In today's post we are going to discuss common terrazzo architectural details.
Designing with terrazzo can be a tricky process. However, having the right details can really simplify working with this material. In this post we’ll discuss a brief epoxy terrazzo system overview and the following details: Terrazzo transitions to dissimilar finishes, crack and joint details, as well as terrazzo stair and base details.
System Overview
Above is a cross section of the thin-set epoxy terrazzo system. This outlines the different components of the terrazzo system and is good to familiarize yourself with. I wrote another post that discusses this system in detail.
Transition Details
One of the most common terrazzo details I’m asked about is a transition to dissimilar finishes. At a standard thickness epoxy terrazzo has an overall height of just 3/8”. It is directly bonded to the surface so there is no setting material is required. For a simple transition to another flooring finish with a similar overall height material, you’ll use a single “L” divider strip to terminate the terrazzo and transition to the adjacent finish. As shown below.
If you work in architecture you know that flooring finishes are available in all different thickness and are placed using different setting methods. Thus, its common to have terrazzo transitions to other floor finishes at dissimilar overall heights. Designers are generally faced with three different situations:
1) Terrazzo to meet a lower elevation such as polished concrete.
2) Terrazzo to meet a Higher Elevation
3) Terrazzo to meet a dissimilar finish with an intermediate elevation
The transition details are all pretty similar but are uniquely detailed based on the specific elevations. If you have a transition detail you'd like for us to evaluate please email us.
Crack Details
Designers have two options when specifying the flexible crack membrane:
Isolated Coverage
Full Coverage
Terrazzo crack membranes are designed to control cracking in the horizontal plane, they are not engineered to mitigate cracking in the vertical plan from settlement.
Crack Stabilization
Regardless of isolated or full coverage the first step in detailing terrazzo substrate cracks is to stabilize the crack. This is done by filling the crack with a rigid epoxy, such as terroxy primer or matrix. Once the crack is stabilized, the flexible crack membrane is applied. In the terrazzo world, we use a liquid applied crack membrane rather than a sheet good.
Isolated Coverage
When specifying terrazzo crack membrane typically isolated coverage is specified. Using this method, the terrazzo contractor will install the crack membrane only where the cracks exist so the terrazzo is bonded to both crack membrane and the terrazzo substrate. When designing it is impossible to know how many cracks will appear in the substrate, unless you have an existing substrate you can evaluate. So designers must estimate how much crack membrane the terrazzo contractor should bid. A general rule of thumb is that approx 5-10% of the terrazzo area will have cracks that need to be detailed. For example, if you have a project with 5,000sf of terrazzo then you’d want to make sure you have 250-500lf of crack detailing. The membrane should be applied at 40mils thickness. It is optional to include a layer of fiberglass mesh on the top surface of the membrane for added tensile strength. Typically cracks should be detailed 6”-12” on either side of the crack depending on the severity. The bigger the crack the wider the band of membrane should be.
Full Coverage
When specifying full coverage the crack membrane will be used under all terrazzo. Generally this is not necessary and adds unnecessary cost. There are a few exceptions to this:
Terrazzo over light weight concrete
Terrazzo over existing natural stone
Terrazzo over existing terrazzo
Terrazzo over existing concrete with extensive cracking
Terrazzo Joint Details
Detailing terrazzo joints can be a tricky and confusing process. We highly recommend you get a trusted terrazzo representative to review your pattern and joint layout. I’m always happy to do this for my architects and designers.
There are four basic concrete joint types that you will encounter when detailing your terrazzo flooring.
Contraction Joint, aka Control Joint or Saw Cut
Construction Joint, aka next day pour joint or Cold Joint
Isolation Joint, aka column joints
Building Expansion Joints
We’ll look at each of these individually:
Detail 1. Contraction Joints (aka Control Joint or Saw Cut)
The term “contraction joint” is taken from ACI 302 document to maintain consistent nomenclature with the concrete and engineering industry.
Detail 2. Optional Joint Detail for Contraction Joints
This detail provides the designer the option of installing a low profile 16 gauge divider strip, in lieu of the filled back to back strip in Detail 1. This detail does provide limited movement compared to detail 1.
Detail 3. Option in Art Work (Movement from substrate may show through)
Detail 5. Terrazzo Control Jointing over Full Crack Membrane
The use of divider strips should be considered in areas where floor temperature changes may occur. Such as glass walls, or skylights, if joints are to be used, the design team must determine spacing. Not to exceed 30ft. These joints can be placed anywhere in the floor.
Detail 4. Isolation Joint.
As noted above, the flexible epoxy membranes are engineered to handle movement in the horizontal plane. They are not engineered to accommodate movement in the vertical plane, as a result of the vertical shear due to substrate settlement or excessive deflection. Slabs to receive terrazzo flooring should accommodate isolation joints where the slab is separated from the load bearing columns or walls for this specific purpose.
Detail 7. Construction Joint (Next Day Pour)
(Construction Joint Detail Option for “Art Work Areas”)
Refer to Detail 3 above.
Detail 8. True Building Expansion Joint
Must be honored through the terrazzo and any other finishes. I like the Construction Specialties joint shown below as it can be filled with terrazzo to minimize the joint.
Terrazzo Stair Details
I’m commonly asked about terrazzo stair detailing. Terrazzo stairs are available in a variety of styles and designs. The beauty of using terrazzo for a stair tread application is your ability to customize. Terrazzo is a poured material so just like concrete you can build custom forms to suit nearly any application. When you specify terrazzo stair treads we break them down into different categories.
Fully Supported or Self Supporting
Open Carriage (Exposed) or Closed Carriage (Concealed)
Tread Only or Tread and Riser
First you should determine if your application is better suited for precast terrazzo our poured in place terrazzo. Refer to our blog post on how to best determine this. Generally speaking, precast terrazzo is best suited for most applications.
Next you should determine if you need a fully supported or self supporting application. Fully supported terrazzo treads are typical for most applications. Self supporting treads are engineered to span between supports or stringers without a supporting structure beneath to give the illusion of a floating tread. Further, if the stair will be exposed from the back side the self supporting treads will show finished terrazzo. Not self supporting terrazzo treads are more expensive due to the extra structural reinforcement and engineering.
Next you should determine if you need exposed edges of the treads (Open Carriage) or if the edges of the treads will be concealed (Closed Carriage).
Lastly, you’ll need to determine if you want a tread only or a tread and riser.
Its very important to note that when specifying precast terrazzo the tread thickness will vary based on the length of the tread. Please consult with your precast manufacturer to ensure proper thickness is specified so you can properly detail the stair elevations. Remember you also have to account for setting material.
Below are some common terrazzo stair tread detail files. If you would like these files in CAD or REVIT please email me brad@bradhedes.com
Terrazzo Base Details
Terrazzo base is an excellent way to complement a terrazzo floor. Terrazzo base is available in two formats:
Flat or Straight Base
Cove Base
Terrazzo Flat Base
Flat base is an economical option that can be produced in varying heights with different top edge profiles and finishes. This base is installed after the terrazzo flooring and is typically produced in 48” precast pieces. We can produce curved and radius pieces for walls and columns.
Terrazzo Cove Base
The sanitary cove base has been commonly used with terrazzo flooring to create a seamless transition from floor to wall and eliminate the ninety degree joint that can collect dirt. This design can also be customized with different heights, cove radius and toe. We can produce with or without a divider strip on the toe of the base. The toe can also be extended further out onto the floor. The cove base is a premium base due to the radius and extra material used for the transition. Terrazzo cove base is typically precast in 48” long pieces. We can also produce inside and outside cove corners. Precast terrazzo cove base should be installed prior to the terrazzo flooring. Terrazzo cove base may also be poured in place in the field for a premium.
I hope this post has been helpful. As always we are here to help so email me if you have any questions. brad@bradhedges.com