After talking to some contractors that want more money than I will pay I have decided to attempt a 24x38 full basement on my own (I'll have one buddy to help when pouring). I have decided on using 8x8x16 block for the walls and there will be no windows and no doors either. The floor plan is for a 2x6 wood supporting wall down the center lengthwise.

My "plan" was to put the footings around the outside (and center if needed) and then build the outside block wall. Next I want to pour the floor in two pours that are roughly 12 feet wide and 38 feet long.

Is it OK to have a seam (caused by the seperation of the two pours) right under the center supporting wall?

If so, do I have to put a footing under the seam or just make the edges of the two slabs thicker near the seam?

Also do I extend rebar out from the first pour across the seam to join into the second pour?

Do I need something for expansion between the slab and perimeter block wall?

I thought to give the wall support by filling every 5th vertical chamber with concrete and a rebar, is this a good spacing for this?

Do I put rigid insulation between the footing and the slab or do rest the slab on the footing and just insulate betwwen the earth and the slab?

See, I told ya I needed advise.

Kevin

 

The best advise you could possibly take would be to hire a structural engineer. After he does his job, most of your questions will be answered, and the rest (involving technique) will be readily answerable here.

 

>(I'll have one buddy to help when pouring). (Kevin)===========

It's going to take you forever by yourself


Go ahead and get outside footings squared, formed and poured. This includes a footing for that center wall (8"X16") if you need to, make sure your basement stays dry plan a tile layout outside and inside the footing. Connect both tile runs through the footing and into a deep sump pit. If the site is really wet, include some runs across connecting with tees to inside tile run.

Now, hold everything. You want to build entire basement wall to finish elevation before you pour floor? Consider only obtaining enough 8" concrete blocks to get one entire course layed on the new footing. You have just formed your floor pour and it will be so much easier to step inside and out over one block when pouring and finishing the floor. Now, the blocks for the rest of the courses were not in the way and it's now time to have the other blocks delivered. Have the driver boom the blocks right down on top of the new floor but it a few days to cure first. You will want them handy because that's where you will need them to finish up walls.......and you are now out of the mud for handling scaffold and laying blocks. It's much easier to handle the concrete this way as opposed to going full height this soon.

====================

<Next I want to pour the floor in two pours that are roughly 12 feet wide and 38 feet long. >(Kevin)
====================

That's ok but the disadvantage will be the seam but that sounds like it will have a 2 X 6 wall covering it anyway.

We always poured the floor right across the footing and butting to perimeter block leaving 4" of block height exposed. No expansion joint or foam in a basement floor because you want the floor to buttress that first block. Grouted rerod every 5th block core? Wouldn't hurt a thing but you are going to have lot's of grouting to do. Check it all out with your local building officials first. Good luck.



bs5

 

Take your plan to your local building inspector. Codes tend to vary from area to area. The building inspector will tell you if what you plan to do is up to Codes and can help you with permits and advise you of what inspections are required in your area.

 

Kevin -

If you try to go with 8" thick block walls, you will need some vertical steel reinforcement in the block cores. You do not have to fill the cores without steel. If you go with 12" thick block, you may be able to eliminate the reinforcement, depending on the soil type and grade outside.

For the wall down the center, you can go with wood frame (2x4 or maybe 2x6 @16" O.C.) or you can go with a steel beam supported by several columns. The second method gives you a more open basement.

For details on basements, go to the National Concrete Masonry Association web site and look in the TEK notes (there are over 100 on different subjects) - the address is www.ncma.org.

The best thing to do is visit you local code people to see what kind of local requirements there may be.

Good luck!!!

Dick

 

All the villages I have ever worked in for the past thirty years have a code for a fire escape window to be placed at the opposite end of the stairwell leading into the basement. This is an oversized basement window that slides open in case the stairwell is burning while you and your family are down there watching TV.

There is also a code for “light and ventilation”, which means that X- amount of natural light and ventilation is necessary for each room.

The best way to pour concrete is monolithically (all at once). 24’X 38’= 912 sq ft = 11.5 yards at 4” thick. You and your buddy will be found dead and set-up in the concrete if you try to pour that by yourself’s with no prior concrete experience. Splitting it in half is ok but I would suggest hiring a finisher on the day of each pour and you and your friend labor for him. Concrete bonds well between two pours for the first twenty-four hours, so prepare the second pour ASAP after the first.

I would NOT split the floor under the support wall, split it the opposite way. Instead of a footing under the wall there is something called a grade beam that can be poured with the floor. What it is… is this; After you grade the gravel base of the floor run a string line where the support wall will be and dig another four inches down. The beam has to be twice as wide as it is deep and the four inch floor is included in its depth, so you now have an 8” deep trench that has to be 16” wide. Place two #5 re-bar’s down the length in the middle of its depth, do this for your footing as well.

You do not need expansion in a basement because it is not exposed to weather extremes, but you do need a vapor barrier over the gravel base.

If you do pour in two sections I would use short #4 rebar (12”) to attach the floors at the seam, your base may settle unevenly.

And YES you will need drain tile; at the very least all around the perimeter and into a sump pump inside, or it will flood. The exterior drain tile lies alongside the footing and is covered with ¾” washed limestone, don’t forget to waterproof your exterior block wall.
If the code says you need the windows I spoke about you will need to install window wells to each window. Have a drain from the bottom of each window well that runs down to the exterior drain tile or the window well may fill up with water.

Good luck buddy, I can appreciate your willingness to take on this challenge.

 

BS5 said:

-------"Consider only obtaining enough 8" concrete blocks to get one entire course layed on the new footing. You have just formed your floor pour and it will be so much easier to step inside and out over one block when pouring and finishing the floor."------

Good idea, or do they make a 4" high block that one could just run a screed (spelling) board across?


-----"We always poured the floor right across the footing and butting to perimeter block..."------

I don't know how to level a pour that wide, how do you do it? Thats why I had originaly planned to make the pours 12 feet.


-----"No expansion joint or foam in a basement floor..."--------

Are you saying not to put 2" rigid insulating foam under the slab?

Thanks for the help.

Kevin

 

Kevin -

You pour the footings and then lay the block. When you pour the 4" floor it should sit on the footing, leaving 4" of the first course of block showing above the floor.

You do not need 4" high block (usually available in 4", 6", 8", 10", and 12" thicknesses in most areas), unless you want to meet a certain unusual wall height. In some areas 4" high sold units are used for the top course.

Insulation under the floor is nice, but usually not needed. If you insulate, do not insulate under a grade beam. Definitely put down a vapor barrier over gravel before you pour the floor.

Dick

 

Hi Dick,

The idea behind the 4" block was to just make the first course 4" high, then it might be easier for someone inexperienced like me to keep the slab level. Is this a bad Idea?


Well, you talked me out of using insulation under the slab. When an action saves money it can be rather easy to convince me to do so. I have some research to do locally including the maximum reach of the shute from the rear of a ready-mix cement truck.


Another question I have is do I need control joints along the 38 foot length of the slabs or do basements not require joints?

Thanks for the help.

Kevin

 

I can't speak for the other masonry trades, but as a concrete contractor I would strongly suggest you hire a professional to pour the floor. Believe me, I do NOT say this just because I'm a contractor and try to discourage DIY's, I am saying it because I have never once in my life seen a (large) homeowner concrete project turn out well. Especially a smooth trowelled slab. An interior slab is much harder to do than a broomed exterior slab.
If you feel that you MUST do it, then at least hire an experienced finisher or two to help you out. They will know what needs to be done and when, and the proper tools to use to do it. There was a similar thread last year where a guy wanted to pour his own driveway. He did it, but really regretted ever having tried. I will go back through the archives to look for it. It may help you out a bit. Good luck.

Pecos

 

Kevin H: "Another question I have is do I need control joints along the 38 foot length of the slabs or do basements not require joints?

Thanks for the help.

Kevin
=====================

If this basement is properly excavated (no deeper than necessary requiring large amount of fill)and drained and on soil of reasonably good compaction and load bearing capabilities I don't believe I would be too concerned with a control joint especially since you are considering pouring the floor with a cold joint in the middle (two pours of 12' width). If you still feel a need why not just settle for a diamond saw cut as soon as you can get on top of the new floor no deeper than 1/2" across the middle in an effort to try and control where an shrinkage cracks might appear.

So far as the floor pour is concerned, Pecos suggestion of hiring a good concrete flatwork crew is well advised. An inexperienced crew needs not to be in charge of your basement floor. You will not get a second chance when that redi mix truck pulls into the jobsite with his drum rotating. They will pour that floor in one shot with no seam down the middle.

bs5

 

Cost?
It is an ancient technology and some villages won’t allow it… and I’ll tell you why.

After you build on your foundation you will be adding ten of thousands of pounds of lumber and all the other materials to it. When your footing settles, and they will… every mortar joint in your block wall is a potential crack that can separate. After you backfill, the dirt puts a ton of weight on your cracked block wall and can push it in on you years later.

A concrete foundation wall is locked into the footing with a keyway, the rebar ties the entire wall structure together so when the footings settle the walls settle with it, uniformly… and sometimes they even crack, but with the reinforcement bar they do not separate. I have seen concrete foundation walls without re-bar crack and push in from the presser of the ground on the other side.

The longer you leave the hole open to lay block, the more dangerous it is to work down there. As the earth sidewalls of your basement hole dry out they are more likely to cave in on you. Back when I was a young man and worked the foundation crews we worked fast, three or four days to complete them… they did not even dig the hole until we were ready to start.

I’d like to also tell you that we have NEVER poured a basement floor until AFTER the house was built and for the same reason. While the building is settling it will crack the floor. Another reason is until the house or structure is over the basement and there is a floor down there without a sump pump… all you are building is a swimming pool.

 

If you don't care about random cracking, crack control joints are not necessarily needed. The joints are to control the location of the cracks that happen, because they WILL happen! The main reason a slab cracks is due to shrinkage as it dries. The wetter you pour the concrete, the more it will shrink and crack. Don't make the mistake of pouring too wet in order to make the concrete easier to move around. You will regret it if you do.

If you pour concrete around a corner that points into the slab, the concrete will crack at that corner. This would be a good place for a joint. If there are no re-entrant corners, divide the slab into roughly equal sections no larger than about 12x12. You could put one down the center lengthwise, and then cut two more widthwise creating six 12'x12'8" sections. The extra 8" won't really hurt much, but leaving larger sections is asking for cracking between the joints. As with any concrete, the joints should be a minimum of 1/4 as deep as the slab is thick. (1" deep on a 4" thick slab, 1.5" deep on a 6 inch thick slab, etc. I would recommend saw cutting them the next day with a concrete saw with a DIAMOND blade made for green concrete. It will make the job go ten times faster than if you try to use a fiber/carbide blade. Wear a respirator for the dust, you don't want to get silicosis.

All basements around here are poured after the basement walls are up, but before any framing takes place. A sump pump attached by an extension cord to your temporary power is left in the sump pit to get water out of the basement after a rain. As noted before, if it's not a walk-out basement, it's a bear to get the tools, trowel machine, etc. into and out of the hole when you are pouring and finishing.

I still recommend hiring some experienced help. Good luck!

Pecos

 

I wish I had your energy!

Before you get too excited about pouring that floor right away, don't forget about your underground plumbing. Maybe I'm stating the obvious, but........

 

When ever we had a job excavated,the digging started three feet beyond the corners in all directions. In this part of the country, three feet was plenty sufficient to set the building lines and waterproof exterior walls and do drain tile as well. A couple of times when basements went into blow sand or with springs (running water) the excavations might not hold. Places like that got a bigger hole excavated right off the bat.

It can be difficult to get materiels and equipment down into a basement excavation. Our solution was to pick a place where there would be no sidewalks or porches or decks and have the excavator (usually a track hoe) dig us a nice ramp. Many times, we could even drive the front end unloading redi mix trucks right down in the hole. Our mud tenders even wheeled the mud wheel barrow by wheel barrow down the ramp. This worked fine so far as we were concerned. Ramps did not have to be all that long to work.

Sump pumps: We talked about that earlier as well. Remember, we tiled and installed a sump with the footings. Whether or not it was wet, with roof or without, and regardless of when the floor was poured. It was not a problem to drop a sump pump in the sump and plug in at any stage.

Concrete walls vs. block. If the sky is the limit so far as funding is concerned, go ahead and pour walls with as much rerod as you want. They look pretty. On the other hand, if this is a project that you are trying to control costs on and you happen to be able and willing to do it yourself, you may have discovered you can probably save your self some bucks. Sure, once in a while they fall down, but then so do poured walls. Like when you rush and backfill the whole thing before any weight is on those walls or run into the middle of a new Wall with a bulldozer. Poured walls are stronger but Block masonry has proved substantially adequate over the years. You make em stronger too by adding vertical rerod(stubbed right out of the footing within block cores and grouted to top usually installing an anchor bolt for top plate. you can include durawall truss tie horizontal reinforcement in every darn course or perhaps every second or third. You can even lay in a course of rerod horizontal by laying a header (lintel) block and filling with concrete which is usually overkill in my book for the average wall.

So how about backfill: We only backfilled block walls at corners and maybe a couple of feet along wall. Until you get some weight on those walls (like floor joists and sheeting and even better a house) you have a giant eggshell sitting there. Even poured walls have limitations but they tend to be stronger.

Forces of pressure over the years: Walkout basements are more susceptible to to damage due to the uneven weight of fill on uphill side. So you plan for a more substantial wall on that side. Lot's of ways to add strength like adding a shear wall or building the uphill wall out of 12" block.

Water pressure: Hydraulic pressure can be phenomenal over the years when exerted inward against a foundation wall. It is imperative to relieve it for either system of block masonry or poured walls. So you can help do that by seeing to it a slope exists shedding surface water away, backfilling with granular soil so water can take path of least resistance and go down to tile and eventually sump. We don't need to dam up any springs beneath the surface with a basement wall because if you do it's trouble.

Weight of structure. Somebody was talking about reducing weight on a typical footing and advocating for poured walls because the block joints could crack under stress. I think if those types of forces were being exerted against a basement wall, one of poured concrete would also be in trouble.
But, if weight is the issue, which wall do you think weighs the most inch per inch?

So, each wall has it's advantages and some of us agree and some disagree but either method needs to be accomplished with good design and careful workmanship. Go for it but it is still a big chore for one person.

bs5

 

Kevin,
I found the thread I mentioned before. It's on page 19 and entitled "how to spread concrete from truck chute". It is about a DIY driveway project, but the gist of it is about the DIY part, not whether it's a driveway or basement. The running commentary, particularly the post-pour follow-up by the DIYer, is particularly telling.

Pecos

 

Here's thread:

http://forum.doityourself.com/showthread.php?t=256997

(Correct me if I'm wrong)

Posted the url as the page #'s will change as new threads appear.

 

Concrete Man,

"Why block?"

Of the contractors I talked to one said that he has 11 foundations ahead of mine come spring and that is if I got on the list today and the other said he didn't plan that far ahead and already had work lined out for spring. Both gave rough esimates of 8K-10K with costs possibly running over. There was one more but I couldn't reach him and he never called back. I am not going to atempt to make a full set of forms to pour the walls. Block is the only thing I think I can handle and I will save some money too (hopefully).

This is a cabin that originally was just going to have a crawl under it anyway so if the basement floor has a few seams and is a little rough thats ok, I'll do my best to smooth it though. All I'm going to do with the basement is store stuff down there and have a workshop/hobby room along with a pressure tank, cold water heater, a wood stove and firewood.

If I seam the two slabs in the other direction like you say I will have 2 big squares which sounds harder to pour than two long skinny rectangles. I want to seam down the middle over a 8" x 16" footer. My other thought is to run a 6" wide course of block down the center supporting wall footing and pour on both sides of it. Then frame my wall on the 6" wide block. Which is best?

Kevin

 

Pecos,
I read through the thread and it reminded me of when my father and uncle poured my dads 48" x 26' shop floor. I'm glad I was in high school for that one.

I'll put joints in. But I think I'll rent the hand tool rather than buy a breathing mask and a saw blade for a one time project.

Late next spring I'll come back and let everyone know how it went.

Kevin

 

Think about what Concretemasonry said about using the steal as your floor support. You can pour the way you planned and eliminate the grade beam and other complications for your basement floor pour. You need to only pour concrete pads for the steal supports along with your footing. But you will have to wait to pour the floor until AFTER the steal is installed.

No need to cut joints in your basement, It stays close to the same temperature year round… shrinkage cracks are different from stress cracks.

Sorry guys I’m not a fan of block foundations especially basements… I have seen to many come apart and leak.

 

No matter what codes you have to follow where you build your cabin (probably none) DO HAVE an escape window in case of fire. If your luck is like mine the stairway will burn when you are down there.

What the heck are you building down there anyway… A dungeon!!

 

Kevin,
seeing as how this is just a workshop/storage under a cabin, I change my opinion. You can do it yourself. If it were me though, I'd rent the saw and blade, buy a cheap paper dust mask, and do the joints that way. Tooling the joints in could be difficult for a novice. If you do tool them, try to get a "walking jointer". This is just a jointer that screws into the bullfloat handles so you can tool the joints from the edge without having to crawl out on the slab. It will save a LOT of time and headaches. Good luck, and post back with your experiences! They will definitely help others who are considering this option. I wish more DIYers who got advice from this board would do a follow-up posting, good or bad. It would be valuable for others.

Pecos

Pecos

 

Local codes require only vertical reinforcement at 48” centers with either #5 or #6 grade 60 rebar depending on soil type. This is for an 8” deep masonry foundation wall with a maximum unbalanced backfill of 7 feet. This means I have to fill about 32 vertical cells and I can spread them out over a few days which is good news.

My biggest obstacle now will be the concrete placement of the far half of the floor. The trucks chute will only reach a few feet over the form and it will be up to me to get it the rest of the way (10 feet or so). I’m thinking of making a chute about 10 feet long unless someone here has a better idea. Hiring a line pump would run $400.

Kevin

 

I know it doesn't seem like it, but to wheelbarrow the concrete from the end of the chute to the corner will be faster than building a chute. There are several reasons for this:
1) unless the chute is covered with sheet metal or some very slippery material, the concrete will stick to it somewhat and the concrete will not slide well. Also, to get it to slide the chute would either need to be tilted at an extreme angle, which would shorten your reach quite a bit, or the concrete will have to be poured very wet.
2) As discussed before, wet concrete is weak concrete. If you want to pour wet, ask your concrete producer about superplasticisers. They allow you to pour wetter without loss of strength. Don't just add water to make it wetter. If you do, your floor cracks will seperate a lot more.
3) If you used a wheelbarrow, you could dump it exactly where you needed it instead of trying to move a heavy chute around, saving time. After you work back toward the truck far enough, you can pour the rest directly out of the truck.

Regardless of whether you believe me or not, I speak from over 20 years of experience on this matter. I've used store-bought chutes and homemade ones (even ones that I lined with aluminum flashing), and none of them were faster or easier than a contractor's grade wheelbarrow.

If you still want to go the chute route, you may consider renting an aluminum chute from a rental yard. They are about 16 to 20 feet long and connect to the truck's chute with a chain. They should be fairly cheap to rent. The same problems though. They are cumbersome to move around and the concrete doesn't slide well unless poured wet. Good luck.

Pecos

 

I'm back with another question. Do I need the corner blocks below grade or are they just for looks above grade where people can see them?

I have also decided to put an escape window in and reduced the length to 28 feet.

So far costs are looking about like this.

Block - $1600 (includes delivery)
Floor pour - $700
Footings - $350

Not sure how much mortar I will need for 12 courses of 8x8x16 block 24 x 28 outside dimensions and filling 26 of the hollow cores with mortar from the footing to the top so maybe someone can give me an estimate on that.

I haven't priced rebar yet but I hope the total costs of the concrete and masonry part of the basement comes in at about $3000.


Kevin

 

I am ready to pour the floor at this time and would like any tips on finishing the floor that one could offer. I know to float the floor right after I screed it but not too much and then after the bleed water is reabsorbed and the concrete is set up a little I am supposed to float it again supposedly with a magnesium float and then after that a steel trowel. I am wondering what is the proper technique and tools one should use for the second floating and troweling. Do I try to stay off the slab and work from the edges with tools that have extension handles on them or do I use the hand tools and crawl out on the slab or possibly a 2x10. The rental shop said they had both kinds of tools and weren’t really any help at all as far as advice goes. The floor will be split into two pours on different days and each slab will be 11.5 x 27 feet.

Kevin

 

Contact your local building code office before proceeding with anything. You need to know the codes and get the permits. If this is a rural property where inspectors and codes tend to be nil, then at least know what the state codes are for construction in your area. Be aware that codes are 'minimum' requirements.

 

I know it has been a while but I should tell how it all went. When pouring the footings all went well except it was difficult trying to pour the heavy wheelbarrow into such a narrow area and we had a new employee from the concrete outfit that couldn’t seem to keep pace with me operating the wheelbarrow. He would either send it to me way to fast or nearly stopped. I made the mistake of not going back through and lifting my rebar up to the bottom third of the footing but it was only sagging in a few places. Pouring concrete is very stressful and I think that is why I forgot.

After it set I laid a four inch high course of block that would be the base of the basement wall and serve as a form for the floor pour. I made two separate pours for the floor with the seam under the supporting wall with only a part of it showing under a door. On the first half I did everything just as I had read off of many sites on the net but when the bleed water absorbed back in it was already too hard and I knew it wasn’t going to turn out like I hoped. I did manage to make a somewhat flat and smooth floor on the first side but at the cost of two very sore shoulders.

On the second half of the pour a few days later I decided to ditch the instructions I got off the net and do things my way which involved working the concrete a lot more than was recommended. The second pour turned out much better but again my shoulders were sore. I also learned that from the time that it is ready to trowel to the time you better be done troweling isn’t a very long time or at least it didn’t seem like it.

A few days latter I had the block boomed down on the slabs and started what was the most miserable part of the entire house. If you are some kind of twisted person who enjoys pain, especially lower back pain, you might enjoy laying block. It took me 11 days to do the basement wall.

Next came something that I severely miscalculated and never seen coming. Code recommended filling cells of the wall every four feet from the footing up and inserting rebar. This works out to filling one sixth of the wall. I knew I had to do this but I had never figured just how much concrete it would take which turned out to be somewhere around a yard and a quarter that I had to hand mixed in a five gallon bucket. I went and bought a paint mixer for 15 dollars and attached to a heavy duty Milwaukee drill for mixing. I would have to say it was the best 15 bucks I spent this summer.

If I had to do it all over I would have done one of those monolithic pours with the footings and floor all in one and I would hire some help for it. I then would dry stack the block, fill the entire wall with concrete from a truck and paying a pumper to come out if necessary and then maybe skim coat the outside of the wall before sealing it.

The best advice I got off here was to use a wheelbarrow to get to where the chute will not reach. I recommend two wheelbarrows.

 

Several suggestions -

You do not have to use rebar in the footing according to many codes as long as it is a reasonable size - 16" or 20" wide by 8" thick for for an 8" wall and 4" wider for a 12" block wall.

Most contractors will pour the footings first, lay the walls, brace and then backfill. After that, pour the floor when the utilities are in. If you have rain expected overnight, lay one course of block on the footing the day you pour footings it to keep it above the water. Around here, it is 3 days to pour footings and lay the 8" or 12" block walls (4 man crew).

Do not lay a 4" high block for the first course. You should use a 8" high block and you should make sure you have the vertical rebar dowels projecting from the footing.

I hope you put in drain tile - interior exterior or both. The material cost is the little and it is the best insuarance (structural and water)you can have.

Even if you dry stack and fill the wall solid, you will still need vertical steel. After dray stacking an 8' high wall, most peole find out it is just as easy and much better to use mortar.

Dick

 

Dick,
I put in vertical dowels stubbed out of the footing into the cells that I filled and yes I put perforated pipe covered with rock around the base of the wall on the exterior that gravity drained down the hill into a hole filled with a yard of left over drain field rock.