Top 10 Slate Tile Installation Errors

Some common mistakes I see or hear about when installing slate floors.




1.) Not preparing the floor adequately – All surfaces should be structurally sound, clean and dry, free of oily and waxy films, and free from any other coatings that could reduce mortar bonding strength.

2.) Using the wrong mortar – Use an appropriate cement based mortar that is suitable for both the substrate and for slate.

3.) Not getting 100% coverage of mortar on the back of the tiles – Any void spots will dramatically weaken the installation – The slate tile will be subject to a bending force (tension on one side and compression on the other) when a load is applied, instead of solely a compressive force. Void spots beneath the tile will cause a hollow sound if the tile is tapped.

4.) Not installing movement joints and/or an anti-fracture membrane – Speak to your contractor about whether these are required for your particular installation.

5.) Poor layout – Installations should be designed so that the minimum of cuts are required. Keep the tiles whole, as much as possible.

6.) Uneven installation – Slate tiles should be installed to ensure that each tile is level with the next to avoid tripping hazards and poor aesthetics.

7.) Sealing the slate prematurely – If the installation is sealed prior to the mortar curing, moisture may become trapped within the slate that can lead to efflorescence. This would require the good sealer to be stripped off, the efflorescence removed, and then a sealer re-applied once the installation has fully cured.

8.) Adding more water to the mortar, after it has partially cured in the bucket instead of using only freshly mixed mortar – Using partially cured mortar can result in poor bonding and future failure of the installation.

9.) Not installing a waterproofing membrane when required – Speak to your contractor about whether this is needed for your installation.

10.) This is my favorite – Installing slate tile upside-down! I noticed a couple of tiles in a store in Vancouver last weekend very noticeably installed the wrong way up. A special machine groove on the tile indicates ‘this side down’!

This is just a quick list (in no particular order) that I compiled. What have I forgotten? Do you have any slate installation errors to add? Please post a comment with problems that you have experienced or heard about.