Planning 4' x 10' concrete top patio table

[Mr.D.]

Yes, that is right, a 4 x 10 concrete top (done in three sections).

The top is the easy part, just heavy.  

The base is a bit more concerning as this thing will be around 700 lbs.

Once this is built, it won't be moving.

It will be on a covered patio with only a couple hours of sun per day.

As much as I would like to use hardwood, I can only afford pine/doug fir/redwood or cedar.

Any ideas would be greatly appreciated.

 

 

[BonPacific]

Do we even want to ask why?

Ignoring why, functionally what you're building isn't too different from a large kitchen island with a thick stone slab top. So I think you're going to be more worried about providing sufficient support and rigidity to prevent the top cracking than worrying about the weight itself.

Are you forming the top in-place? If so (and I would hope so) you may want to look into the systems out there designed for casting kitchen countertops. They include edge profiles that can be snapped off later so all you see at the edge is concrete but the underside can be your plywood or melamine mold. I think Bourbon Moth did a video about one of the systems.

[wtnhighlander]

If the base is massive enough, any softwood will have enough strength to support the top. I would pick the most rot & bug resistant species you can afford.

Looking for a leg & apron design, or pedestal(s)?

[Tom King]

While 700 pounds sounds like a lot, it's really just the equivalent of a few people standing on that area.

[JohnG]

700lb over 40sqft really isn’t that much weight. As mentioned above, the greater concern will be evenly supporting it. At 4’ wide you don’t have too much concern about it tipping unless you’re going for a trestle style base with large overhangs. 
 

[G Ragatz]

Cypress might be another species to consider, if it's available where you are.

[Mr.D.]

Thanks for all the responses so far.

As for why, we have a large enough are to accommodate a table that size.  We started pricing things out, and we were seeing $4000-5000 for the table alone.  Wood prices have also taken off too.  Concrete on the other hand would be under a few hundred. Then came the idea of small fire boxes, creating designs with aggregate and embossing and filling with epoxy, still with all that, well under a thousand.  As for the base, soft wood is used structurally in homes in load bearing situations so I figured on 4x4 legs, at then ends and in the middle and using 2x4 and 2x6 for aprons and stretchers. 

Unfortunately, I am in So Cal, where everything seems to be about 30% higher in price, except for my salary. At the local lumber yard, I was in sticker shock at the price of 4/4 hardwood and even softwoods are bad.  The base will cost more than the top.

As for the base, as mentioned, I am looking at post legs rather than trestles, just getting old and trying to come up with something structurally sound

I was thinking of breaking the top into three, roughly 4 x 4 sections in forms but I am looking at pouring in place.  In the past, I have take two pieces of wood, attached to a sacrificial base and cut down the joint which resulted in a pretty tight joint, was thinking about doing that with a wet saw with the slabs to produce a tight butt joint and maybe doweling in some rebar and epoxy and then clamping them to keep the slabs as level as possible, of course I would make sure that the base was square and level.

[wtnhighlander]

I think your lumber dimension choices will be fine. I might suggest a 'farmhouse table' base design, with legs at the corners, aprons all around, and a low stretcher assembly to keep the legs from splaying over time. A hayrake stretcher design would look nice, and leaves foot clearance for seating all around.

Here is a FWW article on such a design.

[Mr.D.]

I really like the hayrake idea!!!  Thank you for the link.

[wtnhighlander]

As wide and heavy as that table top will be, incorporating a single post leg, dead center, might be a good idea. Should work into the stretcher design easily enough.

[Mr.D.]

I am thinking of actually 2 on the center line lengthwise but spread enough apart so a 20 lb LPG tank can be stored underneath, concealed of course. I have 22" between the fire pits on top, 2 4x4 would take 7" and a tank is 12" in diameter.