A better base for ceramic tiles

Some home improvement blunders can be fixed pretty well after the fact, and then there's the case of ceramic tiles gone bad. This is the classic example of how you've got to start something correctly from square one if you want trouble-free performance. That's the disappointing news I have to give out when owners of cracked tiles with crumbling grout ask me for a solution. Fact is, there's no permanent cure (other than complete tile replacement), and this is why I'm always on the look out for installation methods that offer long-term, crack-free performance.

Up until now I've always recommended a site-poured, mortar bed base under ceramics because it's never let me down in any of the installations I've done over the last dozen years. But even I have to admit that the prospect of laying down 1 1/2-inches of mortar on a waterproofed and steel-reinforced subfloor isn't exactly a picnic. That's why so many professional tile setters have abandoned this traditional approach -- called a thickset installation -- for the more expedient option of gluing ceramic tiles directly to a beefed-up plywood subfloor. That's okay, some of the time, but it also involves a fairly high probability that something's going to work loose in time. This is why I want to tell you about a product that promises rock-solid, reliable ceramic tile installations, without the hassle of a full-blown, mortar-bed marathon.

It's a patented, dimpled polyethylene membrane called DITRA. Developed by Schluter Systems, a German-based company started by master tile setter Werner Schluter, the product boosts the reliability of ceramics by addressing the two weaknesses common to all ceramic tile installations. Tiles and grout are brittle and crack-prone. That's problem#1. This is why any movement of the subfloor leads to trouble. Less obvious is the fact that grout joints are also highly porous, sometimes allowing water to penetrate down to the underlying subfloor where it causes delamination and structural trouble. This is typical tile problem#2 and, as you'd expect, it shows up mostly in bathrooms. DITRA sidesteps both these issues in a way that doesn't seem possible when you first pick up a piece of the stuff and look at it.

It's a lightweight orange plastic sheet with dimpled, square-shaped depressions on one side, and a non-woven fleece fabric factory-bonded to the other side. To be honest, it looks pretty lame. You lay DITRA down on a sufficiently stiff subfloor (it can be almost anything -- wood, concrete, even solid old tiles), anchored with a thin layer of bonding mortar. The new tiles can then be installed immediately on top of the DITRA, set into a layer of thin-set tile mortar, as usual.

So why does a bit of plastic and fabric make a difference? Decoupling is the answer. By creating the chance for movement to occur between the tiles and the subfloor (while still offering full support to the tiles), the DITRA membrane boosts reliability. And in the quite likely event that water eventually makes it's way through the grout in a bathroom installation, it doesn't get any further than the polyethylene layer. DITRA comes in various roll sizes, and costs about $2.00 to $2.25 per sq. ft. You'll find it big box stores and most ceramic tile supply outlets.

Although I haven't yet had the chance to see DITRA in action over the long haul, I'll give it a try the next time I have ceramic tiles to install. And Hydro Quebec's Manic 2 hydroelectric generating station in Baie-Comeau is one of the reasons why. The constant vibrations present in the plant there caused cracking and failure of 20,000 sq. ft. of conventionally installed ceramic floor tiles in the facility. Reinstallation of new tiles over a DITRA membrane solved this problem, including the control of salt water dripping off trucks driving into the plant during winter.