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+--- Thread: Concrete foundation questions (/showthread.php?tid=4626)
Concrete foundation questions - Charles Moore - 11-11-2008
I am a newbie when it comes to construction. I am considering ordering a video titled "the how to guide to building a monloithic concrete slab foundation" from www.learnstrawbale.com. I'm not interested in strawbale construction but only this video.
I have a feeling it won't cover some of the issues we have here.
When making a concrete foundation...
How much base course is required over bare pahoehoe?
How much base course is required over bare a'a?
Should I have the lava ripped first?
Does it (the basecourse and/or lava) compact well?
What else should I know?
Is it possible to pour the concrete directly over lava?
RE: Concrete foundation questions - gtill - 11-12-2008
Definetly watch out for off island information, it might not fly here, even if better. The main thing is compaction, if surface is solid as in pahoehoe, not much base course, if clinker, enough to make it solid.
RE: Concrete foundation questions - Hotzcatz - 11-20-2008
Depending on what you will be putting on top of the concrete slab the details will vary. The requirements for your particular concrete slab should be spelled out in detail on your building plans. Generally, all loose cinders and or a'a lava should be scraped away since cinder compacts too much. "Blue rock" which is a dense lava is frequently the preferred foundation for under the base course. Generally, it is better to not rip or doze the area you want to put the slab if you can help it. If it is "disturbed" soil, then it has to be compacted back down again. Each slab is slightly different depending on the location of the slab and what is going to be built on top of it.
RE: Concrete foundation questions - Charles Moore - 11-20-2008
I plan to build in either HOVE or Hawaiian Acres. I think Hawaiian Acres is mostly pahoehoe, but HOVE looks to be mostly a'a. I don't know how deep the a'a goes there. I would imagine if its too deep its not possible to just scrape it away. Also the footing need to be especially strong cuz it will have a heavy ferrocement structure on it. I should probably talk to a contractor or someone who has built there.
RE: Concrete foundation questions - Sean - 11-20-2008
Seems like most of the building areas/houses I've seen in HPP have have been ripped by the dozer. Not saying the entire lot, but at least the house pad. A contractor and I were discussing this and he told me that those volleyball sized pieces of lava are typically not compacted any more than what you get from the dozer running over them. That seemed pretty surprising to me. From an engineering viewpoint that doesn't count as compaction, just compression, and if it was just crushing big rock into little rock I'd call it consolidation. Proper compaction requires different sizes to fill all of the voids, proper material, proper moisture content and someone who knows what they are doing.
I can hear a hollow sound and a vibration in the posts supporting the roof on my patio that shouldn't be there, but I guess if it's the way it's done, then it's the way it's done...
See you in the surf
RE: Concrete foundation questions - Funkstopper - 12-14-2008
For my house the footings were 14 inches but could be less if it was on lava according to my architect. Pahoehoe on my lot in Hawaiian Shores. About 15 feet had a footing of about 8 inches. The inspector was ok with that but I did have to have a letter signed by the architect.
If you're building on a slab you may want to try acid-staining the concrete. Costs less than $2 a square foot. Less if you do the labor. Great for this climate. No worries about mold growing under the flooring. Cool under foot.
The funk stops here!
RE: Concrete foundation questions - pslamont - 12-15-2008
It will be interesting to see what the building/permit department has to say about this. The monolithic concrete structure weight is a BIG deal.... keep us informed!
RE: Concrete foundation questions - Charles Moore - 12-15-2008
Yes I really like the idea of acid staining for floors and polished concrete for countertops etc.
I wonder if this no polish countertop technique (seen in youtube video) could be used on concrete floors. But instead of having the plexiglass on the bottom (when making a countertop), laying it on top of the slab.
http://www.youtube.com/watch?v=d5gK_CcGOCs
RE: Concrete foundation questions - David M - 12-15-2008
Interesting video. Having done our acid stained concrete floors, not sure I'd want to try reversed. I do think our floors are rather glossy - 2 coats of glossy, solvent based acrylic sealer and 5 coats commercial floor polish.
David
Ninole Resident