POURING THE FOUNDATION FOR OUR STRAW BALE HOUSE

This week has been a roller coaster ride of thrills and chills.   Bruce Lease dug the hole for our house and Mike Flynn set forms and poured the footings.

Our house will have a walk-out basement which will hold the mechanical room, Doug’s and my offices, a guest bedroom and bath.  It is 2/3 the size of the main level upstairs.  We made it smaller because we were not sure how digging into the hill would go.  We hit rock twice while sinking the septic tank.

When the lowest part of the foundation was dug, water started to flow in.  Our concrete contractor, Mike Flynn, said the water would not be a problem.  In fact, that concrete will probably be harder because it will cure more slowly.

Concrete and cement are not the same thing.

Concrete is a mixture of sand, crushed stone, water and portland cement.  Concrete does not dry, it cures through a process called hydration where the cement and water harden around the sand and stone, forming a hard mass.  Concrete keeps getting harder for years, though its strength is rated based on 28-days of curing.

For good concrete, most guys who have your back will use at least a 6-bag mix.  That’s 6 bags of Portland cement per cubic yard of concrete.  Mike made it clear that he doesn’t pour a 5-bag mix, and that 6 is the way to go.

For best results it’s important that concrete should be kept moist for the first 6 days of the curing period.  If the weather is too hot, the concrete will harden too fast for its own good.  On the other hand, it shouldn’t get close to freezing either.  We are in good shape with a 40+ degree rain last night andforecast of highs in the 60s with the possibility for more rain.  We will spray it down, if dryness becomes a problem.

Here’s why we need to use as little concrete as we can when building:

Portland cement is made in a very hot, rotating kiln.  The ingredients, including limestone, marl, shale, iron ore, clay and fly ash, which are heated to temperatures between 2700 and 3000 Fahrenheit (1480-1650 Celsius) to form a new chemical compound called clinker, which is ground into portland cement.  That’s a lot of energy use.

We are weighing that energy consumption inherent in the concrete against the assumption that by using it, we are building a house that should last for hundreds of years.  I believe it can be done.  We lived in a house that was 300 years old in the Netherlands.

There are a lot of materials that have to come into the house through the concrete basement walls:  well water, electricity, propane gas and a furnace venting.   The morning the concrete team arrived, we also had our plumber and electrician out, and they worked with our project manager to make sure everything will come in at the right place.  Mike then sprayed the location of each pipe on the dirt.  It’s a little tricky with one part basement and one part slab on grade, but Mike is going to pour both levels of the house foundation at the same time to make it one solid unit.

The concrete was poured into the footing forms carefully, but every now and then a little bit would spill out on the sides.  This spillage played a crucial role as the drama unfolded.

I’m glad I don’t have to order concrete.

If you order too little you can’t finish the job.

If you order too much, you have a big glob of wasted concrete sitting around hardening in some place you never wanted.  Considering the environmental price we pay to create this stuff, that’s a shame.

As the team came around to the final stretch of footing, things got dicey.  The concrete was sliding down the truck boom slower and slower and then stopped.  They scraped every particle out of the truck spout.

At this point, one of the crew members started running back with a shovel to every single place where the concrete had spilled over the form, scooped it up and carried it to the gap.

It was very, very close.

While we are looking at the form, I’d like to mention that Mike uses a product called Formadrain to pour his foundations.  As the name implies, it functions as both concrete form and drain tile.  We used it on our barn too, and it seems like a good way to go.

In the end, there was EXACTLY enough concrete for this job.  That felt very good indeed.

It rained hard overnight, and the site is a muddy mess.  The crew won’t be back till next week to put up forms for the walls.

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3 replies

  1. Thank you, Eleanor.
    I just got back from watching the basement walls be poured today. I’ll be writing about that for my post tomorrow. Every step is an incredible thrill and often a bit of a puzzle. The intersection of our very good, but very traditional concrete craftsman and our very sustainable and exploratory architect has been a bit bumpy. It is a learning process every step of the way.

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