Slab thickness

corey

I was under the impression that copper and any portland product was a bad mix. Too alkaline, or whatever...

Isn't that why all those 60s slab houses with embedded copper pipe in my area sprung leaks?

[Deleted User]

Slab Thickness

I seem to run into this all the time. People want to retro-fit radiant heat but want to raise the floor hight as min. as possable. Right now I have a customer that wants to get rid of the electric wall heaters and install radiant on top of slab on grade existing. After the tube is installed tile will be the floor covering. I have, in the past, installed 3/8 copper tube covered with 1/2" of mud and tile. No problems yet as long as the water temp is kept as low as possable to do the job/ 110. Any problems? mike

hot_rod

Yes, no, maybe

I have installed tube as you indicated without problems. Typically this would involve the tube in the dry pack, mud base for the tile. Just be sure you have adequate subfloor below the application to prevent flexing and cracking. Usually the tile association info requires 1-1/4" of substrate.

For a regular concrete "redi mix" installation You would need 1-1/2 times the aggreate diameter over the tube. Generally redi mix uses 3/4" aggreate. Keep in mind this thin of a concrete mix is very prone to cracking. Not a good application for tile, or using the slab as a finish floor. With this thin of a concrete pour you would want to use a clevage membrane over the entire area. Gets pricey.

Gyp products are another option. They can pour very thin, down to 1/4" if necessary. Generally not a wear surface and require special care, and sealing, when tile is to be used. Cost wise usually not well suited for small area jobs.

USG claims to have a gyp type of product that can be used as a final wear surface. Colors and stamped or scored options also. I haven't tried it yet, sounds interesting.

hot rod

hot_rod

Plenty of opinions

on what caused copper failure in concrete. Some say the backfill material was the main cause. Boiler slag or cinders were sometimes used as a backfill under slabs. Of course slab movement could be an issue.

From several concrete experts I have heard CCB's are a possible culprit. "Coal Combustion Byproducts" are commonly used in concrete mixes. An inexpensive and plentiful byproduct of coal fired power plants is fly ash. It makes a fine substitue for portland in the mix. Blended properly it can make the mix more workable. Generally beefed up in the summer months to slow the set up time. If the coal is a high sulfer variety, I've heard the fly ash byproduct could become aggresive to copper placed in concrete.

Personally I think it would take moisture to make this happen, similar to a dielectric corrosion. Suppose ground water contacted the slab somewhere. If the copper were exposed at the same location.... Who knows? It always comes back to the ph level issue. Copper has a fairly tight ph comfort range. Soil PH is a major cause of in-ground copper failures.

hot rod

Dana Zaichkin_10

Insulation

Is there insulation under the existing slab? Without insulation under the new "pour" or mortar bed, you will end up heating the original slab and everything underneath - which could be a real problem if there are rock masses or shallow ground water movement below.

DZ

heretic

Interesting

That makes more sense. I never understood why copper would be sensitive to alkaline (portland cement), but those "Coal Combustion Byproducts" are probably acidic.