Pt wood and Cement for deck posts

First I am in Central Florida, no freeze lines, but moist soils. I am trying to decide if I will cement 4x4 posts in the ground, which would save a lot of money. Or do I need to pour footers up to grade and then use simpson ties to mount the wood to the top of them.

I have a fear of rotting wood, but many I speak to says there won't be any issues.

If it is ok, what is the best procedure? I was gonna dig a hole 2-3ft deep, add 2-4" inches of gravel, set the post in, add a few more inches of gravel, add a foot of high strength concrete, then fill the rest with dirt.

 

I used to live in east orange county

Anytime you can install the post above ground attached to the concrete by a strap or bracket - the wood will last longer. I like your method for fence posts but prefer to keep structure members above the ground. PT wood will last a long time in the ground but longer above ground

 

Thats what I figured. Just curious if I did put the post in the ground, how long will it last?

 

That depends on the grade of post you get. If you embed the posts in concrete, you want to be sure and get posts that are rated "for ground contact", that have the highest saturation possible. There are posts that are .25, .40, .60 for instance... so not all posts are created equal. Cheap posts are cheap for a reason.

If you can find PWF grade, use that. (See http://www.finehomebuilding.com/PDF/Free/021160082.pdf)

 

Posts embedded in concrete will last considerably longer if the concrete is full-depth, running all the way to the surface. With tapered tops to quickly deflect runoff away from the posts. Installing as you described will allow water to collect underground at the posts-concrete interfaces, likely to promote premature rotting. Using pressure-treated posts will only slow down the rate of deterioration.

 

Ok, What if I did 4" of gravel/rock, then an inch or 2 of cement, set the post in 18" or so then filled the hole to the top and smoothed it over? is that more along the lines of what I need to do?

If I did this, and used this post, how long will it last?
4 x 4 x 8 #2 Pine Pressure-Treated Lumber-256276 at The Home Depot

 

You're on the right track, with a few modifications:
1. Make sure to tamp/compact the gravel in the hole.
2. Don't set the post in cement (the gray, fluffy powder); it will sink right through it to the gravel. Rather, use the cement to make concrete, and set the post on top of a few inches of that.
3. Fill the remainder of the hole with additional concrete, tamping it as you proceed, and beating on the post frequently to consolidate the concrete. Make sure the post is plumb at all times, in all directions.
4. Slip a 2"-tall circular ring-form (sawn from an old 5-gal. bucket) over the post, set upside-down, centered and secured on the growing mound of fresh concrete at the base of the post.
5. Pour the remaining concrete quite stiff, filling up the ring-form and building up a wad of it around the post, compacting and finishing with a hand float, in a uniform (1"+/-) taper down to the top of the form. If you are into pretty, give the edge a radius using an edger, followed by radial-pattern brooming with a wide (but stiff) paint brush.
6. Following initial set at the surface, keep the exposed concrete moist for a few days to provide ample cure. A layer of wet sand works well.
7. Carefully strip the ring-forms, and stand back to admire your work.

I can't tell you how long the foregoing will last, as there are way too many variables involved. Such things as post quality, degree of preservative treatment, concrete strength and quality, hurricane intensity, etc., will all affect the life-span of your fence. Best guess is anywhere between 20 and 50 years. I'm pretty sure a few fences I built for a company farm in the early 1960s (in Wisconsin) are still standing today. No hurricanes to resist, but a lot of hefty beef cattle wanting to knock them down.

 

Thanks. It's not a fence, it's just above grade deck. What kind of concrete mix should I use? Sakrete high strength, 5000psi, fiber reinforced?

Are the posts I linked to ok? They are rated for ground contact. Unfortunately I may have to stick with stock from Home depot as there are no other good wood yards in the area.

 

Concrete strength isn't critical (within reason)--you can use any mix intended for thicknesses greater than 2". Something around 3000 PSI will be adequate. If you go with a leaner, less expensive bagged mix, I'd "sweeten" every batch of it with a shovel-full of that fluffy gray powder (Portland cement). Just to make sure there'll be enough strength to lock the columns in place.

With your lack of freezing temps, and unless the columns will be super tall, you could save yourself a lot of digging (and some material costs) by making the holes just 18" or so deep, filling them completely with concrete and then inserting a galvanized steel Simpson Strongtie anchor bracket with built-in air gap, into the fresh mud at the top of each. The wood will last much longer than if you embed it that way, being fully exposed to air and sunlight. If you go that route, no need to float a tapered finish into the tops, either; just make them all perfectly flat. Using ring-forms (or even short Sonotubes) that I mentioned earlier will make things nice and neat.

 

The sakrete is high strength concrete mix for above 2" thick. I think it will do the job well. I've decided not to do the posts int he ground, just level off concrete footers like you said and use the simpson ties.

What diameter will I need if no post is being inserted? 8" ok? Also instead of inserting the simpson bracket into the wet concrete, can I build the footing and then tapcon them into the top? This will give me a little flexibility to adjust, and also give me an opportunity to replace the brackets in the future if need be.

 

If I remember correctly the frost line is at 16" - not that it would ever freeze that deep in central fla
IMO width is more important than the depth because of the sandy soil. If you lay out your lumber before you pour it's not too difficult to set the tie downs in the right place. I don't know how well tap cons will do but I doubt it would be as good as having the brackets embedded in the concrete.

 

Properly embedded anchor brackets in fresh concrete will be many times stronger than tapcons drilled and anchored into hardened concrete. Not to mention being many times (by a factor of at least 5) easier and a lot faster to install. If you really are serious about wanting to relocate the deck after it's built ("flexibility to adjust"), maybe you need to sit back and think about things before digging the first footing hole.

In sandy soil, I think you would be better to go with 12" Sonotubes instead of 8". In addition to providing a more stable platform, the 12" are in conformance with the IRC deck building code while 8" are not. If you haven't already, you should talk to your local building department people to see what they require--they may have size and depth requirements that trump the IRC, and you'll need their blessings to be granted a building permit.

 

Actually for what I want to do both them, and Home Depot suggested just using deck blocks. I am not comfortable with those as I don't see a way to keep them from shifting and in the event we do get a hurricane it won't be anchored down to anything.

I figured if a small square block sitting on the surface is good enough, then an 8" column of crete 18" in the ground has to be better right? I was thinking the 8" would be less unsightly than the 12".

What if I dug the hole bigger at the bottom and just used the 8" form for the last 6" or so where it will be just above the surface?

 

That's what I would do, dig the hole big enough to work well and then just frame up a form for the top portion to pretty up what's above ground.