Bus Build: Putting Down Subfloors for our Bus Conversion – S03E03

We had carefully planned out how to cut the plywood in order to secure the subfloor down to the metal frame in the floor. Because the inside width of the bus is 8 foot 2 inches, we wouldn't be able to use a standard 8 foot piece of plywood. See the video and blog post for season 3 episode 2 for the diagram we made for our floors boards.

We went in all gung-ho as we were so eager to get our subfloors down. But, we hadn’t thought through the order of the steps. We needed to ad glue in the correct place on the frame AND then somehow know where the beams were once they were covered with the plywood so that when we drill down we didn't miss the frame. Or worse, drill or screw into the pipes that run down the center of the bus.  We sure felt like idiots when we put the first piece of plywood down on top of the glue and then realized we hadn’t marked the beams on top of the plywood.

We have found a lot of people who have documented the conversion of their school buses or skoolies, but an MCI coach is a little different. We also have been unable to find any documentation or videos detailing the conversion of an MCI D3, which is one of the reasons we decided to document our process in such detail so that perhaps we might help someone else who wants to convert an MCI and not make the same mistakes we have! 

Dummies Guide to Putting Down Your Subfloor in an MCI 102D3 

  1. Place the wood down in the appropriate area and line in up so that you can screw into the middle of the beams.
  2. Using a Chalk Line Reel, mark the middle of the beams so you have a clear line of where you can screw the wood down into the beam.
  3. Remove the plywood so you can apply glue on the appropriate beams.  We used a Silicone Sealant Caulk which seemed to work well, however after the fact a knowledgeable bus guy advised us to rather use a polyurethane sealant for a moving vehicle. He suggested Sikaflex 252.
  4. Place the plywood back in the appropriate spot on top of the glue and first drill a hole for the screw to go into.  Just because you are drilling into metal don’t feel like you need to apply extra pressure, let the drill do the work. Then use self drilling wood to metal screws, we used TEKS, to secure the wood down to the metal beam.

We were using 1/2 inch plywood, our reasoning being that because we chose not to do a roof raise we wanted to conserve every inch we could in the floors and the ceiling.  However we were quickly learning that this was not thick enough to create a strong supportive floor especially over the area in the center that runs over the pipes. As we stepped in that area the floor would sink.  Using ¾ inch plywood would have been a better decision.

We decided to reuse an aluminium ceiling panel that we took out during the demolition and cut it to cover the gas tank in the middle of the passenger side of the bus.  We felt like it would just give us a little peace of mind to have a metal barrier between the gas tank and battery compartment and our bus interior. We used an Industrial Diamond Blade to cut the aluminium sheet to size and sanded down the rough edges. We glued the sheet down to the metal frame first and then glued the plywood to the steel sheet and then screwed it all down into the frame.

Mistakes were made, but through trial and error we seem to have figured out the best way to put our floors down. Hooray!


Up Next
Our batteries are finally charged up so lets hope the bus starts now!

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​Chalk Line Reel
​We used the chalk line reel to mark off where the center line of the beams were on top of the plywood to make sure we drilled in the correct spot.  It is also useful for measuring out our cut lines for the pieces of plywood running down the sides of the bus.

​Gorilla 100% Silicone Sealant Caulk
​This is good for sealing gaps between surfaces, so we used it to seal our plywood floorboards to the metal floor frame of the bus.  It's 100% waterproof, mold and mildew resistant and good for indoor or outdoor use.

Sikaflex 252
We did not use this glue, however it was recommended to us.  Had we gotten the recommendation in time we may have rather gone with this.  My understanding is that it has more elasticity so is better for use in a moving vehicle.

TEKS Self Drilling Screws
​It seats flush into the wood. The point has precise cutting edges to improve drill performance with less effort. Wafer head design has a large bearing surface ideal for plywood.

Masterforce Diamond Blade for Metal

​Up to 65x longer life than standard abrasive wheels for cutting various ferrous and non-ferrous metals. Blades provide constant depth of cut and less machine downtime. For use on 3-3/8" multicutting saws to cut iron, steel, stainless-steel, rebar, copper and aluminum.

By Mela & Don

Mela and Don are sharing their journey as they make conscious decisions to live a more healthy, environmentally friendly life together.

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