Cast Stone Patching Procedure

WHEN TO PATCH:

• Damage that can be seen easily from 20 feet away should be patched. Any corner chips that are ¼” or less in width do not require patching, normally.
• Air & stone temperatures should be greater than 40°F during & 24 hours after patching. Patch during the morning hours on hot days. Avoid patching when the temperature is above 90°F.

TOOLS/MATERIALS:

• Patching material – The best method is to grind up some leftover stone material from the same jobsite, especially for small chips or cracks. We can supply you with matching sand if this is not feasible.
• White acrylic liquid bonding agent. Available from any local building materials store.
• Mixing containers.
• Water
• 2 spray bottles
• Wood, stainless steel or plastic wedges, or trowels
• Sponge
• Damp rag
• Blue tape & plastic

PROCEDURE:

1. Test patch a piece of leftover stone material & get approval before continuing on the rest of the job.
2. Mix a small amount of patching material (3 parts sand to 1 part mix) with only enough water to make a zero slump mix, or about the same moisture as potting soil.
3. Add a small amount (approx. 1 tablespoon) of the bonding agent. Do not use as a substitute for water. This mix should be as dry as possible. It should have just enough water so it can be compacted in your hand like a dirt clod. Mix thoroughly for 4 or 5 minutes.
4. At this time, the color of the patch mix should be close to the color of the stone when wet.
5. Drench the patch area & surrounding stone surfaces with water from a spray bottle.
6. Spray some bonding agent on the patch area & let stand for 5 minutes.
7. Press the patching mix into the damaged area with a wooden, plastic or stainless steel tool or trowel. For large holes, compress the patch mix onto the wooden tool prior to applying. When the patch mix is over 20 minutes old, replace with fresh mix.
8. Smooth the patch with a wooden tool. Use the least amount of strokes as possible. Too much tooling will create a slick surface. Leave a little extra material on the patch.
9. After initial set, burnish the patch with a sponge, sandpaper, piece of carpet or anything that will create a sugarcube finish. Some trial and error may be required.
10. Cover the patch with a damp cloth or piece of plastic for 24 hours.
11. Wait 5 days & wash down with a masonry stone cleaner.
12. A good patch will not match in color right away & will usually appear lighter. Over the next 3 to 12 months, depending on the climate, curing, weathering & ultraviolet bleaching will blend the color of the patch into the surrounding area.