How to stop grout water penetration?

[charlie0123]

Yesterday I did grout water penetration test:

As shown in PIC 1, the left-side grout was mixed with a 1:1 ratio of water to Dunlop Primer and Additive. The middle grout was mixed with water only, and the right-side grout, which was originally mixed with water only, was later coated/sealed with Dunlop Primer and Additive.

Results: After a few drops of water were placed on the grout, the multimeter detected water immediately behind the middle grout. In contrast, it took several minutes for water to be detected behind the left-side grout, while the right-side grout completely blocked absorption.

So, basically, I am not impressed with the outcome of adding tile additive to grout, because (1) it doesn't block water, and (2) slow water absorption means slow water evaporation as well. However, coating the grout surface is not a perfect solution either because it's more like a temporary measure, unless it is repeated regularly.

My original (40 years old) shower tiles were directly glued onto the cement sheet with Liquid Nails (as seen in PIC 2). The shower didn't have waterproofing at all. When a plumber cut a big hole in the wall, he was surprised to see there was no sign of water seepage. I think there were two reasons:

1. Liqid nails glue is waterproof;

2: There was a gap/space between the grout and the cement sheet because the liquid nails didn't cove the edge of the tiles, and therefore the water penetrated through the gout wasn't in contact with cement sheet.

I would avoid using Liquid Nails again. I prefer to use a waterproof tile adhesive and/or non-sand cement-based grout (other than epoxy) for shower walls and floors. Of course, I will ensure proper waterproofing and puddle flange installation. However, I don't like water passing through the grout, then traveling and spreading in the tile adhesive behind the tiles. Any suggestion would be appreciated.

Edit: Anyone used following products:

1. Dunlop Flexible Ultra White Grout: is a non-sanded, supersmooth, flexible grout for
ceramic wall and floor tiles. It offers a smooth finish and can be used in tile joints
between 1mm and 4mm wide. This grout is water repellent, resists dirt pick up
and is easy to clean. 

2. Ardex-FS DD: Non-sanded cement-based, wall and floor grouting compound which is specially designed for polished porcelain to avoid scratching the surface of the tile.

• Water repellent due to special hydrophobing agent
• Dirt resistant – longer lasting new look, as dirt is unable to enter grout.

3.  Sika 500 Ceralastic:

a flexible, single-component, polymer-modified cementitious mortar with synthetic fibres and alkali resistance, with selected fine aggregates and specific additives, for waterproofing and bonding ceramics to traditional substrates.

• Sealing and bonding mortar in one product.
• Simultaneous waterproofing and bonding of tiles; allows grouting between 12 and 24 hours.
• For gluing large tiles.
• Can be applied to hardened substrates with slight moisture.
• One-coat bonding even with large tiles due to its fluid consistency.

• 4.  Mapei ULTRACOLOR PLUS is a cementitious, high performance, quick-setting and drying cementitious mortar for grouting joints up to 20 mm wide. ADVANTAGES:

  Mould-resistant (BioBlock® Technology)
  Grouted areas are quickly ready for use
  Water-repellent and easy to clean (DropEffect® technology)

[JacobZ]

Hi @charlie0123,

Thank you for sharing your findings.

While tile grout additives do add an element of water resistance to grout, this is more about keeping the grout clean than it is about making it waterproof.

I think it is important to note that in wet areas like showers, some water will always find its way through grout lines. Instead of trapping moisture, grout allows it to pass through to a properly waterproofed substrate so it can drain away rather than accumulating behind tiles.

If the floor is at the correct gradient, cement-based tile adhesives will also let water pass through them through capillary action. This allows any water that passes through the grout lines to flow to the drain and be taken away.

The most important element when it comes to waterproofing is the membrane. The grout is just there as a finishing product to make everything look clean and uniform.

Let me know what you think, and if you have any further questions, please don't hesitate to ask.

Jacob