Slip planes in concrete block construction and radon barrier

captainZZZ

I've noticed that it is important to avoid creating slip planes by not having DPC in contact with the radon barrier, (where the radon barrier passes through the inner leaf).

In homebond building manual it states that when a DPM is used, the DPM should lap under DPC for full thicness of inner leaf

My question is:

So why isn't a slip plane created when the DPM is lapped under DPC

Is it because a DPM is lighter than radon barrier?

Mellor

captainZZZ wrote: »

I've noticed that it is important to avoid creating slip planes by not having DPC in contact with the radon barrier, (where the radon barrier passes through the inner leaf).

In homebond building manual it states that when a DPM is used, the DPM should lap under DPC for full thicness of inner leaf

My question is:

So why isn't a slip plane created when the DPM is lapped under DPC

Is it because a DPM is lighter than radon barrier?

Where does Home bound say this. Can somebody link to the diagram (I don't have my copy). I don't remember seeing them lapped in the main detail.

The DPM is essentially the radon barrier. There is rarely separate layers used. DPMs are obsolete now because of the need for RBs, if it is gas tight, then its water tight etc.

captainZZZ

Hi Mellor,

Its on page 37 of the fifth edition, Damp proof membrane is the title of the page. Not sure what page it is on in the current edition of HB manual.

Yea,the radon barrier acts as a DPM now and most/all manufactures say - avoid creating a slip plane - dont have the radon barrier in contact with the DPC.

But lets say we are not using a Radon barrier, we are just using a DPM

then the correct detail is to run DPM up between the block and the perimeter insulation and across the inner leaf, then roll out the DPC on the inner leaf
( now the DPC is on the the DPM)

So why isn't a slip plane formed here?

Mellor

captainZZZ wrote: »

Hi Mellor,

Its on page 37 of the fifth edition, Damp proof membrane is the title of the page. Not sure what page it is on in the current edition of HB manual.

I said I don't have my copy here, so the page is hardly going to help.

But lets say we are not using a Radon barrier, we are just using a DPM

You always have a Radon barrier in domestic construction.

then the correct detail is to run DPM up between the block and the perimeter insulation and across the inner leaf, then roll out the DPC on the inner leaf
( now the DPC is on the the DPM)

So why isn't a slip plane formed here?

This also isn't the correct detail????

The DPM radon barrier goes up and over inner leaf first block.
DPC goes in outer leaf. If you think about the function of what each piece does thne what you suggesting makes little sense

captainZZZ

Mellor wrote: »

The DPM radon barrier goes up and over inner leaf first block.
DPC goes in outer leaf. If you think about the function of what each piece does thne what you suggesting makes little sense

There should always be DPC in the inner leaf, even when a radon barrier is used

The radon barrier can be brought over the first block as you have suggested, but this is'nt the best way to install a radon barrier. If it is brought over the first block the screed and the power float will cut the radon barrier so whats the point in putting it in? it no longer gas/water tight and cant be repaired because the floor is in. Also If it is done like this, then the inner leaf DPC must now be laid on the Radon barrier and a slip plane is created.

The best way is to have the radon barrier go up and over a soap bar in the inner leaf, put another soap bar on that. Now the radon barrier is protected. Then the floor is poured and finished. when the block layer is building the walls above floor level , the inner leaf + outer leaf DPC is rolled out and the walls are built. This method is most suited to the way houses are normally built in Ireland

The detail can be seen here in this, page 5 Fig 6.

http://www2.dupont.com/Tyvek_Construction/en_IE/assets/downloads/iab_02_0154_realshield_radon_plus.pdf



When a DPM is used instead of a radon barrier it must be lapped under the inner leaf DPC.

Haven't got the homebond diagram for you but this is the same detail , its on Page 3, 2nd diagram

http://www.nhbc.co.uk/NHBCPublications/LiteratureLibrary/Technical/filedownload,21417,en.pdf

Sure this isn't seen much anymore because a radon barrier is used in every house. But if a large garage was being built, there is no need to use a radon barrier, a DPM can be used and the correct detail is to lap it under the inner leaf DPC.

And thats why I'm wondering, why isn't a slip plane created here?
or maybe slip planes aren't such a big deal after all.

sydthebeat

theres a 'slip plane' created when ever a plastic membrane is placed in a block course. the weight of the build holds up the structure.

that tyvek detail doesnt really make any practical sense. Usually the inner leaf block is used as the screeding course, especially when using a power floated screed. theres nothing stopping the radon membrane being used as the inner leaf dpc course. If you do this you dont use a secondary dpc straight on top of the membrane.

in my years of inspecting builds ive NEVER seen a radon membrane cut from a power floater.... seriously. All you have to do is lay the next inner block course!! Every power floater ive seen has a disk protector which is probably 20mm outside the blades reach. you just direct the floater with a bit of elbow grease.

notwithstanding the above, its highly debatable whether a plastic on plastic course actually effect a cavity all build in any way, personally i cant see how it would.

Mellor

captainZZZ wrote: »

There should always be DPC in the inner leaf, even when a radon barrier is used

The RB/DRM etc acts as a DPC also. Forget about names and consider function and materials used.

The radon barrier can be brought over the first block as you have suggested, but this is'nt the best way to install a radon barrier. If it is brought over the first block the screed and the power float will cut the radon barrier so whats the point in putting it in? it no longer gas/water tight and cant be repaired because the floor is in. Also If it is done like this, then the inner leaf DPC must now be laid on the Radon barrier and a slip plane is created.

If you install it right it won't be damaged. I've seen plenty of RBs ripped, torn, cyt etc and it was never from a power floater. Normally carelessness in other areas.

The best way is to have the radon barrier go up and over a soap bar in the inner leaf, put another soap bar on that. Now the radon barrier is protected. Then the floor is poured and finished. when the block layer is building the walls above floor level , the inner leaf + outer leaf DPC is rolled out and the walls are built. This method is most suited to the way houses are normally built in Ireland

The detail can be seen here in this, page 5 Fig 6.

http://www2.dupont.com/Tyvek_Construction/en_IE/assets/downloads/iab_02_0154_realshield_radon_plus.pdf

That detail makes little sence. What is the DPC, as shown, actually doing?
Nice bit of marketing from Tyvek, they jsut doubled DPC sales.

When a DPM is used instead of a radon barrier it must be lapped under the inner leaf DPC.

Haven't got the homebond diagram for you but this is the same detail , its on Page 3, 2nd diagram

http://www.nhbc.co.uk/NHBCPublications/LiteratureLibrary/Technical/filedownload,21417,en.pdf

Where the DPM doesn't extend fully over the leaf, a DPC is needed, obviously. But there is no reason to install a DPM like this. Typical RB detail is perfectly acceptable.

SRV

sydthebeat wrote: »

in my years of inspecting builds ive NEVER seen a radon membrane cut from a power floater.... seriously. All you have to do is lay the next inner block course!! Every power floater ive seen has a disk protector which is probably 20mm outside the blades reach. you just direct the floater with a bit of elbow grease.

Hi, would you please explain what you mean by this?

thanks very much..........

sydthebeat

if you are worried about the floater cutting the membrane, just lay the next course of blocks on the inner leaf and use this course as your guide when floating.

it can be down without laying this course, if you are confident enough of being able to guide the floater without going "over the line" of the inner leaf.

SRV

sorry, my knowledge is limited so im having difficulty understanding...........

i thought the power screed first passes over the inner leaf/membrane..........then the power floater before the slab has fully set?

how can i screed if the inner leaf is a row higher?

Does the power screed damage the membrane at all?

In fact, as im here, how does one screed a 31 foot floor slab?

Whats the process? I searched the forum but cannot find much on this.

thank you for your help.:)

sydthebeat

the inner leaf is *usually* used as the level to screed off. Therefore the finished floor level will be the same as the top of the inner leaf block prior to pouring. The screed is *usually* not poured 'over' the inner leaf.

in my suggestion, if you are really worried about the floater cutting the membrane, im suggesting laying the extra block course after youve screed the slab. Then, when it comes time to float, you can use this block course as a buffer if youre worried about cutting the membrane.

screeding a 31 foot slab is not easy
you'll have to screed in sections, say quarters of the slab, using two block boundaries as level. use a metal straight edge... possibly 15' in your case.

see how they do a driveway here:
http://www.wikihow.com/Finish-a-Large-Span-of-Concrete

SRV

ok im getting there.........but i thought the slab had to be power floated on the same day as when it was laid...just as it was at a certain stage of setting?

if i was to lay the next block on inner leaf as a protection for membrane....wouldnt the slab be gone too hard for floating?

maybe my complete lack of knowledge on power floating is the cause of my confusion.

thanks.......

sydthebeat

SRV wrote: »

ok im getting there.........but i thought the slab had to be power floated on the same day as when it was laid...just as it was at a certain stage of setting?

if i was to lay the next block on inner leaf as a protection for membrane....wouldnt the slab be gone too hard for floating?

maybe my complete lack of knowledge on power floating is the cause of my confusion.

thanks.......

the idea is to use the blocks as a guide for the float. As i said in my opening post, in 10 years ive never seen the membrane cut from the floater, this is simply a "just in case" suggestion.
It is only 1 block course on the inner leaf, depending on your floor area you could have it up in an hour. Its just to use as a buffer as the floater has a ring about 20-30mm wider than the blades. Alternatively use a 9x2 propped.

SRV

the propped timber is a good idea i think.....

thanks again......:)