Capping concrete block

Squirl · November 08, 2011, 12:05:22 PM

I have finished building the block in my foundation. I have been asked a few times by individuals if I was going to core fill them. Since I designed my foundation with a balanced back fill I am not concerned with the shear strength. Code states that it can be up to 4 ft of unbalanced fill before requiring core filling or rebar. With no unbalanced fill, I am only worried about compressive strength, and with 600 psi compressive strength of concrete block it far exceeds the requirements of a 600 sq. ft. single story. I explained to the building inspector and other individuals I planned on stuffing the blocks with paper and filling just the top block. I did this already for the sill bolts. I got a few response of "oh capping the blocks." I had found this method in a few of the older books that I have. I have a few questions.

Is calling it "capping" the normal terminology? I can't seem to find much information on "capping blocks."

What is the logic or purpose behind it?

Is it required?

Redoverfarm · November 08, 2011, 12:39:59 PM

In my mind "capping" means just that not filling. You want to seal off the blocks so water does not enter and ultimately freeze to prevent the blocks from cracking. If however you are going to put a sill plate on top then it will accomplish this.

This is what I call "capping". The cap both fills the void in the block but also extends down the face of the block 1/2-1" on the block exterior surface. A authority in Mason & Concrete Work, Max Alth refers to the explanation that I gave in his 1978 illustration and book.

He also refers to "topping" a wall which is basicly filling the voids.

November 08, 2011, 01:11:19 PM

Thank you John. I will be going with sill seal foam and a 2x8 sill plate that will completely cover the block.

Don_P · November 08, 2011, 06:09:06 PM

It is referred to as capping the block. Old code was 4" thick min for 1 story, 8" solid for 2 story. I assume it helps distribute the load but I grew up with the theory it helped block the hidden termite tunnel. Yup crumpled newspaper, foam chunks... or in the old days vermiculite, which I've since learned was probably asbestos laden.

nysono · November 09, 2011, 06:53:50 AM

My concern with putting paper or anything in the block that will absorb and hold moisture is mold. Mine are only core filled where I have the J bolts, the rest are hollow. Sill seal and a 2 x 8 PT tightened down should be enough seal. I know someone who filled all blocks with insulation (unsure which type) and down the road there was so much mold it was unlivable.......just my 2 cents

November 09, 2011, 09:06:07 AM

Mold is a minor concern of mine too. I will probably be pulling the paper out of the unmortared holes. Hopefully the few with crumpled up mortar bags will not be as effected because they are almost 2 ft above grade.

UK4X4 · November 09, 2011, 05:40:59 PM

for Fill just cut 1" thick foam to suit the holes

push into place

I'd be worried about weight and the support to the timber over the years

only supported on the edge of the brick and the middle web

Rather than fully supported over its 8" width

For me for the price of 6 bags of cement and a day - I'd rather cap the walls properly than have issues down the road

nysono · November 10, 2011, 07:35:14 AM

Biggest thing I see right now is the need to get the walls capped before freezing temps. If all the cores fill with water and we get 20 below weather that will be a big problem.

Squirl · November 10, 2011, 11:13:57 AM

Everything is covered with a 40x60 tarp and it overlaps about 5 ft off all sides. Hopefully this will keep water out of the holes and away from the foundation. I am already having some troubles with water in the block. I have a high ground water table and heavy clay soil. Nothing seems to drain.

Redoverfarm · November 10, 2011, 03:34:27 PM

Quote from: Squirl on November 10, 2011, 11:13:57 AM
Everything is covered with a 40x60 tarp and it overlaps about 5 ft off all sides. Hopefully this will keep water out of the holes and away from the foundation. I am already having some troubles with water in the block. I have a high ground water table and heavy clay soil. Nothing seems to drain.

Believe it or not the block are like a sponge. I have seen them wick water up. Make sure you pay attention to the drainage system. If water is allowed to stand around the base of the block the inside will always be wet.