Tutorial 37: Bond Breaker & Panel Finish

The last two entries in the Tilt-Up Concrete Association catalog are the strangest, because neither is really a feature of the panel. Both are properties of the surface the panel is cast on — and between them they decide whether the panel comes off the ground at all, and what it looks like when it does. One of the two ConstructiVision records today; the other is the design problem this track ends on.

Feature

What it is

Standard

In ConstructiVision

Bond breaker

The casting-surface treatment that lets the panel release from the bed

TCA

not modeled — Step 2

Panel finish

The surface finish type (smooth, textured, exposed aggregate, form liner)

TCA

Casting Face Down on the panel, Liner Aggr on the recess

One of these is built, one is not

Panel finish is modeled. The panel-level half of it is Casting Face Down on Main Panel Details — the choice of which face lies against the casting slab — and the material itself is the Liner Aggr column on Recess and Blockout Details. Step 3 is a live follow-along, and it names what is still missing, which is a good deal narrower than the feature.

Bond breaker is not modeled, and the reason is not difficulty. It is a property of a casting surface, not of a panel, and the model has nowhere to put it yet. Step 2 is marked (planned) for that reason, and it is the design problem this lesson frames.

Note

A browser version covers part of this lesson. Open it here — it lists exactly which steps it does not cover, so you know what to come back to AutoCAD for.

What you will learn

  • What a bond breaker is, and why it is the single most consequential thing on this list.

  • Where ConstructiVision keeps the finish decision — Casting Face Down on the panel and Liner Aggr on the recess — and why those two controls only mean anything together.

  • Which face’s finish comes from the bed, and why the casting orientation is the finish decision.

  • Why exposed aggregate on the exterior wants Inside Face, and how to read the two values as a pair.

  • Why the bond breaker belongs to the casting slab, not to the panel — and what that means for where the model should hold it.

Before you start

Lesson

Step 1 — What a bond breaker does

A tilt-up panel is cast on a concrete slab — usually the building’s own floor slab, poured first and used as the casting bed. Concrete cast on concrete bonds to concrete. Without something between them, the panel and the slab become one piece and the panel never lifts.

The bond breaker is that something: a chemical membrane sprayed on the bed before the pour.

It is the highest-consequence item in the entire catalog and it has no geometry at all. If it is missed, or applied thin, or rained on before the pour, the panel does not release — and the recovery is measured in days and sometimes in a destroyed panel and a damaged slab. Nothing else on this list fails that expensively.

Tip

Bond breaker is also the reason casting layout matters (Tutorial 12: Construction Layout). Panels are often stack-cast — poured on top of each other — and each interface needs its own bond breaker. A stack that has been stripped and re-sprayed several times is several chances to get it wrong.

Step 2 — Why it is not a panel feature (planned)

Every other feature in this curriculum belongs to a panel: this panel has this opening at this position. A bond breaker belongs to a casting surface — an area of slab that one or more panels are poured on.

That is a genuine modelling problem, not a technicality:

  • Two panels cast on the same bed area share one bond-breaker application.

  • A stack-cast panel has a bond breaker between it and the panel below it, which is a property of neither panel alone.

  • The product used is a project-level procurement decision, not a per-panel one.

Intended behaviour: a casting-surface property attached to the casting layout rather than to the panel — bond-breaker product and application, recorded once per bed and per stack interface, appearing in the project materials as coverage area rather than as a count. Each panel’s instruction sheet then reports the bond breaker for the surface it is cast on, which is what the crew needs to read.

Step 3 — Panel finish

The finish is the other side of the same coin, and this half the product does record. It takes two controls on two different dialogs, and neither one means much without the other.

The panel-level decision — which face is against the bed. Click Edit Main Panel to open Main Panel Details, and look in the Drawing Details group alongside the panel mark and the drawing scale. Casting Face Down is there, and it offers exactly two choices:

Setting

The panel is cast

Use it for

Outside Face

exterior face down, against the slab

most panels — this is the default

Inside Face

interior face down, exterior face up

finishes that need the outside wall up in the bed

The word “finish” appears nowhere on that control, and it is still the finish decision. The face against the bed takes the bed’s finish; the face pointing up is finished by the crew after the pour. Which one is which is settled here — which is why Tutorial 28: Casting Orientation & Yard Layout comes first.

Bed face

Up face

Finish comes from

the casting surface and the bond breaker

the finishing crew

Typical result

smooth, as-cast

troweled, broomed, or as specified

Changed by

form liner, retarder, a textured bed

technique

So “the panel is smooth on the outside” is not a statement about the panel. It is a statement about which face was down, and what was on the bed under it.

The material — form liner and exposed aggregate. Open Recess and Blockout Details and read to the right-hand end of a recess row. The Liner Aggr column is there: L for a form liner, A for exposed aggregate. Set one on an enabled row and three things follow — the drawing picks up an appropriate hatch pattern, the panel’s concrete volume and weight are adjusted for the material, and the treatment is counted in the materials list.

Finish is therefore recorded against a located area of the panel rather than against the panel as a whole, which is how architectural finishes are usually specified in the first place: a band of exposed aggregate at a given elevation, a form-lined field between two reveals.

Tip

The column is live only on a recess, not on a through-void. Set a blockout’s Thickness to 0 and it cuts clean through the panel, which disables On Face, Z Offset and the finish tiles together. A finish needs a surface to sit on.

The check this makes possible

Exposed aggregate is worked after the pour — the surface has to be open to the crew, which it cannot be against the slab. So a panel specified with exposed aggregate on its exterior should be cast Inside Face down, leaving the outside wall up. That is exactly what Inside Face is there for.

Which makes the two values worth reading as a pair. A panel carrying an A recess on its exterior while Casting Face Down has been left on the default Outside Face has its treated face against the slab, and the two do not work together. Neither is wrong on its own.

ConstructiVision records both and carries them to the drawing, the schedules and the materials list. It does not compare them for you — reading them together is yours. The check is possible at all only because both are recorded rather than assumed.

What is still missing is narrower than “finish is not modeled”, and it is worth being exact about:

  • Finish attaches to a recess, not to a whole face. There is no field that says this entire exterior face is form-lined; a full-face treatment has to be entered as a recess covering it.

  • It is counted, not measured. The materials list reports liner and aggregate as a count of treatments. Finish is bought and priced by the square foot, so take those areas off separately until the list reports area.

  • Nothing cross-checks the finish against the casting face. The pairing in the box above is a reading you do, not a warning the product raises.

Step 4 — The pattern these two illustrate

This is the closing lesson of the catalog track, and these two features make its point better than any of the geometry did.

Most of what a panel book has to carry is not geometry. It is decisions — which face is down, what was on the bed, what the mat designation was, what the fit allowance was, which dowels are field-installed. Geometry is the easy part; it is visible, and an error in it is visible too. Decisions are invisible, and an error in one is invisible until it is expensive.

ConstructiVision’s job across all thirty-seven of these lessons is the same job: record the decision once, and carry it, unchanged, to everyone who needs it. Not to make the decision — that stays with the engineer, the architect and the person running the job.

Check your result

You should now be able to:

  • Say what a bond breaker is and why its failure is the most expensive one in the catalog.

  • Explain why a bond breaker belongs to the casting surface and not to a panel, with the stack-cast case as the example.

  • Find Casting Face Down on Main Panel Details and say what Outside Face and Inside Face mean at the bed.

  • Find the Liner Aggr column on a recess row, and set L or A on an enabled recess.

  • Say which face’s finish comes from the bed, and what decides which face that is.

  • Say why a panel with exposed aggregate on its exterior should be cast Inside Face down, and what to look at when it is not.

  • State, in one sentence, what the panel book is actually for.

Where next

A companion video for this lesson is planned alongside the written curriculum. Step 2 is the only one marked (planned); the bond-breaker half will not be recorded until it exists in the product.