bonding thin precast treads to steel plate

[Prestressed Guy]

I have a project where the architect wants precast treads that are set on a steel stair which consists of an HSS stringer with 1/2" plates welded to it for the treads to mount on. The 1/2" plate is the same length and width as the treads and the architect is calling for the treads to be attached to the plate with thin-set mortar. the mortar will provide plenty of bond to the bottom of the precast treads but I am concerned about the bond between the mortar and the steel. Any suggestions?

 

[BAretired]

I would be concerned about that too. In time, some of the treads may separate from the steel. Maybe welded wire mesh welded to the plate would provide a satisfactory bond with the mortar.

BA

 

[dauwerda]

As thinset is capable of bonding glass tiles I would imagine it can bond to steel as well. A quick google search should allow you to find specific product information on bonding surfaces.

https://laticrete.com/en/solution-c...-and-stone-installation-over-steel-substrates

 

[Prestressed Guy]

I am thinking about calling for an epoxy mortar to give it more bond such as Latapoxy. I am also considering calling for the top surface of the plate to be roughened with a grinding wheel to give it some tooth. Link

 

[GC_Hopi]

Below are some instructions from a precast manufacturer. They recommend epoxy thinset. The lath that BA mentioned is also good but you would do a scratch coat for that kind of application and I dont think you are looking to have a thick joint between the tread and steel.

3. INSTALLATION OF PRECAST TREADS - THINSET APPLICATION OVER STEEL
A. Substrate must be within a tolerance of 1/8” in all dimensions.
B. Steel surface to be free of all foreign debris.
C. Epoxy thinset is used with a notched trowel to achieve full coverage.
D. Set treads level and plumb to meet finished nosing layout marks.

 

[epoxybot]

Have they checked with the Precaster to determine if the precast stair treads can incorporate an embedded weld plate?

 

[XR250]

Are the treads capable for spanning stringer to stringer? If not, I would check the stiffness of the steel plate first.

 

[Prestressed Guy]

epoxybot. I am the precast engineer and no, the treads cannot be cast into the treads due to constraints on weld, paint, access issues...

XR250. The PC treads have capacity for all required loads. The plate was also designed to carry all loads so double covered there.