APP Modified Bituminous Membrane with polyester and asphalt waterproofing

[itez]

Has anyone tried this?

The roofdeck will be topped off with 2 inches of cement. How heavy are cement compared to concrete with gravels? What is your experience on putting 2 inches of cement on top of a waterproof membrane (if structures can support it?)

 

[Ron]

What you are describing is common. It is called a concrete traffic topping slab over a waterproofing membrane.
It is commonly done, but you have to think about the difficulties you'll have in 15 or 20 years when that membrane deteriorates and leaks....you won't be able to easily get to the leaks. If you have a poorly installed membrane, you'll have the same problem within a few months to a few years. That's my major objection to this type of system.

APP (atactic polypropylene) is a high melt point modified bitumen. This makes it very susceptible to installer error. Further, some installers (and some system manufacturers) allow "seam only" bonding. This means that all of the APP material in the center of the sheet is essentially wasted as a bonding/waterproofing material....it is more susceptible to blistering and water intrusion.

If you elect to go with such a system, I would install the membrane and then do a flood test of the whole area, allowing water to sit on the completed membrane to a depth equal to the weight of the concrete topping that will be on it.....for typical lightweight structural concrete that will be about 120 lbs/cf, so the depth of water that would be equivalent would be approximately 4 inches. If regular weight concrete is used, increase the depth to 5 inches.

For such a system, I would only recommend a 4-ply coal tar roofing membrane under the topping slab. I am not a fan of any permanent topping slab over waterproofing.

To answer your question about unit weight, concrete will be from 1-1/2 to 2 times the weight of gravel for equal thickness.

Have you considered using concrete pavers on the membrane instead of a cast-in-place concrete topping? Pavers will provide similar serviceability (assuming your topping will not have vehicle traffic on it) and you can repair leaks in the membrane if they occur, as the pavers can be removed with relative ease.

 

[itez]

If the cement topping will be 120lbs/cf.. then it is 120 * 0.1667 (2inch/12 inch) = 20 lbs/square foot for the topping material??

If yes. How about pavers. Is it heavier or lighter than the cement topping? (and by how much approximate)

The waterproofing product is described here:

http://www.bostik.com.ph/(S(l5rm3f45xtbwg0553ug13b55))/_newsdata/138/object/datasheet.pdf

"An APP (Attactic Polypropylene) plastomeric type modified based-sheet utilizing a specially formulated bituminous compound of distilled asphalt customized with selected high-grade visco-elastic polymers and inert filler."

Question. Isn't it asphalt is bad on health? Any issues on this?

If I'd use 4-play coal tar instead. Is it heavier or lighter than the APP described above? Which is easier to apply?

Thanks.

 

[Ron]

Yes. 20 psf is correct.
Pavers come in a variety of sizes and unit weights. Search the internet...you'll find lots of material
No, asphalt is not bad for your health in such applications. It is an acceptable material for use in a variety of construction applications.
A 4-ply coal tar membrane will be slightly heavier than the APP.

 

[itez]

20 psf would be considered the superimposed dead load. How much do you allowance for SD load for residential, office and retail/commercial?

In your experience, or materials you have handled before, what's the psf for pavers you have seen? 10psf? 5psf? or equally 20psf too?

What membrane would avoid the heat from the sun from getting inside the concrete slab roof that is not heavier than APP?

 

[Ron]

A membrane has little or no insulative value, so it will not prevent heat gain in the concrete. You can get insulated pavers that have insulation on the bottom side, concrete on the top side. Depending on what you need, you can get pavers in a variety of unit weights.

Your other questions imply you don't have a lot of experience in doing such design on your own. I would suggest that someone with more experience in your office or locally could be of more help than you'll get in a forum such as this.

We are all willing to help, but there's a limit to what we can do remotely.

 

[itez]

Thank you.