Anyone have experience with a "Foam Concrete Moisture Barrier"?

Forums › Home Workshop DIY › Anyone have experience with a "Foam Concrete Moisture Barrier"?

nzfrosty

3 posts

Wannabe Geek

#296326 8-Jun-2022 12:55

Hey Team,

We have a 1920's bungalow that has timber floor and concrete piles. I'm wanting to put in some underfloor insulation and a moisture barrier. Unfortunately there isn't enough space to get under the house to do this.

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. This feels like it might sit in the same camp?

Keen to hear your opinions.

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6477 posts

Uber Geek

Subscriber

#2923937 8-Jun-2022 13:24

What sort of soil do you have? How much clearance is there? Are you going by ground level outside or have you eyeballed under the house?

A neighbour was sure his house was almost sitting on the ground but found the ground level outside was 400 - 500mm higher than under the floor. He had being preparing to lift the house but all it took was a day with a bobcat lowering the outside.

nzfrosty

3 posts

Wannabe Geek

#2923941 8-Jun-2022 13:43

I've stuck my head though the man hole and I definitely couldn't fit between the joists and the ground. I've also had someone come around for a quote on traditional insulation + barrier and they said the same thing about there not being enough room, and likely a trench would need to be dug to get under there.

I'm pretty sure its just clay under there, just from looking though the man hole.

tweake

2391 posts

Uber Geek

#2923951 8-Jun-2022 13:56

interesting stuff i have not seen that before.

its a cement/sand with a foaming agent thats poured over the ground. i would check what its permeability actually is. its not the usual closed cell foam that people complain about, which would work very well and is often used in new construction (overseas).

the obvious drawback is you need a fairly flat ground to pour it onto. i wonder what the set time is.

wellygary

8312 posts

Uber Geek

#2923952 8-Jun-2022 13:57

Do you have a damp problem??

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

just remember its not insulation its essentially a way to lay down a plastic sheet on the ground you cannot get access to

bigmacpaddy

71 posts

Master Geek

#2923953 8-Jun-2022 13:59

I hadn't seen a solution for this before. I've had insulmax in the walls and no issues with that. But i also can't get under the house to put a moisture barrier down.

Will be interesting if anyone has any comments or info.

tweake

2391 posts

Uber Geek

#2923965 8-Jun-2022 14:16

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.

tweake

2391 posts

Uber Geek

#2923967 8-Jun-2022 14:20

bigmacpaddy:

I hadn't seen a solution for this before. I've had insulmax in the walls and no issues with that.

thats not something i would do, but then again you probably won't be there when that fails.

even branz doesn't recommend it anymore.

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wellygary

8312 posts

Uber Geek

#2923976 8-Jun-2022 14:39

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.

Aren't the Vents in the outside of the house at ground level there to prevent that by having a constant airflow under the house, resulting in the air under the house being the same humidity level as the general atmosphere,

tweake

2391 posts

Uber Geek

#2924005 8-Jun-2022 16:03

wellygary:

Aren't the Vents in the outside of the house at ground level there to prevent that by having a constant airflow under the house, resulting in the air under the house being the same humidity level as the general atmosphere,

they are meant to, but in reality it doesn't work very well. there is simply not enough constant airflow (for our humidity) and you also fighting stack effect as well. ie it wants to go up not sideways and all that wood work is a sponge.

i have an 80's house, so proper height, vents etc and yet when i did the ground barrier there was a big drop in condensation in the house. thats with sheet flooring which has a whole lot less gaps than plank flooring. that tells me the vents don't do much.

insane

3236 posts

Uber Geek

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#2924074 8-Jun-2022 20:13

This product sounds brilliant for those that have a tight crawlspace. I'd be doing this if I were in the same situation, but would also run my moisture metre over what I could reach through the vents to check how damp it really is before and after.

I now have a polythene barrier and underfloor insulation - it did make a difference compared to when I had nothing.

mattwnz

20141 posts

Uber Geek

#2924087 8-Jun-2022 20:55

So if it doesn't cover 100% what happens to ground moisture if there are any holes?. Holes in polythene sheeting isn't generally a problem as there is usually a lot of space under the floor to ventilate it. The problem with some foams is that they can shrink over time and you could then get gaps it may not then have any access to airflow. I would get some professional advice over it.

mattwnz

20141 posts

Uber Geek

#2924088 8-Jun-2022 20:58

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.

Has BRANZ or anyone else done any research into this?

insane

3236 posts

Uber Geek

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#2924092 8-Jun-2022 21:02

Their website says branz appraised. Whatever that means...

tweake

2391 posts

Uber Geek

#2924099 8-Jun-2022 21:22

mattwnz: So if it doesn't cover 100% what happens to ground moisture if there are any holes?. Holes in polythene sheeting isn't generally a problem as there is usually a lot of space under the floor to ventilate it. The problem with some foams is that they can shrink over time and you could then get gaps it may not then have any access to airflow. I would get some professional advice over it.

it doesn't matter to much. if you get 90% coverage you get 90% reduction in moisture coming off. the 10% left is easily dealt with by normal ventilation.

one down side is blown in rain or water from leaking pipes. at least with poly you just poke holes in the low spots and it drains away (or even better drill holes while its till wrapped on the roll). with concrete/foam it may puddle.

tweake

2391 posts

Uber Geek

#2924104 8-Jun-2022 21:26

mattwnz:
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.

Has BRANZ or anyone else done any research into this?

yes branz has done some. i've read the early report (which is where the fique's come from), i'm told there is a more recent one which i have yet to read.

btw the 1 litres per 10sqm is per day. so with a 100sqm house there is 10 litres of water evaporating out of the soil every single day.

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