Slipform Stone Walls

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mtngun
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Slipform Stone Walls

Post by mtngun » Thu Feb 28, 2008 8:04 pm

Just finished my first day of slipform masonry.

It's too dark to take pictures now but I'll post some tomorrow.

The good news is that I really really really like the way the stone wall looks. It looks like it belongs here, which it should, since I'm using local rocks. Plus, stone doesn't burn, and that's pretty important. There's no fire protection and no fire insurance, but plenty of lightning storms and occasional wildfires. If your house catches on fire up here, all you can do is grab the wieners and marshmellows as you are running out the door.

On the downside, stone masonry is very hard work. It's very slooooow. And even though I am using lots of reinforcement, I worry about earthquake resistance. We do have earthquakes in Idaho.

Originally, I planned to use stone only on the bottom two feet. But now I am thinking the entire first floor. We'll see.

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Re: Slipform Stone Walls

Post by mtngun » Mon Mar 03, 2008 8:29 pm

For the slipform masonry, did you pick that up from helping somebody else build that way, or just from reading about it? There was a Mother Earth article about it - probably 10 or 15 years ago - by a couple who'd written a book and held workshops someplace in Montana. I thought it was a very slick way to do stone construction. It's nice to see you making good progress. I'd be very interested to know how you're handling insulation and interior wall surfaces.

-- John

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Re: Slipform Stone Walls

Post by mtngun » Mon Mar 03, 2008 8:48 pm

jwp, I read several books on the subject, then gave it my own twist. It's just an experiment so judge it accordingly .......
Image

***** Darn it, several pictures of slipform construction were lost during the server move. *****

Slipforming is a messy process that gets too much mortar in some places and not enough in others. You have to knock off the excess mortor (preferably while it is only a few hours old), point the joints, and wash the concrete stains off the rocks.

The rock in this area is basalt and nothing but basalt. It's brown and boring but, like I say, it looks like it belongs here. I will probably haul in some pretty rocks from the Salmon River to accent doorways, etc.

The 2" foam is not so great; 4" would be better, but the foam is very expensive and the 16" wall doesn't have room for 4" of foam anyway (the 16" wall was originally intended to be cordwood, not stone). If I had to do it over again, I would make it 18" wide, with 4" foam.

My logic goes like this:

-- I wanted stone inside and out, for fire resistance, and because it looks appropriate for a mountain cabin.

-- I wanted thermal inertia on the interior side of the insulation. Most stone houses place the thermal inertia on the exterior side of the insulation, where it does no good.

-- I want it to be earthquake resistant. There's remesh in both walls, and there will be rebar at corners and at halfway points. The two walls are tied together with 14 gauge wire on 12" centers. There will probably be additional ties at critical points.

-- I want it to be strong enough and wide enough to support a 16" cordwood wall on the second story, if I decide to go that route (I keep changing my mind).

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Re: Slipform Stone Walls

Post by mtngun » Sun Mar 23, 2008 5:30 pm

'I\'m averaging about a 2' x 8' section of slipform wall each day. That doesn't sound like much, but it's a lot of work.

Typically about 4 - 5 hours in the morning to actually make the wall. After lunch, I set up the forms for the next day's pour. It takes several hours to lay out the remesh and insulation, and then clamp the forms together. The form work will get more complicated and time consuming as the walls rise, because I'll have to set up framing for the window openings, and metal conduit and boxes for electrical outlets.

The rolled 6 x 6 x #10 remesh is a pain to work with, because it wants to curl up. It's worthwhile to spend 15 minutes un-curling it before installing it.

The forms were made out of 2 x 12 x 12' boards left over from the foundation forms. The 12' forms were too darned heavy, so I cut them down to 10'. They are still heavy. Most people use plywood forms, but it seemed more cost efficient to use the leftover form boards. I have two sets, plus a set of short forms that are used for corners. It's nice to have two sets of forms, so you can be installing the next day's forms while today's pour is hardening.

Speaking of which, if I had to do it over again, I would have given those 2 x 12's a coat of polyurethane before using them. Then they could have been oiled to prevent the concrete from sticking, without damaging the wood, so that they could be used later for framing. As it is, the combination of oil and moisture from the wet concrete warped the boards pretty badly, plus the oil made the wood spongy. It's a shame to waste that expensive lumber.

I let the pour harden for 5 hours before removing the forms. It you leave the forms on too long, then it is very difficult to chip off the excess concrete in the joints. I like to pour in the morning, then I can pull the forms and chip the joints in the evening.

I spend several hours each day gathering rocks. There are millions of rocks laying around, but only a few of them are the right size and shape.

Every day I have to haul in a barrel or two of water for mixing concrete. Usually I get it from the neighbor's stock pond.

I have a big stockpile of unwashed river sand/gravel that works great for making concrete. Eventually, I'll run out and have to spend several days hauling in more.

For the past two days I have been experimenting with an acrylic admixture. The acrylic is supposed to make the concrete tacky so it will grip the rocks better. However, since switching to the admix, several rocks have fallen off when the forms were removed (they were easily glued back on with construction adhesive).

So I think I will eventually return to adding a little lime to the concrete. The lime also makes the concrete sticky, and lime is cheap. No rocks fell off when using the lime mix. At the moment I am out of lime, though.

If this were a stick-frame structure, the walls would be done by now -- but it only takes a few minutes for a wooden house to burn to the ground.

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Re: Slipform Stone Walls

Post by mtngun » Sun Mar 23, 2008 6:17 pm

I haven't updated for a while because there isn't much new. The stone walls are looking good, but progress is sloooooowwwww.

My front yard this morning. The local deer are practically pets. I may have to go somewhere else to hunt because I won't have the heart to shoot these.

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One day when I went to get barrels of water for the concrete, there was a herd of elk by the pond. Naturally, this is private property where I won't be able to hunt.

Image

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Re: Slipform Stone Walls

Post by mtngun » Sun Mar 23, 2008 7:00 pm

The second level of stone is complete, bringing is up to about 3 1/2 feet. It is just barely up to grade in the rear, so I will add one more level of stone, bringing it up to 5 feet high, before switching to wood construction. It takes two weeks to do one level of stone, plus this last level will take an additional week to add the window framing, electrical conduit, and bond beam. So figure all of August to get up to the 5 foot mark.
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Electrical stuff has to be embedded in the stone wall. This is the first time I've ever worked with conduit, so I'm not setting any speed records. If you are an electrician, try not to laugh at my work.
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Some days it is hazy due to wildfires.
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I waste a lot of time (and $gas) running back and forth to town for supplies. The nearest hardware store is a two hour drive each way. The road is kind of exciting, too. One lane gravel, washboards most of the way, and logging trucks.
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Junior in velvet.
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Junior and grandpa. Grandpa doesn't look too shabby.
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Re: Slipform Stone Walls

Post by mtngun » Sun Mar 23, 2008 7:01 pm

The third layer of stone is underway and here's how it looks -- it's starting to look like a real wall. (except the image is missing !!!!) This layer takes a little longer because the top surface has to be semi-level, plus special forms will be required around the window openings.

The black spot on the right is a 3" ABS pipe where the electrical service will eventually feed through.

I've used up all the local sources of flat rocks, so I'm having to spend more time and gas driving around looking for rocks. Otherwise, I've gotten the hang of the stonework and it's going as well as can be expected. The weather has been cooperating.

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Re: Slipform Stone Walls

Post by mtngun » Sun Mar 23, 2008 7:03 pm

Here's a pic of the stone walls taken August 31. The 5 foot level is now complete. That brings the dug-in portion of the stone wall about two foot above grade, which
was my original goal.

It will take several days to prepare for the next phase of construction. I've got to do a lot of logging, cut the logs to length, split them, de-bark them, and treat them. Sturdy frames have to be made for the window and door openings. More sand and gravel have to be hauled up the mountain, and a load of sawdust would be nice too.

Once the prep work is done, the next phase should go faster than the stone masonry.

Note the grass is all brown due to the very dry weather.

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Re: Slipform Stone Walls

Post by mtngun » Thu Jun 10, 2010 1:53 pm

Slipform construction leaves the joints between rocks rough and uneven. The joints look a lot better if they are "pointed," that is, filled in with mortar and smoothed out.

Uneven joints from slipform construction.
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The joints are wetted to improve adhesion, then mortar is slapped on by hand. It's a messy process.
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The joints are smoothed with a teaspoon.
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As soon as the mortar is stiff and semi-dry -- but not cured -- the excess is brushed off with a wire brush. If you wait too long, it's very difficult to remove.
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Finished product.
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Like all masonry work, pointing is slow and laborious. I just today finished pointing the inside of the shop, and haven't even started the outside. Since pointing is merely cosmetic, it's low on the priority list.

I'm extremely pleased with my slipform walls. They look good, they insulate very well with zero air leakage, and they'll last forever. Too bad it is so darned hard and time consuming to build this kind of wall.

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Re: Slipform Stone Walls

Post by Highland Drifter » Mon Jun 14, 2010 6:30 am

Looks good Dan. How about posting some pictures showing the whole view of your new home/shop from the outside and some from around the shop? Kind of a photo tour.

Brian

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