What should I do about the gap between my house and the patio?
March 29, 2012 7:09 PM   Subscribe

What should I do about the gap between my concrete patio and the house?

I just bought a new house in Southern California. On the back patio, there is a 3/4 inch piece of wood that separates the concrete patio from the house itself. The inspector said that we should probably remove this. My question is: what should we replace it with? Concrete? Caulk? It seems odd to leave this open. Right now, the ants are making it their personal interstate system.
posted by johnxlibris to Home & Garden (13 answers total) 2 users marked this as a favorite
Did the inspector tell you why you should remove it? The reason would dictate what you should replace it with, if anything.
posted by dg at 7:21 PM on March 29, 2012

Response by poster: The inspector said it would attract termites.
posted by johnxlibris at 7:25 PM on March 29, 2012

Caulk is pretty standard for places like this where flashing would get in the way.

I wouldn't use concrete, the patio will move with the weather in a slightly different way to the house. You want something flexible.
posted by deadwax at 7:35 PM on March 29, 2012 [1 favorite]

In that case, you probably should leave it open. One method of avoiding serious termite infestations is being able to visually inspect all the way around the edge of the house. Filling in that gap prevents you from doing so and provides a hidden path for termites to enter the house, made worse by being filled with (I assume untreated) wood that termites can use for food on the way into your house. Of course, this assumes that you are able to inspect the rest of the house where it meets the ground.

If you want to fill it, probably a 'mud' mixture (sand and cement) would be best. Whether or not you fill it, ants will still use it to access your house and this is where poison comes in if you want to stop them.
posted by dg at 7:36 PM on March 29, 2012

A bit of loose pebble gravel might work.
posted by grog at 7:40 PM on March 29, 2012

I was thinking sand or gravel as well, or something else that won't hold wet organic matter right up next to the house.
posted by slidell at 7:40 PM on March 29, 2012

I have a similar gap between my foundation and concrete porch that has some board filling the space. It's made of some sort of non-wooden grey-looking material, with plastic sheeting on each side, presumably to allow the foundation and house to shift separately.
posted by MonsieurBon at 7:43 PM on March 29, 2012

That strip of wood is an expansion joint, it gives the concrete patio room to expand/contract during temperature changes. You definitely do not want to fill it in with more concrete or anything too rigid: if the concrete patio can't expand, it will crack.

Sand will work. Small grade pea gravel or landscaping glass also look nice.
posted by jamaro at 7:44 PM on March 29, 2012 [2 favorites]

You might google "exterior expansion joint." Most options would have probably needed to be installed when the patio was built, so I'm not sure which could be added from the top later. (On preview, jinx.)
posted by slidell at 7:46 PM on March 29, 2012

You want this stuff. Silent video.
posted by Brian B. at 7:49 PM on March 29, 2012 [1 favorite]

Best answer: I think you'd be sensible to fill this gap with gravel, as I've seen on many patios.

It may be an expansion gap, but I think it also serves as a way to allow any surface water to drain away rather than damaging the side of your house. Patios generally slope away from the building slightly for this reason, but a drainage gap between the patio and any buildings in a wise precaution anyway.

Landscaping glass is awful. It was popular here in the UK in the 70s, where many cemeteries had to ban people from using it to turn their relatives' graves into low-maintenance technicoloured eyesores. Please go with something the looks vaguely as if it belongs in the environment.
posted by le morte de bea arthur at 1:41 AM on March 30, 2012 [3 favorites]

I believe what you want here is variously called expansion joint filler or fiber expansion joint. It's a composite material, generally with an asphalt base, that is flexible, resilient in cold, and fire and rot resistant. Your local big box (or masonry supply yard) should have it by the roll, or you can get alternatives such as a foam backer board or a liquid that will dry to a semi-solid.

OP, when you say "inspector", do you mean your home inspector or a city inspector? You may want to check to see what local codes call for.
posted by dhartung at 3:08 PM on March 30, 2012

You want a backer rod! They come in different diameters and they are sort of like those big pool noodles.

1.) Get a foam closed-cell backer rod slightly larger than your gap and stuff it in there so it is just slightly below the surface of the concrete. It really should be wedged in there instead of laying loose!

2.) Cover the surface of the backer rod with self-leveling concrete crack sealant. It's sort of like caulk. You may have to go through several tubes. (If your backer rod is not wedged in there tightly, it may float at this point and you don't want that.)

3.) If you want to minimize the appearance of this seam, sprinkle some sand on top of the crack sealant while it's still wet.

4.) Allow to dry for 48 hours and avoid stepping on the seam while it's curing.

The backer rod and concrete sealant are flexible yet waterproof, and they won't attract termites.
posted by Ostara at 6:48 PM on March 30, 2012

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