Tile Backerboard Under Legs? End of 2nd Season Update

[phroggie]

Has anyone tired using cement tile backerboard under the legs (instead of pavers)? 1/2" or 1/4"?

I seems to me that this might be the ideal solution. It's a fraction of the thickness, waterproof and a $10 3'x5' board can be easily scored'n'snapped to size. As long as the soil underneath is very flat there should be mostly compressive stresses which cement excels at handling. Any sinking or irregularities in the ground might cause some lateral tensile stresses but the fiberglass should help counter that. (Pavers don't have any fiberglass so in extreme conditions, they'll crack.) I'm thinking that given that, maybe even 1/4" thick board will be enough.

And the best part is that you're only elevating the leg 1/2" at most vs 1" or more for pavers or a lot of extra digging and leveling.

Did I mention it can be cut-to-size?

 

[ajw22]

If you try that let us know how it lasts.

 

[Hollywood20659]

Has anyone tired using cement tile backerboard under the legs (instead of pavers)? 1/2" or 1/4"?

I seems to me that this might be the ideal solution. It's a fraction of the thickness, waterproof and a $10 3'x5' board can be easily scored'n'snapped to size. As long as the soil underneath is very flat there should be mostly compressive stresses which cement excels at handling. Any sinking or irregularities in the ground might cause some lateral tensile stresses but the fiberglass should help counter that. (Pavers don't have any fiberglass so in extreme conditions, they'll crack.) I'm thinking that given that, maybe even 1/4" thick board will be enough.

And the best part is that you're only elevating the leg 1/2" at most vs 1" or more for pavers or a lot of extra digging and leveling.

Did I mention it can be cut-to-size?

Did you use the board?? Did it work

 

[phroggie]

I did indeed use the thinner 1/4" backer board. I cut eight 24"x7-1/2" pads for the U-legs and ten 6"x6" pads for the poles. (And now I have a 60"x6" scrap to add to all the other scraps cluttering my yard.)

So far it seems perfect. There is a little bending but not enough to fracture the board. Most importantly, they remain level since as the pool was filling I was able to adjust their positions and keep them centered. This is in contrast to pavers which you probably won't be able to adjust and if not centered will tend to start tilting.

However, our tract was built in 1951 on ground that I would describe as silt. So it's had 70 years to compact with above ground pools sitting on the site for more than the last decade. So in our case, 1/4" backer board seems perfect. It may not work as well on less compacted/compactable soil.

 

[Newdude]

Hey Phroggie !!! I need to preface this by saying how much I absolutely LOVE these pools. With a strict budget, or as a test to see if the budget should increase in a couple of years when the frame rots, anyone can be swimming in a few days.

That said. It's a bag full of water that will shift as such. The forces upon the legs are so great that they snap 2 inch pavers for anyone who tried.

I wish you the absolute best. When the time comes to do it again, use 4 inch blocks.

 

[phroggie]

Newdude, you raise an excellent point: backer board should probably only be used in certain conditions. The same applies to 1" pavers, 2x8s, etc.

I was shocked to look at magiteck's post hole. Yeah, with water so close to the surface, backer board might not be such a good idea. Living in SoCal or anywhere in the southwest that picture seems like it's from a different planet.

So, yeah, its use should come with a lot of warnings.

Fun fact: in SoCal (Northridge, to be exact) we also worry about the opposite problem: the ground shifting and the "bag full of water" wanting to stay in one place. 1" pavers held up OK during the 2019 Ridgecrest quake. (The 10 year old hoses: not so much.)

 

[duraleigh]

That 1/4" backer board will support a CEMENT TRUCK if the substrate is immovable. If water softens or washes the substrate underneath the backer board it will EASILY crack. If you can keep it dry, all will be fine but that may be a tall order.

 

[phroggie]

End-of-Season Summary:

(As a reminder!: 1/4" backer board is NOT for every situation!)

In our case it worked perfectly. But we have very compacted ground. How compact? I actually swept the bare ground with a broom before taking those pictures. Also, from late April to the end of October we had a lot less than 3/4" (19mm) of rain. (The two pictures on the left were under the pump and were exposed to some spillage.)

There was slight bending under the U-legs but no fracturing, splitting or cracking on the bottom. Over all the backer board did what it was supposed to do: spread the load out without the need for countersinking.

Some rain would be nice now but there's none in the forecast.

 

[phroggie]

So tropical storm Hilary passed about 70 miles east of LA and as a result in a 12 hour span we got more rain than over 10 pool seasons combined. (Yeah, I know, in the rest of the world it would be a normal summer rain, but this is LA.) The picture shows how well 1/4" backerboard didn't work this year.

In spite of that I'll probably replace the pads next year and take some precautions especially in case a storm next year doesn't get that memo that says they're supposed to die in the cold water off the Baja/Alta California coast.

 

[Newdude]

100 year storms come every 5 years now.

But that's still roughly enough for a soft sided pool if you time it right.

 

[CT-Steven]

The technical aspect that was overlooked is the indentation rating of the board. Cement board at a 1/4" has an indentation rating of roughly >1250psi.