concrete overpour over wood floor - reinforcing

stoker

I'm doing radiant pex over wood with a 1 1/2" concrete overpour. The floor structure is very strong and was engineered to account for the static load of the concrete. I plan to lay down a sheet of plastic first to keep the concrete from drying out too quick and to protect the bottom of the walls. I've been getting conflicting advise as to weather I should then lay down 6" steel mesh before laying the pex. Supposedly this would help to prevent future cracking but I wonder how effective it would be when only in contact with the bottom surface of the pour. Any advise would be much appreciated. thx Mark

Zman

No mesh

Mesh in concrete only works if it is imbedded. Laying it on the subfloor will do nothing. if you could center it in the slab it would help, but you can't, it is to wavy. If you are concerned with cracking, fibermesh would help. Also do not use "lightweight" concrete as it will resist the heat transfer. The product you want should weigh about 105# per cubic foot. I would consult the batching plant to be sure you are getting the correct mix for your application.

Paul Pollets

Concrete as overpour

Portland Type II is not used for an 1/12" pour. It is neither self-leveling and will crack heavily, even with additives.. Either lightweight gypsum,( ie:GypSpan, made by Hacker Industries) or lighjtweight concrete (Maxxon Industries) should be poured at 1/12" The properties of each product are well known, as are instructions on proper application.

Zman

Gypcrete

Gypcrete is the the most common product for your application. It is not particularly durable and will crack to some extent. It does install quickly as it is self leveling.

Beware of lightweight concrete. Siggy (John Siegenthaler) has done extensive calculations on heat transfer and recommends 105 lb/cf. I have applied concrete at 1 1/2" with little cracking and good thermal performance. It is not structural concrete at that thickness but is certainly stronger than gypcrete. I would either use gypcrete or consult you local batching plant to get the correct concrete product.

stoker

finished concrete floor

Thanks Paul,

In this case I'm using concrete which will be acid-stained as the finish floor. GypSpan or Gypcrete would need a floor covering on top. Normally grooves are cut into the surface to describe a pattern, to provide stress relief and to direct any cracking. I've seen this done many times in Nova Scotia and it makes for a beautiful and tough floor. In all cases I saw the 6X6 mesh used as described and I was sceptical as to the advantage.

Paul Pollets

Concrete

When we do a "lightweight" finished floor, the concrete product is poured at 2" without mesh.

SWEI

If you're planning to use the concrete as your finished floor

I'd consider using C-Grid instead of wire mesh.  It's great for concrete countertops, since carbon fiber does not rust, you avoid the possibility of staining or spotting.

http://www.chomarat.com/en/category/produits/produits-produits/c-grid/  Be sure you support it on "chairs" to keep it centered in the pour.



If you want the best possible finish, have someone bring in a diamond surface grinder and polish the concrete http://www.concretenetwork.com/concrete/polishing/polishing_basics.htm

stoker

polishing

I like the idea of the hi gloss finish that comes from diamond polishing. I did not to want to add dye to the wet mix but was planing to acid stain the surface with a few colours, borders and so on. How would you do it? Would the floor first be poured and finished, left to harden, then stained, then polished and sealed?

SWEI

staining

Different processes can be applied to wet, green, or cured concrete.  There are a lot of creative options.  Consider coloring the pour and also adding a surface finish for increased depth.  I've seen great results from hand broadcasting powdered dyes between trowel passes to recreate the variation of natural stone.  There are a number of fantastic acid processes as well.  Ask around and see who does what in your area - the options really are nearly limitless.