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cutting windows in a poured foundation

hmj's picture

My neighbor building an addition. Yesterday, the concrete guys put up the forms and poured the foundation walls. There was a miscommunication about the window size - neighbor wants larger windows. So, assuming a concrete saw would be the best way to enlarge the openings, when would be the right time to cut- sooner or later? The forms will be stripped on Monday.

(post #101836, reply #1 of 11)

every minute that passes, the concrete increases compressive strength, to a point.


it's always easier to cut green, fresh concrete, but to be honest, it really doesn't matter when it's cut.  a diamond blade mounted in a saw cuts it whether it was poured yesterday or ten years before.


 


carpenter in transition

carpenter in transition

(post #101836, reply #2 of 11)

Depending upon where the cut is made, and how big, he may run into trouble cutting thru the rebar forming a "bond beam."


My BI cautioned me about this.


 

(post #101836, reply #3 of 11)

Definitely cut the concrete sooner rather than later.


If the concrete between the window opening and the sill plate was designed as being load bearing he'll have to choose another way to support the load.  Often this can be a LVL  rim or a doubled rim joist depending on the amount of weight, span, and what the inspector will allow.

(post #101836, reply #4 of 11)

I have the "chainsaw" attachment for Bobcat.  That is the only way to cut a hole in a foundation wall in my opinion.


Sooner is better than later, but after about 30 days it should be completly cured.


I hope Chuck Norris never potato sacks me!!!!


bstcrpntr ---   I hope to grow into this name.

Wedding has been moved to November 14th. 

Doing a small ceramony now, big party in the spring!

(post #101836, reply #5 of 11)

"

I have the "chainsaw" attachment for Bobcat.  That is the only way to cut a hole in a foundation wall in my opinion."


 


I"ll admit I've never seen that and it sounds interesting.


There's companies that do that sort of work for you.  Core drilling is a specialized trade and quite amazing to watch.  They make quick work of openings in solid concrete walls and slabs.  Then they clean up, wash down, and are out by lunchtime.  Well worth the $$.

(post #101836, reply #6 of 11)

I have frequently used a firm that specialises in cutting cured concrete, for cutting egress windows into existing basement walls. They have a hydrolic saw with a 24" diamond blade that attaches to a special bracket  mounted on the outside of the exposed wall.  Set up , cutting, and clean up take about 45 min. and several hundred dollars, but it is the cleanest, and fastest way I have seen of doing the job.

(post #101836, reply #7 of 11)

The last guy who came out to one of our jobs to cut concrete with the big hydrolic saw was a stocky 6'6" and swung a 20-25 lb. sledge to break up what he cut out like nothing I've ever witnessed.  *chuckle*


It was sort of like watching a Conan the Barbarian scene.

(post #101836, reply #9 of 11)

Which attachment are you referring to as "the chainsaw"?


http://www.bobcat.com/products/att/thumbnails/index.html

(post #101836, reply #11 of 11)

looks like this


http://www.cessco.us/ics/71728.html


hooks to hydraulic lines on bobcat


I hope Chuck Norris never potato sacks me!!!!


bstcrpntr ---   I hope to grow into this name.

Wedding has been moved to November 14th. 

Doing a small ceramony now, big party in the spring!

(post #101836, reply #8 of 11)

The openings can be cut anytime after the forms are stripped. He really should consider hiring a pro with the big diamond saw. Trying to cut a ten-inch thick wall with anything else is IMO foolish and a waste of time.

We needed a 3' x 4' hole in a 40-year old foundation wall for an egress window. It took the contractor less than an hour from the time they pulled up and the bill (in 2004) was $260.

(post #101836, reply #10 of 11)

Nobody has yet mentiuoned the biggest problem he has.

Five will get you ten that there is rebarnot very far under the existing formed openning. The structrue will be seriously compromised if he cuts it. a larger openning can require more rebar instead of less.

i doubt I'd want to do it.

 

 


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