Concrete And Cinder Block Cracks · Understanding Why They Occur · Home Inspection Tips

From my experience, cracks in concrete and cinder block walls raise big question marks in buyer’s minds: what is normal and when should I start worrying?

When pouring concrete contractors know you can be sure about two things: it will get hard and it will crack.


First, let’s see what concrete is all about: it mainly consists of four components – Portland cement, gravel, water and sand. Water triggers a chemical reaction when mixed with cement, called hydration - this allows the mix of gravel, sand, water and cement to gradually harden over time.

In order to better understand why and how concrete cracks we have to discuss compression and tension, two forces that will always affect our future home. Concrete is very strong in compression but rather weak in tension (tension strength of concrete is about 10% of its compressive strength). This is the main reason why concrete is almost always used together with steel reinforcement. Concrete and rebar are the perfect love story:

1. Concrete is strong in compression but weak in tension while reinforcement steel is strong in tension but weak in compression: the perfect match.
2. Their coefficient of thermal expansion is similar – the two expand and contract at the same rate. If that wouldn’t be the case they would literally tear themselves apart over time.
3. When properly used, cement paste creates a surface-film on the steel preventing it from corroding inside concrete
4. The bond between steel and concrete is very strong - this is why concrete can pass stress to the steel and vice versa.


Concrete cracks before hardening are OK. After, not so much...

Cracks occurring BEFORE hardening are usually the result of settlement within the concrete and/or shrinkage of the surface as water evaporates while the concrete is still fresh.

The water-cement ratio is crucial when we discuss concrete: the minimum amount of water needed to start the hydration process (hardening) is 25% of the weight of cement. In practice however, we’re getting close to 50% if we want to have a smooth, nicely flowing mix. And we want that because concrete has to flow and squeeze through all that reinforcement steel. Why is water content so important? Because every drop of water that exceeds the 25% will NOT be used in the chemical hydration process, instead will get stuck in concrete and evaporate later on, leaving a fine network of capillary voids weakening it and allowing cracks to appear – concrete shrinks about 1.6 mm (1/16 inch) for each 3 meters (10 feet) when hardening.

Plastic-shrinkage cracks are very common in slabs- they are short cracks that appear when surface moisture evaporates before it can be replaced by bleed water coming from below. That's why the surface shrinks faster than the interior causing cracks that can reach the middle of the slab. Like when you are pouring a patio slab on a hot, dry and sunny day:


Cracks occurring AFTER hardening are the ones that should be analyzed carefully. They are the result of applied loads and sub grade settlement.

The two main forces affecting any construction are static loads and dynamic loads: static loads remain unchanged for a long period of time (e.g. a structure’s own weight) while a dynamic load is unstable and moving (e.g. hurricane winds). When designing a house the sum of both loads is taken into account in order to ensure its stability over time. If the final result (our house) does not meet the standards for those calculated loads it will suffer from settlement depending on the action of those forces. E.g. cracks may appear after high winds because of the load they apply on the exterior of the walls, or on load bearing beams and columns if they fail to support their own weight. This is very rare though, and it usually means something must have gone terribly wrong in the construction phase.

The shape and direction of the cracks are important hints as to what is going on. There are three main types of wall cracks according to their direction:

1. HORIZONTAL cracks are almost always caused by an applied load. The following picture is a good example of an excessive load placed on top, as the owner decided to place a 5,000 liters (1300 gallons) water tank on the roof:


2. VERTICAL cracks that are wider at the top or bottom are an indication of settlement:


3. DIAGONAL cracks are usually found in the corner of a window, door, beam pocket or other openings. They are called re-entrant cracks and are of no structural concern unless, of course, they allow you to see your neighbors waiving their hands at you.


As a rule of thumb, when checking a house, you should pay attention to cracks that exceed 6 mm (¼ inch), cracks that leak water, or long horizontal cracks.
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Have These Five Things Checked Before Buying A House In The Caribbean · Common Faults & Problems

Most homes on the Riviera Maya and the Yucatan Peninsula are built of concrete and cinder block, for three good reasons: hurricanes, humidity and termites.

home inspection common problems in playa del carmen, cancun, tulum, riviera maya

With proper design and execution a concrete/cinder block house can give you many years of trouble free service. However, the opposite is also quite possible!

Rising Damp Can Affect The Structural Integrity Of A House

If capillarity is not stopped between footings and walls you’ll have to deal with efflorescence (whitish powder on walls) and the aesthetics of it will be the least of your problems... In time, the water moving upwards displaces concrete salts, seriously debilitating the structural integrity of your load bearing walls.

Strong concrete plus the right size and quantity of rebar are a guarantee for minimal settlement once the house is finished, but cement and rebar are not cheap and many home builders choose to cut corners because we’re not in an active seismic area. This will also limit your future development plans as it will be difficult to add another story if your load bearing structure is weaker than it was meant to be.

Nowadays the use of a
vapor barrier beneath concrete slabs is common practice for a good contractor but 10 or 15 years ago this was mostly ignored. Without a vapor barrier, the relative humidity in the slab just below the surface can often be 100%. Since the air is never that humid, moisture is going to move from the slab into the air, drawing more moisture up from the bottom. You will best see this in the grouts of ground floor tiles when the rainy season starts: they will turn dark, or, in extreme cases, you’ll notice drops of water on the floor that seem to appear out of thin air. The relative humidity in the rainy season gets to be so high that water cannot evaporate and starts gathering, thus the drops of water on your floor.

Grounding System and Electrical Installation

Another check point on a home inspection is the grounding and electrical installation. The most common method for grounding is the classical rod driven into the ground. This works reasonably well under normal circumstances but, remember, the Yucatan Peninsula is made up of hollow rock with underground rivers crossing it from one end to the other. It is very difficult to find a spot with a depth of 3 meters without hitting the rock bed. Why is that important? The deeper the grounding rod is driven, the higher the moisture content, thus better conductivity for the grounding system. Grounding rods are generally made of iron and covered with a 0.025 thick layer of copper to protect it against corrosion, but it will most likely be scratched in the process of driving it into the ground which will promote corrosion and render your ground ineffective in a couple of years. Periodically checking your ground impedance (the lower, the better) will tell whether you still have an effective grounding of the electrical system.

Most electrical installations in the area don’t use wiring caps for pig tailing, but electrical tape. In time the tape will dry out and become brittle allowing bare copper to be exposed.

Most times, a thinner cable gauge will be used instead of a thicker one, leading to undersized branch circuits.

All reasons for having your electrical installation checked, making sure everything is working as it should!

Termites

Wood is a precious addition for all interior or exterior designs but beware of termites as the Mexican Caribbean is a termite prone area. Wood that has not been treated will quickly be attacked by various wood loving insects and/or mold. This could pose a serious problem if we are talking about structural elements made of wood. Find out how to get rid of them by natural methods.

Water Infiltration Through Concrete Roofs

Gabled roofs are extremely rare in this area due to the hurricanes that could sweep the area every year between June and November. Most roofs are flat and made of concrete. They are very resistant should a hurricane hit us but are prone to water infiltration due to their inherent flat design. The use of a waterproofing membrane is recommended as bare concrete will not provide a safe water barrier, especially if you take concrete settlement into account. There’s always the possibility of thin, almost invisible cracks, caused by the house settling or concrete curing that can leak in case of a serious downpour.

House Mold

The rainy season will bring very high relative humidity, ideal for allowing mold to grow. Running the air conditioner 24/7 is not always a reasonable option so making sure you own a sane house that is not prone to humidity infiltration and is properly waterproofed and ventilated will be of great help.

A close view of mold on a piece of furniture in a Tulúm house:
home inspection mold furniture tulum
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The Naked, Cooling Truth About Air Conditioning · How Do They Work & How To Properly Size A Unit

If you plan on spending your summer in the Mexican Caribbean you’ll suddenly realize the importance of air conditioning. Let’s have a look at how they work, why they have to be cleaned and serviced and what is the right way of sizing a unit.

Willis Carrier was the one to invent modern day air-conditioning in New York, back in 1902. The electronics have changed a lot since then, but the principle remains the same.

The refrigerant circulating in the air conditioning's copper piping loop is the vehicle that transports coldness from the outdoor condenser to the indoor unit, and heat from the interior to the exterior.


Contrary to the popular belief, most air conditioning systems are not adding fresh air to the indoors, they are just recirculating existent air in order to maintain the desired temperature. A ductless mini split basically suctions the warmer air of the upper part of the room, forcing it true the cold evaporator of the indoor unit where it cools down. The evaporator also dehumidifies the air - water vapor condenses in contact with the cold evaporator (thus the need for drain pipes from the inside unit) .

Most modern AC units come with some kind of filter in order to prevent dust from being spread around when the unit is functioning. In time, dust, pollen and pet hair accumulate in filters, blowers and evaporators until the filtering capacity is exceeded. This creates a dark, dirty and humid environment where germs or mold can start developing affecting our quality of life as we inhale the air that passes through the unit.

How a dirty filter looks:


This is a dirty blower rotor:


A dirty evaporator:

Regular cleaning is recommended in order to avoid potential health hazards and maintaining the recommended air flow. Remember, dust and pet hair can dramatically reduce the efficiency of your AC unit making it run full speed with minimal effects (except raising your electricity bill).

And talking about electric bills, this is another issue when it comes to using AC. Technology has come a long way, modern units can be extremely efficient while older ones can turn into electricity black holes if left running for long hours. The part that consumes most electricity is the compressor, responsible for cooling the refrigerant. Older units are simple on and off devices.
What does this mean? Let’s say you return home and turn the AC on. Outside temperature is around 30 C, you set your unit at 17 C as you want a fast drop in temperature. Your compressor starts working at maximum speed to keep up with the demand. Presuming you have a decently insulated house, in about 1 hour the inside temperature has reached the 17 C (this is just an example, not a real-life situation). The thermostat kicks in and stops the compressor. ...Until the temperature rises. ...Then the compressor starts again at full speed. ...Then it stops, and so on. In other words, once the desired temperature is reached, the AC compressor kicks in and out trying to maintain a constant temperature, trying to save electricity as it does not have to run constantly. Remember we are talking about the older units; the problem is, whenever the compressor starts at full speed, a surge occurs, thus consuming a lot of electricity.

Newer models come with the so-called A/C inverter technology. This allows the compressor to adjust its potency to the demand. It is not an on/off situation anymore with high surges whenever the compressor starts but rather an adaptive pattern where the compressor quietly delivers what’s needed turning faster or slower, thus saving energy. However, inverter units come with a higher initial cost.


Sizing An Air Conditioning Unit

Surprisingly, bigger is not always better. On some home inspections I encounter ridiculously large units in rather small rooms installed in an attempt to save electricity. The logic behind is that when the unit is very powerful it has to work very little to cool the space thus consuming very little electricity.
Unfortunately that’s not how it works. Installing a large system in a small room will only lead to short cycling of the compressor as the exiting air stream bounces back into the returning air stream. With large units the velocity of the exiting air stream is of about 6 feet/second. If the opposite wall is less than 10 feet away, the exiting air stream travels for only 4 seconds before bouncing back to the unit. Since the temperature sensor is usually located on the cooling coil, this quick return of a cold air jet will make it think the desired temperature has been reached, therefore it will stop the compressor very soon after it started operation. Result? High energy bills as the compressor quickly cycles on/off, warm room as it never has the chance to truly reach the programmed temperature and a short life span of the cooling equipment.

It is extremely important that the compressor runs for more than 5 min when started. Why? Because this allows oil to return to the compressor (yes, your AC system runs on a mix of oil/refrigerant to provide internal lubrication). The second reason is its ability to dehumidify – the longer a unit runs the better it is at removing humidity.

So you see, properly sizing a unit has its advantages and can literally save you money.



Willis Carrier with his first A/C unit in 1902:

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Grounding Essentials · Best Grounding Techniques When Building A Home In Mexico · Yucatan & Riviera Maya

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Three Major Concerns Home Owners In The Riviera Maya Can Forget About · Bye Bye Radon, Lead or Asbestos!

Living in a healthy environment while enjoying the comfort of modern housing has become a matter of constant studying in the past decades. You've most likely heard of these three dangerous contaminants that can reach alarming levels inside people's houses under certain conditions: radon gas, asbestos and lead. They have been the subject of many home inspection reports describing their effects on quality of life. According to most studies, they can all become carcinogenic when reaching critical levels.

What is Radon?

It’s a colorless, odorless, tasteless and, most important, radioactive gas. It’s a normal byproduct of the radioactive decay chain. Radon is released when Uranium and Thorium (two naturally occurring radioactive metals found deep into the ground) slowly decay into lead. They have been around ever since the earth has formed and their naturally occurring isotopes have very long half-lives, about billions of years. That means they will be around for quite some time. As radon gas decays, it forms polonium-218 and 214, lead-214 and bismuth-214. They are all short-lived radioactive isotopes that, unlike radon gas itself, have the ability to stick to solid surfaces like dust particles. Scientific research has shown that if contaminated dust is inhaled, such particles can reach the airways of the lung and increase the risk of developing cancer.

Radon gas is VERY dense. In other words, it's heavy; therefore has a tendency to accumulate in low areas - like basements and crawl spaces. Here's how radon finds it's way into a house:


Radon is not a concern in the Yucatan Peninsula. Why is that? First of all uranium concentrations are extremely low, as shown in the following map:


It is well known that Mexico is the country with the largest reserves of uranium in the World, so it's very likely that Mexico is the country that receives most solar radiation on the planet, but the map below confirms us that we don't have to worry about it if we live in Quintana Roo or Yucatan - actually the whole Eastern part of Mexico looks good on this map:


Second, the Yucatan Peninsula is made of rock - you can consider yourself lucky if you dig a hole and don’t reach the bedrock in about 1 meter. That means no house here has a basement where radon gas could accumulate, and even so, it could never reach a concerning level. Third, we are living in the Caribbean, perfect insulation is an unknown concept in the area, there will always be air coming in and out of a house.

Asbestos and Insulation

Asbestos is a very good and cheap insulator, that is why in the 60's and 70's it has been widely used for home insulation. Awareness of its effects on health started growing in the 80´s, until it was banned. Prolonged exposure to asbestos dust has been proven to lead to lung cancer.

The Mexican Caribbean was nothing else but pure jungle some 30 years ago. Most buildings have been constructed after the health hazards of asbestos have been documented. Besides, insulating homes is not common building practice in the area, most buildings are made of cinder block and concrete, chances of asbestos contamination are close to zero. This picture shows house components that may contain asbestos:


None of the above materials and building techniques apply to the Riviera Maya.

Lead Exposure

Overexposure to lead is known to cause lead-poisoning. In 1978 the US Federal Government has banned the use of lead based paints for this reason.


The fact that the development of real estate started rather late proves to be an advantage, as by the time the building boom started lead based paint was banned almost world-wide. All water connections are made using plastic (more recently) or copper pipes (in the past). Lead pipes are unheard of in the area.
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High electricity bills in Mexico? · Understanding the reasons and how to get back to normal

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Five Natural Methods To Get Rid Of Termites · Non Chemical Termite Treatments

On some home inspections when discovering termites the following question pops up: How to get rid of termites without using chemicals? Either by chemical or natural methods, it's almost impossible to get rid of them for good. They will eventually find their way into your home again. Any method works just temporary, however some of them are more effective than others. One thing is for sure - "terminating" the termites is no quick fix! You're going to need to plan ahead, and to repeat the treatments.

Treatment is most effective if you find all their hiding spots. Try and target all colonies at once.

Sample of wooden furniture consumed by termites:

Let's see how you can get rid of them, or at least reduce their number:

Set Up Some Cardboard Traps
Termites simply love the cellulose that is found in wood, cardboard and paper. Compared to wood, cardboard is gourmet food for termites. Creating a cardboard trap is easy: wet 4-5 sheets of cardboard and stack them. Next, place them near the spots where you found most termites. After a couple of days, you will notice that when you flip the cardboard, it will be crawling with termites. Using gloves, carefully carry it into your backyard and burn the cardboard along with the termites. This method isn't going to get rid of all of them, but will certainly reduce their numbers, preventing them to settle into your furniture and closets. It's one of the quickest remedies available.

Use Beneficial Nematodes
This is a very effective method. Beneficial nematodes are a small worm species that are natural parasites to garden insects, including termites. They kill termites within 48h by releasing a particular kind of bacteria into their bodies. When you use beneficial nematodes, you won't be getting rid of just termites, but you'll also be destroying any other kind of bugs that may be harming your home and garden, including wood carving insects.
Unfortunately we don't know any place that sells them in Mexico, but if you can get these nematodes you should definitely use them - immediately after they are purchased. They require refrigeration if not used, therefore buying them online is probably not a good idea because of the shipping. Spray them in the early morning or after sunset, as UV light will harm them. Using beneficial nematodes is an effective technique, there's a good chance that the entire colony will be affected.

Direct Sunlight Treatment
Place the problematic piece of furniture in the sunlight as long as possible, preferably 2-3 days. Sunlight gets rid of certain kinds of termites, they either die or move away because of the light and the heat.

Freezing Treatment
Freezing the termites is a guaranteed method. But this is no option in the Mexican Caribbean, unless you have an enormous freezer, or very small pieces of furniture...

Heat Treatment Using Microwaves
This must be done by a professional, as the required equipment isn't available for anyone to purchase or use. You should call a local pest control company and see if they provide this kind of treatment, and if it's an option for your home. Having your home heated to a very high temperature will surely kill the termites. But as I've mentioned at the very beginning, it's impossible to get rid of them for good, most likely you'll have repeat the treatment once or twice a year.

There are certainly more ways to deal with termites but they´re not part of this article as they imply the use of chemicals. The most common method of dealing with termites here in the Mexican Caribbean is by chemical fumigation.
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Amazing Engineering · 25 Funny Construction & Installation Fails

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