Float or glue on grade concrete slab???

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  #1  
Old 10-14-03, 07:40 PM
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johnnyL
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Float or glue on grade concrete slab???

I want to install hardwood floor on my grade level concrete floor. There are no moisture problems. Is one method 'better' than the other? I know some flooring manufacturers recommend either method depending on flooring. I plan on using a 3/8", 5/16" or 7/16" engineered floor. My gut says to 'float' because the 'glue' method creates more work, cost, and mess. What do you think?

All responses appreciated.

Johnny
 
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  #2  
Old 10-15-03, 10:04 AM
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florcraft
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Floating floor are just plain and simple more comfy to walk on. and you can put an effective moisture barrier for added insurance.
 
  #3  
Old 10-15-03, 12:03 PM
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I looked into glue down and first of all, most here will tell you it's not a DIY'er project. Also, there are a lot of houses around me with 3/8 gluedowns and they all look like crap. Lots of huge gaps and warping etc. I don't think it's a moisture problem because it's very arid here and I tested my slab and found no moisture. It's simply that the expansion coefficients of concrete and wood are not similar at all. Also, 3/8 is just to damn thin. The thinner the wood, whether engineered or not, the more likely are gaps, crowning etc.

IMO floating is not much better but at least it's a relatively easy DIY'er project. I'm in the midst of doing an solid, unfinished install over slab and just to get the slab to the point where I can nail my prefinished to plywood is more work than the complete floating floor install I did on my last house.
 
  #4  
Old 10-15-03, 12:25 PM
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masterjoe
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Unhappy Combination

I agree with AlexH's comment on your choice of plank thickness.
3/8" and 5/16" are too thin for non-glued application, especially on slab where there's more chance of moisture intrusion than plywood subfloor.
7/16" is the minimum that I recommend; I used 5/8" Harris & Tarkett T&G planks. Although it gave you an option of glue-free installation, I still applied insurance beads of glue at the joints. That's a bit more work; but at least, I'll have added protection against spilled water......etc.

Little more work costs free because it's DIY.
Shorcuts can be costly if disaster is bound to happen.
 
  #5  
Old 10-15-03, 07:18 PM
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Thanks for the replies

Alex,

I have considered the same project but have been told by many 'wood floor dealers' that the 3/8 is designed for that type of usage. I've done 3/4 board installations on 5/8 plywood that look great.

What type of vapor barrier and size of ply are you using for your sub floor? How much did you increase the floor height? Any issues with that? What size nails will you use for the 3/4?

Any other comments, anyone?

Thanks,

John
 
  #6  
Old 10-15-03, 07:32 PM
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HRMaddie
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Floating / Glue-Down?

I finished doing a 3/8" glue-down in my living room about a month ago. I have a couple of very minor gaps, but that has to do with installation. Since that was my first time I learned some things along the way on how not to have minor gaps and various other tips. Anyway, the glue-down is a pain the rear to say the least. I would say it is worse than tiling. I chose the glue-down because I didn't like the way the floating floors sound and look. Every floor is different I think the best thing to do is look and research them all and decide what is best for you. Ask yourself how long you plan on living in your house? Are you looking to increase the value of your home, etc?

If you decide to do a glue-down take your time and level the floor. I am not sure if Alex is correct on the coefficient of the floor against the concrete. Everything that I read was saying the engineered floor expands and contracts less than a floating floor. If he is correct, than I guess I will be sinking a ton of money into having someone remove my entire floor, because I will not remove it myself.

I am not a professional just a do-it-yourselfer.
 
  #7  
Old 10-15-03, 08:08 PM
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I'm not saying that it's impossible to do a good looking glue down or even one that might last 10 years. But I haven't seen any without many bad gaps, and I'm sure these gaps were not there when it was installed. They showed up after hundreds of heating cooling cycles.

I think the variables to getting a good gluedown are-

1. Flattening the slab. The glue manufacturers state that it must be 1/8" within 10 feet. It was obvious to me that this would require laser like precision so I called around to see if someone would do it for me and all of the top installers tell me they never flatten the slab! I guess they are just relying on the fact that very few people will sue if you even could after that period of time.

2. Using a hardwood product that is made specifically for gluedown on slab and is warrantied for that use. I was recomended a product by someone that has a very good track record on gluedowns but I didn't even bother to ask the price as I am sure it's well over $10/sq ft.

3. Use thicker products. It's simple physics as to why a thinner product will be more likely to crown/bow.

I agree with you on the floating floor feel. I'd rather do a gluedown than a floating. I think one weakness of floating floors is when very heavy pieces of furniture "anchor" the flooring at opposite ends of a room and when the floor contracts it has no where to go so the glue joint fails. The big advantage of floating floors is the 2 day install.

Also, I'm a bit of a solid unfinished snob and I also wanted to do a feature strip. The install will take me many weekends however and I had to do a lot of research and I also talked to a few installers. One thing I found out is that installers have to make a profit at the end of the day. So, if they get undercut by other installers taking shortcuts, they really have no choice but to do the same.

I wouldn't worry to much about the gaps, my floating floor ended up with plenty of small gaps after 2 years and people always commented on how nice the floors looked. You notice them because you installed it. I used the Woodwise filler product (doesn't dry out) but even that doesn't work very well for me.
 
  #8  
Old 10-16-03, 06:20 AM
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HRMaddie
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Glue-Down

I agree with Alex the specifications for 1/8" in 6', I believe is ridiculous. I think the manufacturers do that just so they have a way out of the warranty. I spent awhile using a string and a straight level going around my room looking for dips. I found many and filled them in to the best of my ability. Now that the fall / winter is coming I will be interested in seeing exactly what my floor does. I am a tad nervous. I have had some friends do a glue-down floor without any problems after a couple of years and they didn't level their floor. Fortunately, I am only going to be in this house for a max of another two to three years, that is why I chose a glue down. Otherwise, I would have went with a solid unfinished floor.

Honestly, I love my floor, I wouldn't purchase the same brand again, due to too many warped boards. I researched for months on end before I chose what I chose. Apparently I didn't do enough, because of the warped boards.

I spent approximately 20 hours just laying my floor down for 250 sq ft, if that tells you how much a pain in the rear a glue-down.
 
  #9  
Old 10-18-03, 02:51 PM
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what brand?

HRMaddie......... what brand floor did you install? Has anyone installed Traffic Master, I think it's Home Depot's brand, any comments welcome......... Thanks
 
  #10  
Old 10-18-03, 05:26 PM
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Here's what an installer recommended - he told me all of these boards fit tight every time.

http://www.kentuckywood.com/plank&strip.htm

I didn't ask for a quote as I'm sure it's big bucks.
 
  #11  
Old 10-19-03, 04:20 PM
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Re: Thanks for the replies

Originally posted by johnnyL
Alex,

I have considered the same project but have been told by many 'wood floor dealers' that the 3/8 is designed for that type of usage. I've done 3/4 board installations on 5/8 plywood that look great.

What type of vapor barrier and size of ply are you using for your sub floor? How much did you increase the floor height? Any issues with that? What size nails will you use for the 3/4?

Any other comments, anyone?

Thanks,

John
Sorry I didn't see this post earlier - but actually I'm not sure I understand. My comment was that 3/8" is very thin for gluedown. For floating I wouldn't be as picky but thicker is always better and I wouldn't take most dealers advice. Ask them if you can see a 10 year old install and ask them details about warranty.

A 3/4" strip on 5/8 plywood has been done for 100 years now - why wouldn't it look great?


As far as my application, I'm glueing and using powder actuated fasteners on 1/2" plywood then screwing and glueing 3/8" plywood on top of that with staggered joints. This is overkill, but my strip is 4 1/4" wide so I need as stable a foundation as possible. I was told the powder actuated fasteners always fail after a while so they are basically used to insure good initial glue contact. Some installers also float the plywood avoiding the glue and fasteners. The way I did it, I figure I'm covered either way, if the glue or fasteners fail, which they eventually will, the plywood will still have structural integrity since it is all tied together.

I think 1.75" fasteners are the best size although for some reason NOFMA recommends 1.5" Perhaps there were no 1.75" fasteners at that time.

Luckily I only have to interface with tile so floor height is not a real big deal but I will still have to have custom reducers made. They will have to reduce by about 1".

Urethane is supposed to be a good vapor barrier but of course I'll also be using a standard vapor barrier above the plywood. If not using glue, it was recommended that I place 6 mil poly down with a 1/8" pad to protect the poly from the plywood.

One thing I didn't fully anticipate is the extra cost of slab install. My total cost looks like -

Maple strip - $4.00
Plywood (2 layers) $1.30
Urethane adhesive - $.70
Rough sand - $1.50
Finish $1.00

Total $8.50 per square.

My friend just had a 3/8" gluedown done and it cost him $10.00 a square. Shortly afterwards his fridge leaked and ruined a small section of the floor. Another reason I'm not crazy about prefinished (or, don't install hardwood in the kitchen!).
 

Last edited by AlexH; 10-19-03 at 05:26 PM.
  #12  
Old 10-19-03, 07:32 PM
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johnnyL
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Thanks for the info Alex!

I have been doing more research and am to the point where I must decide how to proceed. I am deciding between using 1/2 inch engineered product or an installation similar to what you are doing using 3/8 solid.

I found a 3/8 solid Asian Rosewood and would like to use it instead of 3/8 engineered.

Using the 5/8 ply, vapor barrier, and 3/4 finish boards will probably cause too much floor height increase.

Still open for comments or advise on how to come out with a nice finished floor.

Thanks,

John
 
  #13  
Old 10-19-03, 09:41 PM
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In theory you could make it work by gluing the plywood with seams at 45 degrees to the strips (so your nails don't accidentally end up in seam) and then use a 1.5" cleat which requires 3/4"+ vertical.

My contact told me that the urethane glue should last 50 years or so. You can avoid the glue by using powder actuated fasteners but seems like everyone uses a thin pad to prevent abrading the poly moisture barrier with the glueless method.

The danger is that the plywood shifts due to expansion/contraction and causes cracks to open in your flooring.

But if you look at Bosticks website instructions for the Ultraset adhesive they show one of the applications is gluing 3/4" plywood to the slab in 4x4' sheets. But then again they don't sell hardwood.

I would seek professional advice (I'm not one). I got some good advice from the hardwood doctor but I had to pay for it (I think he's on medical leave right now).
 

Last edited by AlexH; 10-19-03 at 10:50 PM.
  #14  
Old 10-22-03, 03:08 PM
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Johnny,

How about 2 layers of 3/8 + 1/4 exterior plywood with staggered seams over 6 mil poly? Using either glue or powder actuated nails to secure first layer and screw and glue second layer. Then your rise would be 5/8" and it would be a pretty good foundation.

Although your strip is thin, it is also fairly narrow which is in it's favor. Hopefully you do not live in an area with wide humidty swings. If you have the time and energy, you also could coat the underside of the srtrips with poly before install. This will even out the stresses in the strip and reduce crowning and gapping.

According to NOFMA, plywood directly over 6 mil poly is acceptable. This is probably what I'm going to do. The glue is just to difficult, messy and costly and I'm not sure it really adds anything to the install. In fact, most of the installers in my area float the plywood (with 2 layers of course). But if you float the ply, do not attach your hardwood to the slab at any point, like a reducer.

I prefer not to float the ply because I'm worried about it making noises in areas where it's not in direct contact with the slab which is inevitable.
 
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