Vapor Barrier Under Slab

[Iolare]

My site is being cleared and temporary worker housing is being built today. Excavation starts after the King’s birthday holiday this week, with footings being poured starting next week. About 1/3 of the house will be concrete slab on grade, and the other 2/3 will be on columns. The portion on columns will effectively be a walk out basement (the site slopes) and will have a cement floor as well.

I’ll be meeting with the builder and engineer this week to make sure we’re all on the same page before we start relative to moisture control. The plans call for compacted sand over the dirt then the concrete slab. I’m planning on installing 6 mil polyethylene between the sand and the concrete. I’ve heard of putting it between the dirt and the sand instead. What’s best here in Thailand?

There will be a retaining wall at that portion of the structure where slab on grade becomes pre stressed slab on columns. I’m planning on talking to the guys about perforated PVC drainage pipes in gravel behind the retaining wall and poly sheet there too.

I’ve finally decided against any wood floors, choosing tile and stone instead. I’ve seen too much cupping of wood floors here, not to mention the termite problem. But even though there will be no wood floors in the house, I want to be sure that it is a dry house. I don’t want to be contending with mold and mildew or extra insect problems due to dampness.

Also, has anyone used a crystalline waterproofing sealer on concrete like Yypex? Maybe that before paint on the basement walls and even on the rough floor before finish tiling?

This would be the time for an insecticide tube system and / or termite treatment of the earth. I’ve heard some say it’s a must do, and others say that the tubes plug up after a few years. Any advice?

Your experiences and advice would be appreciated.

[Iolare]

OK....Let me be the first to say it. It is kind of a boring topic. I think I’ve got a handle on it anyway, and I’ve selected a good builder. So, for those of you who used to play sports, just chalk it up to pre-game jitters. Sorry I posted it.

[teacup]

Well from my experience

I just finished building my house and used 8 mil between the sand and concrete slab as a vapor barrier. I was thinking of going thinner like 6 mil, but the problem is that some of sand particles may have some sharp angles that might puncture through it, so we opted out for a thicker mil instead.

The first challange's how to find a one piece that big enough to cover our 3 car garage space. So if you have to use more than one big piece, just make sure you overlap them in the same direction of how you want to pour the concrete, thus preventing the concrete from going underneath the plastic during pouring.

The second caution I can see with our garage slab is that, with the plastic sheeting underneath, it will take longer time for the slab to cure and dryout completely, so there was no walking on it for us for at least 3-4 week. The good thing is that with this slow curing of the slab, your slab will be stronger than a quick drying slab

[jaideeguy]

Just DO it!!! my first house, the contractor didn't do it [to save a few bhatt?] and now, 7 yrs later i've repainted walls for the third time and blisters are reappearing. the blisters come up less than a meter high and now the only recourse i can think of is to panel [wainscoating] the lower portion of our walls....not a cheap or easy solution, but the only one i can come up with and that opens a whole other can of worms with giving the ants and termites a nice place to inhabit.

any suggestions appreciated

[callao]

Just DO it!!! my first house, the contractor didn't do it [to save a few bhatt?] and now, 7 yrs later i've repainted walls for the third time and blisters are reappearing. the blisters come up less than a meter high and now the only recourse i can think of is to panel [wainscoating] the lower portion of our walls....not a cheap or easy solution, but the only one i can come up with and that opens a whole other can of worms with giving the ants and termites a nice place to inhabit.

any suggestions appreciated

when putting a moisture barrier under the slab typically you would want to put about 4 inches of drainrock ( washed 3/4 inch, no fines) then your moisture barrierthen 1 or 2 inches of sand over that, the drain rock will keep the water level under the slab down to where it shouldn't ever get up to the bottom of slab elevation, just putting it between dirt and sand won't do a very good job I don't think Callao

[callao]

My site is being cleared and temporary worker housing is being built today. Excavation starts after the King's birthday holiday this week, with footings being poured starting next week. About 1/3 of the house will be concrete slab on grade, and the other 2/3 will be on columns. The portion on columns will effectively be a walk out basement (the site slopes) and will have a cement floor as well.

I'll be meeting with the builder and engineer this week to make sure we're all on the same page before we start relative to moisture control. The plans call for compacted sand over the dirt then the concrete slab. I'm planning on installing 6 mil polyethylene between the sand and the concrete. I've heard of putting it between the dirt and the sand instead. What's best here in Thailand?

There will be a retaining wall at that portion of the structure where slab on grade becomes pre stressed slab on columns. I'm planning on talking to the guys about perforated PVC drainage pipes in gravel behind the retaining wall and poly sheet there too.

I've finally decided against any wood floors, choosing tile and stone instead. I've seen too much cupping of wood floors here, not to mention the termite problem. But even though there will be no wood floors in the house, I want to be sure that it is a dry house. I don't want to be contending with mold and mildew or extra insect problems due to dampness.

Also, has anyone used a crystalline waterproofing sealer on concrete like Yypex? Maybe that before paint on the basement walls and even on the rough floor before finish tiling?

This would be the time for an insecticide tube system and / or termite treatment of the earth. I've heard some say it's a must do, and others say that the tubes plug up after a few years. Any advice?

Your experiences and advice would be appreciated.

just to add to my previous reply the drain rock is the key to the moisture barrier working properly, water that does get under there will be able to fill up the rock area and dissapate slowly and putting the visqueen over the rock and under a small amoint of sand will allow the concrete to dry more naturally, pouring right over the visqueen sometimes will make the concrete get spiderweb type cracking, rebar mat or wiremesh in your slab will help if you do get some cracks in your slab they can't move, and for a basement there are additives available here in the US that you can add to the concrete to waterproof it more ( don't know about LOS) but the main thing is to have a drain behind the wall and to waterproof the outside of the wall the best you can, there are cement based waterproofing (thermoseal) or the old fashion way of using asphant base roofing mastic on the wall putting a drainrock field in with perferated pipe 4-6 inches BELOW your floor elevation (perferations down) and backfill with drainrock up the wall to -12inches from FG, and using either some fabric ( mirifi 140 G) or some roofing paper between the dirt and the drainrock and cover tthe top of the rock the same way , that is so the when there is water behind there the silts and clays that get into thae water cannot migrate into your drain rock and clog it up and make sure you connect your drainpipes to solid pipe to daylight so the water can work its way out before it starts to build up behind there , I'm a guy with 20 years of doing this types of foundation work so hope this helps, Callao, I'll be buiding a place outside Vientiane this year

[hgvneil]

now im lost

[Iolare]

We’re underway now and the pre-game jitters are over. Thanks for those tips Callao, and to Teacup for his too. I’ve arranged for the heavier poly sheeting. I like your system with the with a couple of inches of rock under the plastic. I plan on two horizontal perforated pipes behind the retaining wall, one below floor level, and one about half way up the wall. I plan on waterproofing both sides of the basement wall and will probably use the product Yypex. Since the lot slopes, I can run the perforated drain pipes to open air and into drain channels that will be part of the overall drainage scheme for the site. With all the rain we get, this stuff in important.

Here’s an idea related to the drainage pipes. Considering that they will be open to the air, then will travel deeply underground, what about “T”ing in a couple of vertical tubes that would terminate in the house as floor or wall grates? The house will have air conditioning units, but most of the time I plan on open doors and windows with good convective ventilation. Is it possible to achieve a slightly lower than ambient temperature in the house due to air passing through the cool soil before entering the house? I would insect screen both ends to keep critters out. What do you guys think?