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Feb 12, 2006, 9:53 AM

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Help on New House

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We will be building a new house in the Vista del Lago area of Lake Chapala. We will be hiring a “hands-off” general contractor because we have little confidence in our ability to manage the project ourselves. Thus, the success of our project depends on having a good contract that specifies the best components and practise with respect to building materials, wiring, plumbing, etc. We will have an independent engineer design the foundations.

Can people help us by suggesting what we should specify with respect to:

1. Walls, i.e. brick or blocks, size of rebar, cement quality, etc
2. roof, we will probably go the bodega style with some highlights, what cement and finish that will be waterproof and maintenance free.
3. should interior door frames be metal or wood
4. wiring, will be nob standards, but what size wire, how large an entry?, is a whole-house voltage regulator/surge protector recommended?
5. plumbing, NOB standards, recommended copper pipe size and thickness, recommended drain material, size, and thickness, under the floor or around the outside for access?
6. best “plaster” for a smooth durable finish inside and outside

This, of course is only a beginner’s starting list. It there is enough interest, we will announce our (tentative) decisions and new puzzles as our planning takes shape.

Any suggestions gratefully received.

Roger and June


Feb 12, 2006, 12:51 PM

Post #2 of 9 (4410 views)


Re: [heathesq] Help on New House

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I think it will be virtually impossible to find a “plumber” in Mexico with the training and education to install a plumbing system to nob standards in a residence in Mexico. As everyone knows, most toilets do not flush reliably in Mexico. That deficiency has nothing to do with undersized piping. It is because the plumbing systems are not vented here. I have never seen a residence in Mexico with vent pipes protruding through the roof. (I always look for them) The vents are necessary for several reasons, including public health and safety.

Sewer gas is always noxious, sometimes toxic, usually flammable, and sometimes inflammable, it is necessary to vent it out of the system. Flammable and inflammable are not synonyms. Flammable indicates a substance that when ignited will burn. Inflammable indicates an unstable substance that may self-ignite. In other words, it can self-ignite and explode. The content of sewer gas is constantly changing, depending on what has been introduced into the sewer system. If you work in the petrochemical industry you damn soon learn what inflammable means.

All domestic toilets work by siphonage, all of them, including commercial toilets equipped with a flushometer valve. This does not refer to marine, RV, or aircraft toilets. There are only two types of domestic toilets, siphon jet, and washdown. Both of them depend on siphonage to work, when a toilet is flushed the waste material in it is actually sucked into the drainage piping system. When a toilet is flushed, a large amount of water is introduced into the soil pipe; we call it a “slug” of water. The slug of water starts the siphon action in the toilet bowl, never lower the water level on a toilet tank, or in the toilet bowl, you are inviting a stoppage to occur if you do.

If the sewerage system is not vented, two things begin to happen. Pressure begins to build in front of the slug of water, and a partial vacuum begins to form behind it. This slows down the water, and breaks the siphon in the toilet bowl. The result is a stoppage in the toilet.

To install a properly vented plumbing system here would require some drastic revisions in construction methods. Most residences here are built using what is often mistakenly referred to as the “post and beam” method. Actually the post and beam method refers to an obsolete type of wood construction. What is usually used here is a series of vertical concrete columns and horizontal bond beams. The bond beams and some of the columns would need to be penetrated by a properly vented plumbing system, weakening them if they were not modified to add extra strength.

I have never seen true drainage pipefittings for sale in any wholesale or retail business here. True drainage fittings are different than water fittings, having an arc, or “sweep” in the direction of flow. In a venting system they are installed “upside down” to conduct the vented gases to the roof outlets and the atmosphere. Using proper drainage fittings greatly reduces the chance of a stoppage occurring.

Plastic pipe is suitable for drainage systems here. When plastic pipe was first used in plumbing systems nob, it was problematic. The problem was twofold. Those pipes conduct noise efficiently. We found that we had to wrap them with fiberglass insulation as a sound deadener for installations on the upper floors of buildings, or the water flowing through them sounded like a huge leak, especially flushing toilets.

Plastic pipe also has a large expansion rate. This was problematic for plastic pipe used in venting systems. The vent pipes would expand 3 or 4 inches during the day, and contract to their original length at night, breaking the waterproof seals on the roof flashings. A new type of waterproof roof flashing had to be designed with a neoprene seal and a counter flashing attached to the pipe.

If you intend to use copper tubing there is some nomenclature you will find useful to know. Copper pipe intended for drainage is referred to as DWV pipe. That stands for Drainage Waste and Vent. Copper drainage fittings are also referred to as DWV fittings. The thickness of DWV pipe is set to a standard, I trashed all my code books when we moved down here, and I’m not going to the trouble of looking it up now.

Cooper pipe for water is also referred to by special nomenclature, which indicates its thickness. It is designated as type M, type L, and type K. Type M is the thinnest, it is Ok to use in housing, although some local codes nob prohibit its use. Type L is medium thickness and is the most commonly used for all purposes. Type K is extra heavy thickness and is usually used in high-pressure systems, but type L is usually adequate for everything.

It is critical that no copper pipes be in contact with any steel or iron after construction is complete. Do not use steel tie wire to hold copper pipe in place while concrete if being poured. To do so would set up a condition for electrolysis to occur. If necessary, use electricians tape or some other non-conducting material to keep copper pipes from being in contact with any steel components of the building structure. Do not ground an electrical system to any plumbing pipes. That used to be a common method; it is illegal in most jurisdictions nob now.

Electrolysis in this instance is an electro chemical reaction when two dissimilar metal are in contact with one another. The electrons from the metal with the highest content of them, in this case the copper tubing, will migrate to the second metal, which will then reject them and send them back to the first metal. Setting up a very weak electrical circuit. It is, in effect a very low powered battery. The copper pipe will not accept the returning electrons; the water in the pipe will wash them away. This slowly erodes the copper and it will begin leaking.

In 48 years of working in the plumbers and pipe fitters union, I have only seen this condition twice, it is very rare for it to occur. Once was in a home that had a well with a very high iron content for its water supply, and once was in a building with many medical office suites. There were many electronic diagnostic machines there; the installers had grounded every one of them to the plumbing system in the building, destroying it. The only repair possible is to replace all the piping and remove the source of electrolysis. It is amazing to see the results of electrolysis contamination. The pipes will be wet from one end to the other. If you wipe them dry with a rag, while you watch, the pipes will slowly become wet again. You will not be able to discern where the leaks are. There will be millions of microscopic holes in the pipe.

Electrolysis is really bad news. Don’t do anything that by the wildest stretch of your imagination could possibly cause it to occur.

For more information I would suggest doing a Google search for “plumbing codes”, you will find a lot of info there, and some good illustrations. I would also recommend looking at some wholesale plumbing supply businesses online too. Some of them have good illustrations of the fittings they sell. Remember, there is specific nomenclature used in the building trades that the average layman will not understand. If you call to order an “elbow” and the salesperson determines that it is for a drainage system, he will know that what you really want is a “Quarter bend.” He will then ask you if you want a short sweep, medium sweep or long sweep quarter bend?

Good luck, you’ve got your work cut out for you, Rex

"The supreme happiness of life is the conviction that we are loved" - Victor Hugo

(This post was edited by RexC on Feb 12, 2006, 12:58 PM)


Feb 13, 2006, 8:23 AM

Post #3 of 9 (4374 views)


Re: [RexC] Help on New House

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Sometimes the vent stack that Rex talks about is cut flush with a parapet or floor on an upper story. They do not necessarily have pipes sticking out of a roof like NOB. Our home in SMA has vents, but they are all of the type/design I just described.


Feb 13, 2006, 9:43 PM

Post #4 of 9 (4330 views)


Re: [RexC] Help on New House

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Rex is quite right on the plumbing venting issue.

In the UK, the main soil stackpipe is a 4" diameter pipe that runs vertically on the outside wall of the house from its sewer connection to a point above the roof gutter. Connections for grey or black waste water are made at an angle of no less than 45 degrees. The use of a single pipe full height means that effective venting prevents siphon break and carries the sewer gases away at high level.

We have several problems in our house. The plumbing 'vent' is a 2" pipe T'eed at 2nd floor level from a stackpipe that is running horizontally through the floor slab - there are no interception points in case of blockage. On a 3 storey house, this leads to the most obnoxious odours in the laundry room atop the house - at the highest point of the waste pipe.

The external 'inspection trap' for the wastepipe to the sewer is simply a hole hacked in the sidewalk that has no proper connection on the pipes (like a deep-cut clay raceway, as would be common practice in England). The result is that we have appalling blockages very frequently. The 'plumber' says its because we are putting paper down the toilet - pah!

Our main water entry from the street is at the risible pressure of 16lbs/sq.inch. The 'plumber' has kindly fitted a 12mm feed pipe from the meter to 'increase the pressure' - I don't think he understands the difference between flow and pressure or his a*s from his elbow.

Add to this a woefully undersized gas boiler that was selected on the basis of being small enough to fit where the architect wanted to put it - rather than being sized as sufficient for a family of 2 adults and 1 child - and there are some teeth-grinding moments.

But, hey (as I remind myself) - this is Mexico and standards are lower...



Feb 14, 2006, 8:35 AM

Post #5 of 9 (4313 views)


Re: [RexC] Help on New House

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In our house, the plumbing air vent is the flat roof drain - a four inch plastic pipe.

I am not too happy about the roof draining into the septic tank which is small, compared to USU standards.

ALSO, i AM CONFUSED ABOUT THE CORROSION COUPLE. i HAve heard the same thing about copper corroding. However, copper is more electrpositive than iron so it should be the iron which corrodes, not the copper.


Feb 14, 2006, 2:31 PM

Post #6 of 9 (4286 views)


Re: [patricio_lintz] Help on New House

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Patricio - Steel pipe also deteriorates when it is mixed with copper pipe, but it doesn’t seem to have the same severe deleterious effect on steel as it does on copper pipe. I have no idea why that is. I have removed steel pipe nipples that were screwed into copper or brass pipefittings, and even after only a few months they will always have a lot of corrosion inside on the end nearest that copper, they don’t seem leak like copper pipe does when it is affected by electrolysis though. I’m guessing that the corrosion within steel pipes may seal any microscopic leaks.

Steel and copper pipe should never be mixed without the use of an insulating union. They are called di-electric unions. You will see them used on the top of water heaters in homes nob to protect the heater and pipes from deteriorating. In Mexico, the “plumbers” always seem to connect the steel nipples on the top of water heaters directly to the copper pipes with no protective fittings. I’m sure most of them have no idea that electrolysis exists, what effect it has on metals, or what to do about it if they did know.

Storm water should never be drained into any sanitary sewerage system. I know that is a routine way to dispose of it here in Mexico. All the roof and patio drains on our house drain directly into the sanitary sewer. It is a severe hazard to public health to do it that way though. Evidently no competent authority has ever studied the effects it has though. And since there is virtually no accountability in this country, nobody in authority really gives a damn. In a municipal system a large influx of water will overload the system, and sewerage will not be properly treated before it must be released to allow room for more incoming sewage (and storm water) to the plant for treatment. A lot of the storm water also overflows onto the streets, carrying raw sewage with it. Storm water probably has an even more negative effect on sewage treatment if it is allowed to drain into a septic tank

A septic tank is actually a digester. When properly designed they will have at least one interior baffle to slow the digestive process down into two stages. It digests the solid organic waste in it; only a clear liquid effluent will be discharged in a properly designed and sized septic tank. No additives of any kind are ever necessary for a septic tank to work. All the microbes necessary for a septic system to function are already in your stomach.

When the effluent leaves the tank it enters the drain field, which is a field of horizontally laid pipes; either in short (12”) pipe segments, or perforated pipes. The effluent is disposed of by two actions. Either by percolation when it soaks into the ground, maybe it ends up in Lake Chapala, or by evaporation, when it migrates to the earth’s surface via capillary attraction, and evaporates. Theoretically a properly designed septic tank in a moderate climate will never need to be pumped out. In the real world, in a moderate climate, they will probably need to be pumped out about once every 20 years. In snow country or other harsh climates, they need to be pumped out annually.

A septic tank must be properly sized to work correctly. When I was a young man, we used tables to determine the size a septic tank should be, the engineering for the various standards in those tables had already been done, the size of the land determined whether or not a septic system could be installed, no percolation tests were done in the field. In the early 1950s in Napa County, California it was illegal to install a septic tank on any land less than 5 acres in size, that was later reduced to 1 acre lots, before they began doing field tests to determine if any lot was suitable for septic tank use.

Today in most areas nob, an engineer performs the calculations and most tests to determine the size of the tank required, and an engineer, or engineering aide performs and monitors the percolation tests to determine the absorption rate of the land to determine the length of the pipes in the drain field required. Among the things to be considered when sizing a septic system is the maximum legal occupancy of the dwelling, number of bathrooms, types of plumbing fixtures, automatic washing machine, dishwasher, garbage disposal, etc. A critical element is no guesswork.

While prefabricated fiberglass septic tanks are sold, most of them are built in place on the jobsite to a custom size.

Many Americans don’t realize how lucky and healthy they are that we have building codes in most areas up there now.


"The supreme happiness of life is the conviction that we are loved" - Victor Hugo


Feb 22, 2006, 8:21 AM

Post #7 of 9 (4192 views)


Re: [RexC] Help on New House

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I was aware of most of the issues with regard to draining roof water into the septic system. Fortunately, the sewer line is planned for extention to my street soon. Then, I can bypass the smallish septic tank and its seepage pit.


Feb 24, 2006, 8:07 AM

Post #8 of 9 (4147 views)


Re: [heathesq] Help on New House

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We took this thread off subject. I hope that you find your contractor.

Sabrina formerly of San Juan Materiales, builds custom homes for speculation. She had three for sale, all in VdL, Smithville. All of her houses are yellow. One just sold. It was advertised at $169,000 USD. The people just moved in. SHE LIVES IN THE BIG YELLOW HOUSE WITH THE PALAPA ON THE MIRADOR, ACROSS FROM THE MANAGERS OFFICE. Oops, I hit Bloq. Mayus.

Anyone have input for Roger & June?


Feb 15, 2007, 12:40 PM

Post #9 of 9 (4018 views)


Re: [RexC] Help on New House

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"Plastic pipe also has a large expansion rate. This was problematic for plastic pipe used in venting systems. The vent pipes would expand 3 or 4 inches during the day, and contract to their original length at night, breaking the waterproof seals on the roof flashings. A new type of waterproof roof flashing had to be designed with a neoprene seal and a counter flashing attached to the pipe."

Rex, in Canada we use a plastic slip/expansion joint at each floor on the main 3" stack.

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