Crack-Bridging Ability of Waterproofing Membranes - Hydrostatic Slabs

[Drapes]

How do you assess the crack-bridging ability of a waterproof membrane assuming there are no cracks to begin with (i.e. if the original crack width is non-existent or 0mm)?

A discussion on this can be found in the links below:
1.

https://www.thisisconstruction.com....ceptions-about-waterproof-membrane-elongation

2.

https://www.linkedin.com/pulse/how-important-elongation-when-comes-elastomeric-linings-mark-teakle

The following extracts sums up my dilemma:

From 1) "Cracks that form in concrete following application of the membrane, obviously have no membrane distance that is not bonded to the substrate. In other words, there is no bond breaker to provide a section of unrestrained membrane. The original gap is non-existent or 0 mm and regardless of the elongation properties of the membrane post application, cracks will result in damage to the membrane."

From 2) "When the waterproofing membrane is securely adhered to the concrete substrate it cannot elongate. It is stuck firmly in place and no longer has the ability to stretch. If a crack occurs in the concrete substrate under the firmly adhered lining the lining has very limited surface area over which to elongate and it cannot elongate as it could when it was in a free film state during the elongation at break test."

It appears the general consensus is that if the membrane is installed before the crack forms (as you would expect in most cases), then the membrane will be significantly more susceptible to tearing, than if the membrane is installed after the crack has formed (for example, during remedial works). But there is very little guidance addressing the former, which is what I need to determine the compatibility of the membrane with respect to calculated crack widths.

 

[Drapes]

How do others approach this? And what crack widths are acceptable for say a hydrostatic slab if a waterproofing membrane is present?

 

[dik]

The membrane manufacturers have that information... I don't know if it's still available, but there was a product called 'Bluestuff' that was an incredible 'bridging' membrane, and I used it often. There are likely others.

http://pennkote.com/products/product_list/Blue Stuff.pdf

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[JedClampett]

I avoided answering this to begin with because you didn't mention if these were liquid or sheet applied membranes and I didn't want to click on links that might or might not be spam.
So you're talking about liquid applied membranes. Now I'm not sure if this is in regards to water bearing structures or roofs or walls against soil.

But enough griping and on to your questions. My business is to design water containing structures. A crack wider than 2 mils might leak. And it's much preferable to have a tank that doesn't leak before you put the membrane on than to expect the membrane to seal your tank. That's what we specify. We detail tanks according to our best practices and test them before any linings are applied and repair them then, as needed. Even more preferable is no liner at all.

If you're expecting a fluid applied liner to seal leaks, you might be very happy. Or you might have to listen to a lot of excuses why your case was different or the applicator did a bad job.

If you have an existing tank, you're stuck. First I'd recommend injecting epoxy in cracks. Alternatively, there are many good swelling polyurethane products (Sikafix HH) that enter cracks and seal them.
If you're bound and determined to use a fluid applied membrane, the liner manufacturer should have a procedure to bridge cracks. It's usually tooling them out, applying a flexible sealant and a bond breaker and putting the liner over that. If you have a lot of cracks, that's tedious and expensive.

There's also flexible sheet liners, like HDPE or PVC, only attached at the perimeters and above the water line that will seal over cracks. Not cheap, but pretty foolproof.

 

[dhengr]

Drapes:
There are a bunch of spray-on damp proofing systems which contractors try to foist off on owners as water proofing. They are not water proofing. All they do is start to seal the surface of the conc. or masonry, they really do not bridge cracks. They are so thin that they do not retain their elasticity, so as to bridge any gaps or eventual cracks. There are also a number of good water proofing systems which usually involve some sort of an adhered, and joint sealed, membrane material with significant long term elasticity when protected against UV light. You really have to study the manufacture’s literature and talk with contractors who know what they are doing with each particular detail. As with all things these days real technical info. and knowledgeable recommendations are sometimes hard to come by, for all the ad and sales hype.

 

[dik]

Blue Stuff, if available, is a really tough membrane... and very elastic. I haven't used if for a couple of decades, but it is listed on Pennkote's site.


Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Ron]

Unreinforced fluid applied membranes will not retain crack resistance for the long haul. Use a quality fluid applied filler with an open reinforcing scrim.

 

[Drapes]

Thanks everyone for your feedback and insights.

To give a little more context - this is not a remedial measure, and not considering a liquid applied membrane or filler.

We have a hydrostatic slab (below the water table level), which will need to be fully tanked. A sheet applied membrane will be installed and adhered to the underside of the slab (i.e. positive side waterproofing), but the slab has not currently been designed to be watertight (approx 0.8 to 1.0% reinforcement only), so crack widths are expected to exceed 0.3mm.

Is this a reasonable approach though? If yes, then as per my original post, I would like to ensure the waterproofing membrane (the specific type of which is yet to be confirmed) is compatible with our calculated crack widths in order to avoid any sort of premature failure. But then it appears the crack-bridging ability of a membrane (which is often quoted on the manufacturer's literature) is only applicable for post-installed membranes which assumes there is an existing crack already (i.e for remedial works). If the membrane is installed prior to the crack forming (as you would expect in my case), apparently the membrane will be significantly more susceptible to failure, for reasons I noted in my original post. Whether this is true or not is up for debate, and hoping to seek clarity herewith.

The links and excerpts I initially provided on this go into more detail.

 

[dik]

Ron... I've used it with a 'fabric' for reinforcing...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Ron]

@dik....same here. The various scrims I've used were either fiberglass or polyester.

@Drapes...ideally, for your application I would place a mud slab (I think your term for that is blinding), of relatively low strength concrete, with a proper roofing membrane placed on the slab. My preference would be a 4 ply coal tar built up roof membrane, but might not be available in your area. 2nd choice would be a 4 ply asphalt built up roof membrane. Other than those, you can use a modified bitumen membrane, either torch applied or hot asphalt applied. Last choice would be a synthetic single ply membrane. The materials are good but highly dependent on workmanship. Any of them will hand the crack widths you anticipate.

Then place your structural slab on top and sleep well!

 

[Drapes]

Thanks Ron, sounds like a plan!

Do you know what order of magnitude crack widths these sheet membranes can typically tolerate?

Is it even necessary to check compatibility of sheet applied waterproofing membranes with crack widths? Or are they generally robust enough by default?

From the responses provided so far, it appears the liquid applied membranes are the ones that are a lot more vulnerable to failure when subjected to cracking in the slab, especially when the cracks form after the membrane has been installed.

 

[Drapes]

Hi everyone,

Just touching base on this again to hopefully close out - any further comments or insights on my latest queries would be much appreciated. Thank you all

 

[NorthCivil]

I reckon as a failsafe allow for a drainage pump

it will be a lot cheaper and more amenable to run a pump if you are encountering leaks than to attempt to waterproof the entire leaking foundation once its covered with soil and a building over