bought at HDepot too, but it's expensive relatively speaking. You would be better off finding a steel / aluminum supplier in your local area so you don't have to pay shipping. Maybe you need two 4x8 sheets. About $80 / sheet.

The dissimilar metal issue is aggravated by salt water spraying off the tires. I would go to a local NAPA and buy some truck splash shields and put that as the first layer. Then the aluminum. This should be lapped on the inside of the existing so water sheds off the top and doesn't enter the baggage compartment. Make sure there is no trapping of the water in pockets. Silicone all seams. Spray undercoat on all of the exterior parts after the whole thing is reconstructed.

After the metal is up and screwed from inside to outside, apply a sandwich of pressure treated plywood (Menards or Home Depot) to the inside of the foam, floor to ceiling.

Glue and screw all layers together using self tappers from inside of the box to the outside frame and through. (HDepot hardware aisle). I haven't seen them carry #2, but the phillips work excellent too. Use a new bit on an impact battery screw gun. Apply some silicone sealant on the screws.

Apply short pile indoor / outdoor carpet to that (Home Depot) using carpet glue (Hdepot) once the box is made.

Then undercoat (HDepot or auto parts stores) everything outside.

[Chargerman]

I wouldn’t put aluminum back in that location. I would go with aluminum and the weight difference is not something you should have to be concerned with. If an extra 50-100lbs is going to put you on the edge of the coaches CCC then shame on Newmar. I also would go with nothing less than marine plywood but my first choice would be a plastic sheeting with a similar yield and strength. I would want the repair to be much better than what the factory did and never have to look at the area again or be concerned if it’s compromised in the future

Good luck to all with your repairs!

[Geo19Irv]

RV manufacturers (even high end like Newmar) use Interior grade particle board as sub flooring. When it gets wet the glue melts and the board falls apart. Shame on them for being CHEAP: exterior grad is twice the price but will not disintegrate. RV Manufacturers use exterior grade plywood in wet areas like bathrooms and don't scrimp.

[Chargerman]

Originally Posted by Chargerman

I wouldn’t put aluminum back in that location. I would go with aluminum and the weight difference is not something you should have to be concerned with. If an extra 50-100lbs is going to put you on the edge of the coaches CCC then shame on Newmar. I also would go with nothing less than marine plywood but my first choice would be a plastic sheeting with a similar yield and strength. I would want the repair to be much better than what the factory did and never have to look at the area again or be concerned if it’s compromised in the future

Good luck to all with your repairs!

I meant to say that I would go with stainless steel in place of the aluminum