Thinset stains on a slate outdoor table can be stubborn, but with the right approach, you can restore its natural appearance. Here’s a step-by-step guide to effectively remove thinset stains:

1. Scrape Off Excess Thinset: Use a plastic scraper or putty knife to gently remove dried thinset without scratching the slate surface.

2. Apply a Vinegar Solution: Mix equal parts white vinegar and water. Soak a cloth in the solution and place it over the stain for 15–20 minutes to soften the thinset.

3. Scrub with a Soft Brush: After soaking, use a nylon brush to scrub the stain gently. Avoid wire brushes, as they can damage the slate.

4. Rinse Thoroughly: Wash the area with clean water to remove any residue. Repeat the process if necessary.

5. Seal the Slate: Once clean, apply a slate sealer to protect the surface from future stains.

For tougher stains, consider using a commercial thinset remover, but test it on a small area first. Regular maintenance will keep your slate table looking pristine for years.