concrete wash pad

My 17 year old son wants to put a 20'x 20' concrete pad in to pressure wash his 4 wheeler and pickup truck off on. We are in the northeast (just outside of Buffalo Ny). Plan on making it 6" thick.Biggest tractor that would go on it is 8,000 lbs.The question is, can this pad just be poured with out any kind of footer?.We plan on using steel mesh as reinforcement and digging down to keep it slightly above grade.Any input on base materials and such would be great. Thanks, Bill M.

Cut out the topsoil and compact some crushed stone and pour a one foot by one foot thickened edge when you pour your slab.Jim

That is mighty thick just for that. I would think you could get by with a 4".

What good will a 1 foot x 1 foot edge do when they have at least a 3' freeze dept up there?

Flaoting slab. I would use a non-frost suseptible material on the subgrade, ie. ballast, modified subbase, something that won't expand when frozen. Roadstone will, too many fines that will hold water.

Yes that will do fine. It will be a "floating pad". Probably doesn't have to be that thick either.

It keeps the edge from breaking off. Also give a little more stength when it floats.Jim

I would measure my pickup first and possibly lengthen it to 24' as I know my suburban measures 19' and I would think an extended cab crew cab pickup as many have, would be close, obviously your choice. If your in well drained soil already I would throw down a 8-12" of clean compacted sand.
Poor a 4" thick 4500 psi mix. Order at at least 7% air entrainment. Install 1/2 rebar 24" on center. Run it both ways tie it and place on chairs(busted up concrete block works well)to hold it up to correct height. Get plenty of help and poor this mix relativly dry. (3"slump)
Pick your day cool temps, clouds and little wind. Pushing the weather and help factor because you want the lowest water cement ratio you can work with and still get finished. Adding water to increase workability will weaken your mix. Cure slowly for 3-4 days, keep the top moist and covered with wet burlap or cover with curing compound. Always been an age old debate about using mesh. Personally, I just came back from my 4th week of bridge construction class. Looked at plan after plan of multi-million dollar bridges. NO mest to be found in ANY part of those structures. In frost areas a floating slab structure will crack, the close 1/2" bars helps ensure the impending cracks stay tight and the sections stay in the same plane. Good Luck!

1' x 1' or more thickened edge is very important. I'd also saw-cut the slab as soon as I could, into 12' or 15' squares. That way the cracks (and it will crack) will follow the saw-cuts, and you'll never notice it.

I poured a patio that size last summer, Had some Amish do it. Poured it 5 1/2 in put a lot of concrete wire in it. also about a 5 ft walk on one side and a 20 ft walk on the other. put double wire where they joined. Also put 1 in blue board insulation under it all. It is on top of about 8 inches of 5/8 chips. Hasn't cracked yet. I know there is two types of concrete, that, that has cracked and that,that is gonna crack! Vic

I poured one like that in 1976, with a 12" x 8" wide wall around the outside, 4" thick, reinforced with 6x6x10ga. mesh. It has cracked, but stayed in place. Great place to work outside. And by the way, I was forced into it by the kids, gotta have a place to play basketball.

Ive poured numerous slabs for customers over the last fourty years, and have tried many different bases ,I find the best is to remove topsoil or sod without disturbing the subsoil if possiblethen if you have good drainage away ,fill with 3/4 inch screened gravel about 6 inches in depth, this keeps the moisture from building directly under slab and when freesing occurs the gravel will shift under the slab ,I also would pour 6 inches thick with 5/8 rienforcing at one foot centres ,also would go at least 24 feetlong to accomadate longer units ,and slope pad 4 to 6 inches and only backfill about 2 inches up on concrete , in no time the slab be lower thal lawn or whatever from buildup of grass trimmings or dirt washed from vehicles ,its a floating slab so let it float. also have done some with a styrafoam frost barrier under usually use 3to4 inches of foam extending 2 feet beyond pad to keep frost from migrateing under pad, cost another 2-3 bucks a square foot . control jointsat ten and twelve feet recomended ..

Maybe one day, you'll want to re-use the pad for a small shop or garage? I think the removal of topsoil, and compacted crushed rock as a foundation are good ideas, also the thickened perimeter and maybe a few "J" bolts for future considerations.

I'd design it to put a garage/shop on, then use it for a wash pad in the mean time.

Just my 2 cents...

Troy

I think my wife would kill me if we ever built a shop on the pad. it will be sitting in front of our 88x54 pole barn.Although, the boy is bugging me for a heated section of the pole barn (cant take the cold,not as much natural insulation as dad I guess). bill

A 4" slab would be thick enough for that purpose. I would make it 6" around the edges and put a good bit of sand under it. The sand will cushion it against the soil shifting. Since it will be exposed to the weather I would use a six bag mix or rather todays terms would be rated at 3750 psi.

I seem to recall when I first saw people doing this years ago they referred to them as "Alaskan Slabs".
I do remember that they always made the outside edges thicker and put a layer of crushed stone or gravel as a base.
I"ve seen a few inside pole barns.

Only problem I see is now you have to clean the pad off ! Especially if you get some nasty thing full of grease to wash off.

Nice thing about doing it in the gravel drive a pass with the blade takes care of clean up.

I live 35 miles west of Buffalo, NY and built my shop 10 years ago. Poured 20X20 ft. pad in front of it. Like the post below I skimmed the top soil and put in 4 inches of gravel. Compacted with a tamper from the rental store. Put down an inch or two of number 2 stone and used wire mesh.
Used 6 inches of 4500 lb. cement batch. Scored down the middle and no cracks yet.
Probably overkill, but maybe I tried to make up for all the years I could only afford gravel, 2,3,4 inches of cement. Regularly run my loader over it
and it weighs around 27,000 lbs.
ps Nice weather we have had this winter.

lots of good advice posted...

My thoughts,

1) Air entrainment is best for keeping the concrete from freezing.

2) The city or county, have approved mix designs that they use. You can get this same mix. they have done engineering for their climate and use. the ready mix company will have copies of this too.

3) Keep the slump as required by the mix design. (don't let em pour it too wet), let em cry...

4) Place this concrete on a stable (compacted) base.

5) Saw cut (score) the slab early to control the cracks. You can groove it with a tool instead of cutting if you want. I'd say at least at the halfway point. 3/4" is plenty deep for a cut or groove.

6) Tamp it! this helps fill voids and works the concrete around any reinforcing you might have, (I recommend it).

7) Don't finish it slick.

8) provide drainage.
...sl

thank you for all the constructive input. sounds like most of you are in agreement. Bill

(quoted from post at 20:24:47 03/07/12) My 17 year old son wants to put a 20'x 20' concrete pad in to pressure wash his 4 wheeler and pickup truck off on. We are in the northeast (just outside of Buffalo Ny). Plan on making it 6" thick.Biggest tractor that would go on it is 8,000 lbs.The question is, can this pad just be poured with out any kind of footer?.We plan on using steel mesh as reinforcement and digging down to keep it slightly above grade.Any input on base materials and such would be great. Thanks, Bill M.

Click to expand...

Sub grade is the issue, frost in Buff would be approx 36", if you are in granulars the soil is not frost susceptible . If you are in silts and clays you need to remove 30" of material and replace with Gran B or A and make sure you add sub drainage so the grans do not get saturated. Alternately you could provide 12" of gran along with 2" of Sm rigid insulation under the slab, plus drainage. Insulation and granulars must project 36" beyond the 20' x20' perimeter of the slab.

After that if you want to use a simple flat plate that will work without saw cuts as long as you provide reinforcement, use 4x4x6 ga welded wire mesh in FLAT SHEETS, and a 5" slab, 4 percent air, 3" slump, 4000 psi ( salt protection ), do not, do not, under any circumstances add water to the mix on site!

If workability is an issue use a water reducer in the mix or super P.


Ensure your steel is pulled up in to the centre of the slab, I would also use 2 slip sheets of 6 mil plastic under the slab and make sure the sub grad is very flat. This will prevent shrinkage cracks. If you go with thickened perimeter as suggested in other posts you will need to saw cut the slab into 10x10s as the slab will crack. The thickened edges trap the slab from expanding and contracting symmetrically.

You also need to provide proper curing, use a curing compound, avoid pouring on hot dry days with wind. Cool, cloudy days at 50 degrees are the best for amateurs.

Hope this helps

Jim

A 6" slab is fine. Do not cast a footing around the perimeter. Wire mesh will work. You might think about No.3 rebar but rebar will cause more cracks than wire. Saw cut control joints in the slab 1/3 the depth of the slab on no less than 10' x 10' centers the day of placement, not the next day or a week later. DO NOT dig the slab down below grade. You want to break the bond between the slab and the ground. Burying the slab will increase the bond and prevent the slab from moving when the ground freezes and heaves, causing the slab to crack. Talk to your local ready mix company about base. Does anyone in your area use 1.5" drain rock or pea gravel for base. The ready mix supplier always gets accused of selling bad concrete when the cracks appear and will be well informed about what you need to do to avoid a similar problem. Put as much rock as you can afford under the slab and drain all the water away from the slab and the base. A wash pad in an area that freezes is just waiting for the ground to expand and heave. If the slab is totally separated from the soil, it will rise in one piece and subside in one piece when the ground thaws. Hope this helps.

There's 200 ways to screw up good concrete. You didn't mention what time of year you would be placing the mud and what the weather conditions would be like. These factors will have a big impact on your slab as well.