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I get a lot of e-mails from people confused about grout. When they get to the tiling stage of their bathroom or kitchen renovation they get stuck. Or they've been living in a new home for a while and find the grout in the floor tile shows dirt in all the high-traffic areas. They get sick of cleaning it and start looking for an easy fix. Usually, they're told they should have sealed the grout the first time but that they can apply a sealer now. Or they can apply a surface grout colour to mask the dirt.

Who wouldn't be confused? Go to any hardware store and you'll find all kinds of products marketed to protect and seal grout. Check your Yellow Pages and you'll find all kinds of guys listing grout-sealing or grout-colouring as one of their services. A lot of the time, your own contractor doesn't know the right answer.

To seal or not to seal?

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Grout is porous and will absorb liquids that are spilled on it. Light-coloured grout on the floor will show dirt. You can't get around that. So a lot of people think a clear sealer will make grout more resistant to moisture and make it easier to clean.

Sealer soaks into the grout and supposedly makes your tile and grout waterproof. People who want to sell you grout sealer will tell you it keeps it easier to clean, and helps prevent mildew from growing.

But I don't recommend that you seal your grout.

In my opinion, grout needs to be able to breathe, so that any moisture that gets in behind your tile is able to escape. If you seal the grout, that can't happen. No matter what, moisture - steam and water - eventually will get through the grout, or through a crack in your tile. So, if your grout is sealed, how will that water evaporate back out? It can't. And that will lead to problems. I've seen it hundreds of times.

If your grout is driving you crazy because you can't keep it clean, it's not a big deal to remove it and replace it with a darker-coloured grout that won't show the dirt. Just chisel it out carefully - it's tedious, but just requires some elbow grease.

Seal the tile, not the grout

Many tiles - especially natural stone such as slate, marble and limestone - are porous and need to be sealed. (Note: porcelain and ceramic tiles are not porous.)

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You have to seal natural stone tile before the grout is applied, however. If you don't, the grout will be absorbed into the tile, ruining the finish. If that happens, it's impossible to get the grout out of the pores of the tile. So, you can't let your contractor tile, grout, then seal the whole thing - it would be a huge mistake.

Build it right

Every time you take a shower, the grout will soak up water. In an older bathroom, there likely are cracks in the grout that allow in even more moisture.

Some of this water will evaporate throughout the day, but some will penetrate behind the wall - leading to mould, mildew and rotting of the structure.

I've heard of people sealing the grout to provide an extra layer of protection against water infiltration. That's like using a wad of chewing gum to plug a hole in your boat. It might work for a while, but it won't fix the problem.

If your bathroom is older and a fully waterproof membrane wasn't installed behind the tiles, water has been getting in for years. If you are renovating anyway, it's a good time to fix it. Remove the tiles, and investigate the condition of the subfloor and structure. Believe me, if it's an old bathroom, you'll find mould or rot, and, for peace of mind, you'll want to have it done right.

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I've seen renovations in which, to save money, old tiles were removed and new ones laid onto the existing wallboard and subfloor. That's just stupid. Don't do half the job to save some money, then try to seal the grout hoping to keep water out.

You need to make sure you go all the way and waterproof properly. Lay your tile properly. Don't seal your grout. And don't let anyone tell you that you should.

Mike Holmes is the host of Holmes on Homes on HGTV. For more information, go to www.holmesonhomes.com

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