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Thinset Quick Start Guide


Thinset is a great waterproof adhesive. Tile setters for over 125 years have been using this material to install ceramic tile PERMANENTLY.

Why is thinset so fantastic? It’s simply Portland cement and fine silica sand. Sometimes there might be another additive in the blend to increase strength.

Portland cement is the only thing that holds sand and rock together in most concrete you walk or drive on, so you KNOW it’s strong and waterproof. Waterproof in this sense means once the thinset is cured and hard it will not crumble or dissolve if it's subjected to water all of the time.

If you use thinset outdoors in a cold climate, over time freezing and thawing of water in the thinset MAY destroy it. But in non-freezing conditions, properly mixed and installed thinset will not be harmed by water for many decades.

I’ve rated this guide two hammers out of five because it’s really simple to work with thinset. It would rank just one hammer if it wasn’t so heavy!

The most important thing to realize when working with thinset is water is both your friend and foe. You need water to mix thinset and make it just right, but TOO MUCH water - or adding water if it gets stiff - can RUIN the thinset!

Watch the video below unless you’ve come here from YouTube having already watched it.

Be sure to look at the RELATED CONTENT links at the bottom of this page. Lots of goodies there for you.


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  • STOP AND READ all the mixing and safety instructions that you see on the bags of thinset. Seriously, read them. Follow the instructions.
  • Thinset, once mixed, should resemble warm cake icing. Not too thin, but thin enough it’s pourable or it falls off the mixing knife.
  • Only mix enough thinset as you can use in 15 or 20 minutes.
  • Knee pads! Wear great knee pads or a use a cushion.
  • Use a crack-isolation membrane under the thinset, when possible, to prevent cracks.
  • Use a damp sponge to get up every speck of dust from concrete slabs or other subfloor. You’ll get better bonding.
  • Apply the thinset to damp concrete or subfloor for BEST bonding.
  • Use the proper sized notched trowel for the ceramic tile you’re installing!
  • The floor should be FLAT for best results. Fill in low spots or use a self-leveling compound.
  • If the thinset pulls up as you trowel and you don’t get completely filled or solid lines of thinset when using the notched trowel, it means you’ve got DUST on the floor or the thinset is too dry.
  • If it’s hot and dry where you’re working, use COLD water to mix the thinset. This will help retard the hydration reaction allowing you some extended work time. Use ICE in the water if necessary to get it COLD.
  • Do NOT retemper (retemper means add water and stir) the thinset if it gets stiff in the mixing bucket. If you add water to stiff thinset to make it workable, you break the microscopic Portland cement crystals and the thinset will NOT be as strong as it could be. This is why you only mix as much as you can use in a short time.
  • Celebrate your Victory!

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7 Responses to Thinset Quick Start Guide

  1. Thinset is NOT waterproof! Giving bad advice to unsuspecting homeowners is terrible specially since your site is called ask the builder! Please stop giving tile advice if you do not know about the products being used, it hurts my industry and people start to distrust tile as a long lasting covering. Thank you

    • Jeremy,

      Oh I'm so sorry to embarrass you in public, but we need to STOP people like *you* from giving out bad advice.

      Do you know what the ingredients are for thinset?

      I'll share them:

      Portland cement
      silica sand

      Do you know the definition of waterproof?

      Here's one:

      "impervious to water: a waterproof hat.
      • not liable to be washed away by water: waterproof ink."

      After thinset hardens, water does not dissolve it.

      Water does not cause it to lose its bond between the tile and the substrate.

      Thus, it's *waterproof*.

      What makes you think it's NOT waterproof?

  2. I'd agree with Jeremy. I think very few people would consider Portland cement waterproof. Water can pass right through cured cement; that's not waterproof. A really common mistake is that people will put up drywall and then put thinset+tile directly on the drywall to create a shower wall. And then the moisture goes right through and the drywall molds up or even loses structural integrity. Another common mistake is people will put up cement board without anything to protect the studs behind it (because someone told them cement is waterproof). The cement board handles the water, but the studs rot...

    Making cement water proof requires a waterproofing membrane. For tile walls, there's waterproof backer board and paint on membranes for non-water proof backer boards.

  3. Thinset isn’t waterproof it will soak up water. Throw a dry tile in a pale of water and it will soak up water like a sponge. even ceramic needs to be glazed to be waterproof. I just tore out one of those thinset only showers it was absolutely rotten.

  4. So, it seems to me that thinset WILL withstand the EFFECTS of water on it, BUT it allows water to pass through to the tiles' surface, possibly allowing flooding and/or corrupting the grout. Am I correct? Thanks.

    • Thinset is basically Portland cement and fine silica sand. There may be some modifiers in some blends. Read my past concrete columns to understand how water can pass through concrete. Thinset is just a type of concrete.

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