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Gerard G Posted: Aug 04, 2015 03:21 PM	spraying cc under home to slab??? I have a house in New Orleans that was built after Katrina in 05. Home owner had home raised and now wants to spray to slab underneath. I plan to spray a test panel to see if any moisture exists in slab but what is the correct application as I have never sprayed to a slab before? Should a primer be used? I am worried that I will have a good bond at first but down the road the foam will release/seperate from slab. Any help or suggestions are greatly appreciated.
mason Posted: Aug 06, 2015 02:43 PM	Always check first with your foam manufacturer for their recommendation. If there is a waxy or greasy surface to the concrete, you may need to blast it and prime it. If there is just dirt, typically power wash will do the trick. As for primer old concrete usually does not require a primer, but a test spray will help let you know Moisture: There are a number of ways to check the moisture of the slab to determine if foam will stick to it. We are mainly concerned about the substrate surface moisture and moisture from the space underneath the slab. The best way to determine if there is too much moisture on the substrate is to feel the concrete, it typically feels damp and cooler than the air. Then spray a little foam on the surface and then peel off the layer. Check the cell structure for evidence of moisture, such as poor cell structure, poor adhesion, hairy like filaments of foam at the foam/substrate interface. In order to determine if moisture from the ground can affect the foam you need to analyze the slab. How high is the slab from the ground? Is it open to the outside or part of a crawlspace that is enclosed? If it is high and open then moisture from the ground is not an issue. If it is enclosed then you should use plastic on the ground to act as a vapor retarder and make sure the foundation does not wick water to the enclosed space. Coincidentally, our Consultant's Committee at SPFA just published an Ask The Expert column on measuring moisture content in concrete for SPF applications. Check your latest issue of SprayFoam Professional or Email me at masonknowles@aol.com and I will provide a copy of the article.
Gerard G Posted: Aug 06, 2015 05:01 PM	Thanks for all your help. The house is 10' off the ground and has been raised for a year. The home owner pressured washed the under side of the slab when it was raised but the plastic is still stuck to the slab from when it was orginally poured on the ground. Removing this plastic is going to be a task in itself and enclosing the underside of the house as well as felt papering the driveway under the home is another job. Spraying technique is something I am on the fence about seeing as the underside of the slab is far from a smooth flush service to spray too. I am considering attempting the first pass to be sprayed like a roof then the second pass more of a touch up where it needs it then finally a third pass like a roof again. I am hoping to have something that does not look to ugly as there are many other homes that are having the same problem which are possible future jobs. The other questions I have is should an acrylic coating be applied to the foam because of the height of the home. I would think there will have some UV rays effecting the life of the foam or I could be wrong. Also should I spray under the front porch or just the living areas? I have mixed thoughts about this as I would think spraying the porch will help. On the other hand will heat from the top of porch slab area transfer into living areas? Once again I appreciate all the help.
mason Posted: Aug 12, 2015 07:56 PM	Sorry, I replied to this last week but don't see it posted. I think you will get some reflected UV on the foam so at least around the edges you should coat it. There are many acrylic coatings made for SPF. Check with your supplier for their recommendation over their foam. It would not hurt to spray a couple of feet over on to the porch side of the slab but I don't believe you need to spray the whole area.

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Gerard G

Posted: Aug 04, 2015 03:21 PM

spraying cc under home to slab???

I have a house in New Orleans that was built after Katrina in 05. Home owner had home raised and now wants to spray to slab underneath. I plan to spray a test panel to see if any moisture exists in slab but what is the correct application as I have never sprayed to a slab before? Should a primer be used? I am worried that I will have a good bond at first but down the road the foam will release/seperate from slab. Any help or suggestions are greatly appreciated.

mason

Posted: Aug 06, 2015 02:43 PM

Always check first with your foam manufacturer for their recommendation. If there is a waxy or greasy surface to the concrete, you may need to blast it and prime it. If there is just dirt, typically power wash will do the trick. As for primer old concrete usually does not require a primer, but a test spray will help let you know

Moisture: There are a number of ways to check the moisture of the slab to determine if foam will stick to it. We are mainly concerned about the substrate surface moisture and moisture from the space underneath the slab.

The best way to determine if there is too much moisture on the substrate is to feel the concrete, it typically feels damp and cooler than the air. Then spray a little foam on the surface and then peel off the layer. Check the cell structure for evidence of moisture, such as poor cell structure, poor adhesion, hairy like filaments of foam at the foam/substrate interface.

In order to determine if moisture from the ground can affect the foam you need to analyze the slab. How high is the slab from the ground? Is it open to the outside or part of a crawlspace that is enclosed?

If it is high and open then moisture from the ground is not an issue. If it is enclosed then you should use plastic on the ground to act as a vapor retarder and make sure the foundation does not wick water to the enclosed space.

Coincidentally, our Consultant's Committee at SPFA just published an Ask The Expert column on measuring moisture content in concrete for SPF applications. Check your latest issue of SprayFoam Professional or Email me at masonknowles@aol.com and I will provide a copy of the article.

Gerard G

Posted: Aug 06, 2015 05:01 PM

Thanks for all your help. The house is 10' off the ground and has been raised for a year. The home owner pressured washed the under side of the slab when it was raised but the plastic is still stuck to the slab from when it was orginally poured on the ground. Removing this plastic is going to be a task in itself and enclosing the underside of the house as well as felt papering the driveway under the home is another job. Spraying technique is something I am on the fence about seeing as the underside of the slab is far from a smooth flush service to spray too. I am considering attempting the first pass to be sprayed like a roof then the second pass more of a touch up where it needs it then finally a third pass like a roof again. I am hoping to have something that does not look to ugly as there are many other homes that are having the same problem which are possible future jobs.

The other questions I have is should an acrylic coating be applied to the foam because of the height of the home. I would think there will have some UV rays effecting the life of the foam or I could be wrong.

Also should I spray under the front porch or just the living areas? I have mixed thoughts about this as I would think spraying the porch will help. On the other hand will heat from the top of porch slab area transfer into living areas? Once again I appreciate all the help.

mason

Posted: Aug 12, 2015 07:56 PM

Sorry, I replied to this last week but don't see it posted.

I think you will get some reflected UV on the foam so at least around the edges you should coat it. There are many acrylic coatings made for SPF. Check with your supplier for their recommendation over their foam. It would not hurt to spray a couple of feet over on to the porch side of the slab but I don't believe you need to spray the whole area.

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