Need 2nd opinion on what concrete guy said

[MoreCowbell]

I have been posting sporadically here for the past year as I work through my DIY crawlspace-to-basement project. I am just about ready for my concrete floor which incidentally will be the first thing I'll not be doing myself for obvious reasons.

I've spent some time on Angie's List and found a concrete company that had a large number of very positive reviews. They came out to do an estimate yesterday. I asked a number of questions that they answered to my satisfaction. However, they told me a couple things that I was a bit unsure of and I'm wondering if I could get a second opinion here.

The first regards sub base. The current surface of the grade happens to be at the level where the bottom of the slab will start. However, I mentioned that my plan is do dig down another 3"-4" and put down a gravel sub base to act as a capillary break followed by a vapor barrier. The guy said that since the current surface is virgin soil and is dry despite the unusually very wet June and July we've been having, he said not to bother with the sub base a just put the vapor barrier on the virgin soil (clay). Everything I've been reading suggests a gravel or crushed stone sub base. Is that really overkill like the concrete guy said? He knows I would be doing that part myself so it would make no difference in his work.

The second issue regards reinforcement. His recommendation is to go with a 4000 psi mix with fiber and to forgo any rebar or remesh. Is that a good idea? The slab thickness will be 3.5".

Unfortunately, I'm having a tough time getting anyone else to come out for an additional estimate. I'm kind of off the beaten path where I am.

Thanks,
Rob

P.S. Just for kicks I'm attaching a picture of where I am currently (disregard the mess )

 

[Chris]

Unless you have bad water problems I would say the gravel may be overkill as well. If the soil under it will stay stable you should be good without the extra work.

Also we rarely do rebar any more in flat work and go with a stronger mix. My concrete guy that works for me has had a pad at his ranch 4" thick and was a six sack mix and it is about 30 years old with not a crack in it.

I just poured my RV parking last week with no rebar and used a 6.5 sack mix and am at 4.5 to 5" thick. No curing cracks so far and I drove my 1 ton flat bed fully loaded after 4 days onto it already.

The main reason we did not use rebar on my pad is that it is so hot out here that the metal heats up and sets off that part of the concrete too quick which results in cracks down the road.

I am not a concrete professional but i do work with it quite a bit.

 

[BridgeMan]

With the base material looking as dry as it does in the picture, after a wet Spring and Summer, I'd be inclined to skip the gravel base course myself. If this was in a situation where subsurface water was present, then gravel would be justified.

I've never been too keen on fiber reinforcement after experimenting with it on a few bridge deck overlays. However, using a 4000 PSI mix is definitely a step in the right direction, provided it's not poured too wet and has enough (grooved) control joints. Make sure the joints are at right angles to the walls and terminate at the support columns, because that's where cracking will want to originate from.

I'm curious what the "obvious reasons" are for you not wanting to make the pour yourself? You seem handy enough, and could save a ton of $$$. I don't know the dimensions of your basement, but judging from the picture, I'd guess the quote was up at $5000 or so, with the concrete costing only a tenth of that amount (based on 300 S.F. at 3.5" thick).

 

[MoreCowbell]

Thanks for the replies. I feel better about the suggestions the concrete guy made.

Bridgeman, I guess I should not have made it seem like such a crazy idea that I would pour the floor myself. Since my original post, I'm thinking more about it and I'm starting to take the idea seriously.

The floor is about 580 sf. At 3.5" thick that is about 170 cf of concrete - and I only have a 3.5 cf electric mixer. However, I'm thinking that I could break the job up into the same sections that I would be cutting up with control joints anyway.

I've done a boat load of digging already with this project, so the manual labor involved with pouring the floor is not too intimidating so much as my lack of confidence in getting a decent looking surface. Maybe I can start with the section that will be hidden by the stairs to see how it goes. I guess I shouldn't worry too much about it since after all it is a basement.