Bathroom Sub-Floor

Evidence of a mouse in the house!

Eeek! A mouse! Or maybe a rat!?! Man, that’s a huge hole! About 7″ high and chewed right through the concrete block wall in the future bathroom! Yowsa! I would hate to meet that rodent in the dark of night!

Ben jack hammer through the wall

Okay, no, not really. That is not a rodent hole but rather a hole in the wall that Ben, Will and I jackhammered out for the waster water pipe. It took about an hour. It should have taken five minutes as that block was supposed to be empty. Most of the cores of the concrete blocks in our house are filled with concrete for added thermal mass and strength. Some have rebar in them – the verticals marked with X’s by Hope last fall. Some have O’s and those are supposed to be empty so that I can drill them out like this for utilities. This particular block, the one I needed to drill out for the septic pipe, accidentally got filled with concrete making the task take much longer than intended. But now it is done – it just took patience and a Makita hammer drill banging away at the wall 1,000 times a minute for an hour.

Ironically, the core above is empty as intended. But my hole must be low down for the plumbing. Our project for the day was to put in the sub-floor for the bathroom. This is where the plumbing will all go. Since the house is built on a slab and I didn’t want to put the plumbing under the slab or in the slab it must go above the slab. The advantage of this is it gave me more time to think about how I wanted to do the plumbing and it means the plumbing will remain accessible via removable stone tiles in the bathroom floor.

Dammed Sub-Sub-Floor and Mix Master Ben

We started by making a perfect smooth floor. To do that Ben and I first made a series of dams out of pink foam that would stop the self leveling batch of concrete (1.75 half gallons or 0.875g water) from flowing right out of the bathroom. We did this because our original slab was kind of bumpy. Had we made a perfectly smooth slab to begin with this step would not have been necessary but we poured it first in the cold and not everything went perfectly. I knew that at the time and figured that I would just do this to compensate. We then washed the floor with portland cement so it would be wet to accept the new concrete. Worked great and the new concrete will bond well to the old rough concrete.

The plumbing is concentrated in the bathroom with the kitchen sink just on the other side of the partition so all my pipe lengths are very short. This helps keep down costs and means that any spills are in the bathroom or under the sink. No “water, water, everywhere!” as Hope is wont to say.

The bathroom floor is designed to drain out through a floor drain making it easier to clean. This is important because a clean house is a happy Holly. I want to design and build things to be as self maintaining as possible – as easy to clean as possible. If it can look nice as well, that will be grand.

Lastly, the bathroom is small. Very small. Some would say tiny. But by folding it through several extra dimensions I have been able to shoe horn a large bathtub, shower, sink, separate toilet stall, storage and marine aquarium with a sump into the 30 square feet of space. At one point I also had a washer and dryer in the design but decided that was really pushing things.

Poured Sub-Sub-Floor

I poured the first buckets of concrete along the walls and then progressively worked my way out. 2″ sheets of pink foam is good for standing on while floating the concrete smooth. This was done last night so that this morning it was firm but would still take scoring and the mortar for the next layer as we build the channels for the pipes.

What our intrepid explorer Ben is doing in this photo might shock the sense of morality of some elephants. This is a four foot long vibrator. Normally it is used for, er, um, vibrating concrete, yes, that is what I meant. This is a concrete vibrator. You stick it down the hole and vibrate the concrete. This causes compaction of the concrete. Here Ben is using it on the slab floor of the tiny cottage. That vibrates the whole floor which in turn vibrates the concrete that we had just poured causing it to get perfectly level and smooth. It worked beautifully. When we do the ceilings I’m intending to attach the vibrator the legs of the scaffolding to vibrate the ceilings as they harden in their molds. I know, weird.

Bathroom Floor Plan

All that happened above was from last night. This morning, to Ben’s horror, I began drawing with a nail on our beautiful smooth, level floor. This is the bathroom floor plan that shows what sections are where and how the plumbing will go. Will and I then laid out our plumbing pieces for one last check to make sure everything fits. It would be a major bummer to set this in concrete and later realize we had an angle, curve or length wrong. The plumbing design is shown in light yellow in this photo.

A brief tour of the bathroom. Starting in the lower left corner of the image and going clockwise:

  1. Chimney for the wood cook stove & water pre-heater. With the wood stove right there we’ll have a warm bathroom in the winter, how cozy!
  2. Doorway stepping down into kitchen – Door is hinged on the west side which is the top in the picture allowing the same door to be used for either the bathroom or the toilet stall. This effectively turns the bathroom into two rooms, a neat trick for a family living with one bathroom in a small house. Currently in the old farm house we have one bathroom but lack this trick door and sometimes wish we had it.
  3. Kitchen Sink by the west window on the other side of the partition – close by to minimize plumbing distances.
  4. Toilet Stall with opening window to the west.
  5. Shower/Bathtub – A paludarium for people and plants.
  6. Aquarium Sump – A deep well of soles for foam fractionation and s
    urge generation.
  7. Bathroom Sink – To be built in using ferro-cement and a reverse mold according to my current thinking. Experiments to come.
  8. Aquarium – Below are storage shelves, possibly in a cabinet. Above are storage shelves for medicines and other non-toddler things.
  9. Central Floor – Enough room to towel off, brush teeth & hair, floss, etc but don’t try to swing the cat. The water from the tub and shower will flow out through pipes under the removable stone floor for heat recovery and nice warm toes.

Blocks Mortored in place.

The concrete partition and streatcher blocks shown above define the channels and floor supports. The scoring marks in the soft sub-floor of concrete are for better adhesion of the next layer of concrete.

Will & Walter floating the next layer.

The next layer of concrete did the all important sloping so that any water that might get into the plumbing channels below the floor would drain out rather than to the rest of the house. The one trick was the drum trap for the bathtub is 8″ tall. The blocks are 7 5/8″ tall. Adding concrete to get the slope further takes away from the height so the drum sticks up above the top of the blocks and into the a hole in the granite that forms the floor. The difficulty was getting a continuous slope from under the tub around the spiral and out the rat hole blocked by the pink foam on the right wall. We did it.

Final Sub-Floor.

Next we fill the concrete block cores and I drew grooves with my fingers to cause the flood plains of the various areas to drain even better. Just a little extra insurance that water won’t pool. Then we ran the vibrator to smooth things out.

Outdoors: 34°F/19°F Sunny
Farm House: 58°F/48°F no fire
Tiny Cottage: 54°F/40°F low due to my leaving door open in morning

About Walter Jeffries

Tinker, Tailor...
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6 Responses to Bathroom Sub-Floor

  1. Anonymous says:

    I’m very impressed with this project. You’re a brave man for working with so much concrete. Measure thrice! I’m particularly encouraged by all the young hands that can help. Every mouth to feed comes with two hands to help.

    Brian H – Greenville, WI

  2. karl says:

    i’ve always admired that single door double bath trick. in the cottage we intended to build i designed that in to the bath room also.

    i think you should submit your construction efforts to a comprehensive study could be the precursor to a coffee table book.

  3. Thanks, Karl for those links. I’ll explore them.

  4. Mark says:

    I hope the picture of the young hammer-driller was posed. Otherwise, I have but two words: safety glasses.

  5. Yes, Ben posed for that photo. Normally when using the hammerdrill we have safety glasses on or a face mask. Although truth be told, the hammer drill doesn’t throw chips interestingly enough, especially when going through PVA fiber reinforced concrete.

    Speaking of which, the concrete block, which has no fiber, was easy to cut – that took about 5 minutes max. The PVA fiber on the other hand was very tough and took the remainder of the hour to cut. It made me appreciate just how much the PVA fiber adds to the concrete strength.

  6. Ryan says:


    How is #9, the floor working? Would you do it again?

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