Alternative subfloor material

[kdenault]

Upon starting the tear down of the interior in my 1975 20'Argosy Moho, I began to realize that the better part of valor is to replace the subfloor. It's not completely bad, but there are enough soft spots to warrant a replacement. So, I'm embarking on a frame-on subfloor replacement ! I know there has been some discussion on this forum of the use alternative materials for the subfloor. One that comes to mind to ply-metal?? Does any one have any experience with this, or any other alternative material which my be more water/rot resistant than regular exterior grade ply? I'm only doing this once!!
Kathleen

[kdenault]

bump

[Area63]

Originally Posted by kdenault

Upon starting the tear down of the interior in my 1975 20'Argosy Moho, I began to realize that the better part of valor is to replace the subfloor. It's not completely bad, but there are enough soft spots to warrant a replacement. So, I'm embarking on a frame-on subfloor replacement ! I know there has been some discussion on this forum of the use alternative materials for the subfloor. One that comes to mind to ply-metal?? Does any one have any experience with this, or any other alternative material which my be more water/rot resistant than regular exterior grade ply? I'm only doing this once!!
Kathleen

Nyloboard comes to mind.
Nyloboard-The Next Generation of Green Building > HOME

[pjude]

Hi! I am a remodeler and have used advantec as a subfloor for years. It is weather resistant(house framers use it here on the second floor and do not worry about the product getting wet since water does not affect it. It comes in 3/4 4x8 sheets for about 25.00 per sheet at all of the bigger home improvement stores....hope it helpsPete

[Over59]

This is a motor home floor? It's one thing to have the shell fly off the trailer going down the road, but your in a whole different level of fun and excitement.

Look at the produces the boat guys use. In general this stuff is light and covered with epoxy and is very strong.

There is also marine plywood.

Doing a shell off would give you great access to the mechanical.


Good Luck.

[Over59]

Originally Posted by pjude

Hi! I am a remodeler and have used advantec as a subfloor for years. It is weather resistant(house framers use it here on the second floor and do not worry about the product getting wet since water does not affect it. It comes in 3/4 4x8 sheets for about 25.00 per sheet at all of the bigger home improvement stores....hope it helpsPete

Indeed that is great stuff and comes in sizes.

[VIKING]

I opted to go with 19/32" exterior plywood siding after doing some research into alternatives. The siding is 48-1/2" wide with a 1/2" rabbet in each long edge. This gives you 1/2" of overlap between panels, and keeps the 48" centerlines between seams. If you use 48" wide material it will not be enough to allow for an overlap at the seams. Most alternative materials are only 48" wide. If you rabbet the edges of 48" sheets you will miss the bolt holes more and more as you work from one end of the trailer to the other.
The glue used today on exterior plywood is far superior to what was used in the past, so it should hold up better than the original.
The cost for things such as marine grade plywood range from $85 to $150 per sheet. I am in the wood products industry, and the best deal I could cajole from a regular supplier was the $85 figure. Most folks would be paying over $100 per sheet. That's $465 including tax for my best deal. The siding was $37.50 per sheet, $205 including tax for the whole floor. The $260 savings is going towards my new air conditioner.
I used some old water-based floor finish to seal the underside of all of the flooring material to give it additional protection from moisture in the bellypan. After that I cut the pieces to shape and size, and then I sanded and sealed all edges with Kilz mildew resistant water-based exterior primer, then a coat of exterior latex paint on all edges, and about 3" in from the edge all the way around on both the top and the bottom. The additional protection from this treatment should give me similar longevity to marine plywood. I had all of the finish on-hand from previous projects, so no additional cost was incurred for those.
The seams are being lapped and glued with Titebond III exterior glue to create a single piece floor. The original was lapped and bolted down without glued seams, and it was apparent that it lead to more damage, faster, by not sealing the edges together. The seam that lands in the doorway was water damaged from the doorway to the center of the floor, about 3-1/2' into the trailer. Water that got onto the floor at the doorway traveled along this seam that far!
The last point I want to make is that many of the restorations I have seen pictures of had extensive damage to the floor under the walls and the C channel. Mine was no exception. It was uniformly rotted all the way around the perimeter, with the exception of the areas where water actually leaked onto the floor. There it was completely gone. I am going to drill 1/2" holes down through the floor and C channel into the bellypan area about every 8 to 10 inches inside of the walls, and seal them with aluminum screen material to keep critters out, and allow a place for moisture to escape the walls. I haven't heard much discussion about this aspect of the floor, but my belief is that any moisture in the trailer will eventually become vapor and will condense on the inside of the exterior skin, then run down to the floor and C channel where it will sit and cause rot and rust/ oxidation, then it would eventually turn back to vapor. This would be a cycle, rather than a one-time event. It is like a water pump. My Safari had extensive water damage inside, but no signs of mildew or mold, which leads me to this conclusion. water has to sit for a long period of time to grow mold and mildew, but if it is being distilled every day it can cause water damage without ever molding. My plywood cabinets actually were delaminated to the point that when I removed the door hinges and handles the veneers came completely apart. The glue was gone from between them.
I hope this helps with your decision. Keep in mind, there are as many approaches to this as there are people doing it, so see who else chimes in here and take the best ideas you can for your own.
Good Luck,
Rich

[Over59]

I think Rich has some go advice. Esp about the rot at the edges. This is easy to confirm by trying to tighen or back out the screws. In my 59 the wood looked OK but the screws had no hold. Wood rotted around the screws. I think from condensation of moisture in the wood on the metal screws over the past 50 years. I'm a shell off fan it you're putting in the time and money anyway.

[AireHeads]

I'm a boat builder/major repairs.

First Rich’s advice about sealing the edges is of utmost importance. Any wood panels should have their edges sealed, this includes interior cabinetry. The way to keep wood from rotting is to keep it dry, seal it up as you build. I would stay away form panels that are treated, as they may not be compatible with aluminum.

The reason marine plywoods cost more has to do with the quality of the veneers used. At the high end all the veneers are A grades (no knots, plugs, or voids) important in a boat hull, but not so much for a trailer subfloor.
The glues used in most exterior plywood is the same as in marine plywood. Strength comes from the quality and number of veneers used to make the panel. A sheet of ½” with 7 plys is much stronger/stiffer than one with 4 plys. The marine grade has nothing to do with rot resistance; it has to do with strength and weight. It is used for hull and deck parts. Most interior cabinetry is good quality cabinet grade plywood, and is not made with exterior glue, but is water resistant. Most damage comes from water being absorbed because the panel edges were not sealed.

Exterior A/C Fir plywood is the same wood and glue as fir A/B marine plywood, the difference is the quality and number of veneers. MDO (medium density overlay) is close to marine in quality, make for sign boards and other exterior use will be available in most area and is a high quality product. Its surface looks like kraft paper, and is made to be painted, or you can get pre-primed on one or both sides. In my mind if it’s worth the time it’s worth good materials. In the end taking the time to do the job right painting and sealing as you go is as important as the material used. Good workmanship and less expensive materials will out last the best material and poor craftsmanship. Good plywood sheathing like Rich used will last as long as the original plywood if not longer. I prefer the fir plywood, but that is a prejudice that comes from boat work, it’s a stiffer stronger panel but probably over kill for this job.

While OSB decking materials made for houses will obviously work and they will be the most economical, not necessarily the best. They generally will be heavier and thicker to achieve the same strength, and not made to with stand movement, I would be leery of OSB products for trailer floors.

In boat work you never have a joint in the plywood on a beam or frame; it is always between frames, with a butt block backing up the joint. This allows for better fastening to the beams, and ties the panels together.


michael

[pjude]

Hi! The floor under the carpet in my 86 345 is 3/4 osb and has held up to many miles of travel and window leakage. OSB is non-directional meaning in can be used in any direction it does not need to be used across the grain as plywood does so there is no waste with the product. It is available in a Tand G with panels being 49x97.Pete
PS being a remodeler I have had many a sheet of plywood "blister" or delaminate so I do not recomend it for anything other than carpet that can be pulled up and the bad pcs repaired or removed.

[Lothlorian]

I did my whole bathroom sub floor in Nyloboard. Looks and works just like plywood. Never rots, never gives off toxic chemicals, feels rigid like plywood, cuts and nails just like plywood. I have had it in for over a year and I never worry about leaks or rot. So far it has been great. Check out their website. I have been to the plant and even had the opportunity to go through a house they built with Nyloboard, Good stuff. It is also green material because it is made from recycled carpeting. Nyloboard will send you samples.



Brian

[byamcaravanner]

...plus the good news is Nyloboard now has a distribution network through the following distributors:

Piedmont Plastics (East Coast) known as RegalPiedmont on the West Coast.
or
North American Composites.

[VIKING]

I'm not familiar with Nyloboard, but I know that some of the plastic products available do not hold up well to combined heat and stress. Similar problem with some wood composite materials that don't hold up to combined moisture and stress.
I know someone who used recycled plastic material that looks like wood decking to make a top for a picnic table. After the first year in the elements it developed a sag between the supports and drooped about 2" down in the middle. I have seen the same thing on decks and handrails on some homes around here. Plywood outperforms pretty much all of the alternatives in this respect, which is critical in the application we use it for. Even Medex, the exterior version of mdf, is not as structurally ridgid as plywood when subjected to loads. I wouldn't trust OSB for the same reason. It has short strands of material compared to plywood and the glue is more exposed to the elements due to the structure of the panels. Savings wouldn't be significant with any of these alternatives either, and weight can be significantly more than ply also.
I guess I'm still a believer in plywood, even after seeing what mine was like after 45 years.
Rich

[Lothlorian]

Nyloboard (recycled carpet) is not plastic. It is a Nylon product. I have a left over piece of nyloboard in my yard. It has plants on it and it has been out there for over a year. It is on the north side of my garden shed laying on the ground. It gets water on it every day. It is as strait, hard and durable as the day I bought it. I also have a piece of carpeting in a hole behind my house. It was the only thing that did not rot away after they took all the scraps from building my house and buried them in a hole. That was over twenty years ago. That carpeting is still there.

Nyloboard is relatively new so it will take years to see how it will hold up. I do not have a sag in my floor. I put a support in the middle because I had to cut the floor in half to get it to fit.

I hear much about OSB. I like OSB but I tried to make a hot tub cover out of it and it crumbled after six months on the hot tub. To much moisture.

Brian

[Dismayed]

I looked at the Nyloboard web site, but I couldn't find any information on weight or strength. It did say that sheathing has to be at least 1/2". It's not easy to replace the subfloor on an AS, and I'd rather only do it once. So I'd rather wait on Nyloboard to see how it fares over the span of a few decades.

[Lothlorian]

My original sub floor was 3/4" thick. I went with 3/4" thick nyloboard. I took my grinder and gave the board a quick once over on the edge to help slide it under the Channel. It fit very well and tight.

After reading countless threads on rot in the bathrooms especially in the 70's airstreams I am very glad I went with the Nyloboard. My orginal floor in the rest of the airstream was in pretty good shape. I had a couple small rot spots I fixed with a product the historical society uses. It wasn't rot doctor. It turned those soft spots into very hard areas. It worked great. It soaked through the rot spot and killed the rot. It turned as hard as fiberglass. Then I used laminate on the the floor after I sealed the whole floor with Thompsons and Behr heavy duty stain.

[CapnTom]

I just did a shell off floor replacement in my 50 Liner. It had a 5/8" floor but I opted for the 3/4" A/C fir for replacement. I sealed it with sanding sealer then primed the underside. I installed the boards gluing all the joints with the titebond exterior glue and made sure all the joint butts butted over the original double framed members. All the wood was securely fastened to the framing members and fish-bone framing. (a note here: this unit was an original pipe framed designed unit. But a PO had an a-frame installed forward of the steel axle assembly. So basically I have a ladder type unit 2/3rds the length of the trailer. This was a great find. The chassis is in great shape.) After securing the wood I then put new c-channel all the way around the perimeter. Originally it only had pieces of c-channel around the craved ends. I made these by using 2 L-channels. In addition to the C-channel I also installed an L-channel under the flooring around the perimeter upward as an edging and then used elevator bolts and fender washers every 8" to secure the C and L-channels to the new flooring. I felt this would give the floor to shell connect more strength. So basically when you rivet the shell back in place the rivets will go through the shell, belly pan, L-channel and c-channel.

No doubt this was a lot of work and if I had to do it again I'd still do a shell off replacement. It's the only way to go.

[Lothlorian]

Wow! Those pics look great.

Nyloboard has technical data on their website. You just have to search for it. They will send you samples also.

Brian

[JamieB]

The other thing I would recommend is a tiling substrate over the subfloor (if you're installing tile vs. a wood/pergo). Potentially, this could even save you the need to replace all of the subfloor, since it's waterproof.

You can even lay it directly over the existing flooring, so you don’t have to spend time ripping out old flooring before laying tile. And, it’s super thin, so it won’t raise the profile of the floor. Also, I guess this goes without saying, but it's super light.

There’s tons more information here:

US Gypsum Company - Waterproofing membrane for ceramic tile installation

Full disclosure: I work with USG, but this seems like a good contribution to the discussion of subfloor in general.