Looks interesting. Although once it's there, there is no going back. 

nzfrosty:

I've been doing some googling for possible solutions and came across foam concrete moisture barrier. (https://www.foamconcrete.nz/ground-moisture-barrier/) Apparently they spray it into the vents on the foundation and can get about 95% coverage, and is about 50-75mm thick. Has anyone else had done this before? Every time I read about liquid foam being sprayed into houses for things like insulation, it is normally negative.

neb:  I can't imagine its waterproofing abilities are very good. Whatever this stuff is it's not what's normally meant by foamed concrete.

That's something I have also been thinking as I look into this more. When laying down concrete aren't you supposed to put down a moisture barrier under the concrete to protect it? Sounds like it defeats the purpose of a concrete moisture barrier

tweake:

 

wellygary:

 

Do you have a damp problem??

 

if it is dry under the house there is probably not much to be gained sealing it....

 

 

thats actually a common myth.

 

if the ground is dry it means the moisture is evaporating out if it into the air. then that damp air migrates into the house either directly through the gaps in the floor (big problem on older homes), or the moisture soaks into the wood work and migrates through the wood and evaporates back out into the house. stack effect, it all wants to go up. common soils evaporate about 1-2 litres per 10sqm (according to the old study, i have not seen the newer study someone mentioned its even higher).

 

if the ground is wet then you have drainage issues.

 

That's interesting. The ground underneath our 100yo bungalow is bone dry... However there are vents all around so I expected no vapour could form or migrate upwards through the floorboards.

neb: Foamed/aerated concrete (technically autoclaved aerated concrete) is a very widely-used building material in Europe, combining concrete's strength with light weight and good insulating properties. However it's used as concrete blocks, not poured under a house, I can't imagine its waterproofing abilities are very good. Whatever this stuff is it's not what's normally meant by foamed concrete.

It used here too. Hebel is one product which is an autoclave aerated concrete block product.  I don't know much about it, I only came across it because a friend had their house clad with it.  IIRC it did have to be coated.

johno1234:

 

tweake:

 

thats actually a common myth.

 

if the ground is dry it means the moisture is evaporating out if it into the air. then that damp air migrates into the house either directly through the gaps in the floor (big problem on older homes), or the moisture soaks into the wood work and migrates through the wood and evaporates back out into the house. stack effect, it all wants to go up. common soils evaporate about 1-2 litres per 10sqm (according to the old study, i have not seen the newer study someone mentioned its even higher).

 

if the ground is wet then you have drainage issues.

 

 

That's interesting. The ground underneath our 100yo bungalow is bone dry... However there are vents all around so I expected no vapour could form or migrate upwards through the floorboards.

 

 

 

as i said thats a common myth.

this is why a ground moisture barrier is a healthy home requirement. 

Bung: You could try putting a sheet of paper on the ground and covering it with some plastic. If there was any appreciable condensation the paper would get damp.

I've got bone dry sand under the house and good vents. I've pushed some of the sand around to give access while insulating. As yet I'm not convinced that levelling it so I could put plastic down would be worth the trouble.

the common test is to put 1sqm sheet of plastic down and seal it to the ground/floor/material. leave it over night i think it is (can't recall how long its meant to be left) and check for condensation on it. poor man version is put down a rubbish bag, weights around the edge, leave it for a week. not only condensation on the plastic but the ground is wet under it.

some areas, like sandy soils may be so dry that its not really an issue. but then again sand is really easy to smooth over. just lay plastic down and pin it, which is quick. its when your fussy and tape/seal everything that it takes a long time.

however be aware the stupid govt standard is for it to be sealed and no holes, which is stupid (pen pushes for ya). you always want drain holes and it needs to be pinned down so wind doesn't flap it around.

nzfrosty:

 

neb:  I can't imagine its waterproofing abilities are very good. Whatever this stuff is it's not what's normally meant by foamed concrete.

 

 

 

That's something I have also been thinking as I look into this more. When laying down concrete aren't you supposed to put down a moisture barrier under the concrete to protect it? Sounds like it defeats the purpose of a concrete moisture barrier

 

Plastic is put down underneath concrete slabs as a moisture barrier (because normal concrete is porous) in the same way that plastic is retrofitted under timber floor houses to stop rising damp. No need to 'protect' the concrete, so things like concrete driveways don't have plastic underneath (or if they do it's about the curing process).

I would assume that this foaming concrete stuff has additives which make it watertight otherwise it would be wholly unfit for purpose