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Topic: Wood Rot on New to Me 2005 MB -Undercoating Spray Recommendation (Read 325 times) previous topic - next topic
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Wood Rot on New to Me 2005 MB -Undercoating Spray Recommendation
This wood beam under the rear cabin up against the bumper is rotten.  It's exposed to the elements so I assume this is something that is expected to happen, no?  Should I be concerned?  What are my options for fixing it?
Re: Wood Rot on New to Me 2005 MB
Reply #1 –
  my 1990 looked very similar to yours underneath. I can’ t say I fixed the problem but I decided to throw a fresh coat of paint over the wood, and then  I sprayed an undercoating spray on top of that. It seems to be holding up 11/2 years later.
jon🦈
1990 MB
 
Re: Wood Rot on New to Me 2005 MB
Reply #2 –
You need to figure out the extent of the rot.  Take a screwdriver or ice pick and poke at the wood and see if it crumbles - find the entire area that crumbles e.g. the boarders of the rotted area.

You need to know where the rot extends to (e.g. to what areas inside that back wall).

You need to figure out what is causing the rot and fix that so it will not continue to rot (no point fixing the rot if it will continue to get wet).  Somewhere around the rear windows is a very common place, seams at the top of the LD in the rear that let water run down the wall, can be a place.  Even splash up from the road can cause dry rot since in older models that area might not have been protected well from splash up (I have no idea what year they started to do that).

Then you need to plan to fix the rot - standard wood rot fixes are:
Replace pieces you can.
Sister joist if you need to and that is possible.  If you can't replace the old piece, take a new piece and securely attach it to take the weight the rotted wood was supporting so you are providing the same structural support.
Paint with a dry rot epoxy if you can't take pieces out.

Be concerned about structural pieces... they support weight and that weight needs to be supported while you are doing your repairs of the rotted wood.

There have been pictures on this forum of people who fixed rot issues.
I don't remember seeing one for this particular spot though it is common to have problems.

You likely want to take care of the rust areas also (clean them and seal them against new water).  That rusts might indicate the rust came from road splash-up because it got the entire area.  But that back wall is a problem area if windows and roof seams and end caps are not kept sealed well.
Jane
Jane & Scott
Currently have a 1989 TK  LD we did a lot of upgrades on.
Bigfoot 25RQ Twin on order with early summer 2024 ETA

Our smartphone autocorrects into very poor English.
 We disclaim the illusion of ignorance this creates as we have enough ignorance we rightly claim.
Re: Wood Rot on New to Me 2005 MB
Reply #3 –
Quote from: Jane and Scott  - 
You need to figure out the extent of the rot.  Take a screwdriver or ice pick and poke at the wood and see if it crumbles - find the entire area that crumbles e.g. the boarders of the rotted area.

You need to know where the rot extends to (e.g. to what areas inside that back wall).

You need to figure out what is causing the rot and fix that so it will not continue to rot (no point fixing the rot if it will continue to get wet).  Somewhere around the rear windows is a very common place, seams at the top of the LD in the rear that let water run down the wall, can be a place.  Even splash up from the road can cause dry rot since in older models that area might not have been protected well from splash up (I have no idea what year they started to do that).

Then you need to plan to fix the rot - standard wood rot fixes are:
Replace pieces you can.
Sister joist if you need to and that is possible.  If you can't replace the old piece, take a new piece and securely attach it to take the weight the rotted wood was supporting so you are providing the same structural support.
Paint with a dry rot epoxy if you can't take pieces out.

Be concerned about structural pieces... they support weight and that weight needs to be supported while you are doing your repairs of the rotted wood.

There have been pictures on this forum of people who fixed rot issues.
I don't remember seeing one for this particular spot though it is common to have problems.

You likely want to take care of the rust areas also (clean them and seal them against new water).  That rusts might indicate the rust came from road splash-up because it got the entire area.  But that back wall is a problem area if windows and roof seams and end caps are not kept sealed well.
Jane

What's interesting is that this particular beam/spot sits next to the wall (in between the rear wall and bumper) so it can only go up the length of the board width.
Re: Wood Rot on New to Me 2005 MB
Reply #4 –
I know this is a common problem... I would LOVE to hear from others who have further investigated this issue in their LD.
Jane
Jane & Scott
Currently have a 1989 TK  LD we did a lot of upgrades on.
Bigfoot 25RQ Twin on order with early summer 2024 ETA

Our smartphone autocorrects into very poor English.
 We disclaim the illusion of ignorance this creates as we have enough ignorance we rightly claim.
Re: Wood Rot on New to Me 2005 MB
Reply #5 –
Quote from: jalamaJon  - 
  my 1990 looked very similar to yours underneath. I can’ t say I fixed the problem but I decided to throw a fresh coat of paint over the wood, and then  I sprayed an undercoating spray on top of that. It seems to be holding up 11/2 years later.

What undercoating spray would you recommend?
Re: Wood Rot on New to Me 2005 MB
Reply #6 –
The undercoating I used, you can buy at any auto parts store. It is 3M professional grade rubberized undercoating.
jon🦈
1990 MB
Re: Wood Rot on New to Me 2005 MB -Undercoating Spray Recommendation
Reply #7 –
Howard, the concern is how it got wet - enough water and often enough to rot the wood.

The guess on the forum has been that water ran down the back wall and got onto that piece of wood.
But I have not seen pictures that confirmed this (e.g. someone who took apart that back wall or used a borescope to look inside the wall and confirmed there was nothing above it that was also rotted or showed staining that indicated water had flowed down that wall).

Again, since this issue is commonly reported, if anyone has investigated this further it would be nice to learn from them.
Jane

Jane & Scott
Currently have a 1989 TK  LD we did a lot of upgrades on.
Bigfoot 25RQ Twin on order with early summer 2024 ETA

Our smartphone autocorrects into very poor English.
 We disclaim the illusion of ignorance this creates as we have enough ignorance we rightly claim.
Re: Wood Rot on New to Me 2005 MB -Undercoating Spray Recommendation
Reply #8 –
Quote from: downgrader  - 
This wood beam under the rear cabin up against the bumper is rotten.  It's exposed to the elements so I assume this is something that is expected to happen, no?  Should I be concerned?  What are my options for fixing it?

You should NOT expect to see this in a well-maintained LD.
Use an ice pick and probe all the way across the board to help determine the extinct of the rot and general location of the leak above that allowed water into the wall. Check inside, around the rear window and corner, looking for soft spots around the bottom and sides of the window.
Let us know what you find.

Mid-Baths often have leaking rear windows, either between the frame and body or around the glass in the three-piece window. The slope of the rear wall slows the descent of rainwater, a leaking seal at the top or side of the window frame provides a possible pathway.
If the damage is limited to one side, suspect a leaking end cap.

How to repair depends on extensive the rot is. You can find the leak, seal it and hope for the best or try to fix some or all of the damage.
If the damage seems to be limited to just the bottom board, it can be replaced without a huge effort,  correctly repairing more extensive damage is a repair job beyond the talents of most hobbyists.
If the bottom board is rotted all or most of the way across, replace all of it. If only partially rotted, a vibratory tool, with a wood cutting blade can be used to cut the bottom board back to good wood and make a clean, straight cut, allow a fresh piece of primed 2 X 4 to be slipped in.
The bottom board is a 2 X 4, nothing special. Removed the 1/4" carriage bolts that secure the bumper to the body and pull out the damaged wood, the rotted sections will fall apart.

There is an obvious leak and it appears to have leaked for a long time seeing how badly the sheet metal and wood are rotted.  I would expect to find more damage up in the wall. Not finding and sealing the leak makes this repair a waste of time, finding it is your first task.

Larry



Larry
2003 23.5' Front Lounge, since new.  Previously 1983 22' Front Lounge.
Tow vehicles  2020 Jeep Wrangler Rubicon, 2001 Jeep Cherokee
Photo Collection: Lazy Daze
Re: Wood Rot on New to Me 2005 MB -Undercoating Spray Recommendation
Reply #9 –
Hi Howard. Rocks and things are constantly thrown at the forward edge of the bumper. That peels off the thin undercoating on the wood. Then if it is raining, or you are just driving on wet roads, it throws water up on that board. Yours looks to be extra rotted.  On the two LD's I've worked on, I clean it off as best as possible, use painters tape on the wiring looms, and put about a can of spray undercoating on it. Don't get it so thick that it drips on the driveway, or you (ask me how I know!). You can let it dry for a day or so and put on another layer, until you are satisfied that it won't soak up any more water. I didn't check the back wall on my TK, or the MB, I don't believe any water was coming from above, just splashing underneath.
    Instead of the asphalt emulsion, better results from pick-up bed spray. More of a black Alkyd paint experience.  It must have been good stuff, it's banned from sale in Ca now!  RonB
    Rust-Oleum 15 oz. Non Skid Black Truck Bed Coating 248914 | Zoro.com   Home Depor has it also.
RonB (Bostick) living in San Diego
Original owner of "Bluebelle" a '99 TKB
Re: Wood Rot on New to Me 2005 MB -Undercoating Spray Recommendation
Reply #10 –
Quote from: Larry W  - 
There is an obvious leak and it appears to have leaked for a long time seeing how badly the sheet metal and wood are rotted.  I would expect to find more damage up in the wall. Not finding and sealing the leak makes this repair a waste of time, finding it is your first task.

Larry, have you torn apart back walls to know how they are made?
Is that board being discussed the sill plate of the wall? 

Note:  I attached a picture.. A sill plate is structural and holds up the wall.  If it is rotted thru, you should care because a rotten board will not do a good job to hold up the rest of the wall. 

If the board is not structural (not a sill plate)... If the water came down the wall and rotted other wood in the wall, you should care - the entire wall is structural (ok, not the veneer, but the framing).

If the board being discussed is not structural and no water came down the wall (e.g. no rot above that board, the top of that board is not rotted), then likely the cause is splash up from the road.  A cleanup and protect from future water damage could take care of this problem.

But that board served some purpose or it would not be there so I do'nt know what it would be used for if the board is not structural.

I have used this to repair a board that needs structural integrity and can't be replaced/sister-ed.PC Rot Terminator but there are several brands out there.

Jane

Jane & Scott
Currently have a 1989 TK  LD we did a lot of upgrades on.
Bigfoot 25RQ Twin on order with early summer 2024 ETA

Our smartphone autocorrects into very poor English.
 We disclaim the illusion of ignorance this creates as we have enough ignorance we rightly claim.
Re: Wood Rot on New to Me 2005 MB -Undercoating Spray Recommendation
Reply #11 –
Quote from: Jane and Scott  - 
Larry, have you torn apart back walls to know how they are made?
Is that board being discussed the sill plate of the wall? 

Note:  I attached a picture.. A sill plate is structural and holds up the wall.  If it is rotted thru, you should care because a rotten board will not do a good job to hold up the rest of the wall. 
PC Rot Terminator but there are several brands out there.

The bottom board is a sill plate and yes it is structural. The wall framing is glued and stapled together, along with the interior paneling, so everything is structural. The coach is built as a monolithic structure, so a rotted sill plate will not immediately causing visible problems. I know of one or two LDs with extensively rotted rear walls that are still used regularly.
Searching the photo archive will provide many photos of the framing during construction. There are a couple of photo-documented rot repair threads to search for where the rear walls are disassembled and repaired.

Here is a photo of what the inside of a rotted bottom board looks like.


When the spray-on undercoating is old, it will peel off but the bubbling over the rotted wood, along with the rusted sheet metal are signs of water coming down the inside of the wall.
When replacing the bottom board, I don't seal it to the coach preferring to provide an escape route for any water that gets inside the wall. Before inserting a new bottom board,  prime and paint the new wood, and any exposed old wood, to provide moisture protection from splashing.

The Factory seals the bottom board tightly to the wall, great as long as there is never a leak.
When a leak occurs, the water gets trapped at the bottom of the wall and rots the bottom board (sill plate) from the top down.
Most of the time, there is no indication of decay until the bottom board rots though and becomes visible. Rot can be detected earlier by probing with an ice pick.
This is why preemptive sealing of end caps and window frames is important.

For all but the small repair jobs, Git Rot and similar epoxy products are very expensive and usually ineffective. Many times the liquid epoxy finds a small hole and drains away.
Amazon.com : Boat Life Git-Rot Penetrating Epoxy Pt. Kit : Boating Cleaners...

Larry


As an Amazon Associate Lazy Daze Owners' Group earns from qualifying purchases.
Larry
2003 23.5' Front Lounge, since new.  Previously 1983 22' Front Lounge.
Tow vehicles  2020 Jeep Wrangler Rubicon, 2001 Jeep Cherokee
Photo Collection: Lazy Daze
Re: Wood Rot on New to Me 2005 MB -Undercoating Spray Recommendation
Reply #12 –
I forgot to attach the picture so others could see what a sill plate is in a wall structure.

Thanks Larry for the information. I would have guessed that but didn't know as I haven't torn apart the back of an LD (yet at not yet ;D ).

Jane
Jane & Scott
Currently have a 1989 TK  LD we did a lot of upgrades on.
Bigfoot 25RQ Twin on order with early summer 2024 ETA

Our smartphone autocorrects into very poor English.
 We disclaim the illusion of ignorance this creates as we have enough ignorance we rightly claim.