I’ve seen a rash of under built floor repairs in the field, so today, I AM SOUNDING THE ALARM! For all you DIYers out there, or simply homeowners who care, it’s wise to over build your floor repair when you take out a piece of your existing sub floor to repair rot or damage.

What I’m seeing when I’m on the job is a lot of cutting of subfloor without proper BLOCKING put back in to support the substantial weight of a new tile floor. A certain degree of rigidity must be present in a subfloor when it is meant to support tile. Notice the photo below. You have the two joists. That was originally sufficient when supporting a whole sheet of tongue and groove plywood. The tongue and groove locked the plywood together, so it was supported. But once you cut out a piece, it has to be supported around all four sides of the plywood that is going back in. If you put a piece of plywood back without supporting the sides (by putting in additional blocking) there will be too much movement! Tile and MOVEMENT do not mix!

Do you know how you judge if your subfloor repair has too much movement? It’s easy! WALK ON THE REPAIRED FLOOR. The spot without extra blocking will flex and move, that’s bad. In certain instances, even with ¾” plywood, you’ll feel like you could put your foot through the floor! Don’t ask how we know! 😊 But you will notice if you put blocking in, between the joists, like in the photo below, the movement will stop and the floor repair will be far more rigid.

This particular area (the shower pan) will have over 500lbs of material on top of it. Build it STIFF and STRONG.

What’s the point? What is the conceptual, overarching theme of building with tile? Over build, Over engineer, over block. MORE IS BETTER. Tile is a permanent finish and it does not like movement. Any movement in a substrate results in cracked grout, lifted tile, etc. A tile floor needs to meet specific deflection specifications.

So, if you’re using tile, if you think something needs to be built stiffer, DO IT. Cement board, for example, does nothing to add to the strength and rigidity of a floor. Always, add wood, stiffen it up and you will have a flooring that will last the lifetime of your home. That’s the whole point of tile!

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