Bettina Landgrebe on Donald Judd's Concrete Works
This lecture was first presented by Chinati conservator Bettina Landgrebe at the October 10, 2009 symposium on Donald Judd’s freestanding works in concrete
Hello, everybody. Francesca has given you an extensive overview of the conditions that led to the conservation of the concrete pieces, and I will now talk about some of the actual conservation work that was done. I’ll begin with an aerial overview of the concrete pieces, taken in July, 2007 by one of the crew- members of the psi Geotechnical Engineering Services from El Paso. They prepared a report on sub-surface soil conditions for works Nos. 1-6 at the request of Bob Kirk, who at that point was overseeing the conservation treatment.
The purpose of the report was to determine the depths of load-bearing soil and the soil conditions most likely to be found underneath the pieces. The boring sites chosen were as close to the pieces as possible, to ensure that the test results would accurately reflect the soil conditions underneath. The photos show the rig approaching work No. 2, and one of the actual borings at this site.
Rigs were set up and drilling began. The test borings indicated relatively loose near-surface soil. The densities of the soil across the site seemed to be very inconsistent, which explained the severe differential settlement of the pieces.
As a result, the footing recommendations for works Nos. 1-6 varied. For works Nos. 1 and 6, spread-footing foundations needed to be placed at a depth of 4 feet below the existing grade, while works Nos. 2-5 could be supported on soil with foundations at a depth of 3 feet below the existing grade.
At the end of April 2008, work No. 6 was braced and digging started at the southeast corner of unit B (for identification purposes, clockwise from the north, each unit in a given work was assigned a capital letter). Work No. 6 was one of the pieces where spread-footing foundations had to be placed at a depth of 4 feet. It was also the most complicated of all the works, due to its configuration. The drawing shows the single units placed tightly together, without any space between them [fig. 1]. Bob Kirk felt that the foundation treatment should begin with this difficult piece. In principle, the process would be the same for each unit and piece, but I will mention specific circumstances of the foundation work on other pieces later.
Photos show work No. 6 braced, and a detail of the inside bracing of unit 6-C [figs. 2, 3]. This was necessary to stabilize the pieces during the entire process of digging underneath the works and the pouring of new foundations. The braces were reusable for different pieces and could be adjusted with a turnbuckle.
Digging began at the southeast corner of unit B; arrows point out the so-called supporting concrete blocks under the corner of this unit [figs. 4, 5]. In this case it was very easy to remove the old foundation block, as it was not attached to the bottom of the unit at all [figs. 6, 7]. In order to keep the unit in its position during the procedure, it was supported by jacks.
While the foundation form was prepared for pouring, digging was also started under the other units, where you can clearly see the misaligned floor and wall panels [figs. 8, 9]. There was about a one-inch difference between the wall panel and the floor panel. I will return to these units later in order to show you the pouring of the first double foundation.
On May 7, the first form for pouring a new spread-footing was placed under the southeast corner of unit B. The form has two parts: one for pouring the sub-base of footing [figs. 10, 11], and the pedestal form [fig. 12]. The photo shows a detail of the wire cage with adjustable inserts set within the form [fig. 13]. The wire cage inside the form reinforces the concrete. The protruding wire cage ensures a good connection between the footing and the pedestal during the pouring of the concrete [fig. 14].
A first layer of concrete was poured into the sub-base of the footing and allowed to sit for a few minutes in order to harden slightly and fix the rebar grid and the wire cage in place [fig. 15]. Then the remainder of the concrete was poured into the spread-footing form and allowed to sit. The photo shows the concrete mixture with large pebbles which was added to strengthen the mix.
During the pour, the concrete needed to be vibrated in order to spread evenly inside the form [figs. 16, 17]. After the filling of the footing form, the concrete was leveled and allowed to harden for some time before the footing was covered. Covering of the footing was necessary to avoid spilling over of the concrete during the pour of the pedestal.
Photos show the covering of the sides and front of the foundation footing and the concrete being poured into the pedestal and vibrated again [figs. 18, 19]. After the concrete had hardened, the plywood forms were removed from the new foundations. Once the first new foundation form supporting the southeast corner of unit 6-B was finished, you could see the huge difference from the earlier forms [figs. 20, 21].
The rebar wire cages which were situated inside the pedestals contained two or more adjustable inserts, depending on the size of the foundation. These inserts were used to lock a unit into position once the new foundation was poured and again after leveling of the unit had taken place. Steel plates were glued to the
bottom of unit B at the position where the leveling bolts protrude from the new foundation form [figs. 22, 23]. The leveling bolts were adjusted until they touched the steel plate, and in this way could support the unit.
The process of pouring a double foundation for work No. 6 was different and much more complicated than pouring a single foundation. The double forms are twice the size of a normal foundation. A double foundation supports two units at the same time, and two reinforcing wire cages with leveling bolts were used inside the forms [figs. 24, 25].
To support both units adequately, the form was set approximately 4 feet back under units B and C, which made it impossible to pour into the top of the form. The concrete mixture for pouring a larger double form is different as well; it was self-leveling and self-rising, which made it possible to pour from the side. A flexible hose attached to the side of the double form was used to facilitate the pour [fig. 26]; it was attached to the bracing of the units in an almost vertical position with rope [fig. 27]. This position ensured that gravity would aid in the pouring of the new foundation.
For this pour, the same ratio of water to cement was used as for pouring the single foundations. Specific admixtures made the concrete more fluid. Also, the pebbles added to the mix were different from the pebbles used for the single foundations [fig. 28]. Their size was much smaller than usual, but more stones were added to the mix to ensure the same strength of the concrete [fig. 29]. The same system of steel plates glued to the bottom of the units and leveling bolts was employed here as well, but more plates were used, because the foundation is supporting two units at once [fig. 30].
The photo shows the new large double foundation supporting the north side under work No. 6 [fig. 31]. The drawing shows the new double forms in blue and the single forms which were used to support work No. 6 in red [fig. 32].
Before I move on to other conservation work done on the concrete pieces, remember that, in general, the old foundations were smallish concrete blocks situated beneath the corners of the single units and were sometimes attached to the units with a variety of rebar and/or steel plates [fig. 33]. However, there were two pieces where the foundations were designed in an entirely different way. A drawing shows the foundation design of works Nos. 3 and 5. Instead of smallish blocks just supporting a corner of the concrete work, here the supporting concrete blocks measured approximately 1 V feet in cross-section, and spanned the entire length of the short side of a unit.
On the one hand, these large concrete blocks definitely provided more support
than the small blocks. On the other hand, they posed a serious danger to a single unit, as they were very heavy, and not resting on load-bearing soil; they pulled at the side of the single units that they were supposed to support. However, it was decided to leave these supports in place, as it seemed too dangerous and timeconsuming to remove the large concrete blocks. The new spread-foot foundations were poured directly underneath the old foundations. They were much smaller than the foundations for works Nos. 1, 2, 4, and 6, but together with the new large foundations, they now support the single units adequately.
The conservation work done on the concrete works did not progress in a linear fashion; various conservation tasks were carried out simultaneously. While one group of workers was doing foundation work, another group was cleaning pieces.
I will present all the structural work done on the pieces first, and continue with the plumbing (re-aligning of wall panels) of works Nos. 1-6, before moving on to the more aesthetic work, such as the cleaning and treatment of old and new patches.
Before we started to plumb the pieces, a structural engineer was contacted in order to evaluate the stability of the pieces and determine to what degree the single units were out of plumb and had to be adjusted. Photos show the plumbing of work No. 1-B [figs. 34, 35]. For this task the single units had to be braced again, in a slightly different way. If, for example, the south wall of a unit was leaning toward the south side, strong chains were wound around the bracing of the south wall and anchored to two trucks or a backhoe. With the help of a ratchet, the two trucks acting as a counterweight, and very careful pulling, the wall was pulled straight toward the north side until it was plumbed as straight as possible [fig. 36].
Due to the configuration of work No. 4—some of the units are placed tightly together—it was not possible to use trucks or backhoes as a counterweight to pull the wall straight. Instead, unit 4-C had to be braced and used as a counterweight in order to plumb work on unit 4-D [fig. 37].
The walls of works Nos. 3 and 5, however, were much more difficult to plumb. In these pieces, the foundations were much heavier than the foundations of the other pieces, which made the plumbing much more difficult, more time-consuming, and generally less effective [fig. 38]. In order to plumb the north and south walls of 3-A, the roof of this unit had to be raised slightly [fig. 39]. Each time, after the wall of a unit had been plumbed, the leveling bolts of the new foundations were adjusted in order to keep the unit in the position which had been achieved during plumbing. It was not possible to plumb all walls totally straight [fig. 40].
I will continue now with conservation work which can be considered to be structural as well as aesthetic work. As Francesca already mentioned, there were
old repairs throughout all of the pieces [fig. 41], including a corroding roof box. The roof boxes facilitate the connecting bolts between the roof and the wall panels of the later pieces, works Nos. 7-15. A photo shows rebar reinforcement which is situated too close to the concrete surface. The bottom arrow shows cracks only; the top arrow shows an area where the expanding rust on the reinforcing steel has already lead to losses in the concrete surfaces. Problematic areas were located and loose concrete was removed from around the rusting steel. Areas that needed to be treated were marked [figs. 42, 43].
After the concrete has been removed, you could see that rust had formed on the steel [fig. 44]. The image [fig. 45] shows a roof box photographed from the top of the unit, with the connecting bolt between the roof and the wall of unit 15-B visible. The steel was then treated, the rust removed, and then primed against future corrosion. The next image [fig. 46] shows the patching material still wet after the process.
The next two pictures show different kinds of losses. On the back wall of unit 5-A there were shallow and deep losses, [fig. 47] mostly the result of tension between the floor panel and the wall panel. There was almost no distance between the floor and wall panel due to differential settlement and non-sufficient foundations. These losses had to be patched to restore aesthetic integrity [fig. 48]. Irregular, large losses were usually cut square, to facilitate an even, adequate and long-lasting filling, whereas smaller losses were left as is and filled with a different kind of patching material.
Francesca described the various stains and streaks that were observed before cleaning [fig. 49]. A variety of cleaners were used, depending on the stains. In general, a cleaning procedure went as follows: the concrete surface to be cleaned was thoroughly pre-wetted from the bottom to the top. The diluted cleaner was applied to the surface using a low-pressure spray, roller, or brush. It was left to sit on the surface for three to five minutes, reapplied, and lastly agitated by brush. Afterwards, the cleaning solution was rinsed off with pressured water, again from bottom to top. Working from the bottom of the wall to the top ensures that streaks are avoided, and that cleaning solution does not drip onto dry concrete surfaces and stain them [fig. 50].
Before I explain a specific cleaning procedure in more detail, let me introduce the true nemesis of art conservation at the Chinati Foundation: the common Mexican free-tailed bat [fig. 51]. The following photos will show the stains inflicted by bats on the concrete pieces, and how these stains were treated [figs. 52-55]. The cleaner used in this case was a paint-stripper, applied with a brush.
However, with this method it was still not possible to remove all the bat urine stains, so we adopted a different method. In order to allow the paint stripper to remain on the surface for a longer time, it was mixed with a marble poultice [figs. 56, 57]. This ready-mix marble poultice was mixed with water and the paint stripper until it formed a smooth paste. This paste was applied to the surface with a large putty knife and left on the surface between twelve and forty-eight hours, depending on the stain. It acted like a compress, drawing out and holding the material, which stained the concrete surface. The poultice was removed from the surface with a brush after drying, and in some instances the poultice cracked during the drying process and was already falling off by itself.
Work No. 12, with its six cave-like structures, is an ideal nesting place for bats; there were more or less resistant bat stains in all of the units. Most had to be treated several times to successfully remove them. This treatment had to be repeated to eliminate most of the traces of the bats.
The last topic I will talk about is the adjustment of old repairs. In both these photos you can see the patches which were done right at the beginning of the fabrication because Judd was not satisfied with the edge lines [figs. 58, 59]. Francesca has already mentioned that the patch and concrete surfaces have aged differently, which means that the patches are much more visible now than when they were first applied. We decided not to remove the historic repairs—first of all because they’re historic, second because they might be epoxy-based and very hard, and thus their removal would most likely have damaged the edges even more. So we decided to leave them wherever possible, patch missing parts, and in-paint the old fillings to match the surrounding concrete surfaces.
After a lengthy discussion with conservator friends who have extensive experience with treating and in-painting concrete, an in-painting system was recommended and used on the patches. This new paint bonds insolubly with the surface it is applied to. The photo [fig. 60] shows the left side of the back panel-the in-painted area on the left, with the right-hand side still to be adjusted. The next photo shows the in-painting of the back panel completed [fig. 6i].
Here we see Ben Meisner, former conservation intern and interim caretaker of the Chinati collection, in-painting the east elevation of unit 2-B [fig. 62]. You can also see the whole arrangement of in-painting colors and materials [fig. 63].
The final image shows the historic fillings before and after in-painting [fig. 64]. The form and color of the unit after in-painting is no longer disturbed by the light gray fillings, and the unit is basically unified. Thank you very much.