How to Repair Grout for a Glass Block

Written by robert sylvus
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How to Repair Grout for a Glass Block
Bad-looking grout can make a good block job look horrible. (glass blocks image by Stephen Orsillo from Fotolia.com)

Glass block grout and mortar contains portland cement, white sand and waterproofing additives. Many masons use pre-mixed mortar as grout. The colour of both materials match once they dry. Glass block mortar uses slightly larger granules of sand in its mixture. If the grout feels smooth, then the mason used glass block grout. If the grout feels rough and wears away skin while rubbing it, then the mason used glass block mortar. Masons grout large sections of the wall or window at a time, and repairs to the grout often include whole sections of block.

Skill level:
Moderately Easy

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Things you need

  • Dust sheet
  • Masking tape
  • Grout saw
  • Razor knife
  • Vacuum
  • Glass block grout
  • Water
  • Bucket
  • Margin trowel
  • Grout float
  • Sponge
  • Rag

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Instructions

  1. 1

    Cover everything below the glass block with a dust sheet. Seal the edge of the dust sheet with masking tape.

  2. 2

    Cut a 1/2-inch-deep groove in the centre of the grout joint with a grout saw. A grout saw uses a diamond-tipped blade. Hold the saw with one hand and work it back and forth along the grout joint.

  3. 3

    Score the seam where the grout meets the glass block with a razor knife. Avoid scratching the glass block's surface.

  4. 4

    Force the razor knife into the scored seam next to the glass block. This will snap the grout loose from the glass block's edge. Use the blade to remove all of the grout from the 1/2-inch deep area of the grout joint's repair area. Do not pry on the block. If the grout refuses to break free, then score a deeper line along the seam and try again.

  5. 5

    Clean up all of the debris with a vacuum. Run the vacuum along each grout joint.

  6. 6

    Mix glass block grout and water in a bucket with a margin trowel. Check the manufacturer's instructions for the correct grout-to-water ratio. Stir the grout until it has the consistency of bread dough. When mixed correctly, glass block grout sticks to the margin trowel.

  7. 7

    Press the grout mixture into the grout joints with a grout float. Start at the top of the repair and work down.

  8. 8

    Blend the grout to the glass block with a wet sponge, using circular motions. This creates professional-looking grout joint edges, but leaves a mess on the block.

  9. 9

    Wash the glass block with a damp sponge using straight swipes. Swipe the sponge at a 45 degree angle to the grout joint to prevent removing excessive grout from the joint. Start at the top of the repair and work down. Rinse the sponge after each swipe.

  10. 10

    Allow the grout to dry for 24 hours, then polish the glass with a clean, dry rag.

Tips and warnings

  • Check the tile department of a home-improvement store for a grout saw if the glass-block department does not carry them.
  • Never use a hammer and chisel to chip away the old grout. This will break the edge of the glass block.

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