Expert: Bruce E. Johnson - 2/6/2011

Question
I hope you can help with my problem. I want to install carpet in my house but the concrete slab floor has a one and a half inch dip in the middle. All four sides slope to the middle. Think of this as if there were a drain in the middle of the floor, but there is no drain. I guess when they poured the slab they didn’t care how level the floor was because they put brick over the entire slap when the house was built. They put a bed of mortar on the concrete, set the brick in, then mortared the joints. When I took the brick up the mortar did not adhere to the concrete slab very well. The floor is now just like it was when it was poured. I checked on floor leveling products but they are $55.00 for a bag that will cover 30 sq. ft. at a half inch thick. The house is 1500 sq. ft. Can I use Portland cement to fill in this dip? If so, will I need a bonding agent? Any other suggestions? Thanks!

Answer
Hi Robert, most topping products consist of the same things sand, cement, and bonding agent.  If you are using a carpet company to come in and install the carpet I would ask them what they would charge to level your floor..Commercial carpet installers have several good leveling products for this type of work. Dry pack is another alternative.  Dry pack is a sand cement combination mixed in a very dry format and packed onto a slab that has been painted with a bonding agent.  But to answer your question, yes you can mix up  your own topping using a mortar mix, cement and latex bonding agent.  But honestly I don't think it will be any cheaper than just purchasing the premixed stuff.  Any time you bond to a slab the slab must be treated properly to accept the patch otherwise the patch will eventually break loose from its bond especially where the patch is thinning out to zero. Clean the area well and allow it to dry.  If the existing slab has a real smooth tight surface finish you may need to etch the slab to accept the patch.  Etching is done with some type of acid, generally hydrochloric or muratic.  Follow all manufacturer's instructions for "etching concrete".  Once the slab is cleaned and etched if necessary roll on a coat of latex bonding agent. While the bonding is still tacky lay down your material using a long straight edge and a level or laser to insure the floor is being leveled properly.  I hope this information helps please feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com