Slipforming, The Next Generation, part 1
Copyright Danielle N. Gruber February 2001

“Are you building a castle?” Sure, why not. “Are you nuts?” Sure, why not.
Forward
From the peaks of the mountains to the floors of the valleys, one can occasionally spot beautiful, simple rock homes dotting the landscape. For me, the love of a rock building was founded in a little rock barn which I yearned to remodel into a home. The rocks were cracking, and the cement was giving way, and yet the building was rich in it’s simplicity. The windows would never have passed inspection. They were all very high, too high to look out of. But the light which cascaded through them, bounced off the walls and gave a glow to the floor below. Magic things happened there, I was sure. I loved that barn, and I vowed to someday build something similar for myself. But, as I researched the project, I heard from countless people warning that homes built of rock were uncomfortable. “Those homes are cool in the summer and downright cold in the winter,” they’d say. So, I decided to do more research. As luck would have it, shortly thereafter, The Mother Earth News magazine had a story about a man named Tom Elpel, who was slipforming homes in Montana. Mr. Elpel had some great ideas about warming up cold rock homes. One idea was to use polystyrene beadboard insulation as an interior form. He had not tried the method, but thought it would work. I agreed and gave it a try.
Slipforming using the beadboard panels was a terrific idea. Tom Elpel’s ground work in traditional slipforming was clear, concise, and very helpful. I say honestly, I could not have completed the slipformed portion of my home had it not been for him and his dedication toward documenting the process. Today, I have a home that is beautiful, warm and energy efficient, and it contains my pride at having played a part in its building process, along with my father, who graciously mixed virtually all of the cement in a $200 mixer for me. It is with thanks and gratitude to Tom and his family, and my father and my family, that I am documenting my process to help pave the road a little farther for the next generation of slipforming.
The Process
The first step, for me, was to read Mr. Elpel’s book, Living Homes, and the Reader’s Digest Back to the Basics. These books contain clearly how to begin construction of the most important part of the slipforming process, the slipforms themselves. I built my slipforms exactly as Elpel suggested, with two additional implements: a large clamp, and a square. The clamp came in handy when the green 2 x 4’s twisted and the square kept the interior, 21″ boards lined up while screwing them together.
My home was 32′ x 64′, so I made 24 slipforms each measuring 2′ x 8′. Four were for each end, and eight for each side, plus a couple of small fill-in forms. Looking back, I could have done it with less, because, on my lot using the beadboard panels, it was impossible to easily access all sides. You can start with one full wall, or even half of one wall. However, as Elpel suggests, these forms are wonderful for use as planking, and creating this amount gave me some for scaffolding planks, some to use where I was working, and more to use in preparation for the next day’s work.
Slipforms completed, I began searching for the beadboard panels. Mr. Elpel gave me a reference to a company in Montana, but the shipping was beyond my hopes. They referred me to a company in Denver, Colorado called Advanced Foam Plastics. While their product had not been used in this application to their knowledge, they offered a product which had traditionally been used for roofing insulation and is more readily available everywhere. It was 5 1/2″ of polystyrene attached to 1/2″ of oriented strand board (OSB). It is a very strong, very efficient board which is often used on roofing. They suggested it might work. The nice thing is that the panels can be built at any height from the standard 8′ height up to 12′. I wanted 9′ ceilings, so that is what I ordered.
Slipforming using beadboard panels is similar to traditional slipforming. The footings are built the same, except extra width is necessary for the beadboard panels. Since the floor inside this home had not been poured, I elevated the panels by 2 inches, using a recycled 2″x 10″ wooden plank (the same I had used to form the footings) underneath them. Pulling the 2 x 10’s out afterwards was difficult. If I built this same home over again, I would order the panels long enough to compensate for the future floor, and place them directly on the footing.
The cement and rock portion of the wall is 9″ thick, and the insulated panels add another 6″, so the total wall is 15″ wide. That 15″ wall needs an additional 4″ for the slipform on the outside, and an additional 4″ ledge for the beadboard panels on the inside. This brings the total width of the footing to 23″. I opted to add an additional 1″ to make my measurements an even two foot. Giving yourself an extra inch costs little in concrete, but is wonderful in the event any of your forms slip.
My home was built into a hillside. The back wall was back-filled so rock work was not necessary. The front of the home was resting on the slope, so I made my footings 3 feet wide along the leading edge.
Since my home is sitting on a 40′ vein of river rocks, I poured a footer 10″ thick and used 6 one-half inch rebar runners along the 2′ sides. I increased it to 8 one-half inch rebar runners along the front.
Inserting the vertical rebar into the footer: A confusing aspect was how to insert the 10′ vertical rebar into the cement, leaving it 9′ or higher, swaying in the wind. If you insert the long vertical rebar runners into the cement as it cures, and the rebar wobbles, even a little, you have compromised the strength of the attachment into the footer. Many people suggested cutting the rebar into two foot increments as we poured the slipformed walls. But, because the rebar temporarily supported the panels, keeping them from falling over, I wanted to keep the rebar as high as possible.
Elpel mentioned that in the past he had driven the vertical rebar through the fresh concrete of the footings into the ground beneath, but later learned that this allowed rust to creep up the rebar and compromise the strength of the connection between the footing and the wall. To avoid this, we inserted six-inch long, 1/2″ PVC pieces into the cement every two feet immediately after the footers had been poured. The PVC held tight, and later, after the concrete had cured sufficiently, we hammered the rebar into those PVC pieces. The fit was very tight, and allowed no wobbling of the rebar within the hole. Of course, the rebar above the hole was able to sway, but it was held tight into the footing and allowed no seams along the vertical rebar. While this 9′ of rebar was awkward, the most important benefit to leaving it that length was the rebar acted as a vertical brace for the beadboard panels. The panels leaned on the rebar. While this might not work in high wind areas, it helped to temporarily support the panels until we secured them in place.
The first beadboard panels: The first panels I put up were the corner pieces.
I am a strong woman, and managed to get the first corner up by myself, but it took the patience of Job, and would have been significantly easier with 2 or 3 people. Anyone who saw me trying to do it alone would have thought I was a nut, and might have been right. I put the 9′ x 4′ panel, OSB board side toward my back and piggy-backed it over to the corner, where I had set out a couple of 2 x 4’s to brace it once I got there. Carefully, I backed up and set the edge of the panel in place, then reached for my 2 x 4’s which were within arms reach, and braced the OSB board side of the panel. With one person on a windy day, this would have been impossible, and would have resulted in the panels falling, or creating a kite-like atmosphere while you try to piggy back it. Unless you are really head strong, I would recommend 2 people.
The vertical rebar on the other side was very helpful, and I was glad I had not cut it off. It literally held the first panel in place while I ran to get the next one. Getting the first two corner panels in place was tricky, especially since it was critical to get them square.
The space between the beadboard panel and my exterior slipform was 9″. Spacers cut to this length made tightening the forms much easier. One caution: If you tighten the forms too tight, the spacers protrude into the beadboard. This makes getting them out while you are pouring concrete difficult. It also makes positioning of the rocks difficult. Put spacers in your forms, but my advice would be to keep them “girl-tight,” not “man-tight.”
At this point, with the vertical and horizontal rebar in place, and with the first bead board panel up, I set the remaining panels in place. With scrap 2″ x 10″s, I put a 45 degree cut on each side and pre-drilled 3 holes on each side of it to make screwing it into the OSB easier. This gave me a wedge which I could then screw into the corner, holding the corner at an exact 90 degrees. I used a square, which to the horror of my male helpers, I called the “L.” Once the two panels were up and square, I screwed the wedges into the corners. By the fourth corner, my father had thought up an easier way to accomplish the same end. Get a relatively large piece of scrap lumber, maybe 3 – 4 feet wide and long. Make sure it has a square edge on two corners of it, then screw a 2 x 4, level horizontally on each side of the panels, about half-way. Position the plank on top of the two ledges you created and screw your plank into the ledges. This accomplishes a nice tight corner which will not sag or change over the time necessary to complete your home. It seconds as a make-shift shelf to keep small tools.
The pieces adjoining the corners are easily placed. It helps to have scrap lumber around. Scrap pieces roughly 4″ x 7″ were wonderful to screw evenly across the joints between one panel and the next. Three or four of these scraps make the seams almost unnoticeable.
Wire-reinforcing: With rebar and spacers in place, and the first beadboard panels in place, you are ready to wire-tie the slipforms to the panels. This is an important step because too many wires in the slipform make it difficult to set rocks in place. I found that I needed about four sets of wires: two near the bottom, two near the two-foot level of the slipform at about 1′ and 3′ along the beadboard panel. Pre-drilling holes through the OSB board on the panels made the job easy. This job is possible for one person, but is much easier with two. It is so easy, that I had one of my kids yell when my tie wire had popped through the insulation. From there, I could pull it through and insert it into the slipform as needed. But occasionally, as you are pushing the wire through the OSB board and into the beadboard, the wire does not make a straight route and winds itself into the beadboard, never to appear on the other side. This is why it is easier to have someone on the other side. Once I looped the wire around the rebar, then through the slipform, I tightened it with a common nail. The nail anchors the beadboard to the cement.
One visitor suggested that I use the slipforms on both sides of my wall, which sounded so intelligent that I had to try it. The interior slipforms were placed right over the OSB board on the panels. What I did not foresee was the difficulty of fastening the wire ties this way. If you forego the interior slipform, the panels are strong enough, and the wire tying is easy. But with an additional slipform on the interior, the benefit of the wire tying is lost because you need to cut the wire to remove the slip-form. First, you do not need the slipforms on the inside of your wall. The panels are strong enough. But secondly, when you wire tie to the panels, you do not need to cut the wire. Both ends of the wire are fed through the panel leaving no tie on the interior wall. This is good because when you apply your interior treatment, in our case, drywall, there was no need to remove the wire ties. We did try the slipforms on both sides, but wire tying the walls then had to go completely through both sets of slipforms. Removing them meant cutting the wire. This left no remaining tie to secure the panels to the concrete. With our method, if the panels should ever come free of the cement, they will never fall off the wall, because the wire ties holds them in place.
Anytime you trek into new frontiers, there are ideas which look logical on paper, but simply are not effective. Using slipforms on both the interior and exterior proved to be one such idea. Another suggestion was gluing the insulation to the wall later. With much thought and a couple of phone calls, this concept was thrown out too. Without tying the panels into the wall, the weight of the drywall might eventually them away from the cement. One day, sitting in your living room, your whole wall might fall on top of you. We avoided this possibility, but I bring it up because anyone building a new home gets lots of advice and some of it is incredibly tempting to try.
Incidentally, I telephoned the beadboard panel company to ask if wire tying would be necessary. They could not insure the bond between the cement and the panel over time. Weight and gravity, they thought, might make the panel eventually separate from the cement without wire ties, so I opted to put them in. A bonus to the wire ties, is that, if you drywall, you can attach the drywall directly to the panel right over the wire. No wall preparation is necessary. A cement worker who looked at the inside of my home, insisted that we would need to fir out each panel before applying drywall, or the drywall would be a headache. I’m happy to say he was wrong. I’ve never done an easier drywall job. The panel, up toward the top, was not exactly level, but the slight deviance was minimal and with paint and drywall, it is almost impossible to see.
Protecting the panels in wet weather: Leaving the bare OSB board out over the first winter, with no roof to protect it, scared me. A friend of mine, who is quite knowledgeable about wood, told me to paint the OSB board on each panel with a coating of half turpentine, half boiled linseed oil. This treatment waterproofs the panels sufficiently, that the OSB board did not show disintegration over the winter. Living in the Rocky Mountains, that was a testament to this treatment.
The beadboard has a flexibility which is both an asset and a drawback. It is important to keep a level close by and check the wall often. When you are going up 2′ at a time, the upper level of the wall can sag out of level. It is easy to return it to level if you catch it before the concrete has been poured, but impossible if you don’t catch it before the concrete cures. In two corners, toward the top, the panels began to sag a little. Since it was maybe an inch out of square, we did not lose sleep over it, and it covered easily with drywall, but it would drive a perfectionist crazy, and unnecessarily, I believe.
Removal of forms: It was my experience, that in the fall, with moderate temperatures, the concrete and rock combination set up sufficiently in 5 hours. At that time, we carefully removed the forms and chipped out what cement was not desired, then left the cement alone to continue to cure overnight. A couple of times we were not able to chip off the cement until the next day, and it was much more difficult. In one section, we left it until the following night, and, in the dark, with bugs and lights, we hammered the concrete out. Sparks were flying from the hammer and the chisels, and we vowed never to do that again. The wall was no worse for the wear, but removing the cement was almost impossible.
The system we found most workable was to start at about 9:00 in the morning. My 73 year old father agreed to help me by mixing the cement in the electric mixer. (Tom Elpel said you could buy these mixers for a couple of hundred dollars. That’s exactly what we paid and the mixer is still working fine after mixing almost all the cement in our large home. ) My dad would mix the cement and pour it into a wheelbarrow where I would scoop it up in coffee cans and carry it to the wall where it was easy to control and pour. Men came along and thought it would be so much easier to carry five-gallon buckets of cement, but, as I suspected, they all had dental appointments after a couple of hours.
I knew I couldn’t afford to get hurt, and a coffee can of cement is not that heavy. The pace was easy to keep up, and after a couple of weeks, I got strong enough that I graduated to mop buckets, filled half-way. For three hours every morning, for three months, my dad mixed cement, and I carried it in either coffee cans or mop buckets. At noon, when the heat was unbearable, we would quit, eat, nap and recuperate. Occasionally, I would take the truck and go get more rocks and unload them. Often, I would prepare the next days forms during the afternoon, so that the next morning, we were set to go. I will add, it is amazingly tempting to try to carry more cement. My husband came up to help one day and filled the mop bucket to the top because he did not want to make two trips to the mixer. When I went to lift that bucket, it was heavy and hurt my shoulder. I was nursing that shoulder for 3 weeks. Better to make 100 trips and not be hurt than 1 trip and knock yourself out of play.
Lots of people came to visit the site. Most tried to find a more efficient way to get the concrete to the wall. I have come to believe that my pace, while slow, was perfect. By 5:00, when the forms were removed, I was happy to be chipping a reduced amount. My forms never broke. The two times I tried to hurry, I regretted it. One was on the back wall where we poured cement from a cement truck with no rocks in it. My bracing slipped and the weight of the wall pushed out the cement. Luckily, that part of the house was going to be backfilled. But the extra time to straighten the wall was not “efficient.” I would have been better off to spend the extra time and not lose ground. The lesson remains, if you have patience, you won’t be as likely to hurt yourself, you’ll be more apt to finish the project, and with the beadboard, you are already doing two or three jobs in one since you are doing your exterior siding (rock) the structural wall (cement), and the insulation (the beadboard) and it’s all ready to apply drywall to the OSB board.
Filling the holes and gaps between levels: When the first level of slipforms is removed and the cement is cleaned out from between the rocks, you have a very clean looking wall. Setting the second set of forms one level higher leaves gaps and holes through which the new cement escapes and runs down the wall you just spent hours cleaning. This happened to me and plugging these holes was nearly impossible with wet cement pushing out the plugs. After some experimenting, I discovered that I could break off chunks of scrap beadboard insulation slightly bigger than the holes and wedge those scraps into the holes to prevent the new cement from escaping. It also did a much better job of preventing drips and streaks. It is not fool proof, but reduced the cleaning work substantially. Later, after the concrete has set up and the form is removed, the insulation plugs are easily removed and saved for the next level of holes and gaps.
Windows and doors: The windows were purchased at a local discount window outlet earlier than we began building. Shopping for the windows first, is a great way to save a lot of money. When you have an oddly shaped window hole, the stores see dollar signs as you walk inside. But, purchasing the windows long before the building began, I was able to take advantage of top-of-the line windows at reduced prices, simply because I could use a 41″ x 63″ window. Tom Elpel clearly describes how to construct your window frames. Putting them into the wet cement, wedged between the slipforms and the panels, was more of a challenge.
To save money, I recycled the 2 x 10″ lumber we used to form the footings. It was rough-cut lumber from a local company, so it was a full 2 x 10 inches. Since the cement part of my wall was only 9″, I had to cut a ledge into the beadboard so the window frame would fit. This worked nicely because it helped hold the window frame in place. I hammered 30-40 nails and screws into the bottom of my window frame, then, when we approached the mark on the beadboard, we set the window into place and tapped it into level.
Careful measurement is necessary when the windows holes are cut into the beadboard. I left over-lapping beadboard around each edge so that when the window was placed inside, the insulation would come to the edges of the window and not the edges of the frame.
Reflections on House Plans: In my humble opinion, not enough people think about how they really live. Here’s the lazy woman’s guide to building a castle: Forget the view for a minute and start the plan backwards with driving up in your car. Your garage needs to be wide enough that everyone in it can open their doors and still have enough room to move. If you buy groceries – you need your kitchen close to your car. It makes unloading the car a much easier task. You need your dining room close to your kitchen for the same reason: carrying food is an accident waiting to happen and any respectable lazy person hates cleaning up food on the floor. So, now you’ve got the garage and the dining room close to the kitchen. You’ll like that for a long time. I promise!
Also, anticipate accidents like broken legs and imagine having to urgently use the bathroom in that condition. For that reason, and because respectable lazy people don’t like cleaning muddy footprints across their floor toward a far-off bathroom, I have a bathroom next to the garage and I have never regretted it. I would advise building everything to handicapped standards because 1) you could be run over by a truck tomorrow and you’d be ticked if you couldn’t get around in your own house, and 2) you might be financially broke after getting run over by said truck and need to sell the place. Rich people who want to buy your house are getting old and so are you. You diminish your resalable audience if you refuse to make the doors a teensy bit wider to accommodate walkers, wheelchairs, adjustable beds, the Tonka Toys of the elderly.
Lastly, I would (and did) put a bedroom on the ground level with the garage/kitchen/dining area. It’s made having guests of any age a delight instead of a nightmare.
Also, you won’t find this in a home plan book – but make your kitchen bigger than you would have, and provide people a place to sit and kibitz. They will anyway! And if you have a tiny kitchen, you’ll want to kill them for clogging your space. I made my kitchen large and haven’t regretted it either. We’ve danced in there while making dinner and that’s pretty rich, too! If you remember, there is a counter where I can allow people to sit while keeping me company in the kitchen. In practice, they have done exactly that and I can hand them peppers to chop and they feel included and loved. It’s, as Martha Stewart would say, “a good thing.”
Lastly, always have a tiny, run-down, dilapidated shed nearby, even if you don’t need one. (We use the old goat shed for this purpose.) It allows you to show unappreciative guests where they can stay next time they visit. : ) I know, you didn’t want to know that….
To see Slipforming, part 2, Money, Jail and City Life, click here.
Explore posts in the same categories: On a serious note, Slip Form House posts, Stuff to do when you're over 40
September 14th, 2009 at 4:28 pm
Soon, and very soon, you should start charging for exclusive/proprietary information! Where do I send my money, eh?
And, doncha know, there are thousands of little ol’ ladies who have no place to send their money now that Billy Mays is dead.
Cash cow ahead,
Charlie M.
September 14th, 2009 at 7:12 pm
Thanks Charlie! I needed the vote of support today! (More than you know!!!) And to be likened to Billy Mays? That was a bonus!
Now, as for the cash in your briefcase (that cash you’re wanting to send since Billy Mays is dead) – I’m going to get some blinking neon just-can’t-ignore-it button so I can begin my Speedo-pool-boy-feeds-the-horse fund. As I mentioned privately to you, I do not have a pool, but will put said Speedo-cowboy to work feeding the horse poste-haste. I’d also like to amass enough to buy myself an umbrella drink since I truly believe I have earned it. And for those of you worried about what Husband Ken will think – he assures me that any Speedo model worth his salt will charge a LOT OF MONEY to feed a horse in the dead of winter wearing only the Speedo, and that should such a cowboy apply for the job, I will be greatly disappointed when said Speedo hits the 30 degree weather. If that happens, I will have hot chocolate at the ready to drown my sorrows….because I’m a resourceful type of gal. : )
Again, thanks for the suggestion, and I’ll get right on it since I don’t want to miss a single donation. I’m giggling just thinking about it – especially since the blog traffic will increase significantly if ANY pool boy shows up! In the meantime, I shall continue to gather the meager funds generated when people click on the ads.
September 15th, 2009 at 11:49 am
I think you should name the pool boy Speedo. Try it out on your husband (the name, that is–again, Foghorn Leghorn voice).
And he would probably reply, as did the men who cringed when you referred to the square, “What the ‘L?”
September 15th, 2009 at 4:15 pm
Hubby thinks that his account has an ample credit in it due to having to live with me – and that he has no desire or obligation to trot around outside feeding horses in sub-zero degree weather in a Speedo for my amusement. Fuddy-duddy…. However, regarding NAMING the pool boy/horse feeder “Speedo,” Ken thinks this might be appropriate since feeding anything in your underwear becomes a feat of speed by virtue of the cold. He knows. He chased lambs in a blizzard in a bathrobe – another story, another time. Thanks again for the funny comments!
October 21st, 2009 at 7:57 pm
Wow, what an amazing project. I love rocks, am always collecting those I find here and there to line my garden beds. Of course I truly covet the ones which are entirely too large to lift. ; )
They always look great and help to keep a little moisture around the beds where my plants can put it to good use.
October 21st, 2009 at 8:35 pm
Hi Greg. Thank you so much for the feedback. I have been floundering since August not knowing where the communities were that would be interested in this sort of thing. I’m tickled to be finding like-minded folks.
I also know all about “coveting” those rocks I cannot lift. I set every rock but 2 in my home – those 2 being irresistible – and too big for me to lift. I am very, very glad to have the house part done. I did not get garden shots this year – but next year I will try to get the raised garden photos up. I think rocks and gardens are a natural for each other.
Anyway, thanks so much for taking time in your busy day to visit – and comment. That means a lot to those of us just beginning in the blog world.
October 22nd, 2009 at 10:49 am
This comment was from Blackjava, from the Blog Catalog, reprinted with his permission:
Hello Dani I just want to say how impressed I am. I love stone work. I was in construction for almost 40 years. I never had the opportunity to work with stone. I don’t know if I would have had the courage and determination to take on a project like yours. I love your blog series.
October 22nd, 2009 at 10:58 am
My reply to Blackjava was this:
Thanks for the comment. Regarding courage, all you need is ignorance to be brave! I had NO IDEA what I was getting myself into! I was just stubborn enough to hang in there. Don’t give up your dream to work with stone. My dad was 73, and it is a highlight of his life!
December 30th, 2011 at 3:52 pm
Hi Dani!
Wow, I commend you for all your hard work and determination! You have another follower (ME). You’re my inspiration, especially being a strong headed woman with a dream; one who lived it through to the end.
My man and I plan to start building in June 2012, and I’m wondering if I could get your email to ask you a few specific questions regarding your building techniques. I’m confused (an often occurrence) about the seams of the OSB board and determining the dimensions necessary for footings to hold the load of all those rocks n concrete. I’m also confused on the wire tie ins. I’d really appreciate any help you can give me, because I too, am walking into this a little blind. I plan to document the process as you have and I’d love to share my experiences with you and I hope you can be a distant mentor to me.
I look forward to hearing back from you.
Thanks,
Jen
PS-Your home is a one of a kind beautiful castle. I look fwd to being the queen of my own castle one day.
December 30th, 2011 at 5:01 pm
Thank you, Jen, for the kind words. They make it all worthwhile! I wish you the best on your home. Also, I commend you for committing to the documentation of your process. That is my one regret – that I didn’t take more pictures along the way. It seemed like I was always covered with cement and hesitant to bring my camera into the mess. Anyway, kudo’s to you. I’ll be in touch.
Dani