Patio settles and creates potential water issues

 
Posted10/12/2018 6:00 AM

Q. I completely enjoy your column and advice/direction. We moved into our new home seven years ago and thought we were so clever to have a patio poured before the grass went in, so the concrete truck would not damage anything. We did due diligence. My husband works for a municipality and worked on a concrete crew frequently, so he has a very good understanding of the process and do's and don'ts. So, we did lay a healthy layer of gravel and tamped it down until the cows came home.

We had a large patio laid -- 23 feet long by 13 feet wide. However, when all is said and done, it seems we did not prepare as well as we thought. The night we poured the patio, there was a heavy storm, and water seeped into the basement through foundation cracks. Because, on the new-home walk through, we previously ID'd many foundation cracks with the builder, the builder was asked to, and did, repair all of them after the storm/leakage event. So, we have never had a drop of water in the basement again -- thankfully. And we want to keep it that way.

 

However, on the concrete patio, the 13 feet to one side of the stoop has settled dramatically -- it has dropped about 4 inches. The 10 feet to the other side has dropped also, but only about 1 inch. We are worried of course that with each rain, water is draining back against the foundation. Over time that just can't be good, especially considering the foundation's history. We see our options as:

• Tear up and replace the patio. Ouch.

• Build an overhang, which will keep the rain from falling on the patio. Thus blocking any sun we Chicagoans might ever get in the few months we have sun (feeling UV deprived).

• Pour more concrete on top of the old, leveling it out. This will result in a rather large drop off to the grass, I think. Can't picture it.

• Hire one of those companies who "push" the concrete up and then fill from the bottom. I am concerned that the pressure, being uncontrollable, will actually result in pressure onto the foundation wall, which of course would be disastrous. And, of course, the existing cracks would still exist in the top of the patio. Not sure if that would solve the problem? Or if it is safe for the house?

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• Build a room addition over the patio! Yah. The next time I have $75,000. Next paycheck.

The patio is not pinned to the home. The concrete does has rebar in it. What are your thoughts please? We need some good advice to protect our investment.

A. The backfill in a new house is generally done with loose fill unless a stone fill was used. This loose fill will take a long time to settle unless it is tamped in 6-inch layers as it is dropped in the foundation trench. But this entails some risk if it is done before the first floor framing is complete. It's a matter of coordination on the part of the builder.

The gravel fill you used and tamped was still laid over loose fill, which the rain helped compact faster than it would take if it remained dry. As a result, the concrete patio settled because it was not pinned to the foundation. But if it had been, a big void would have developed underneath it, which would need to be filled as it settled more over time. This is often done with a cement slurry, not an easy process.

Regarding your concern about potential future leakage, make sure the grade is kept gently sloping away from the foundation if it continues to settle and keep a healthy grass stand on it. After seven years, the grade has probably settled as much as it will.

                                                                                                                                                                                                                       
 

As to your choices, if you can find locally a contractor who does mud-jacking, see if he or she is willing to attempt it after checking the site. In your photos, it appears as if your house foundation is made of poured concrete, so mud-jacking is less risky than if you had a block foundation.

The next best option would be to have a concrete contractor pour a new cap over the patio and pin it to the foundation. A concrete adhesive should be used to make sure of proper adhesion between the old and new. This may result in a drop to the backyard, but is this a serious problem?

Q. My daughter and son-in-law purchased a home in December and have been diligently working on the various updates and repairs that need to be done. One project is removing plants and trees next to the foundation in order to add fill, regrade sloping away from the foundation and plant grass as you have recommended more times than I can count. Great advice!

We are all puzzled with this side of the house where the chimney meets the soil. This row of bricks appears to be sitting on concrete blocks which are hole side up. At some point the holes may have been covered with mortar which has since deteriorated? We want to know if the holes need to be preserved or if they can be filled in with soil when we regrade on this side of the house. I have enclosed photos. The purpose of these holes evades us. The house was built in South Burlington, Vermont, in the 1940s. We're hoping you have some insight here.

A. Standard line concrete or cinder blocks are manufactured with webs and chords to reduce weight. Some blocks are solid, but smaller in size to keep weight manageable. It is standard building practice to lay blocks with the cores up. Blocks are used as foundation where they will not show to save costs.

The unusual thing in the case of your daughter's house is that they extend beyond the brick chimney. This is not a problem as evidenced by the age of the house.

I doubt that there ever was a mud cap on the open cores. The holes can simply be filled with dirt as the regrading progresses.

• Henri de Marne, a former remodeling contractor turned columnist and consultant, is the author of "About the House with Henri de Marne" (Upper Access Publishing). He continues to take questions from readers for this column and his website, www.henridemarne.com. Email questions to aboutthehouse@gmavt.net.

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