When you lay the hardwood planks in place, they will be secured to each other using a grove and lock system and sometimes with glue. But you will also secure the flooring to a structure under the floor with nails to assure that the flooring is secure and firm. Generally this calls for laying a structure of plywood sub flooring that will provide the base to which your hardwood floors are attached. Here is a link that might be useful: F.A.Q. About Installing a Hardwood Floor

Solid strip hardwood flooring has less than 0.2% movement parallel to the grain. Every joint between the strips opens and closes as the wood shrinks and swells with moisture content. Only one side of each strip is actually nailed, allowing each piece to move separately. Non 'tongue and groove' wood that is face nailed can be a problem. The wood can split at the nails since it cannot move. 'Engineered' wood flooring is often installed so it moves as a single large pieces of wood in every direction (especially if it has cross ply type construction). Clearance must be provided in both directions, and for a large are can quickly mount up to inches of movement.

Aaaaaand again we start playing in the "nasty" sand box that is gypcrete. Gypcrete is horrible to try to patch. Your PROFESSIONAL will do this. Do not attempt to do anything with that gypcrete. Don't cut. Don't pull. Don't dig. Don't do anything! Get your friend (whom I believe should be paid FULL face value for this job....because it is one of the TOUGHEST jobs out there) to do all of this. Gypcrete requires SPECIAL patch and SPECIAL primer and SPECIAL TECHNIQUES to deal with. Either DIY 100% or let a professional do this 100%. This is one substrate the homeowner should NOT help with. Let the professional handle it. Please do not "buy something, use it and return it". It sounds rather underhanded. The companies that sell these devices have to deal with returned devices...and most of the time they have to toss them because someone "used them" in the wrong way and they are now defective. And you don't use them "1 time". You use them on 10% of randomly selected boards on a DAILY basis (or ever 2-3 days if the wood is damp). By the time you are "done" using this device, you will have tested 100 - 1000 planks. Either purchase and KEEP the device or let your professional friend do the work with his OWN device. Remember: if you would not LIKE to have someone do that to you, please don't do it to them. I think a bit of "Do unto Others..." is warranted here. And please pay your friend the going rate. Gypcrete is a PITA!!! You have NO idea!

You need to ask for a separate quote for each line item. Here's some charges you may not have thought of: 1. Floor material by the sf (plus 10% extra) (I'd check the calculations, also). 2. Transition strips or other specialized molding (stairs?); sometimes has to be stained to match, depending on the product line. 3. Baseboard (you gonna keep what you have or choose something new while you have the chance?) 4. Glue (it's very expensive, and must be the exact type recommended by the manufacturer of the wood floors. Read your specs carefully and inspect the glue product when they bring it. 5. Demo of old flooring. Where I live, that was, as I recall, $2/sf for wood/tile demo and $1/sf for carpet demo. And disposal--better make sure about that. 6. Costs to move your furniture. Make a plan for that. 7. Lastly, floor prep. You won't get an estimate for this, because they can't see what's under your floors until you pull them up. It could be minimal, it could be....maximal.... and this "floor prep" line item was where I ran to Yelp and the BBB and the contractors' state licensing board, and anywhere else out on the internet to find out just how satisfied were all the prior customers. With whom are you entering into a contract ? I chose a local, family-owned independent retailer, in same location for 25 years, with about 100 stellar 4.5-5 star Yelp reviews. I read them all. I did my research because floor is a big-ticket item. I asked a lot of questions about which crew would be my installers, and I specified in the contract which ones would do my install. (The "A-Team" as I called them). I asked for things like: no quarter round (flooring cut more precisely so that the baseboard itself covered the gap; no transition strips in between the flooring and the 2 different types of tile that abuts the floors (this required some artistic ramping up of the wood floors (undetectable); picture frame details around the hearth. In the end, I recall install costing $5.50/sf plus glue ($2000), plus the cost of materials. Maybe it was more than that. It's been awhile. Lastly, you likely haven't thought through installing a floor on top of old floor. How will it meet up with abutting flooring? You will still have to removal all your baseboards and reinstall. That costs as I recall, maybe $1.50/linear foot (plus materials). Probably you will negate any warranty on the flooring. If you are installing near cabinets/kitchen, you won't be able to slide out your appliances.