floor elevation compound

[releky]

What particular floor elevation compound do you use to make the floor or tiles higher? In my country. 100% of construction use sand mixed with cement as the filler. See the following picture:

http://www.pbase.com/rele/image/153741119

The tiles and sand elevation load is this.

15 kn/cubic meter x 0.05m = 0.75 Kn/m^2

The beam would have additional 0.75x20 = 15 Kn.

Do you think 0.75 KN/m^2 Superimposed Dead Load for a floor is low or high? what load do you typically use? And would elevation compound even be lower in weight? how low in square meter?

 

[Ron]

I understand your issues and it is unfortunate that such construction is allowed to exist. It is a danger to the public.

I also understand that a mortar bed does not need a compressive strength equivalent to the strength of the structural concrete; however, it must have a compressive strength sufficient for durability of the application, which is greater than the 100 psf bearing that you noted. Bonding adhesive above and below the mortar bed does nothing if the mortar bed fails in tension or horizontal shear.

Learning more about concrete technology and mix designs will help you to counteract some of the difficulties of delivery time and concrete consolidation.

Remember...good concrete consists simply of cement, good aggregates and water. Unfortunately, bad concrete can consist of the same ingredients.

 

[jimstructures]

releky,

I stand corrected. That gives us 11.3 kN per m^3 still no where near the desired 4 kN per m^3. In college for the concrete canoe contest we made floatable concrete, less than 62.4 lbs per ft^3 or 9.8 kN per m^3 with a glass bead aggregate. But it wasn't very strong so we used half gravel and sand and half glass bead aggregates that worked but still wasn't very strong and was nowhere neat 4 kN per m^3. I don't think you are going to find a suitable aero-gel aggregate.

Jim H

 

[releky]

After spending time with the tile installer. I learnt how exactly they do the proportion of the mortar bed mixing and this is how the millions of buildings in the country are done. Here's how. It's 1 part cement and 2.5 parts sands. But the water added is very few just enough to wet the mix. So the texture of the final mix is not paste-like but soil-like (rough), the reason for this is so they can level the tiles, because it's harder if the bedding is paste like. This works well because it's also what's done in hotels and all buildings in the country. Note adhesive is added above the mortar bed and below for adhesion of the tile.

I weight the mix in one square carton and 1 inch thick. It's roughly 87 Lbs/feet^3 or 13.6 Kn/m^3. It doesn't reach 23.56 Kn/m^3 because the lack of enough water prevent complete adhesion into paste-like texture (meaning there is microscopic aid voic). But the final mix is strong enough to take 100 lbs/feet^2. Remember this is done in all buildings in the country.

Now my question is. If there is not enough water in the mortar mix. And the hydration of the cement is just partial. Would it continue to hydrate when water gets into the bedding (let's say months later)? I need to know this important because I don't want hydration to continue months later and the weight to become more (would it?) Remember the water in the chemical reaction with the cement form the final weight of the concrete. So any water seeping to the bedding may continue the hydration. What is your opinion?

 

[hokie66]

If the mortar weighs only 87 lb/cu ft, it is very porous. Therefore, it will be a reservoir for any water which infiltrates. Whether or not it hydrates cement depends on how much cement remains to be hydrated.

 

[a2mfk]

Based on the photograph and the description, and like I said on the previous post on the same topic, this appears to be "mud bed" or "thick bed" installation, and is basically the Old World method that has been used for hundred if not thousands of years (in different versions). This is still very common in Spain in my experience.

It seems to work very well to level the floor and also does not directly bind the tile to the floor, so it is uncoupled, and therefore cracks and movements of the floor slab do not necessary transfer the stress into the tile assembly. Having inspected tile failures and experienced them first hand with my own property, the failure is due to long term moisture expansion of the tile which fails the mortar bond to the concrete slab in shear and tension. I do not think this is as critical with thick bed installations as described because the tile is not bonded directly to the rigid slab, the sand-cement mixture provides a slip plane for the tile. Though you could still have problems in long tile runs like hallways or large rooms if you do not have expansion joints. Also depends a lot on the tile.

But the poster said they use some type of adhesive to bond the tiles to this layer. I wonder if this is still done while the mud is still green?

Some info here:

https://www.tcnatile.com/faqs/65-mortar-bed-compressive-strength.html#faq70

http://en.wikipedia.org/wiki/Thick_bed_mortar

Anyway, back to the topic at hand. If this is typically how tile is installed in your locality, then the structure should have been designed for this dead load. There is not much you can do to the weight of sand, cement and water to make it weight less, as Hokie has indicated.

It sounds like you (releky) are a field/site engineer, and as such it is not your responsibility to re-engineer the building as it is being constructed. If you go away from the tried and true methods, what if you have tile failures? Will you be held responsible?

Have you been discussing these issues with the structural engineer who designed the building?

 

[releky]

Yes, the adhesive is put below the mortar bed and between the tile and mortal while the mortal is still wet. Again, it's not paste-like texture like in structural concrete pour but soil like texture. The tile installer didn't compact the soil-like mortal. What they do is level the soil mortar to the height of the neighboring tiles. Then use the wooden side of hammer to notch the tile until it goes deep enough to be same level as the other tile. Btw.. the tile is only 8mm in thickness synthetic granite, china made. So for 2" soil-like mortar bedding with 1 cement part to 2.5 sands part (white sands) and little water just to wet it, and only 8mm compact space (the thickness of the tile insert), I wonder how big is the pores inside (akin to honeycombs). I'm looking for a molecular software to simulate the density and effect. And noting that water has specific gravity of 2.32, it shouldn't add so much weight.

Also please confirm if the following analysis is correct. When you add water to sand/cement mortal mix. The purpose of the water is not only for chemical reactions or hydrations of the cement and water and binding with the aggregates and workability, but putting water has effect of making the sand particles bind closer. So in the finished 2" soil-like uncompacted bedding with many pores, putting water can't make the unhydrated cement become large in volume that can fill the pores. So water infiltrates months later won't make the 13kN/m^3 porous mix to become 23kN/m^3. Agree with this?

Yes. I'm a field engineer and the designer said to make it as thin as can be but if not possible, then thick.. this is what every designer of all buildings in my place think... the flooring being part of Superimposed Dead load. I just want safe allowance and can change tile bedding mix if I think it's necessary.

 

[darthsoilsguy2]

well for a US-specific mktg plug for a colleague's business.... SuperCap is an interesting approach. short video to check it out

http://www.youtube.com/watch?v=yDlXC8SOrG8#t=148

 

[hokie66]

"And noting that water has a specific gravity of 2.32,..." That would be...wrong!

 

[a2mfk]

On a raised floor slab with tile on it, where is this excess water coming from?

Seems like you are over-thinking this. Keep the dead load under what the drawings state or what the structural engineer said he designed it for, and let the tile guy do what tile guys do in your area. You should have an engineer in your locality who knows all these things and can help mentor you....

 

[releky]

I meant concrete has specific gravity of 2.32

I asked the tile installer why he has to use soil-like texture. He said before they used typical concrete paste-like mix and what happened was that after a few years the tiles rise up with respect to other tiles. What is the cause of this? The tile installer doesn't know since he is not familiar about hydration. He said all the country tile installers use the technique used in Saudi Arabia or soil-like texture mortal bedding due to the problem encounters decade ago.

Now what would be the advantage if the soil-like texture mortal bedding is thicker as one of you (a2mfk) mentioned it has advantage (note what I meant by "soil-like texture mortal" being due to not enough water to turn the 1:2.5 cement sand into paste as I explained previously)

The designer is not familiar with such tile installer details. He used told me to use the thinnest as much as possible or the lightest and learn how to do it and decide what to use and so I need to know the technique used by tile installers.

Also what would happen if the tile is just attached using adhesive directly to the floor? Isn't it the rest of you use this? won't you encounter any rised tile or crack?

 

[TDIengineer]

I have used lightweight concrete on metal deck to help reduce building mass in high seismic zones. BUt I have never used lightweight mortar to make the superimposed tile load less because the building can't take the added gravity load...

This is funny stuff... LOL

 

[releky]

After long consultation with the designer. He told me he actually didn't consider tiles and thick toppings in his calculations which is very tight owing to steel prices very high. After consulting with other designers. We decide to remove the tiles (it is already fully done). But we can't use bare slabs for foot traffic. Can anyone recommend what other lightweight flooring (maybe wood) available? What synthetic flooring is available and what synthetic copolymer compound to use (we need to rise it 2" thick for proper elevation). Thank you.

 

[a2mfk]

You are in trouble if the engineer did not allow enough dead load for tile and a mortar bed. Do you not have a boss who is an engineer who has a lot more experience with local practice and can help you?

What dead load did the engineer provide for flooring installation? Wood flooring can have significant weight and wood in general is not very effective for leveling. The leveling compounds I am familiar with are expensive and not lightweight.

Tile "tenting" is mostly commonly caused by a failure of the mortar bond in shear due to long-term non-reversible moisture expansion of the tiles. Each tile expands slightly, generating compressive forces in the tiles, and if the mortar bond fails, the tiles relieve the compressive stress by tenting upwards. All ceramic products being to absorb moisture after they leave the kiln, some more than others. An exacerbating factor would be shrinkage of the slab.

 

[releky]

Here's the layout of the property

http://imageshack.us/photo/my-images/138/qwqv.jpg/

The designer said he made a mistake and there is only 164 kN capacity in the middle horizontal girder. All the beams are 0.5 depth by 0.3 width. There is sufficient longitudinal rebars but stirrups in the middle are only 0.2 m apart while at the sides it's all 0.1 m. Bottomline is, he used the analysis of triangular shear and realised after construction (after checking everything) that the shear should be constant from the middle to the sides. So the present girder can't support additional superimposed dead load. So he added 80 kN by putting carbon fiber. There is carbon fiber installed last month. But you know carbon fiber are controversial. What if it won't work. Therefore I and another engineer can't trust it. The carbon fiber is supposed to support the tiles and 2" mortar bed and some live load. But FRP for shear is not tested. Therefore we can't take chances and need to make lighter mortar bed. The boss says ok to make it lightest. But he doesn't have any idea about lightweight flooring system.

Can you think of any plastic based mortar bed (say entirely synthetic plastic) that can make it say only 7 kN/m^3? Right now the mortar bed is about 15 kN/m^3. We want to deduct about 10 kN of mortar bed load to make it lighter. The owner said even if the floor system is not very good. It is better to be safe than worry. So no problem if cement mortar bed can take the movement of the tile better than synthetic plastic and has to be replaced often Btw.. I weight of the tile is only 1.5 (not typo) pounds per square foot (it is light being only 8mm thin) so the problem is the heavier 2" mortar bed.

 

[releky]

I won't replaced the entire floor.. only the middle portion near the girder or the tributary area form by the secondary beam nearest to the center. I need to take off about 10kN of mortar bed weight. Is there just no synethetic compound (not composed of sand and cement) that is just 8kN/m^3 that can work with the floor with good misc. characteristics? Can't no such compound ever be fabricated or synthesized?

 

[releky]

By the way, in many millions of buildings with mortar bedding. Many experience cracking after 3 years. What happened is that mortar bedding itself just rise up against the tile. So you can't say it is the tile that compresses against the mortar bed. Any ideas why the mortar bed cracks upwards? Is it because they did it so thin or the concrete so hard? The tile installers and most local engineers can't explain it.

Whatever, I think I have to invent synthetic plastic that can be make flowable so they can be poured into slabs acting as tile bedding with good compression, shear, tension and moisture control. If anyone has seen this. Please share it. If none. I think I need to invent it myself.. so need crash course in chemical engineering.

 

[a2mfk]

With design engineers like the one you are describing, excessive deflection of the floor slab will put additional compression into the tile assembly. But tile tenting ultimately is a result of the mortar bond failing, in most instances this is due to poor surface preparation and/or workmanship issues.

Can you use vinyl flooring? Lightweight, durable, and can look like tile or wood. If you can get it where you are. But I know of no lightweight leveling compounds that also have good enough compressive strength to support tile.