1986 TMC 102A3 - Subfloor Question

jraynor · November 02, 2018, 05:53:06 AM

Good morning All,

So for my subflooring, I am using a combination of 2 layers. I removed the original flooring and the first layer was 23/32 plywood laid to match the frame members front to back. The final layer will be a 3/8" layer that will be laid in a crossways of the first layer (side to side). When I placed the first layer I placed the plywood against the side rails since the main rails that held the bus seats were 3" wide. So with the width of the bus on the inside about 98," there is about 1-2" of gaps that runs down the bus where the plywood doesn't cover it all. There is no issue with weakness here but my question is, before I put down the second layer, what should I fill these cracks with? I was thinking rock hard putty but was thinking that was not necessary since I'm covering them with another layer and thought maybe expanding foam would be best. Just something to fill the void to keep cold air out and its easier to put in.

As for insulation, I plan to insulate from the underside.

Let me know what you suggest or what you have used for such voids

richard5933 · November 02, 2018, 06:32:25 AM

I wouldn't recommend rock hard putty. The floor will flex with the bus, even if just slightly, as you go down the road. Rock hard putty is, well, rock hard. Doesn't flex well. Foam might work short term, but I've not seen it do well with both sides exposed. It does break down over time as well.

Why not just cut a strip of wood to fill the gap? Just be sure that the top layer overlaps so that the seams are not one above the other. Lots of glue and screws to keep the layers together.

chessie4905 · November 02, 2018, 06:39:41 AM

I hope you coated bottom and outside edges,at least, to seal against moisture intrusion from water or condensation.

jraynor · November 02, 2018, 08:07:50 AM

Quote from: richard5933 on November 02, 2018, 06:32:25 AM
I wouldn't recommend rock hard putty. The floor will flex with the bus, even if just slightly, as you go down the road. Rock hard putty is, well, rock hard. Doesn't flex well. Foam might work short term, but I've not seen it do well with both sides exposed. It does break down over time as well.

Why not just cut a strip of wood to fill the gap? Just be sure that the top layer overlaps so that the seams are not one above the other. Lots of glue and screws to keep the layers together.

Yeah that's why I'm deciding against it. The foam won't really be exposed. It will be against my plastic layer vapor barrier and the top layer plywood. So it would be sealed. And the edges shouldn't line up as most of the lower layer was cut to 7' to maych the beam spacing. But it may at one point and I'll be keeping an eye out for that. I would fill it with my plywood but they vary so much it would be a pain. Some that easily forms to the size would be way easier. I may go with some type of sealant like caulking possibly. I still have a few days so I'll let it ponder.

And as for caoating the plywood, I have a layer of plastic as a vapor barrier to protect the wood

Astro · November 02, 2018, 09:10:13 AM

Quote from: jraynor on November 02, 2018, 08:07:50 AM
And as for caoating the plywood, I have a layer of plastic as a vapor barrier to protect the wood

That is a disaster waiting to happen. Water will get trapped between the plastic and the wood and the water will win. I suggest a re-think of your vapor barrier plan prior to moving forward. Plastic sheeting is NOT durable.

richard5933 · November 02, 2018, 09:39:45 AM

Quote from: jraynor on November 02, 2018, 08:07:50 AM
...I would fill it with my plywood but they vary so much it would be a pain. Some that easily forms to the size would be way easier. I may go with some type of sealant like caulking possibly. ...

Sounds like you need to watch a few good videos on how to scribe a line against an irregular edge. It's really quite easy and in the long run will produce results much better than what you're planning to do. Here's one that describes the process really well. It may add a couple extra hours to the floor install, but in the end you'll save yourself many more hours of frustration as the caulking starts to fail in the future.

https://www.youtube.com/watch?v=LAM9I6kidx8

There is absolutely no substitute for having parts and components fit together properly. Caulking is not flooring and is not designed to be used the way you're describing. Do it right the first time and you'll have something to be proud of. Fill the gaps with foam or caulking, and one day in the near future you'll find yourself trying to drive a screw into as you install your interior and realizing that foam doesn't hold screws well.

jraynor · November 02, 2018, 09:55:40 AM

There is going to be another layer of 3/8" plywood that goes over it, not the final floor. It'll be a 2 layer subfloor then the final floor goes on that. This will simply be something that fills the void. If I use screws or nails for something they will hold in the 3/8 plywood

Jeremy · November 02, 2018, 12:29:44 PM

Quote from: Astro on November 02, 2018, 09:10:13 AM
That is a disaster waiting to happen. Water will get trapped between the plastic and the wood and the water will win. I suggest a re-think of your vapor barrier plan prior to moving forward. Plastic sheeting is NOT durable.

Absolutely agree - you need to seal the wood itself, not provide a way for water to remain indefinitely trapped against it.

On the other point, there is no better solution for filling the gaps between your plywood than to use plywood. It doesn't matter if it's fiddly or takes a long time to do - just do the job right and it's one less thing that'll cause you regrets in the future. 'Experimenting' with foam or mastic on something as fundamental (and as difficult to get to later) as the middle layer of your floor doesn't bear thinking about

Jeremy

chessie4905 · November 02, 2018, 01:32:19 PM

They used to sell 5x9 plywood. Probably special order now.

richard5933 · November 02, 2018, 01:40:48 PM

Plywood is cheap compared to the cost of having to do this over again down the road.

Do it right and be done with it. You're only at the early steps in your build - way to soon to start taking shortcuts.

Also - not sure what the advantage is of having a multiple layer floor like this over just using a thicker plywood to start with. You'll have to take care to get the layers to bond together so that you don't have lots of squeaking going down the road or when walking in the bus.

Jim Blackwood · November 04, 2018, 07:31:39 AM

I have a favorite phrase that has become known on other forums as "Jim Blackwood's maxim", to wit, "If it's worth doing it's worth doing twice." And the corollary, "If it isn't worth doing twice it may not be worth doing the first time."

This has saved me from tremendous levels of frustration over the years, simply because I go in knowing fully well that I can expect to redo the job before I am satisfied with it. That doesn't always hold of course, I make every effort to do it right the first time and my goal is to NOT have to do it over. But if it turns out that way, it wasn't unexpected, and it is just standard procedure. Makes it WAY easier to accept redoing a job that is "almost good enough".

Now pulling your plywood back up to coat the bottom and edges is a pretty large PITA. But all the fasteners are new and that helps immensely. All your holes have been drilled so it will go back down more easily as long as you line it back up the same.

And here's a thought for you. When adding on to the house I came across a heavy, thick, paintable vapor barrier which came in a 5 gallon bucket, was yellow, went on very thick with a roller and on exposed areas of the original concrete slab has held up to the weather perfectly. (I wish it would deteriorate a little because of the bright color and I don't want to paint over it.) I don't remember whether I bought it from Home Depot or off the internet but for something like this it would be ideal. It was designed to be a vapor barrier. I'm sure you could find a comparable product.

Since it has thickness I'd suggest you coat the bottom, then do the sides as you join it to the other floor so the edge thickness doesn't build up over the number of joints. Then if you have any left over I don't see where it would hurt to coat the top as well.

Jim

chessie4905 · November 04, 2018, 08:14:24 AM

You could special order 5x9 full thickness plywood in multi layer,if possible, and eliminate the gaps. It'll be more expensive, but a more satisfying job. You could use the left over to start partitions, cabinets, and enclosures.

https://www.menards.com/main/building-materials/panel-products/plywood-sheathing/roseburg-3-4-x-5-x-10-acx-fir-plywood/1251070/p-1444452505105.htm

Dave5Cs · November 04, 2018, 09:18:34 AM

We used 5/8" silent floor tongue and groove plywood 4X8 sheets ran across the bus from back to front. Worked well. You could also use a product called Red Guard. It too is a moisture barrier for tile and wet walls can be painted or covered.

Jeremy · November 04, 2018, 11:48:10 AM

Short of glass sheathing the plywood (which is what I've done myself, but which I realise is probably OTT) my next choice for sealing it would would be a thick layer of bitumin paint I think, simply because bitumin-coated plywood is available off-the-shelf for roofing and so it's obviously a proven solution. Bitumin paint is quite cheap too.

Also - while I don't know what the reason was for using two layers of plywood rather than a single thicker layer (which all-things-being-equal would be superior I think), you've actually given yourself an excellent opportunity to incorporate a layer of lead-substitute soundproofing material between plywood layers. Again you can buy ready-bonded sheets that are a sandwich of plywood and the lead-substitute stuff, and I think taking the effort now to do the same thing with your floor is something you'll be very pleased you did in the future

Jeremy

pabusnut · November 04, 2018, 12:06:35 PM

On my 4905, I used 3/4" plywood. I had to "rabbit" the edges to get it under the exterior walls, so I could bolt through it at the edges. All my joints(the original only had perpendicular to bus length) were made over the tunnel edges and bay walls, which resulted in a lot of odd pieces left over, and required nearly twice the actual sq ft of the floor. I also removed the seat rails at the same time(toughest stainless steel on the planet).

Prior to installing each piece, it received three or four coats of exterior water sealer(in hindsight I should have used several coats of marine urethane).

The only problem I have had with the floor since installation is that my peel-and-stick tiles I used in the bathroom don't stick so well and tend to move a little in very hot weather. That tiny area of floor will probably be replaced with a sheet vinyl at some point.

I don't think you can even get a single sheet to do the whole width, as you can't physically turn it and get it under the walls.

Whatever you do--do it right, because it is the foundation of everything, and your personal regret will never go away.

Steve