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philip mullins Posted: Aug 10, 2007 03:49 PM	hair brain idea? this may be a bad idea but i will run it by you guys anyway. a friend of mine is just about to move into his newly constructed home. he some how discovered that he has a wash out problem under his slab near the center of the home. he has had 3 structural engineers look at it and determin that it will not wash out any farther. the affected area is between 2 grade beams that are about 8 feet apart. he has been told that it should be fine as is. and to repair it would be very expensive. so, heres my idea. drill a hole in the slab over the affected area then fill with cc foam to fill the void. i have seen this done with concrete but, since his house is almost done we dont wanna make that much mess. if we try this we will only have to remove one tile from the floor. since he has been told he will prob be fine as is, he is leary about spending the money for the foam. even though i told him i would only charge him for materials. so first of all do you think this would be a viable repair? and second, with no way of knowing the size of the void, do you think it would be worth the money?
Posted: Aug 10, 2007 04:07 PM	wouldnt it be cheaper to rent a grout pump and pump in some grout mix of some kind? or just call a slab jacking company.
mason Posted: Aug 11, 2007 09:09 AM	Polyurethane foam (pour-in-place) has been used to shore up concrete sidewalks and foundations where the dirt has been washed away. A 2 lb foam has compressive strength of approximately 20 psi, so you can do the calculations. I tend to agree with Mr Foam on this one. It would be hard to control the application (easy to get voids and foam spilling out in areas that you do not want it.) Plus pour foam applications are different than sprayfoam applications. You have to match the rise time of the foam to the application and the flow rate of your equipment. Typically a 2 lb foam with a 2 minute rise time has a cream time of 30 seconds. So, to prevent pouring foam on rising foam which can hurt the physical properties or even catch the foam on fire, you could only pour 15 lbs of foam at a time. 15 lbs of foam would only fill in 5-6 cubic feet of the void. I would guess this void is larger than that.
Posted: Aug 12, 2007 07:20 AM	i would run and hide... you gots to know when to say when... and when to say no... (when this slab settles and cracks,,its your foam that was supposed to keep it from happening) this sounds like a liability nightmare waiting to happen... i would have the person who prepared the grade and who poured the slab R&R it... didcha know that their are plenty of "engineers" out there who's "proffessional opinion" can be bought to say what ever the person "paying for the opinion" wants... ...and sunday morning coming down...
mason Posted: Aug 12, 2007 09:30 AM	A 2lb sprayfoam or pour-in-place foam can withstand easily the weight of a concrete slab. In cold storage applications it is common to spray 4-5 inches of foam on a foundation then cover it with 4-6 inches of concrete. Even with point loading from racks and forklift traffic foam supports the slab just fine. In this scenario, though I believe it would be hard to install the foam correctly. First the cavity to be filled is at least 8 foot, We were not told the length of the cavity or the depth. But let's assume 8 foot by 8 foot by 2 foot deep. That would be 128 cubic foot of space to fill. Assume a 20% waste factor miminum and you would need over 300 pounds of foam to fill the cavity. As I said earlier you can't pour foam on rising foam without having serious consequences. So, you would need a proportioner that could pour 600 lbs a minute to beat the cream time. You could try making smaller pours but that greatly increases the chance of getting voids in the application, and that would compromise the structural integrity of the job. So I agree, this job doesn't sound practical and could have serious liability attached to it.
philip mullins Posted: Aug 12, 2007 10:53 AM	tx for the replies guys. the affected area is only about 3x5, and less than a foot at its deepest point. and as far as liability goes, its a friend of mine so... we were just brainstorming how to fix it without having to bring in a conc. pump. and i was curious if this technique had been tried before. i been reading a few articles about filling mining shaft openings and i guess it got my wheels turning. since all 3 engineers said it should be fine and my boy is already suing his contractor for many more serious problems, he's gonna let this slide. the good news is he spent most of the past 2 days dealing with it and i never had to move a single piece of furniture,lol. i think i will mention that in church thismorning! since i am busy all week and wont have time to help,lol "cause theres something in a sunday that makes a body feel alone"

Author

Comments

philip mullins

Posted: Aug 10, 2007 03:49 PM

hair brain idea?

this may be a bad idea but i will run it by you guys anyway. a friend of mine is just about to move into his newly constructed home. he some how discovered that he has a wash out problem under his slab near the center of the home. he has had 3 structural engineers look at it and determin that it will not wash out any farther. the affected area is between 2 grade beams that are about 8 feet apart. he has been told that it should be fine as is. and to repair it would be very expensive.

so, heres my idea. drill a hole in the slab over the affected area then fill with cc foam to fill the void. i have seen this done with concrete but, since his house is almost done we dont wanna make that much mess. if we try this we will only have to remove one tile from the floor. since he has been told he will prob be fine as is, he is leary about spending the money for the foam. even though i told him i would only charge him for materials.

so first of all do you think this would be a viable repair? and second, with no way of knowing the size of the void, do you think it would be worth the money?

Posted: Aug 10, 2007 04:07 PM

wouldnt it be cheaper to rent a grout pump and pump in some grout mix of some kind? or just call a slab jacking company.

mason

Posted: Aug 11, 2007 09:09 AM

Polyurethane foam (pour-in-place) has been used to shore up concrete sidewalks and foundations where the dirt has been washed away.

A 2 lb foam has compressive strength of approximately 20 psi, so you can do the calculations.

I tend to agree with Mr Foam on this one. It would be hard to control the application (easy to get voids and foam spilling out in areas that you do not want it.)

Plus pour foam applications are different than sprayfoam applications. You have to match the rise time of the foam to the application and the flow rate of your equipment. Typically a 2 lb foam with a 2 minute rise time has a cream time of 30 seconds. So, to prevent pouring foam on rising foam which can hurt the physical properties or even catch the foam on fire, you could only pour 15 lbs of foam at a time.

15 lbs of foam would only fill in 5-6 cubic feet of the void. I would guess this void is larger than that.

Posted: Aug 12, 2007 07:20 AM

i would run and hide...
you gots to know when to say when...
and when to say no...
(when this slab settles and cracks,,its your foam that was supposed to keep it from happening)
this sounds like a liability nightmare waiting to happen...
i would have the person who prepared the grade and who poured the slab R&R it...
didcha know that their are plenty of "engineers" out there who's "proffessional opinion" can be bought to say what ever the person "paying for the opinion" wants...

...and sunday morning coming down...

mason

Posted: Aug 12, 2007 09:30 AM

A 2lb sprayfoam or pour-in-place foam can withstand easily the weight of a concrete slab. In cold storage applications it is common to spray 4-5 inches of foam on a foundation then cover it with 4-6 inches of concrete. Even with point loading from racks and forklift traffic foam supports the slab just fine.

In this scenario, though I believe it would be hard to install the foam correctly. First the cavity to be filled is at least 8 foot, We were not told the length of the cavity or the depth. But let's assume 8 foot by 8 foot by 2 foot deep. That would be 128 cubic foot of space to fill. Assume a 20% waste factor miminum and you would need over 300 pounds of foam to fill the cavity. As I said earlier you can't pour foam on rising foam without having serious consequences. So, you would need a proportioner that could pour 600 lbs a minute to beat the cream time. You could try making smaller pours but that greatly increases the chance of getting voids in the application, and that would compromise the structural integrity of the job.

So I agree, this job doesn't sound practical and could have serious liability attached to it.

philip mullins

Posted: Aug 12, 2007 10:53 AM

tx for the replies guys. the affected area is only about 3x5, and less than a foot at its deepest point. and as far as liability goes, its a friend of mine so... we were just brainstorming how to fix it without having to bring in a conc. pump. and i was curious if this technique had been tried before. i been reading a few articles about filling mining shaft openings and i guess it got my wheels turning. since all 3 engineers said it should be fine and my boy is already suing his contractor for many more serious problems, he's gonna let this slide.

the good news is he spent most of the past 2 days dealing with it and i never had to move a single piece of furniture,lol. i think i will mention that in church thismorning! since i am busy all week and wont have time to help,lol

"cause theres something in a sunday that makes a body feel alone"

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