Aggregate Face Embedment Makes for a Perfect Mortar Repair Match
When we work with a contractor who really knocks it out of the park with a masonry restoration project, we're excited to share it. DNA Contracting achieved this at New York University’s Silver Towers at 100-110 Bleeker Street. The 30-story towers were designed by notable architects I.M. Pei and James Ingo Freed, which adds another level of importance when restoring a building with such historical significance. Where DNA Contracting shined was in matching the mortar patches with the surrounding masonry.
New York University’s Silver Towers at 100-110 Bleeker Street. Designed by I.M. Pei and James Ingo Freed.
Our role at Cathedral Stone is to help you match color, but a true match should also match texture. And matching texture means making choices about which aggregates will make the best match. It was determined that the Silver Towers building needed two aggregates: a sand aggregate and a pebble aggregate. The aggregate mix would be applied to the surface of freshly installed patches (as opposed to mixed into the mortar prior to application).
Here’s how DNA Contracting achieved a seamless look:
1) There’s no one-size-fits-all when patching with aggregate. DNA Contracting took the time to find the right color and type of aggregate (e.g., sand, pebble, gravel) to use to create the closest match available. They've been doing restoration work for so long that they're skilled enough and have the knowledge to do this, even on a project like this where the building required different aggregates and colors on various areas. If you encounter a project like this and don’t have the expertise, bring in an outside consultant.
2) The specifier chose our Jahn M90 Self-Cure mortar, which saves time and money because the patch can be completed in a single lift. Other mortars require extensive drying times when multiple lifts are being used to achieve the depth requirements or to prevent sagging. When working on a building of this height, you want to be one-and-done for each area and spend as little time on scaffolding as possible. Right?
Creating a close match depends on many factors beyond the color of the aggregate.
Different types of aggregate (sand, pebble and gravel) must also be considered.
Amount of water in the mix is important.
3) DNA Contracting paid close attention to the amount of water in the aggregate mix. A common mistake is making the aggregate mix too wet. Too much water will lighten both the aggregate mix and the patch.
4) Timing. The mortar mixture with the aggregate needs to be installed on the surface of the patch immediately. We’ll repeat that: immediately. It’s what we call a “two-bucket job.” The mason will work with two buckets—one with straight mortar for the patch, one with an aggregate mix ready to be installed on the surface immediately.
5) Then, two hours after installation, DNA Contracting masons used a dry float for tooling the aggregate surface. Masons will often wet (or over-wet) the float, but, again, this will lighten the color of the patch. Dry is the preferred method.
Using proper techniques and materials, DNA Contracting achieved a seamless look.
I’ll say DNA Contracting achieved one of the best aggregate embedments I’ve ever seen. It’s the little things that matter when working with aggregate: choosing the right one, paying attention to the amount of water in the mixture, the right timing during installation, and the tooling technique to finish. DNA Contracting brought it all together. We look forward to working with them again in the future.
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