FINISHED IN 2020! Sharward's Partial Garage Conversion

Post by **sharward** » Sun Dec 11, 2005 4:21 am

Those pictures are of the east wall. The water is in the ditch along the west wall, which is about a foot deeper than the east and south. I'm considering backfilling the west wall so that it's close to even with the east and south.

Thanks for the cheers!

Post by **sharward** » Mon Dec 12, 2005 3:34 am

I just ordered a DVD titled "How-To Build a Monolithic Concrete Slab Foundation"...

...from The Dirt Cheap Builder...

It ships out of Northern California, so I should get it soon.

Note that I'm not planning on doing all of the slab work myself... But I think it's good for me to educate myself thoroughly on the process so that I can properly interview contractors and effectively supervise the pour and finishing. Also, in the event that I do have to "bite the bullet" and consider doing the pour myself...

...then at least I'll have a clue!

Post by **sharward** » Mon Dec 12, 2005 12:02 pm

I've been busy contemplating how to set the concrete forms. I'm essentially torn between two schools of thought, specifically along the existing foundations (where I chipped away the excess concrete):

Set the forms in a rather conventional way, using stakes and forms that are intended to be removed after the concrete has cured, then fill the gap with some kind of closed cell foam (perhaps in liquid form?) after the forms have been pulled;

...or...
Install perimeter isolation boards first that will also act as forms for the pour, with the intent of leaving them in place after the concrete has cured.

#2 seems like it would be easier, less expensive, and "tighter" along those existing foundations. However, I'm concerned about damage occurring to the perimeter boards during the pour or screeding process that could jeopardize the isolation properties of the slab, since those boards will obviously not be nearly as strong as conventional wooden forms.

Bear in mind that this "debate" only applies to the 40-or-so linear feet where the new slab will be bumped against the existing concrete foundation (east, south, and southwest walls). It does not apply to the L-shaped area that will ultimately join with the existing garage slab... So you needn't worry about the isolation boards breaking loose and having concrete blowing out and spewing out of control. Since there is more room along the L-shaped area, I do intend to do conventional wooden forms there, then adding the perimeter board to the slab after the forms are removed.

I'm also considering using Roxul DrainBoard, assuming I can get my hands on it. Here's the spec sheet. It's a water-repellant mineral wool insulation board, designed for use below grade on the exterior of a foundation wall. It comes standard in 1" thickness (or maybe 2.5", but that's special order). I might consider using two sheets glued together to make 2" thickness.

Here's an illustration to hopefully make option #2 more clear.

Please share your thoughts -- especially if you have concrete experience!

Thanks...

len-morgan · Post by **len-morgan** » Mon Dec 12, 2005 10:48 pm

Good Morning, Keith!

While the only concrete experience I have involves a jackhammer and a trip to the ER, I do have some thoughts.

First off, on the Roxul product, I read the data sheet and appears that you don't want to have the product touching the foundation (see the picture on page 2) so I would think that you'd need at least a plastic sheet next to your current foundation, then the Roxul, then ANOTHER plastic sheet should be on the new pour side. Even before reading the data sheet, I wondered what would be the effect (especially considering the amount of water that is in your soil), of having a wet blanket of rock wool laying against your current foundation.

Next, what is the stiffness of the product? Is there any chance of flanking between foundations through the Roxul (or anything else you put there for that matter.

Have you thought about (I'm sure you have) putting a standard board form and then just removing it and leaving an air gap between the two foundations?

I would be concerned about the vertical rebar in your picture. You'll have to make very sure that it doesn't rest on the concrete "rash" that may be lower than you chipped off. If this is the method you go with, you might consider putting the rebar between the two layers (i.e., it holds the small piece tight against the foundation you could use spray adhesive or something to hold the bigger piece up against the small one during the pour. This would allow you to pound the rebar an inch or so below the top of the Roxul which would prevent the top of the rebar from puncturing the vapor barrier.

I don't see any drainage at the bottom of the Roxul board. If the water (perhaps from an overflowing washing machine?) hasn't got anywhere to go, I think it's just going to sit there soaking the material. That may be ok but again, with no plastic barrier on the current foundation/slab side, that can't be good.

If you are only using the rebar to hold in the board, I'm not sure it's even worth it. Wouldn't the weight of the new concrete pour hold it just fine?

I wish I could speak from experience on this but just looking at it logically (which I know doesn't always apply to things accoustic), you've got my thoughts.

Cheers!

len

Post by **sharward** » Tue Dec 13, 2005 2:12 am

Thanks Len. Good food for thought. I've clearly got some more thinking to do.

I guess I hadn't really seriously considered just leaving the gap empty. That may not pass code, though (think: termites).

len-morgan · Post by **len-morgan** » Tue Dec 13, 2005 3:39 am

sharward wrote: I guess I hadn't really seriously considered just leaving the gap empty. That may not pass code, though (think: termites)

You have cement eating termites in California!!!!???? Boy, things have changed a LOT since I lived there!

I'm not sure what the Roxul product would do except give them indigestion. Besides, from a few pictures back, it looks like you have a pretty effect moat system. If it worked for the Saxons, I don't see why it wouldn't stop termites.

len

Post by **sharward** » Tue Dec 13, 2005 5:12 am

No, no, no...

My understanding is that if there's a hole in the slab (and a gap between slabs would qualify), termites can enter from the ground.

Post by **sharward** » Tue Dec 13, 2005 9:17 am

How about if I stuff a small amount of rockwool into the crevice, then use expandable spray foam sealer (closed cell) over the top? The rockwool would act as a backer rod of sorts, and since it wouldn't go down very deep, it probably wouldn't soak up much moisture. Quick, easy, fairly cheap...

dbyboth · Post by **dbyboth** » Tue Dec 13, 2005 12:00 pm

sharward wrote:How about if I stuff a small amount of rockwool into the crevice, then use expandable spray foam sealer (closed cell) over the top? The rockwool would act as a backer rod of sorts, and since it wouldn't go down very deep, it probably wouldn't soak up much moisture. Quick, easy, fairly cheap...

Keith,
I have only been on this forum for a couple of months now and have probably read 90% of what's been written since August or so including all of your thread. I don't see how you find time to work on your project with all the posting you do! I have a building that I plan on building a studio in in about 6 - 9 months. This stuff has been great for me as I get ready to enter the planning stage early next year.

In your drawing above, you might wan to look into something like this to fill the gap between the two pieces of concrete:

http://www.apscork.com/apscork/fiberboard.shtml

This stuff is designed to fill the joint between two slabs and allow for the concrete expansion.

Perhaps you could cut the expansion joint board to fit the depth of your hole, line the perimeter with it, then back fill about three or four inches of the hole with sand. Forget the rebar holding stakes, I believe you will have problems keeping the plastic seal around them. The flatter the surface you are covering is, the easier it will be to place the plastic.

The sand will support the barrier until the concrete is poured and will provide an isolation under the barrier to ensure that there will be complete separation between your floor slab and the perimeter slab. I don't see why you would need two layers of the insulation. You may have to use wooden stakes in the corners to support them. I have poured concrete slabs before, and believe me, the weight of the liquid cement will ensure the form is pressed against the perimeter. I think the air gap in the photo under the short piece of insulation will cause you problems.

I don't believe you need wooden forms where the existing concrete wall is the sole purpose of the form is to support the concrete and define it's edge, the fiber board can do that with the concrete perimeter behind it just fine.

...db

dbyboth · Post by **dbyboth** » Tue Dec 13, 2005 12:02 pm

I just noticed, there is a resiliant rubber version as well:

http://www.apscork.com/apscork/rubberjointfiller.shtml

....db

Post by **sharward** » Tue Dec 13, 2005 4:18 pm

db, you rule -- thanks so much for your product recommendation, your ideas, your drawing, and of course your interest in my project!

You (and Len too) have given me lots to think about, and I want to fully absorb these ideas!

Thanks again...

len-morgan · Post by **len-morgan** » Tue Dec 13, 2005 10:56 pm

One more thing to think about...

If your foundation doesn't need a vapor barrier, why would your new slab? Is it because it's laying horizontally over a larger surface than the concrete footings of your current foundation? Inquiring minds want to know!!!

len

dbyboth · Post by **dbyboth** » Tue Dec 13, 2005 11:18 pm

len-morgan wrote:One more thing to think about...

If your foundation doesn't need a vapor barrier, why would your new slab? Is it because it's laying horizontally over a larger surface than the concrete footings of your current foundation? Inquiring minds want to know!!!

len

It's a good questions with some merit.... my thought would be that plastic is cheap and I can't see how it hurts anything, and you already know there's water......db

len-morgan · Post by **len-morgan** » Tue Dec 13, 2005 11:53 pm

But if that's the case, wouldn't the current foundation be sitting in the same water?

len

Post by **sharward** » Wed Dec 14, 2005 1:29 am

It's just an opportunity to do something right on the new slab that should have been done on the main slab but apparently wasn't.

It hardly costs anything...

You know, the more I think about it, the more I'm leaning towards just stuffing the uppermost portion of the gap with some rockwool, pushing it down enough to leave an inch or so deep of a gap, then filling that inch with the foam-in-a-can stuff... It really does seem to simplify things. Can anyone think of a reason not to do that?

--Keith