Selling Power TV: How Social Media Has Changed Our Business

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carpenter

How do you think that these columns were built?

Check the year for the Nathanial-Rogers House

Flocculate with Expansive Clay

This entertaining topic comes up once again, this time in reference to a thread on Pat' Morrissey's LinkedIn Group, Means, Methods & Materials... in an ongoing discussion regarding rising damp in masonry.



Google books, "Clay Materials Used in Construction " edited by G.M. Reeves, I. Sims & J.C. Cripps

12.1.2. Bentonite

The name bentonite is popularly used for a range of natural clay minerals of the smectite group, principally potassium, calcium and sodium monnnorillonites derived from the weathering of feldspars. The name derives from the discovery of large deposits near Fort Benton in Wyoming. USA. Because of the chemistry and micro-structure of the clay particles they have a strong ability to absorb water and are able to hold up to ten times their dry volume by absorption of water. Montmorillonite (after Montmorillon, southwest of Paris) consists of very thin flat crystalline sheets of clay minerals which are negatively charged and are held together in 'stacks' by positively charged sodium or calcium ions in a layer of adsorbed water. In particular the soil particles comprising a stack of sheets of sodium montmorillonite form extremely small and thin platelets, being typically of the order of 1.0 pm or less in length and 0.001 um thick. The ability to absorb water comes from the relatively low bonding energy of the sheets, which allows water molecules to be adsorbed onto the internal and external sheet surfaces. Calcium ions provide a stronger bond than sodium, so that calcium mommorillonite swells less readily than sodium monnnorillonite. Potassium ions provide much stronger bonding between clay sheets as the potassium ion is of exactly the right diameter to fit between atoms in the sheet structure with negligible gap between the clay sheets. A similar material to mommorillonite but with potassium bonding is the non-swelling clay mineral known as illite. The substitution of sodium by calcium or potassium ions in monnnorillonite greatly reduces the ability of the clay structure to hold water.

The very small particle size of bentonite results in an extremely low hydraulic conductivity for intact clay, with a coefficient of permeability of typically less than 10-1" m/s. This allows the clay to be used to form 'impermeable' or 'waterproof layers and sustain high hydraulic gradients across thin layers with negligible water flow. The swelling property is also important in such applications, since should water permeate a layer of dry bentonite it will swell even against high pressures and tend to seal any crack or fault which might otherwise develop into a leakage path. The volumetric swelling of particles can be up to 13%. but that of an agglomeration of particles is somewhat less depending on their packing.

Many applications of bentonite involve the use of slurry. Mineral particles in a slurry generally carry electrical charges, the nature and intensity of which vary with the particle surface characteristics and the chemistry of the liquid phase. Polar water molecules may then be adsorbed on to the particle surface, forming a layer of 'bound' water surrounding each particle. The result of the two effects is to produce repulsive forces between particles, which are greater than attractive Van der Waal's forces except when the particles are very close together. The particles in a slurry therefore tend to keep apart from each other in a 'dispersed' condition (Fig. 12.1a). The effects are most noticeable with small particles (clay/silt rather than sand/gravel, and in practical terms only with finer clay particles) since the relative surface areas are much larger. and gravitational forces are much smaller. Under some conditions the plate-like particles of clay minerals may have different charges on the edges and faces of the particles, and are able to clump together in a 'flocculated' structure (Fig. 12.1b). The large flocs settle out of the slurry much more readily than the small individual particles.

Some slurries demonstrate the effect known as thixotropy, whereby they 'set' into a gel if left undisturbed, but revert to a viscous fluid (sol) when sheared. The alternation between sol and gel may take place any number of times. The phenomenon is well known in 'non-drip' paints. A gelled 'house-of-cards' type of structure with edge to face connections is illustrated in Figure 12.1c; gels of thin clay particles may contain only a few per cent of solid material. The gelled structure is also able to support larger soil particles and prevent them from settling out. Bentonite slurries are thixotropic and typically form a gel at concentrations of a few per cent by mass in water: this is an important property of bentonite slurries in many applications. For a more detailed discussion of the nature and properties of bentonite slurries see Jefferis (1992).

Bentonite clays occur, and are mined and processed commercially, in many parts of the world. Some natural deposits, notably those from Wyoming, have a high proportion of sodium. These tend to produce slurries with high viscosity but relatively low gel strength. The deposits mined in the UK, near Woburn, are mainly of the calcium form, and these are converted by ion exchange to the sodium form by ball-milling with sodium carbonate. These materials tend to be less dispersive and give lower viscosities for the same slurry density, but higher gel strengths. As natural products, bentonites vary widely around the world in quality and content of other minerals, even after commercial processing, and these variations must be taken account of in their specification and use.

Bentonite is available commercially in a variety of forms. but nearly always in a dry state, as powder (in bulk or bags. like cement), pellets or blocks. For applications in construction it will usually be hydrated, although in some waterproofing materials the hydration is allowed to occur in situ. For use as a slurry, the bentonite is mixed with water at a rate of a few per cent of solids by mass. The aim is normally to produce a slurry in which the bentonite particles are well dispersed and fully hydrated. For good mixing and rapid hydration, a high-shear colloidal mixer (shear rate >900/s) should be used, and the slurry then left to stand for some time while the clay particles hydrate. The quality of the slurry obtained depends on the hydrogen ion concentration (pH) of the water used in mixing; saline or acidic water or water containing impurities may cause the clay particles in the slurry to flocculate. This may initially cause the slurry to 'thicken', but there will then be a tendency for the flocculated particles to settle out of suspension and form a sludge. However there is not normally a practical problem with seawater coming into contact with a slurry, provided the slurry cannot mix freely with the seawater and has previously been fully hydrated with fresh water. Deliberate flocculation with flocculating agents may be used to help remove bentonite from suspension when the slurry is no longer required or has become too contaminated with cement, clay or silt. A combination of low hydraulic flow into the slurry (so long as hydraulic heads are low), and long diffusion times for salt compared with exposure times, usually causes few problems in the presence of seawater.

Bentonite is also used in combination with other materials, in particular other soil materials and Portland cement. At one extreme a small quantity of bentonite may be added to a concrete mix to produce highly plastic concrete able to undergo quite large deformations without cracking: while a small quantity of cement in a bentonite slurry can produce a hardening slurry with a small shear strength. Natural clay, silt and sand may be used as 'fillers' to produce cheaper material while keeping most of the benefits of the scaling ability and low permeability of the bentonite. Gleason et al. (1997) found that about 5% of sodium bentonite and 10-15% of calcium bentonite had to be added to fine sands to achieve a sand-bentonite mix with a permeability of less than 10-9m/s. Hardened bentonite-cement slurry mixes containing 180 kg/m3 of cement and 60 kg/m3 of bentonite had permeabilities of about 10-7m/s with calcium bentonite and 10-8m/s with sodium bentonite. These mixtures arc discussed further below in relation to various different applications. Small quantities of polymers and other chemical additives may also be used to enhance or modify the properties of bentonite slurries for particular applications. These are also discussed further below. [not below here, though, you gotta go read the book if you want more!]

From our small perch what can we see ahead for the future?

As a New Year approaches and despite that we are unable to see very clearly into the future we are able to appreciate the future’s potential to be of interest and entertainment.

We were asked to list projects that we see on our horizon but there is a superstition that we abide that to talk about future work, or even to talk about ongoing work, has a tendency to skunk the odds.

We have been involved with a number of projects that we will likely have nothing to do with in the future but that we will continue to be interested in their progress.

Though it is proper to mention the lead of the design teams in each case we worked with a number of friends and associates who we will not mention here as the lists would get long winded and complicated.

The Edison Memorial Tower in Menlo Park, NJ, where Edison invented the light bulb, is currently working through a prequalification phase prior to going to bid. The project involves restoration of John Earley pre-cast concrete panels -- this is artisan work. The lead architect is Farewell Mills Gatsch Architects. We very much enjoyed working with them to provide in-field support during their design phase investigations. The most memorable statement of the project, "Where is the water?"

The McCarren Park Pool restoration in Brooklyn, NY (in hip Williamsburg) is a Robert Moses structure that we lived across the street from for a number of years when it was an empty and abandoned mound of brick and concrete. It is currently an ongoing project. I had an opportunity to meet the contractor at a holiday party and enjoyed hearing tidbits. The lead architect was Rogers Marvel Architects. We worked on their design team to provide field mock-ups and probes. One memorable adventure was the entire day that it took to do a 1 sf of repointing mock-up in a blizzard... the drive to NJ to get 2 bags of the specified sand took up most of the day. We also regret that our friends at Brooklyn Brewery will probably not be able to continue to host concerts at the pool once it is completed. I also managed to get a flash fiction published about a dead man found at the pool as reported in a small news clipping. He was missing one arm. We did not get to meet him.

The Brick House at Philip Johnson's Glass House. We were advised to be discrete when talking about this National Trust site. I enjoy informing non-architect friends about the glass house by talking about the brick house first. Though a relatively small structure thie project should prove to be an interesting one. The lead architect here was Li-Saltzman Architects.

High Bridge Aqueduct is a curious project for us in that rather than being a vertical logistic problem, as occurs quite often in the NYC environment, it is a horizontal one. We did a series of probes there and with the 1,600 ft length we had to bring in our tools and equipment and materials each day and remove them at the end of the day and fully transport them out of the area (we bought a small yellow wagon that we are very happy with)... nothing could be left behind for fear it would be thrown over and off the bridge. We also had a really good time exploring the innards of the aqueduct pipe, and I mean that literally as our last steel coupon we extracted by cutting from the inside out. The lead on the project is TranSystems.

The Fulton-Nassau Crossroads Program is down near Ground Zero in Manhattan and we had an opportunity to do a few facade storefront probes. Lower Manhattan has to rate as one of the most congested and street populated areas of the planet other than maybe urban population centers in Japan and Asia. Managing to go down there and grind and cut through stucco on the street in broad daylight, safely, with tourists and such walking past, and then to come back again and patch it all up to look good was a tiny but interesting accomplishment. The first day it took us an hour to figure out how to get our small truck, when we were only a few blocks from the site, through the maze of narrow one-way and blocked streets to actually end up at the site and parked. We cheated. Lead on this project, for us, was Li-Saltzman Architects.

It was a year ago the day before Thanks Giving that we did a probe in a plaster ceiling at NY City Hall for Beyer Blinder Belle Architects  and it is this year, a year past our initial brief escapade in making another hole in the built environment that we have got ourselves involved in wondering what will happen to the restoration of the wood windows. We remain wondering.

Our friend Leland Torrence up in Connecticut involved us in an exterior condition survey of two public schools in Providence, RI and other than the usual fun filled field days for the survey the major task was sorting through 1,000+ photographs then assembling them in a Blogger based online visual report, with a few drama laden videos and to do so in such a manner that a report would be produced that would convey the magnitude of the exterior conditions of the masonry of both schools, with a conceptual budget that we also worked up for a 5-year remediation plan. We had thought that it would be really neat to produce a visual report on an iPad and then to send the pre-loaded device to the architect... but the budget for the project did not include for expensive toys and thus we went with wrestling the nearly for-free Blogger format to produce an intelligible online report experience. It helps that once something is developed in a Blogger format that it can be easily cut and pasted into a for-print hard copy report. Now that we know how to do it we hope to have more of this type of communications work in the future.

Warning: turn down your computer volume.

We await what will awake in the New Year. May we all be blessed with work, health and good business!

For Drill Bit Geeks Only!

As a probe contractor for investigations of existing historic building fabric, which can include anything from silk wall covering to pine floors to concrete cores to marble and steel... we enjoy drilling holes and the technology of the tools.

Seasoned Greetings

Should unit prices be required in the bid process?

I could not sleep last night and it had nothing do with the moon eclipse. But I did run across a discussion on unit prices in bids and it is a topic that I find interesting. I got into a bit of rant on it. Rather than do one throw away into the I-way ozone cloud I figured I might dress up my thoughts on unit prices and share them here and elsewhere as well.

I enjoy estimating and bidding as a sport.

I consider estimating for historic preservation work to be the most challenging, complicated and rewarding form of estimating in the entire world of construction.

I have been doing it for a long time. Over the last few years I have been working on writing a book about misadventures in estimating in historic preservation with a mind to reveal enough secrets, foibles and weaknesses that I will never be able to return to doing it again.

I am not quite there yet.

I am interested in sharing, ranting on all sides our thoughts and impressions on the estimation and bid process as it applies to historic preservation work.

The initiating question is: Should unit prices be required in the bid process?

Unit prices do complicate the bid process but what I find most difficult with them is that it is not always clear what their intended use is.

I agree that if they exist that they should be for the purpose of pricing additional work or reasonably unanticipated conditions but in my experience that use is rarely the primary reason that they exist, or that they seem to increasingly proliferate in number. My first leaning toward a recommended practice would be toward a clarification in the bid documents as to what the intent and fair use of the unit prices would be applied to in the management of the project.

Compared to other areas of the construction industry in historic preservation (and I do not mean our bread n’ butter maintenance projects) there is not a great deal of standardization of work activities but there is a great deal of need for and reliance on specific labor skills of unique individuals. When I encounter unit prices they range from work activities that may on the surface look to be relatively simple but in fact be quite complicated to activities that are so unique that nobody, including me, has a clue what they should cost.

A price in economic parlance is information and what I find is that the first use of unit prices is as information used in evaluation of the honesty of a bid.

People – friends of mine -- who evaluate and compare bids quite often have no idea what a work activity should cost and so they line up all of the bids, and all of the unit prices in a matrix, and if the unit prices appear to be deviant from the comparative trend then they place a focus on the areas of greatest deviancy.

An honest evaluation would look at where unit prices run low as well as high, but a less than honest evaluation will only focus on higher unit costs in an effort to negotiate them lower. That lower cost being an objective where the goal of the evaluator is low cost and not necessarily the eventual economic and qualitative success of the project.

I run across clauses such as, “Unit prices that are deemed excessive in cost will be cause for rejection of the bid.” A problem with this approach is that though the unit prices provide information what they reveal can be false and misleading, and generally the people making the interpretation have no clue as to an objective truth or falsity of the information as they are usually the ones who wrote the specification that may very ambiguously describe the scope of the presumed unit price. And in a majority of cases they will never have been in a situation of themselves having to actually provide the specific item of work out of their own resources.

On a bid sheet a unit price may be described in two to three words and a problem in bidding is figuring out what those few words will mean later in the management of the project.

For example “Repointing of brickwork”. I am quite often asked by contractor associates what this unit price should be. Without knowledge of the potential complications one tends to assume that there is a standard market price. There is a perceived standard market price, a price that those who evaluate expect to see listed as the unit price, and in general it is too low of a price for the reality of the resources needed to do the work. Beyond the issues of quantity in a small or a large amount, which is generally a question of logistic and mobilization overhead wrapped into the unit price item, there is also a question, at least in historic work, of skill technique that can vary quite widely as well as a range in cost of specialty materials.

Are the joints to be cut out with a diamond grinder or by hand with a hammer and chisel? Do we actually expect that the joints will be cut by hand with a hammer and chisel as is often specified but as is nearly impossible to actually do in practice? Does the sand for this repointing cost $2.98 per bag or is it a specialty sand to replicate historic mortar at $25.37 per bag? Are the additional units to be done in the same general area or on another portion of the planet? Will our competition on the bid know the difference?

This gets very complicated when the unit prices are reflected back into the number of units in the base bid and the use of the unit prices is an expectation that the lump sum in the base bid reflect the unit price times the number of units but not accommodate other needed resources to complete the work.

This becomes a real problem when one is dealing with public works bids where, depending upon the practice of the public agency, everything is based on unit prices applied to quantities of units, and worse where the logic of the separation out of the units is inadequate and poorly thought out. Made all the worse when there is no room for discussion as in bid sheets that clearly indicate that prices are not to be annotated. [In my old age I refuse not to annotate bid sheets in the determination that it is better to shoot me now. I have been known to scribble all over bid sheets in my irritation that they were so poorly constructed that I want to scream and do other unseemly unsocial acts of vengeance.]

I have always been of the contention that when the quantity of additional units exceeds the base bid by 10% that there should be a change order negotiation. This is not always well received or accepted in argument as a 10% deviancy tends to reflect that the bid documents were not very well put together to begin with.

I recognize that one driving motivation behind the honest making factor of the use of unit prices is that we all operate in a world where we often either cannot tell who is cheating or honest, or that we have no choice but to contend with cheating as a standard way of contractors managing projects and therefore need protections. We also need protections from the protections. Whatever I may think of unit prices it can all be folded into strategic game theory and like sinking into a cosmic worm hole we may find ourselves coming out of the argument before it even started.

I have also been of the contention that deduct of units should not include deduct of profit and overhead. This is the general argument in favor of having unit prices listed as Adds and as Deducts. This can work well in practice as long as it is clearly understood what resources are applied to the unit cost to begin with.

The spread between the Add and Deduct is also information and the estimator needs to accommodate how that information will be interpreted and used. If it is used to interpret that overhead and profit is 500% and that the entire bid is overpriced because of that then it provides one more problem to deal with.

Most specifications that I encounter stipulate that the unit costs will include all overhead costs including taxes, fees, mobilization, logistics and profit. I am in favor of unit prices being bare bones and clearly defined and that overhead and profit is included in the base bid as separate line items, excepting for the problem when unit prices exceed a reasonable threshold, referring back to the 10% margin I mention above.