Inspection of existing concrete homes in Mexico 1

[Kenton54]

I am a pre-purchase home inspector about to start inspecting homes in Mexican resort towns, most of which are concrete, most of which apparently gets mixed in the street in from of the home being built.
I'm 30 years in residential/light commercial construction so I have something of a handle on concrete, but I'm open to any suggestions about how to inspect an existing concrete home.

1. How can I tell if beach sand has been used for finings?
2. How to spot excessive organic material in the mix?
3. How to spot mud that's been poured when it was too hot without the use of retarding agents. (what're the proper retarding agents?)
4. What else should I look for?

Thanks,
Kent

 

[Qshake]

While I'm no expert on Mexican ready mix I would look for the following:

Beach sand - If on the Gulf coast, most sand is white thus I would expect to see with some rubbing of a wall fine grained, white sand if it was used. The pacific side is much more difficult since beach sand is more brown in color.

Organic material tends to be lightweight and in many cases will float to the top of the concrete causing pockets or pop-outs perhaps leaving some residue behind. Be on the look out for dark residual material in pockets.

Concrete poured during a hot day in a situation where it's mixed in front of the house with laborers and not truck mixed will have cold joints which may be discerned by color based on time set. Too much retarder and the concrete will appear to be very gray (greenish) in color for an extended period of time. It will be almost wet to the touch and much will rub loose relative to normal hardened concrete.

Other items to look for that cross my mind are lack of proper clearance on reinforcing - that is the reinforcing shows or the concrete cover is very thin in places.

Plumbness in walls and level in beams. Forms may not have been set/shored properly. Look for form blow-outs, areas where the forms bulged due to pressure of wet concrete.

Honeycombing of course - lack of good vibration/consolidation of concrete. It's not uncommon for concrete in those parts to go without or the usual substitute is to have laborers bang on the formwork with hammers.

I'm sure others will help out with additional concerns...



Regards,
Qshake

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[dik]

If it's like construction in third world countries, consider all the possible ways of hiding/disguising things and add two...

The items regarding aggregate can be tested using pertographic microscopic approach or chemical approach. You can test for chloride ions or other deleterious material using chemical means. I've used phenothalein for testing for chloride penetration for parking structures... might be a simple test for sea salt (I've never worked with this). Organics can be tested by weighing and oxidizing... Other than that, best approach is visual and a very strong qualifier that the review is visual only and that there may be latent defects not possible to determine using normal means...

Dik

 

[cvg]

I would also try to discern if the walls are reinforced or not and the amount of reinforcement. Since most of Mexico is at risk from earthquakes, an unreinforced concrete wall is an extreme liability.

 

[Kenton54]

I'd like to determine the presence of rebar but other than spending a lot of money on equipment that can scan trhough concrete, I don't know of any good way. -Kent

 

[cvg]

well, if your client is willing to gamble on buying an unreinforced concrete wall, then I guess the equipment would be too expensive. However, your more educated clients may be willing to pay some peace of mind. What about insurance? Won't an insurance company be interested in knowing that the structure is unreinforced? Maybe you can find a subcontractor to do the work.

How about using a metal detector?

 

[Kenton54]

At this point, there are people spending millions of dollars on homes in Mexico wtih no inspections at all. When I querried realtors and lenders looking for work inspecting homes in Mexico, they didn't know what I was talking about. So a lot of what seems to go on down there makes little sense.

 

[cvg]

well, I think I would at least test out a simple metal detector and see if it will pick up rebar. Also look for other seismic design features such as sill anchors, shear walls, wall to rafter ties, etc. If these are present, I would suspect that the concrete would also be reinforced. I would also present some data to the customer indicating what the seismic risk is and see if that doesn't elicit a response.

 

[Kenton54]

Metal detector is worth a try and I have one, good idea. Home will usually be complete by the time I see them, but it's sometimes possible to see things.

 

[boo1]

If its in a developement, look at the other homes being build you can learn a lot before it is covered up.

 

[Kenton54]

Some of them may be, there are starting to be some high-end developments down there, but I expect most to be custom and complete.

 

[henri2]

When conducting a home inspection in the United States, typical tasks and inspection checklists are usually consistent with ASHI standards of practice

http://www.ashi.org/inspectors/standards/standards.asp#Introduction

. For standards of practice used in different states where home inspection is regulated start with this link

http://www.homeinspectionexam.org/regulations.html

Section 3 of the ASHI standards deals with the structural system. Home inspection is basically a non-invasive visual examination and does not include structural engineering evaluation. This this is dealt with in Section 3.2. If you do not have a background in structural condition evaluation survey and structural design, consider teaming up with an engineer who does, and then offer this as part of your service.

I understand that US based home inspectors have been performing home inspections in mexican resort communities..and some have now even set up operation in mexico. Have you contacted any of them to discuss challenges etc?

 

[Kenton54]

I've been looking online for expatriot Inspectors working in Mexico or even Inspectors working out of the US and flying down with absolutely no luck. I did find one Inspector online near Guadalajara, but the e-mail address is no good.

I'm 30 years in residential construction so I have a pretty good idea where and how to look for problems... and when to recommend an engineer. I've worked with a number over the years.

ASHI, NAHI and NACHI Standards are all pretty similar and while I haven't studied them all in detail, I think they were all written with protecting clients while limiting Inspector Liability in mind.
Yes it's non invasive and not technically exhaustive but I still use a moistue meter with probes (among other instruments) and also offer resistograph testing.
-Kent