NASCLA Accredited Commercial General ContractorFinishesHard
A contractor is installing natural stone tile on a floor in a commercial building. The owner is concerned about potential discoloration or staining of the tile from moisture or efflorescence rising from the concrete slab. Which preventative measure is MOST effective to address these specific concerns for natural stone?
- AEnsuring a minimum 1/2-inch grout joint.
- BBack-sealing the natural stone tiles prior to installation.
- CUsing a rapid-setting thin-set mortar.
- DApplying a breathable, penetrating sealer to the face of the stone.
Show answer & explanationAnswer & explanation
Correct answer: B. Back-sealing the natural stone tiles prior to installation.
Back-sealing natural stone tiles with a suitable sealer creates a barrier on the unexposed side, preventing moisture and mineral salts from the substrate from migrating into the stone and causing efflorescence or discoloration on the finished surface.
Why the other options are wrong
- A. Grout joint size does not prevent efflorescence or discoloration from moisture migrating through the stone body.
- C. Rapid-setting mortar helps with installation speed but does not prevent moisture migration or efflorescence within the stone itself.
- D. Sealing the face of the stone helps protect against topical stains and moisture absorption from above, but it does not prevent moisture and efflorescence from migrating up from the substrate.
Back-Sealing Natural Stone
The application of a penetrating sealer or appropriate barrier coating to the unexposed (back and sides) surfaces of natural stone tiles prior to installation to prevent moisture, minerals, or contaminants from migrating from the setting bed into the stone.
- Prevents efflorescence, discoloration, and picture-framing.
- Crucial for moisture-sensitive stones or installations over concrete slabs.
- Ensures the aesthetic integrity and longevity of the stone.
Memory trick: For stone, back-seal the bottom, face-seal the top, no efflorescence will pop.