Rain water on footings 4

[scoopgh]

We had our footings for our new home poured seconds before a heavy rain. The surface has some dark spots and some of the gravel is at surface. After the rain I saw about half in or more water sitting on top of the concrete that remained until it evaporated.
What affect could this have on the concrete?

 

[Ron]

The surface and near surface strength will be significantly compromised. Use a screwdriver and see how far you can penetrate the surface. If more than about an 1/8", have the contractor bring in an engineer to evaluate. Assuming you have adequate thickness, you can have the upper 1/2 to 3/4 inch of concrete removed to get back to sound concrete.

If you are using masonry for the walls, you can add a bit thicker initial mortar course and compensate for any surface removal. If wood frame, your framing will need to be shimmed (with full bearing, pressure treated) to prevent slight elevation bust.

 

[scoopgh]

Thanks Ron.
With a flathead screwdriver I can twist it and dig just about 1/8 inches, but no more. Not all areas allow this penetration and are very hard.
I always thought the more water in concrete the weaker it would be.

 

[Ron]

scoopgh...you're probably OK. Water does not mix with the placed concrete. It just sits on top. Except for the shallow influence that you were able to find, there was likely no other affect.

 

[phuduhudu]

Just to back up what Ron said, I was very worried when I saw a heavy downpour soaking an RC slab the contractor had just cast. The surface looked bad but apart from a thin layer the concrete was very sound and the water probably helped with the curing. Carl Bauer

http://www.bauerconsultbotswana.com

 

[scoopgh]

Due to the integrity questions of the concrete. We were able to negotiate with the general contractor to have a structural engineer take a core sample and have a look at the cold joint. I ll let you know the results. You can follow my other concerns at the below link on this website. Thanks to everyone!

http://www.eng-tips.com/gviewthread.cfm/lev2/26/lev3/72/pid/592/qid/9604

We are also looking into a waterproofing method for the exterior of the basement walls, and would welcome any input. The contractor would like to use the asphalt mopping. He claims to use it all the time with no problems. We have read that the uncured chemicals in concrete will break down the asphalt or it becomes brittle underground. We plan to live in this home forever so a lasting product is key.

 

[Qshake]

Please see my response in your other thread.

 

[pgcpaul]

I was amazed this Saturday morning to see the road contractor pouring 6-8 inch thick concrete on new 5-lane highway in front of my property. Big revolving trucks dumping concrete into the bed atop limesone sealed with tar and puddles 1-2 inches deep in the pouring rain. A huge 10-ft wide forming machine leveled the surface and vibrated as it crawled along. I took pictures. Should I send these with a letter to the city Dep of Pub Works?

 

[RDK]

For pgcpaul

I would defiantly send the pictures to the authority responsible for the road. Just don’t expect any quick response. I’d send them to the highest level of the public utility and also to their political overseers. (If I was in a particularly nasty mood the local newspapers as well. Get a local structural engineer who doesn’t work for the utility to provide supporting comments on how bad the construction practices are)

For scoopgh

What you call waterproofing is really damp proofing. For the concrete basement wall to hold back water 100 % would be expensive and unrealistic. Even swimming pools leak. And they have soil pressure on one side and water pressure on the other. A basement would have water and soil pressures both on the outside. High pressures will result in small cracks that will then let the water into the house.

Dry soil has a unit weight of around 90 to 130 pounds per cubic foot. They also act like solids rather than liquids. Imagine piling dry sand at the beach. The sand will support itself at some natural angle of repose. This reflects the lateral pressure that would be on a basement wall. The steeper the sand will stand up the less pressure on the wall. Fully saturated soils can be up to 150 pounds per cubic foot. Now pile wet sand, it will have a flatter pile. That means that more lateral pressure will be exerted on the wall and the magnitude of this pressure will be greater due to the higher unit weight.

A better solution would be to ensure that no standing water occurs against the foundation wall and only rely on the damp proofing to shed the water as it travels through the soil to get below the foundation. Any of the damp proofing methods described will be adequate if they only have to shed moisture, none of them will be adequate if the requirement is to hold back water for a long term.

Use a granular backfill and weeping tile to drain the water away quickly. If you need details let me know as there are lots of standard details available. That way the wall only has to resist the moisture for a short time and then any moisture in the wall can also escape to the now dry outside rather than the interior.

The prime cause of water in a basement is the roof. Often the rain gutters simply serve to concentrate the water in one location and this allows the moisture to seep into the basement. A common situation, especially in new houses is that the backfill around the basement walls settles and the water cannot drain away from the foundation. Make sure that the rain water from the roof drains away from the house before it starts to seep in. Surface drainage is the fastest, extend your downspouts and have a positive slope right from the house to either the street or some other drainage path.
Rick Kitson MBA P.Eng

Construction Project Management
From conception to completion

http://www.kitsonengineering.com

 

[noemi]

It has been raining for days, and the trench that was made for our footers are now puddled with water. Can footers be poured in these trenches?

 

[boo1]

Allow them to dry, or you can pump the water out before you pour.

 

[conceng]

For your rain drenched footing trenches, you will want to pump out all the water and remove any remaining disturbed soils. If the near surface soils are disturbed, you may need to go a couple of inches lower and make up the grade difference with concrete or a layer of stone on the bottom. The main thing is make sure your footings are bearing on natural, undisturbed soils.

 

[BVM]

On 5/28/03 3pm new footings were poured for my addition.
One hour later it poured and the forms were sitting in 1-7 inches of water.
By 6pm the contractor had it pumped out and the footing were just sitting in mud with some puddles on top of the footings.
This morning at 6 am I pumped out another 1-2 inches of water.
I took a screw driver and was able to stick it into the footings, nickel size chunks 1/4 deep would flake off when I tested it in 3 spots...same result for areas with puddles as without.

Questions...what sort of test should be done before pouring the walls? When should it be done?

Any other advice...I'm not a concrete professional.

-B

 

[conceng]

-B,

At only 15 hours, the concrete should still be quite weak and would have only reached final set maybe 5 to 8 hours earlier depending on the mix and constituent properties. It takes time to harden and typically doesn't gain full strength until after 28 days. I've seen certain fly ash sources retard the final set to 12 or more hours. I depends on the mix design.

If you are really worried about it, I would have somebody cut a core after 7 days and test it at 28 days to see if reaches the design strength. If the rainwater wasn't allowed to mix with the concrete but only sat on top of it, there should be no problem. Did the concrete seem harder below that 1/4 inch? It may be that only the top 1/4" is compromised due to the rain. The puddling/flooding should not affect the concrete negatively.

 

[BVM]

Thank you for your reply.

I called a local structural engineer and got a similiar response...that the if the concrete was already able to bear load when the rain came then the water should actually help, not hurt the hydration process.

I spray painted a large screw driver tip and tried to stick it in the concrete. It seem real firm but not rock solid below the peice that crumbled off the top. The paint indicated scratch marks of only 1/8 of an inch.

-B

 

[wsheppard]

re: waterproofing concrete

There is a product called 'Densicrete' that you should take a look at from WickTek (

http://www.wicktek.com)

This has been used for years in waterparks, commercial roofs, etc., but is still rather unknown. Independent lab tests as well as actual years in the field have shown this product to be very effective. Since it penetrates the concrete, rather than lays on top in a 'layer', it doesn't have the same life-span as other 'coating' types of products, much better I think.

Densicrete will also increase the structural quality as well, usually by 20% to 30%+, i.e. higher PSI.

We are building a home with a concrete flat roof and are using this product. We will also use it on the basement poured walls as well.

NOTE: Densicrete won't magically fill big cracks that already exist, it increases the *density* of the concrete itself. Be sure to look at the application notes, they are simple but specific, i.e. concrete must cure 28 days before application, temperature ranges, etc.

PS - I don't own any stock in this company, unfortunately. Also, I'm not an engineer and you should do your own research. Hope this helps.