Structural repair and replacement of rotten wood

This thread is from April 2019. The OP has probably solved the issue by now.

If you already have the cabover open, why experiment with it, why not replace it and be done with it.

Without at least good pictures it is only guess work to determine the extent of the damage and whether rep air or replacement is required . Although minwax hardener is a good product I am almost certain it would not work in this application and wood filler will add no structural strength to a beam .

joerg68 wrote:
When should you replace? I am not a carpenter, so just take my personal opinion from experience fixing one camper floor section. Any structural wood that has lost maybe more than 20 or 25% of its useful cross section should probably better be replaced than repaired? Remove as much as needed to find solid wood and a good place to anchor to, then splice in a new piece.
Use an oscillation saw such as a Fein cutter or one of the cheaper knockoffs if you don't have one yet. It will make it a lot easier to make awkward, difficult cuts without tearing everything apart.
Wood that is not really structural, like camper wings or luan/plywood sheets covering something, I would probably not hesitate to fix with any of the methods mentioned above. Although these parts are often just as easy to replace than to repair...

TC lower floor is small, so easy to repair. I actually needed a shim for my new, taller truck, so I just screw whole sheet of plywood under and that reinforced weak floor.
But when it comes to cabover floor, you need to go from end to end, what means pulling siding out.
I pulled my fiberglass siding since it delamintated on most of the floor anyway, but than took me well over a week, to glue it back few inches at the time with lot of boards with several supports to hold the siding till glue dries.
Meaning would I have only couple of rotten members in cabover - I would pull the interior paneling and do the resin/fiberglass repair.
Each job scope needs to be asses well to be successful.

To me if it was easier to replace the wood I would do that. Sometimes it get to complicated to replace the whole cross member, in that case I would go with a metal strap that would bridge the rotted section and screw the strap into good wood if the rot did not go entirely through the cross member. The last option if there is enough fiber left in the rotted wood I would use an epoxy resin thinned with acetone so that it can absorb into the rotted wood. There are a number of thinned resins like Water Glass or Git Rot but thinning your own is much cheaper. The solvent will flash off quickly but will allow a greater absorption into the wood. Pure resin has very little strength by it self so there has to be enough wood fiber left to restore the strength of the cross member.

When should you replace? I am not a carpenter, so just take my personal opinion from experience fixing one camper floor section. Any structural wood that has lost maybe more than 20 or 25% of its useful cross section should probably better be replaced than repaired? Remove as much as needed to find solid wood and a good place to anchor to, then splice in a new piece.
Use an oscillation saw such as a Fein cutter or one of the cheaper knockoffs if you don't have one yet. It will make it a lot easier to make awkward, difficult cuts without tearing everything apart.
Wood that is not really structural, like camper wings or luan/plywood sheets covering something, I would probably not hesitate to fix with any of the methods mentioned above. Although these parts are often just as easy to replace than to repair...

I have a log home and there's a great company I've used to repair rot in logs and other pine/softwood lumber called Permachink

Here's the stuff they sell; (two stages)
M-Balm
You don't remove the soft, punk wood. This stuff converts it to solid strong wood again.
https://www.permachink.com/products/wood-restoration/m-balm

E-Wood
Once you've preserved the damaged wood, you fill in the wood that is missing with this stuff.
https://www.permachink.com/products/wood-restoration/e-wood

I am big fan of epoxy laminates. Messy stuff, but playing with it for 50 years I know how to keep it clean.
Even when you have 50% of the wood gone and rest barely holding, you can soak the leftover with epoxy and add fiberglass on top of it.
Done right it will be stronger than original wood and mostly waterproof.
1 qt of fiberglass resin cost $16 at Home Depot.
I replaced most of wood under cabover on my Fleetwood Caribou.
The camper has skeleton aluminium frame, so I screw new 1x1.5 rails to it and then replace about 70 % of length of the cabover wood frame.
Turned out I was sleeping supported by 2 toothpicks, so I put solid 2x6 board under the nose.

I used CPES Rot Doctor

I had a similar problem with my fifth wheel. It is a lot of work as you know, do it once and replace the wood. It will definitely be stronger.