Foam Core Floor Repair. Epoxy?

[wowens79]

I’m looking to repair some soft spots in my floor. It is not water damage, but where the foam has compressed in heavy use areas.

I’ve seen a couple of YouTube videos where they drilled a grid of holes in the floor and pumped an epoxy resin in there and supposedly when it hardens up it is good to go.

Has anyone tried this, and does it work? These guys did it from the top and you had to put new flirting down, but I’m thinking is I came from the bottom I might could save the flooring.
Thanks

[KimberlyHoward]

GrandpaKip wrote:
When I repaired an area by the door on a previous trailer, I used some 2x6’s as the foam was 1/12” thick. Glued and screwed them to both top and bottom plywood. Very solid.

Thanks for the feedback. My foam is several inches think. It's a lightweight camper, so the subfloor is thick foam sandwiched between two very thin pieces of plywood. We should have completely removed the foam sections and replaced with new, but we didn't realize such a small divot would create so much give. The new plywood floor is in place and painted, furniture re-installed, and new LVP installed over it. I'm looking for a "back fill" option for the two small areas that doesn't require removal of everything we just put down.

[GrandpaKip]

When I repaired an area by the door on a previous trailer, I used some 2x6’s as the foam was 1/12” thick. Glued and screwed them to both top and bottom plywood. Very solid.
Should have been 1 1/2”, not 1/12”. Bad proofreading.

[KimberlyHoward]

Did anyone move forward with the epoxy repair of the soft subfloor? We have an 08 Jayfeather. Purchased it with unknown floor rot. We removed and replaced the rotted areas with 1/4 plywood (to match the existing). Upon removal, some of the foam board came out. We backfilled with a lightweight expanding foam, but it compresses too easily, so there are two areas that give a little under weight. So we fixed the rot "the right way" and now I'm looking at an epoxy backfill to fix this "give". I'm curious of your thoughts.

[NCMODELA]

The problem with taking up the foam and replacing it is the aluminum floor joists run in between the foam. So that is not possible. The problem with putting 1/2” on the top is that the floor of the slides will now hit that coming in right?

I have this same problem and been trying to figure out how to fix it without expoxy.

[wowens79]

Thanks for the thoughts. My first plan was to put 1/2 plywood over the entire floor, but with the price of plywood, thoughts of the slide causing issues with the thickness, I was hoping for another solution.

My youngest started college in the fall, so we are thinking another year or soon this camper to see if we want to keep a bunkhouse, then probably more of a couple camper.

[bgum]

Would it be better to use this epoxy AND 1/2 inch marine plywood?

[valhalla360]

carringb wrote:
I’ve done epoxy injection on many composite structures, and I world regardless of core. Most 5-min epoxies are compatible with polystyrene, and it makes a good filler when added to resins. I wouldn’t go any shorter than 5-min set because it’ll probably start to set before it’s all injected.

That brings up an important point, you do want some idea of the void size. Epoxy setting is an exothermic process.

In large enough quantities, it gets hot...I've had to throw a mixed cup onto the grass while working on the boat because it was too hot to hold. Usually it just solidified too quickly and I wasted a bit of epoxy.

If there is a large void and you fill it all at once, you get a snowball effect. Because the heat can't escape and epoxy cures faster at higher temps, it generates more heat with even less time for the heat to escape, it cures even faster...in extremes, it can melt the foam or even potentially burn the plywood. See the link...they were measuring temps in excess of 400F.

https://www.epoxyworks.com/index.php/controlling-exotherm/

[Gdetrailer]

valhalla360 wrote:


The foam that got compressed is already compressed, so it's less likely to compress a lot more.

While it's possible areas around the original compression will fail, the limited space in RVs tends to create very distinct walking paths. If an area hasn't degraded yet, it's unlikely to do so in the future as it rarely get's walked on.

The skins in the sandwich construction rarely fail in compression or tension, so the holes won't be a big concern. If you go in from the top, they will be filled flush anyway and work in compression. Epoxy does fine in compression.

Tearing out the floor entirely, is a drastically larger project and generally not cost effective.

Slapping a 3/8" layer of plywood on top will leave a spongy spot. 1/2" would be the bare minimum and you may still notice it flex a little. 3/4 much better but now you are significantly eating into the CCC of the RV particularly if it wasn't large to begin with when there is a cheaper viable solution. Also, any of these can be much more challenging if you have a slide that needs clearance over the flooring.

The foam isn't the real problem, it is the fact that top of the subfloor is too thin. Most likely less than 1/4" thick! That leads to the wood fibers and glue in the subfloor to break. Once that happens you are now depending on the foam core and the underside of the floor structure for strength.

You don't just "slap" another floor on top, you GLUE the new subfloor to the existing floor.. This is called laminating and even 1/4" or even 3/8" material glued/laminated on top of the existing floor will increase overall strength well enough to reduce any flexing.

Older RVs like my 1980s trailer used 5/8" plywood as the top of the floor, 2" of polystyrene expanded foam insulation (looks like beads) and 1/4" plywood on the underside..

Newer RVs use 1/4" on the top and 1/8" inch on the underside.. A failure waiting to happen.

[carringb]

I’ve done epoxy injection on many composite structures, and it works regardless of core. Most 5-min epoxies are compatible with polystyrene, and it makes a good filler when added to resins. I wouldn’t go any shorter than 5-min set because it’ll probably start to set before it’s all injected.

[NRALIFR]

I’ve never had those type floors, but I’ve done a lot of difficult repairs on my TC that involved removing laminated structures down to a single inner or outer layer, then rebuilding what was removed. I’m pretty confident I could cut out the open area of that floor down to the bottom ply, then replace it with plywood that would preserve the height of the floor surface. I’d try to make the top ply patch even bigger than the plywood patch that would be replacing the foam that’s there now so the seams aren’t all on top of each other.

Are there ever any wires or plumbing running inside that type floor? Sure hope not.

:):)

[valhalla360]

Gdetrailer wrote:

valhalla360 wrote:

Gdetrailer wrote:
Doubt it would work for long, resins without some reinforcements like fiberglass tend to be brittle and will just crack and shatter under the flooring.

The fix would be in compression, so it shouldn't crack or shatter (or if it did it won't matter).

The issue with coming up from the bottom is stopping it from draining back out before it sets. You can't thicken it because you want it to flow into the voids which are likely quite narrow. Also, you need somewhere for the air to escape.

By going from above, gravity tends to keep it in place and allows it to find the voids. The other holes allow the air to escape.

All "depends" on the thickness of the void you are dealing with.

Pretty much any modern RV uses the same foam core sandwich floor with a thin plywood or strandboard bottom and top layer, random reinforcement cross studs and foam insulation laminated in between.

The problem however, manufacturers to save weight and money have shifted to using thinner layers of bottom and top plywood or strand board that flexes much more. This additional flex over time breaks down the wood and the foam..

Adding something that turns solid as it cures in the middle while it can help short term, in the long run eventually is going to fail as the other foam beside the resin degrades. That failure will be the weakest component in the system.

Drilling holes also compromises strength in a laminated system and drilling on the underside will weaken wood that is not in compression..

I know folks tend to gravitate to the "easiest" way which is to drill bunches of holes then fill with a liquid fix but it only fixes a symptom of an inherent problem.

New floor coverings are not all that expensive so one could easily lay a new subfloor over all the floor areas you walk over and floor areas where movable furniture may be. Done correctly you will never notice a 3/8"- 1/2" floor height change. Even in the largest RV you would be talking less than 200 square feet.. Will not add all that much weight, will not cost all that much and in the end a long term fix.

The foam that got compressed is already compressed, so it's less likely to compress a lot more.

While it's possible areas around the original compression will fail, the limited space in RVs tends to create very distinct walking paths. If an area hasn't degraded yet, it's unlikely to do so in the future as it rarely get's walked on.

The skins in the sandwich construction rarely fail in compression or tension, so the holes won't be a big concern. If you go in from the top, they will be filled flush anyway and work in compression. Epoxy does fine in compression.

Tearing out the floor entirely, is a drastically larger project and generally not cost effective.

Slapping a 3/8" layer of plywood on top will leave a spongy spot. 1/2" would be the bare minimum and you may still notice it flex a little. 3/4 much better but now you are significantly eating into the CCC of the RV particularly if it wasn't large to begin with when there is a cheaper viable solution. Also, any of these can be much more challenging if you have a slide that needs clearance over the flooring.

[NRALIFR]

I think before I would mess with drilling holes and injecting epoxy, since you’re going to have to replace the floor covering anyway I’d just cut out everything down to the bottom ply of the subfloor and replace it with plywood subfloor material. I would confine the cutting to the open/walkable floor area unless there was water damage that needed to be fixed.

:):)

[Gdetrailer]

valhalla360 wrote:

Gdetrailer wrote:
Doubt it would work for long, resins without some reinforcements like fiberglass tend to be brittle and will just crack and shatter under the flooring.

The fix would be in compression, so it shouldn't crack or shatter (or if it did it won't matter).

The issue with coming up from the bottom is stopping it from draining back out before it sets. You can't thicken it because you want it to flow into the voids which are likely quite narrow. Also, you need somewhere for the air to escape.

By going from above, gravity tends to keep it in place and allows it to find the voids. The other holes allow the air to escape.

All "depends" on the thickness of the void you are dealing with.

Pretty much any modern RV uses the same foam core sandwich floor with a thin plywood or strandboard bottom and top layer, random reinforcement cross studs and foam insulation laminated in between.

The problem however, manufacturers to save weight and money have shifted to using thinner layers of bottom and top plywood or strand board that flexes much more. This additional flex over time breaks down the wood and the foam..

Adding something that turns solid as it cures in the middle while it can help short term, in the long run eventually is going to fail as the other foam beside the resin degrades. That failure will be the weakest component in the system.

Drilling holes also compromises strength in a laminated system and drilling on the underside will weaken wood that is not in compression..

I know folks tend to gravitate to the "easiest" way which is to drill bunches of holes then fill with a liquid fix but it only fixes a symptom of an inherent problem.

New floor coverings are not all that expensive so one could easily lay a new subfloor over all the floor areas you walk over and floor areas where movable furniture may be. Done correctly you will never notice a 3/8"- 1/2" floor height change. Even in the largest RV you would be talking less than 200 square feet.. Will not add all that much weight, will not cost all that much and in the end a long term fix.

[valhalla360]

Gdetrailer wrote:
Doubt it would work for long, resins without some reinforcements like fiberglass tend to be brittle and will just crack and shatter under the flooring.

The fix would be in compression, so it shouldn't crack or shatter (or if it did it won't matter).

The issue with coming up from the bottom is stopping it from draining back out before it sets. You can't thicken it because you want it to flow into the voids which are likely quite narrow. Also, you need somewhere for the air to escape.

By going from above, gravity tends to keep it in place and allows it to find the voids. The other holes allow the air to escape.