Chile Forum

Fine with me, but if anyone else (maybe Jason?) has comments on damp-proofing I'd appreciate a post . For me there wouldn't be much water to collect, since it rains so little (and my space for storage is very limited), but it surely makes sense further South. In the ideal case, I suppose damp-proofing comes into play where you need something that should be humid (grass roots) up against something that shouldn't (concrete) and water management does the rest.

James.

well the problem with all concrete is it that water moves through it if it is not sealed in some form. Just the temp difference inside your house to the ground will draw the moisture through if it is not sealed. You don't need to run a hose outside for it to move water.

Ah yes, obvious once you mention it but very easy to overlook.

Sorry, I haven't got around to posting on this yet. We had the company Christmas party on the weekend and I have the ceiling texture guy coming this Friday to finish my basement and the carpet going in on Monday, plus my usual 9-5 job, so things have been a little hectic.

With out making it sound like it is a hopeless situation the damage is already done. The ground under your house has moisture in it naturally, so you are going to get the wicking no matter what unless they put gravel or some sort of poly down before they poured the concrete, but you can still minimize the amount of water that is being drawn into the walls.

Looking at the picture you posted best solution would be to use one of the spray products (if they are available) or 2 coats of tar with a brush to make sure you get 100% coverage. Then weeping tile wrapped in filter cloth then bury it in gravel, as was mentioned before. You can skip the weeping tile if you want but then you are relying on the heat to evaporate the water from the bottom of your trench and it is going to stay a bit cooler in the trench because it is full of gravel and the sun won't get to it, so now you have the problem of where that water is going to go. It really is a tough problem to solve with out spending a fair bit of money on it.

But anything you can do to minimize the amount of water touching the foundation the better.

Thanks, Jason, for taking some time out to comment when you're so busy. Peoples' posts here have been quite helpful in getting my head around the problem.

What you say obviously isn't great news, but it's good to recognize the limitations I'm working against and I'm still optimistic about improving things to an acceptable point. Even slapping some tar on the footing must put us in a better position than most of the surrounding 100 houses (which are considered locally to be well built!)...

So does anyone know whether weeping tile and geotextile filter cloth are available at Sodimac/Easy and what they're called in Spanish? I take it the idea of the geotextile is to prevent the drain tile from getting clogged with dirt (rather than acting as an impermeable guide for the water)? I'm still not sure whether it's practical for me to install drainage without consulting someone about the retaining wall, but I'll think about it some more...

j. Ro wrote:But anything you can do to minimize the amount of water touching the foundation the better.

Yes, that's really where I'm coming from. The damage doesn't look substantial yet (just paintwork), but better slow it down as much as possible...

I was originally perplexed that my bank's survey said "useful lifetime: 40 years" for a new building when we have many less solid structures hundreds of years old in Britain, but perhaps I'm beginning to understand now...

James.

Hi!

Now looked more in detail at your photo. Looks like the concrete was dumped into the ground directly without any moulds. The irregularities on the surface of the concrete will increase the total surface area that is in contact with soil and water and acts like a sponge. 2 layers of tar should help in this case. However you will have moisture creeping up a bit from the bottom. Making your trench 50-100mm deeper than the base and filling this with coarse gravel should help. You should be able to buy filter cloth. Believe it or not it is actually used here in some cases. Install the cloth in your trench , fill with coarse gravel, cover the top with the same cloth and then add your final layer of soil.

Thanks, Gringo. My thinking was going much along the same lines, so it's good to have an accordant opinion.

I'm a bit wary about excavating past the bottom of the footing though, in case any material gets destabilized from underneath, eg. when washing down the front to clean it before tarring. I know from past experience that soil under a heavy weight isn't that easy to displace accidentally, but once a bit of soil is loose it will never provide support again... which in bulk would be a much bigger problem than the damp! What you say certainly makes sense though and I might go a bit deeper to help avoid this. I should find out how deep the footing really is.

I also had a crazy idea about tilting an impermeable membrane away from the wall so water can't drain onto the footing, but I suppose it would also trap damp from underneath when the seasonal temperature changes (and if it worked, it would already be a known technique).

Cheers,

James.

Hi!

You dont have to excavate below the footing right beside it. You can do it around 5-10 cm away from the footing when you get to the bottom. It may be a better idea to dig down only to the bottom, wash and then dig the final part.

I worked my way through my early years of college as a partner in a landscaping company that did a lot of drain tile along with retaining walls.

first, geotextile and draintile can be found at sodimac. In fact I seen it in my sodimac constructor's catalog just the other day (available at the help desk for 2,000 pesos by the way), but can not seem to find it now. geotextile is the same in Spanish, drain tile has a different name. Neither was very expensive. you can always make your own with pvs pipe and punch holes with either a drill or saw. still, the real stuff is easier.

Generally for laying drain tile you lay plastic in the bottom, overlapping it up and out the sides, to create more of a drain. Against a house I am not sure if the plastic is needed, but that is your intent anyway to capture and get the water away from the house and block it from being absorbed. don't think it would hurt. You dump gravel / river rock on top of that tile filling the trench and hiding the drain tile (i.e. it just looks nice too).The geotextile is more for stopping the tile from clogging over time, but with just 1-2 inch river gravel on top and a tile that is say 1 foot underground (wherever your footing is )it really should not be that big a problem.

I made a pile of money off of laying drain tile back in those days. Our cost was something like .50 a foot (labor included), and we charged $25 a foot. We made more money off of drain tile than decks and porches, retaining walls, sidewalks, and just about everything else we did because it was so easy to do and the margins were so big on it. We could loose our shirt building a deck or retaining wall we bid incorrectly, and make up for it on the drain tile we laid around it.

So I dug the trench a bit deeper, to around the bottom of the footing (~70cm). Then my neighbour and I went up to the building site, found one of the brothers that owns the construction company, explained that their office had been saying they'll send someone for months and asked him to come and look at our damp. He agreed to help out and the next morning the builders came past with a power washer to help clean up the front of the concrete. Then today they stopped by and smothered the footing with a thick layer of tar in about 10 minutes flat using a motorized fumigator. Tomorrow they are supposed to bring me a cubic metre or so of gravel to back-fill the trench, bring a machine to strip the paint off the bottom of the wall so we can seal it with penetrant sealer and take away the soil I've dug up. Things have therefore been progressing a bit faster . Much easier with the right industrial equipment.

What's more, the owner admitted that there's supposed to be an impermeabilizante (Cave Fugo) directly mixed into the concrete of the "sobrecimientos" but that the maestro's don't always do it properly, so now he's taken to overseeing the mixing in one of his large trucks . That would probably explain the problem...

James.

I thought I'd post a better summary of damp-proofing products for masonry, as my initial conclusions weren't 100% accurate. There are a lot of different things on the shelves, but it seems to me that they mainly fall into 3 categories. Bear in mind that this is just a bit of homeowner's research with some speculation thrown in:

Non-breathable impermeabilizantes (impermeable, film-forming sealants, eg. Sipa Water Proof, a water-based acrylic sealant). These produce a glossy surface that doesn't let water in, but also doesn't let water vapour out, which seems like a Bad Thing. Conveniently, it can be applied over paint (but not overpainted), helping protect the paint from bubbling due to moisture, but then your rising damp basically just keeps rising and appears further up the wall. Sooner or later, the impermeable film is going to get some cracks or holes in it (eg. from abrasion or seismic movements) and then you have a nice surface that lets water in but doesn't let vapour out -- oops. The damp may then have to escape from the interior walls. So for above-ground use I would generally prefer something breathable. Below ground (where preventing water absorption is presumably the main concern), asphalt paint seems like a good option as a durable, elastic, impermeable barrier.

Bloqueadores de humedad (eg. Chilcorrofin ImperBlock, Sika Igol Sellamuro). These are also film-forming sealants, but they are described as being permeable to water vapour and gases (or "poro abierto"). The data sheets say they are acrylic or "synthetic" resins. They can usually be overpainted and the instructions only suggest removing existing paint if it's in poor condition. Different types of bloqueadores are sold for indoor and outdoor use, including a type that resists the negative pressure from damp coming through the interior wall from outside (sounds like a band-aid solution, but useful if you can't easily solve the problem). My impression is that the distinguishing characteristic of a "bloqueador de humedad" is its ability to adhere to the substrate under pressure from water and salts, holding back efflorescence. These are 15-25k /gallon.

Hidrorepelentes (eg. Cave Clear-S, Sika Igol Transparente). These are what US literature calls penetrants. They are not film forming but simply block the pores in the masonry to prevent liquid water entering. I believe they are the most breathable type of sealant and should be durable since they're not just a superficial film. They seem less common here, but you can find them on the shelves if you know what to look for. Most can be overpainted. Although I have read that penetrants should be applied to unpainted surfaces to allow absorption, as you'd expect, the instructions for the Chilean products don't say to remove existing paint unless it's in poor condition. Cave Clear-S is siloxane. From the Cave web site, they also have Clear-A, which is siliconate. Igol Transparente is silicon. There is also Igol Incoloro, which is hard to classify as the active ingredient is unspecified, but sounds more like a bloqueador de humedad. The only product I can find containing silanes as well as siloxanes is BASF/Degussa Masterseal SA (via Google), but who knows where you can actually buy that -- seems like the Clear-S should be good enough. The penetrants are highly volatile and the recommended method of application is with a fumigator-type (garden) spray. They are actually cheaper per gallon at $7-12k (Cave is $5k more in Easy than elsewhere), but each tin only covers a few square metres. They are sold as "reducing efflorescence" rather than blocking it, but maximizing breathability seems like a key consideration, so these look to me like the best approach for avoiding above-ground water absorption.

You can read a comparison in Spanish of the properties of different penetrants/sealant compounds here:

http://www.arqhys.com/arquitectura/sell ... migon.html

I have read one site claiming that organic penetrants don't last longer than a decade or so before breaking down and recommending RTV silicone rubber instead, but good luck finding that in Chile...

Cheers,

James.