I am building a simple 8' square deck as base for 92" square spa. Part of the area was previously a flowerbed, where 2 large trees were removed (including stumps). While getting the whole deck level is doable, I'm concerned that the density of the soil in the previous planter is such that the Deck Blocks could settle substantially over time with approximately 100 lbs/sq ft. on them. The easiest solution would be to put 3/4" exterior grade plywood beneath the deckblocks, which would hten disperse the load away from any one deck block. I suppose you could dig a section out wherever there was any doubt, and load it with crushed rock to provide a better stable solution. What would you recommend?

Thanks.

Or you could put the dek blocks on top of a concrete stepping stone which has a larger foot footprint than 11"x11". Personally, I dont like the idea of using plywood 'marine' or otherwise underneath.

Kieth,

You are correct that the blocks will settle Unevenly. sorry for not getting back to you sooner. You should not put wood under the blocks. The wood will only settle just like the blocks would. You might want to consider another method of building. You are really limited to the options you have here. Because you are putting a spa on top of it you don't want to take any chances.

Deckman