Home Forums Hunting & Shooting Hunter's Campfire Any Flooring Experts?

I'll start off by saying my carpentry skills are fairly basic, but I want to learn to tackle more myself. I'm more mechanically oriented, but I generally enjoy DIY projects. I'm also a bit of a perfectionist, so doing my own work usually takes time, but I end up with a better result than when I pay people. Anyway after getting some quotes to install hard wood flooring in a section of our house I decided to attempt it myself. What most of the videos I've seen online don't prepare you for is the unlevel subfloors that I found under the carpet. It seems like quality wasn't a concern when they framed the house. I had a friend that is a custom home builder come by and help me with a few small tasks to get me started. He told me to get Mapei Self Leveler Plus and put it down in the low spots on the floor. I started this process and did several spots, but I'm really having concerns. One section has it almost the length of the room near the wall. I have another client that is also a builder and after telling him about it, he seemed really nervous about me using that under flooring that will be nailed down, rather than floating floors. His concern is it breaking away when you shoot a staple or cleat through it, but he's never done it and is curious to hear how it goes. This lead to further Google searching with some people saying they shot staples through it and it's fine, while many others are saying you can't nail through it as it'll crack it and lead to it crumbling over time. I've seen suggestions on everything from putting shingles over the low spots, using multiple layers of roofing felt in the low spots, using cedar shims, etc. I talked about this more with the guy who originally recommended it and he didn't seem concerned and seemed to think it didn't really matter if it cracked under there since it was just holding the flooring up and the staple was going into the actual subfloor and joist. Now I'm kind of at a loss on where to proceed. I just don't want to end up with a huge issue 5-10 years down the road where I'm having to redo all of this, as it's been a ton of work and I haven't even gotten to the point of laying the floor down.

So my options now are to attempt to chip this stuff away from the plywood and go with either many layers of felt, or a shingle, or similar. Or to cut the subfloor up in these spots and use a shingle or layers of felt to level it from there. Or option #3 is to leave this stuff and staple through it. What are your opinions? Am I going to have issues down the road from this stuff? It'll be a pain to remove/replace what I've put down, but I've only done one room and it'll be much easier to do it now rather than after I lay the flooring if using this stuff is a bad option.

How much deflection are you talking about,

Hard wood staples are usually not long enough to reach the joist.

What will be directly under the new flooring, plywood, mdf, t & g. These would determine how I approached the issue.

I’ve used the self leveler on concrete floors before tile. It is a skill in itself to get it level. When stapling or nailing any material such as flooring. It is common when you hit something hard , the staple can curl and come to the surface of your floor. I would think a leveler that was like acrylic mastic might work better. Hope you don’t have low spots over 1/2 inch. You might try going to a hardwood flooring supplier and ask what the floor guys are using. Most pros do not buy at the box stores. You need a straight edge , longer the better, and go over your floor. Get good with a trowel! You might think about screwing your old subfloor down to eliminate squeaks. Make sure you store the flooring in the house to acclimate. Leave enough space for expansion.

You have several issues going on at once. First why is the floor so unlevel? Does it need structural support? The best flooring job in the world won't be worth much if the floor isn't stable over time.

Next how much of a gap needs shimming? I might would lay an extra layer or two of felt here and there, but you can't shim out something that's way off.

Yep, stxhunter (aka Ron Jeremy).

Typically the flooring guys are knocking down high spots even on a brand new house. Is that big low spot between joists or?

Some good advice here, This is a birch floor at our cabin. We used a Portnailer.

Never seen a wood subfloor bad enough to not be able to take nail down wood floor. If anything some sanding on the high spots, should be all you might needs. Floor leveler like that is typical for putting in vinyl products. Not nail down hardwood. Have you acclimated the wood floor for the range of moisture content in you area? Post pictures of the subfloor in the house and the product you’re using, It will speak volumes on your situation.

I will admit it is indeed rare, but the OP has yet to inform us the degree of diflection

The portanailer uses barbed wedges.

It doesn't matter if it cracks or not once it's under there. Use it! I use it all the time in my home improvement business. Anyone who mentions it cracking is not a flooring "expert".
Heck, you could even use play sand as a leveler if you wanted to, though definitely not recommended.

I disagree , when you shoot it with floor staples it will crack and as the flexing of the subfloor lossens those cracked spots it will begin to crack and pop when you walk on it. the real concern should be why its so uneven .first then you have to install a product that will work with the situation. just because you want a nail down product dose not mean thats the right product for the situation. OH and I have been doing floors for 36 years doing all kinds of flooring products. I would not call myself an expert , but I have worked in many ALOT of multi million dollar homes and offices. But I will tell you IT WILL MAKE NOISES.

Thanks for the replies so far. It's about a 1/4" variance in the worst spots. I'm trying to keep everything within 1/8th of an inch. The worst spots are actually around the edges rather than in between the joists. It's like the boards around the outside on one wall are all about 1/2" lower.


The subfloor is plywood. I've already had to screw some pieces down to fix squeaks, and one section wanted to sag in between the joists. So I cut that up and braced in between the joists to give it some support. It really tightened that up.

There's multiple issues going on in my unprofessional opinion. There is some slight sagging in the middle between joists on a few spots, but that's relatively minor. Less than 1/8". The joists are 24" on center which seems too far apart. This is why I've had to cut the floor up and brace the worst.

The next issue is that there are two spots where the joists seem to be slightly higher which is creating a crown in each. They are joists that have walls under them on the floor below. I'm not exactly sure what went on here during the framing.

The 3rd is the issue I mentioned above. Along one wall it seems like the edge sheets are slightly lower. It's like that joist is lower underneath. Its the biggest variance and is about 1/4" +/- lower.

Neither of the contractors I know are flooring guys, but they are both telling me I need to address anything over 1/8" or it's going to be hard to install and I'm going to see and feel it in the floor. So that's what I've been aiming for.

I have been letting the flooring sit in the house to get acclimated to the moisture level here.

If the floor joists are lower under the walls, and joists are 24" apart , the walls are carrying too much weight for the 24" joists can support. I am not sure , it is hard to tell with a post . I dont do all that many hardwood floors anymore , since the laminated stuff became the craze. There are some things you need to make sure of.. If the joists can support the weight that the wall is bearing, it may be settled after all those years. It is very hard to prop a joist up from underneath if it is low and holding weight. That would mean you would have to raise the joist, the wall , the ceiling joist
and rafters.. If the floor is lower just around the walls, it seems they settled. If they are done settling, you can just put a 4" strip of plywood around the where the subfloor is low , screw and glue it and you should be good. Again, i am not sure exactly what the problem is so I am guessing a little. If it helps, it is rare to take out carpet to install hardwood floor and not have repairs. We always have a few low and high joists. If it is only 1/8", we dont care, but 1/2" is not good. Pictures might help.

were no building codes required or permits when the house was built? Post some pictures of it. Sounds like the floor may need to be sheeted first. Before tung and grove osb they used plywood then 3/8 partical over that to help the floor not sag between joists and where there was 2 pieces of plywood butting up.

I'll have to take some pictures. The house was built in a county with both building codes and permits were issued. It's in a large subdivision and it seems like the majority of the houses in the neighborhood are all built the same way. I'll have to take some pictures tomorrow to post.

The majority of wood I've done has been glued down engineered wood. I'm sure cumminscowboy has more knowledge on this type of installation than I do.