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Thread: Backfilling with Expandable Foam

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    Backfilling with Expandable Foam

    I have sagging fiberglass steps on an inground liner pool. I am getting a new liner and the pool company said they can drill holes in the steps and fill with "foam packs" that they say they want to charge $169 per pack for. I happened to be home when they sent a couple of teenage boys out to do this. By the time I was done mowing the lawn and went to say hi to them they had already drilled the holes and were spraying a $4 can of Great Stuff foam insulation into the holes. I am fairly certain that this will do nothing for supporting my steps. When I questioned the service manager he told me he would have to check into it and never responded. I asked the owner of the store and he said they use it to get the biggest voids filled so that they can save me $ when they put in the expensive packs. Am I out of line thinking that expandable foam was not what they were supposed to do and they are just trying to cover their tracks due to me catching them?
    44,000 gallons, vinyl lazy L, Pentair Intellichlor SWG, Hayward 1 1/2 hp Super Pump, Rheem propane heater.
    Defiance, MO

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    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: Backfilling with Expandable Foam

    Welcome to TFP!

    There are a couple of things going on here. First, the only real fix is to cut a hole in the deck to get behind the stairs and fill in behind correctly. Because of the deck cut that is usually a troublesome expensive project. Filling in with expanding foam can help, sometimes it even helps enough, but it isn't the right way to fix it. Second, I'll just bet they intended to use the $4 expanding foam all along, and were just making up something about foam packs to justify a higher price.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    Re: Backfilling with Expandable Foam

    Thanks! I truly believe they are wishing I did not catch them at this.
    44,000 gallons, vinyl lazy L, Pentair Intellichlor SWG, Hayward 1 1/2 hp Super Pump, Rheem propane heater.
    Defiance, MO

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    ConcreteJack's Avatar
    Join Date
    May 2011
    Williamsburg, VA

    Re: Backfilling with Expandable Foam

    Polyurethane foam is frequently used for filling voids underneath and lifting roadways, interior floors, bridge abutments and all kinds of other heavy structures. We use it pretty frequently to void fill under and lift pool decks and have even used it to raise a concrete pool (the pool itself) that settled. There are specific formulations of polyurethane foam for geotechnical/ground contact applications, particuarly in wet environments, which are different from canned foam. The expansive properties of polyurethane are excellent for tricky void fills like under step assemblies, but canned foams are not designed to be flowable (they come out of the can foaming, as opposed to staying liquid for a couple of seconds before expanding), so they don't necessarily fill expansive, narrow voids very well.

    Due to the somewhat strange ("inventive"?) methods builders use to hedge against spongy steps, it can sometimes be tough to get grout to flow into all of the voids at low enough pressure to avoid deflection of the steps by filling only through the surface, which usually costs a couple hundred dollars.

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