Gunite for the south wall

In this episode, the gunite crew from S.A.M. Gunite Pools comes back to shoot our south wall. They had just finished the roof on the Friday before, so the equipment and materials were already in place. The form work was lath covered rigid XPS insulation over steel stud framework. Easy-peasy… Easy to watch anyway.

The Video

The Forms

We started with a steel stud framework and attached 2 inches of XPS rigid insulation (Pink Board) to that. The window bucks were treated wood, cut to match the curve of the wall. We also had some 4 and 6 inch tube steel in the wall to take loads from the earth covered awing that we will add in a later step. Then we covered the XPS with lath to hold the shotcrete and we were ready to go. You can find more details and pics on the formwork here

This is a pretty easy and robust way to form a wall, and includes built-in continuous insulation already in place from day one. The steel studs also leave a 4 inch deep cavity that I expanded out with some furring strips on the inside so I could fit 5 inches of additional insulation.

The Tools

For more on the difference between gunite and shotcrete, please see this other comparison page.

The Bat’Lath was used a lot in this job to trim down the walls to the correct thickness before troweling. This did create a fair amount of waste, but I am sure it was worth it compared to trying to push around that much concrete.

Carlos using the Batleth on the wall…

The Gallery

A picture is worth a thousand words, but these pics also have captions, so bonus words!

Shooting a Gunite Roof

This one is the long awaited shooting of the gunite roof. As per usual, we’ll start with the time lapse video and end with a gallery. If I am up for it, I’ll post some lessons learned in between.

The video

Lessons Learned

Gunite vs Shotcrete: This topic was already covered, but I’ll link to it here. I’ll also add that it is all in the mix. If your gunite is just a basic sand and portland mix, it isn’t going to be as strong as a shotcrete mix with some fancy additives, heavier aggregate, etc.

Lath and Screen vs Hardboard: For the shotcrete, the lath and screen worked well. None of the shotcrete passed thru the screen because it uses a pea stone aggregate. However, the gunite used sand as the aggrigate and did pass thru the screen. The hardboard was great in some ways, but the weather really beat it up and gave it a rippled surface.

Shooting and finishing: Both are important. My shotcrete crew could have done just as good a job as the gunite crew, but they didn’t. For shooting, you want someone who understands what you need to get done and is just putting up what you need. If they are paid by the cubic yard, they may put up more than you need, etc. You definitly want enough finishing people to finish the surfaces adequately. If your crew is strong on shooting, but doesn’t have enough man power to finish, you will be sad.

Cleanup… If the crew treats cleanup as an afterthought, you will be sad. There will be mess. Make sure the crew has enough man power to deal with it. Beyond that, you probably need to keep your eyes open for things the busy crew may miss. For instance, I wish I had better covered some of the near by boulders to prevent them from getting gunite on them and I really wished I had better cleaned off the polished concrete ribs before the gunite set. That mistake cost me many many hours.

Do it yourself? My rule of thumb is that if a job takes tens of thousands of dollars worth of specialized equipment, you probably shouldn’t be doing it yourself. Add the experience, skill and stamina required and I would double down that you probably shouldn’t be doing your own gunite or shotcrete. That said, I do know of some who have and kudos to them.

Gallery:

Digging for Fresh Air

This is an in-between event where we dug in some ventilation ducts to transfer fresh air to the rooms that need it.

The Video

The Gallery

Installing QuadDeck ICFs for the Mezzanine Roof

I wanted to experiment with flat roof structures also, and it seemed like the best way to do that would be with the Quad Deck panels (we also used these to cover the basement).  This is some explanation of how we did that.

First, the video.

The Video

 

The Basics

Quad deck is fancy formwork (Insulated Concrete Formwork, AKA ICFs) for pouring a concrete slab over an open space.  To increase strength of the final concrete structure, Quad deck shapes the concrete into Ibeams.  It also includes its own internal steel structure to help it resist deflection before the concrete cures.  The EPS (expanded polystyrene) foam is the tough 25 PSI stuff.

When installing, there are a few key concepts to be aware of.

First, you need to support the weight of wet concrete until it cures.  This means you will need secure shoring.  The brochures show fancy specialized equipment, but scaffolding and cross beams works also.  These need to be strong, so do a little math and make sure that your shoring can handle the load.

Second, the concrete is going to try and push the ICFs apart.  If it can separate them, it will just spill thru between them and you will have a huge mess.  Toe nailing screws thru the shoring cross beams and into the steel reinforcement in the ICFs can prevent them from moving apart.  The “experts” who installed my basement used drywall screws.  I had a much easier time using self tapping metal screws that could easily tap into the steel reinforcement in the Quad Deck.

Third, don’t forget you will need to remove the shoring later 😉  The guys who did my basement often put screws in at angles that were only possible if the Quad Deck wasn’t there.  That gave me quite a hassle.  Build your shoring from below so that it can be removed from below.

Fourth, keep in mind that the concrete needs to sit on the perimeter ledge.  You will be removing that shoring, so the concrete needs to be firmly distributing its weight on the ledge around the perimeter.  This means you need to remove all the insulation from the edge of the QuadDeck panels.  It is tempting to leave some and let the ICF overlap the edge a little, but every bit of the ledge covered by the ICF is a bit of the ledge not supporting the load.

Fifth, you will need to mind the gap.  After installing the quad deck.  you can use spray foam insulation to close up any gaps between the wall and the quad deck.  Remember from 4 that we don’t want any insulation on the ledge.

Sixth, following your rebar specs, and especially rebar for the bond beam around the perimeter, is critical for strength.  Concrete is terrible in tension, you need the rebar for any sort of flat floor to carry a load because that load inevitably creates tension, especially in the bottom of the Ibeams.

Seventh, this is a pour, so close all the sides…  Also, make sure that the perimeter wall is to the correct height for easy finishing, etc.  Don’t just mark the wall where they should fill to, trim it off if you can.

Maybe I’ll come back and add more later.

The Gallery

A pic is worth a thousand words and here are a bunch of pics.

Building the forms for the radial vaults

In preparation for shooting the gunnite on the roof we needed to put up some forms that would keep the concrete from just falling thru.  The radial vaults have simple curvature, so we could build the forms from boards pressed up against the steel arches.  Making that happen took some compromises in the plan.  As usual, challenges arose.  Enjoy.

The Video


The Chimney

In the video I forgot to include any footage of the chimney going in.  Basically, I built this form so the shotcrete would create a good base for my chimney on the vault.  My one regret was that I didn’t think to close the top of the form in order to prevent the gunnite from going inside the chimney hole.


The Gallery

A picture is worth a thousand words and here a bunch of pictures