Dr. Mor & Associates
13036 Mindanao Way, #6
Marina del Rey, CA 90292 
Phone: 310.574-0080

Concrete for Footings and Foundations:

House is Sinking

Hi Dr.,
I have a couple of questions. Our house is built on a slab. it is ranch house. For some reason on section of the house is separating form the rest. It is a brick house one story. We now have two large cracks in the walls in one room. I think that the slab may be sinking or has broken. The house is about 50 years old and I thought the sinking/settling would have already taken place by now. What should we do?

Is there a way to put a second story on a house that sits on a slab?? what considerations do we have to take into account because there is no "foundation" I do not know the thickness of the slab.

Please help. Thanks, MP

Both questions require a structural/geotechnical engineer to review the conditions. In general, you are right about the expected stability in older houses. However, if it is built on very expansive soils, and soil moisture conditions changed, movement can happen. You may have heard about all the damage to houses in Southern California due to slope movement after excessive rains.  Movement can also happen if someone in your area is pumping water out of the ground close to your foundations, or natural ground water level changed for any reason.

You may also have to consider the remote possibility of structural failure in the foundations (if you have structural foundations) that can occur over time due to corrosion of steel or chemical attack on concrete.

Regardless, it sounds serious enough to require immediate investigation.

It is possible to add a second story. Any qualified engineer can calculate it easily based on the size of your footings and soil conditions. You may have to reinforce the footings or add some external supports, but it is not very difficult.

Good luck

Winter foundation / basement pouring

My wife and I are about to build out new home. Its rather expensive and we have every intention of making this our last move. I subcontracted my last home when land was still available to the general populace.  Now however, I am have no choice but to have someone do it for me.

My concern is its near mid November here in Michigan. I have expressed a great deal of concern to my builder about my desire for a NON WINTER foundation/basement pour. He assures me I have nothing to worry about and this is actually the best time. My experience with this is my sisters home, who I had warned about a winter pour. She pleaded as I have done with my builder to postpone till spring. They poured anyway.

The result was 10+ MAJOR cracks and leaks, resulting in MAJOR mess and dust throughout on numerous occasions (3).
Can you comment on winter pours ? What to look for, what would you do ?

Can you point me to some areas I can learn more about it ? Am I having chest pains for nothing ?

You wrote:

"My concern is its near mid November here in Michigan. I have expressed a great deal of concern to my builder about my desire for a NON WINTER foundation/basement pour. He assures me I have nothing to worry about and this is actually the best time."

I would not say that! But there is no reason why they cannot do a good job if they follow the correct practice.

"My experience with this is my sisters home, who I had warned about a winter pour. She pleaded as I have done with my builder to postpone till spring. They poured anyway. The result was 10+ MAJOR cracks and leaks, resulting in MAJOR mess and dust throughout on numerous occasions (3)."

The cracks were probably not the result of freezing alone, but the dusting sounds like it was.

A few points:

  • I expect that in your area the good contractors know how to pour concrete under these conditions, but maybe not...
  • The building department may be a good place to inquire about their recommendations regarding concrete practice and inspections.
  • For information on placing concrete under freezing conditions the best source is the "American Concrete Institute" which is based in Detroit. They have publications that teach contractors (and homeowners) on the correct practice for any situation. Try calling 313-532-2600 and ask them. Their publications are used as part of building codes by many cities. These can be found in most engineering libraries.
  • Another excellent source is the "Concrete Construction" magazine based in Chicago. They have excellent articles on these subjects. Try calling 708-543-0870.

As for what to look for:

  • Concrete hardens through chemical reactions. These stop when it freezes and as a result it remains weak longer.
  • Water that freeze inside the concrete as it hardens make it porous and weaker. One of the results is dusty surface as you observed.
  • The main problem occurs when concrete freezes in the first few days. After that it is strong enough and generates enough heat (from chemical reactions) to harden fine.

The main points to look for:

  • Do not pour concrete in freezing temperature or if you expect freezing to start soon (hours).
  • Soon after pouring (few hours - when it is dry enough to sustain walking) cover it with blankets (burlap; tarp; hay; sand...) to insulate it from freezing air and let its internal heat keep it warm.
  • Keep it covered for at least a week if temperatures are low. However, practice in your area may be different but still effective.

Thanks for that very timely comeback, I really appreciate your time and will certainly run down your leads for information. I will let you know what happens. Should I be concerned about the #bags in the mix ? Any additives they may use - calcium chloride ? What about this stuff the Army used for sub-freezing concrete pours ?

Would you mind if I forward you the details when I get this from my builder ? Any points I could put in a legal document for them to sign ?

Again, I appreciate your time.

>Should I be concerned about the #bags in the mix ?

Not really. The mix design is probably done by a ready-mix supplier who knows what he does. Just make sure they use the correct specified strength (2000-3000 psi for foundations) and the number of bags will be a function of that.

> Any additives they may use - calcium chloride ?

Calcium chloride accelerates hardening and may help avoid early freezing damage. If used conservatively by someone who knows not to use too much it can help.

>What about this stuff the Army used for sub-freezing concrete pours ?

I am not sure what you are referring to. I doubt that your situation calls for such drastic measures and the local contractor probably is not that sophisticated. You can wait for a nicer day...

>Would you mind if I forward you the details when I get this from my builder ? Any points I could put in a legal document for them to sign ?

No, by all means do let me know.

Sorry, I do not give legal advise. I believe that any contract which requires satisfactory concrete will suffice.

[I found you through] AltaVista, searched on concrete, cold etc. Your resume showed up and I thought I hit gold - I did. I really appreciate your time and will certainly let you know what happens. If I have a problem, I would love to send you a core for analysis. I know I sound paranoid, however its the last house I intend to build.. Again - thanks for your prompt, courteous, concerned response.

Foundation Failure

The foundation of my fathers home is crumbling due to time and weather.
It is a pier and beam construction.  Is there a product or do you have some ideas on how we can repair this ourselves ?  Perhaps an epoxy or grout which can be applied easily ?

Crumbling sounds like a very serious situation.
If you are noticing actual separation in the piers, or even visible cracking I would suggest a more permanent repair.
Same goes if you notice deflections in the beams or floors above.
The best repair will be to replace the crumbling piers with new ones.
You do that by using jacks to slightly raise and support the beam, remove the old pier, and install a new one.

I am assuming you are talking about pre-cast piers.
If these are the cast in place type you may have to recast the whole thing.
Depending on clearance under the house and how much money you wish to spend I would suggest going with an expert.  They can be quite reasonable.

Check with your homeowner insurance (I hope you have one).  It may cover the repair.

If you decide to repair the piers then go with structural epoxy.
But be aware that those require preparation and thorough cleaning of the cracks which you may not be able to do.
Always call the manufacturer's technical support for recommendations.  I find them very good and helpful.

Foundation Stem Wall

Orlando, FL

I want to build a new home in the Orlando area. Some builders use a concrete slab. Others use something called stem wall. Which method is best, and why?



I am not sure what they mean by "stem wall". Stem walls are part of a concrete foundation and the structural wall rests on top of these short concrete extensions of the footings.

Are they talking about raised wood frame floor as opposed to concrete slab-on-grade?

In my experience, the raised floor may be more expensive to build, but if done properly will make living in the house more comfortable by separating the living area from the ground. That is, if you don't mind some flexibility and creaking in the floor...

Concrete, if done properly, is stronger and resists fire and termites.

One advantage of raised floor is allowing plumbing and wiring under the house in accessible area. That really helps for any repairs or remodeling.

Does that help? Let me know if stem wall means something else in Florida.

Thanks for your quick reply. I'm not sure what "stem wall" means to the Orlando builders. I'll have to ask them some specific questions. In the meantime, your comments have given me a better perspective.

Thank you!  R.

Dr. Mor,

Here's what the builder's rep told me about stem wall, but I would appreciate an unbiased interpretation. I don't get the sense that there is a raised floor.




A stem wall is a three step process, (footing- stem wall- concrete pour) whereby a monolithic slab is a one time concrete pour within batter boards.

A stem wall is more expensive and more time consuming. We prefer the stem wall foundation because of its strength and quality. If you get the foundation right, the rest of the house will come out much better. Monolithic is a cost saver, however it does meet all codes and is widely accepted. It's like the different between a Chevy and a Cadillac.  Both drive about the same, but the Cadillac just feels better.

Foundation strength for second floor

We are considering adding an above the garage room.
I understand that the foundation may not support a second story as-is. The house is in California and was built in 1960. It has a slab floor in the garage and a curb around the edges which is about 6"x6" where the sill is. I'm not sure about the width of the base of the foundation.

Is it possible to strengthen a foundation by adding to it? Or is it usually a requirement to tear it out and put in a new heavier foundation?


It is possible and practical to add to the foundation. In most cases you will need to dig next to the existing foundation, drill holes in the concrete and insert dowels that will extend into the new concrete. If you make sure that the new concrete is securely tied to the old (using these dowels) you can usually assume that they will work together to support the new loads. However, it is possible that the existing foundation is sufficient. Consult a local engineer for best results and safety.

Foundation Crack

problem: What is best to use to repair a small crack in
basement foundation

Sheridan, USA

A small crack may not require any repairs unless:

1. It allows water to reach the reinforcing steel, or
2. It is part of a structural problem that has been repaired.

The most common repair for structural cracks is Epoxy Injections. These are usually done by professionals who have experience and the needed equipment. In the case of a single small crack you may have to resort to a do-it-yourself kit which you can find by searching the Internet.

In my experience, unless you see moisture transmission through the crack (including white deposits on the surface), it is best to leave it alone. If the crack is caused by structural stresses you need to make sure that these are taken care of before injecting since it is likely that a new crack will open next to the repair.

Hope this helps.

Foundation slab cracking

The house is 15 months old. the garage is cracked and is getting worse. After 3 months in the home if we tapped the concrete it made a hollow sound. Now the sound has spread and the crack is getting larger. We also have hollow sounds similar to the garage in certain areas of the home. The mortar between the bricks over the garage are cracking. The crack on our covered porch is getting bigger. And we have cracking at the top of the driveway by the garage. How can we find out if the slab was done improperly or if it wasn't graded properly. We are very concerned because the builder bought back homes because of foundations or soil settlement. They were settled quietly so I don't know the details. I do know for sure one lady had no center supports under the slab. Basically, how can I find out if everything was done properly. Does this sound normal for such a new home? Thank you so much for your advice.

Mt. Juliet Tenn.
No, it sounds very wrong. Especially the part about the builder buying back homes.
What you describe sounds like soil settlement (or expansion) problems, and
depending on the extent could be normal and repairable or not.

Why don't you contact the builder? Most will settle as fast as possible to avoid costly litigation. If you are persistent and make them understand that you are not going to accept half measures, and that you are not going to give up - they will. Repairing such damage can be very expensive, and it may seriously impact the resale value of the house. If they offer to repair, make sure that you have your own expert (Engineer) review everything - and make sure they pay for
If you are not "in love" with the house, it may be best to get a replacement and move on with your life. Repairs are going to be stressful and disruptive for a long time.

I would suggest contacting a lawyer who specializes in construction to review any agreement. He will help expedite the process but be aware that lawyers make more money in litigation and you should make it clear to him that you do not want to go there.

Start here to search for construction defect lawyer in your area: http://www.martindale.com/xp/Martindale/Lawyer_Locator/Search_Lawyer_Lo

To find if everything was done right you need to hire a testing laboratory/construction inspectors/engineers who can investigate and find out all that.
The lawyer should know where to find these experts - but it will be expensive.

Be very polite and friendly when dealing with the builder - but make sure you know what you want before you start negotiating and stick to your demands. They can afford to pay more than you can afford to lose.

Good luck.
Thank you, and for getting back to me so soon. Your advice is very much appreciated.

Wet Foundation

At our 30 year old family cabin in Northern Canada, we are having problems the timber piers settling. Unfortunately, the piers are sitting directly on the saturated ground, no concrete footings were ever placed at the time of construction because to get below the frost line would have meant extensive manual excavation. At the back of the cabin, due to settlement over the years, there is only about 8" of clearance from the bottom of the joists to the ground, making any retrofitting of any footings difficult. We continually jack the cabin and keep placing varying sizes of timber plates under the piers as the old ones sink out of site. My question is, would shallow excavation below the piers (while the pier is supported by jacks/temporary posts) followed by the introduction of 3-4" cobbles assist in increasing the bearing capacity of the soil? Or should I try something else? Last year I installed a perimeter drainage system (4" Big O Pipe surrounded by drain rock and enclosed in filter cloth) which assisted in drying the soils out a bit, however, excessive moisture still exists. Thanks for any assistance you can provide me!

Vancouver, Canada

This question is a little more complicated than what I can handle here. In general, such a situation calls for either support on bedrock, or using deepened foundations that reach below the frost level. I would have expected the settlement to stop after so many years, which indicates that there is more than simple settlement going on. I am sorry, but you should discuss it with a local engineer who is familiar with the soils and possible solutions.
Thanks Doc,
As you stated, this is a complicated problem and as a Civil Technologist I could solve it as you suggested by placing deep foundations, however, the expense is prohibited! Would the cobbles assist in increasing the bearing capacity?
Water, nice to drink but a pain in the ass when it comes to foundations!

Thanks again,

ps. A series of springs in the area are providing the water to some degree. I hoped that the perimeter drain would have captured most of the water!

Foundation Repair

We are thinking about buying a 75-yr old home near CassLake, 2-story, only 900 sq. ft., no basement. We suspect foundation problems (sagging in the back, smells musty, no gutters, no vents, etc.).
We, of course, think this is the cutest thing we have ever seen, but do not want a money pit.

Before we have it inspected, and proceed with negotiations, do you have any thoughts and some earthly idea as to cost of repair?

Dearborn, USA

I am sure you realize this is impossible to estimate, even if I had all the information about the house (such as plans, type of foundation, roof, soil type, etc.).
The only way to get a rough estimate is to ask a local contractor who has experience with this type of house.
If not for the sentimental value of "the cutest thing..." I would have said that the most economical way of fixing it is to R&R (Remove & Replace). Such old houses have to be brought up to current codes (if the extent of the repairs exceeds a certain amount) and that sounds like a major job in that case.
So, if the price is right and you are ready to take a risk you can buy and live in it "as is." Otherwise, repairs are probably close to a "money pit."

But again, I know nothing about the place. Get a local contractor and you may be surprised (one way or the other). He may even give the estimate for free in the hope of getting the job.

Good luck.

Concrete strength gain

Question: I just poured footings for a retaining/stem wall. The footings are 1' deep, 3' wide, and 36' long. How long should I leave the footing forms in place, and when can I put up the forms for the stem wall and pour it??

Astoria, OR

In most cases, concrete is strong enough to maintain its shape after 24 hours. That means that an element supported by ground like the footings can be stripped after 24-48 hours. However, most people use low strength concrete for footings (2000 psi) and that may require a longer period to gain the strength you want. As a rule of thumb, concrete gains about 70% of design strength in 7 days (1400 psi for a 2000 psi concrete). That is strong enough to carry its own weight and more than enough for stripping.
Bottom line: 48 hours should be ok. 7 days is long enough for any application.
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