Self-levelling compound after UFH install

[Mrmikemaynard]

Hi,

I'm having UFH gypsum overlay boards installed on an (insulated) concrete subfloor. UFH specaliststs have recommended using a self levelling compound before enginered wood floor is laid on top. They won't do the self levelling and carpenter won't do it, so I'm trying to figure out:

a) what type of self levelling compound would be comptabile with the gypsum boards, could I use latex based one

b) whether I could do it myself (I'm a very green DIY novice!)

Would very much welcome advice on either question.

Best wishes, Mike

 

[C.J.]

You’re specific floor that you’re going to be having installed will have some sort of spec regarding installation over radiant heated floors (Under Floor Heating). Often times a certain minimum thickness of self leveler will be required. 1/2”? 3/4”?

 

[Mark Brown]

I would not recommend laying a SLC on the overlay boards. I think there would be too much movement in the system to really get a proper bond.
If you are planning on installing the engineered wood as a floating installation then just do that and make sure you keep the water temperature low enough to not exceed the manufacturers recommended temperatures. Alternatively you could lay a 1/4 inch Ulay over it and install it as a glue down. That would work as well. You would have to map your piping diagram so as not to puncture the piping during the installation of the plywood.

If in fact you are doing what I think you are doing, that would be my best advice.

 

[Commercial Floor Rep]

Ardex makes a product called GS-4 that is a Portland / Gypsum hybrid self-leveling. It's made for installation over plywood substrates and therefore can handle substantial movement without cracking. We use it a lot to repair lightweight concrete / gypcrete. You'll have to prime with P-51 primer first and then apply the appropriate thickness of GS-4.

As Mark stated, I would probably avoid using a traditional cement based self-leveling as most of them are not designed or warranted for your application.

Self-leveling is not the easiest thing in the world to do and really should be done with a team of 2-3 people. There are specialty tools involved (rakes, smoothers, etc.) and you need to be mixing sufficient quantities as to not lose your "wet edge". I would strongly suggest hiring a professional to do this. Your typical residential flooring installer doesn't generally do self-leveling underlayments. You'll probably need to contact a commercial flooring contractor to get this done.

The flooring contractor should be able to source the product or with a few google searches you should be able to locate a supplier or purchase it online if necessary.

I wish you the best with your project and let us know how you made out.

 

[C.J.]

Even though I am a solid Ardex guy, I have not tried GS-4 yet. Can you self level with it? I’ve used Schonox APF for self leveling over crumbly gypcrete. That stuff is excellent, not that Ardex isn’t, but it does have a shorter working time so you gotta really be on point. Even more so than a Portland based leveler. Double prime and have adequate manpower. 4 guys wouldn’t be unreasonable. 3 guys that worked together in sync could pull it off.

I’ve had basements that have needed leveling and the customers ponied up for a commercial outfit with a pump truck to self level and it turned out excellent. A big job for a residential installer is often considered too small to hassle with for a commercial outfit but they really are the ones qualified to deal with the job. It’s a lotta work in a little amount of time with a fair amount of set up and break down.

 

[Mrmikemaynard]

Thank you very much for your responses. Super helpful. Responding in turn.

Minimum thickness requirement - none in the installation guide - it's Galleria engineered wood, just flags need to keep floor temp below 27 degrees. I've contacted manufacturers for advice.

Bonding - planning to go self leveling compound, 3mm DUARALY Heatflow underlay, planks.

To DIY or not - decided against it!

Self-levelling compound - thanks for suggesting products. Will help me ask rihht questions to floorer tomorrow.

Will let you know how it goes!

 

[Mrmikemaynard]

Does anyone have experience with using this product? Could it be suitable?

 

[C.J.]

@Mark Brown loves Mapei. He may have some experience with it. Most, if not all, of the major players will have a product suitable for your needs. A call to technical services would be time well spent.

 

[Mark Brown]

I haven't ever heard of it, but then again I am in a backwater part of the world where we just got cable tv last week....
Some of that isn't true but in the long run, contact them. They are most helpful and would rather tell you it is a bad/good idea than have you make errors and blame their product. Fiber reinforced flexible SLC sounds like a winner to me.

Might I ask where you are?? I am willing to bet not a North American Market??

 

[Mark Brown]

Some more advice, If you plan on levelling your floor, do not plan on a 3mm topping. It does not really flow all that well at lower thicknesses. I would double it at a minimum. I know it says it can be done and it can be done but I can assure you it is not something that is easily accomplished. I have botched more self leveler trying to save a few bags than I ever have by just pouring deep and going for broke.

 

[highup]

I haven't ever heard of it, but then again I am in a backwater part of the world where we just got cable tv last week....
Some of that isn't true but in the long run, contact them. They are most helpful and would rather tell you it is a bad/good idea than have you make errors and blame their product. Fiber reinforced flexible SLC sounds like a winner to me.

Might I ask where you are?? I am willing to bet not a North American Market??

He said the floor temperature should not rise above 27°, so I'm betting that he probably lives in North Dakota. I hear at 32° people up there start dying of heat stroke.

 

[Mrmikemaynard]

I'm in London, UK! Noted on thickness, but want to minimise step between hall without UFH, and lounge with UFH....

 

[C.J.]

Some more advice, If you plan on levelling your floor, do not plan on a 3mm topping. It does not really flow all that well at lower thicknesses. I would double it at a minimum. I know it says it can be done and it can be done but I can assure you it is not something that is easily accomplished. I have botched more self leveler trying to save a few bags than I ever have by just pouring deep and going for broke.

True dat. Short working time because of being gypsum over gypsum and the fiberglass adds another layer of difficulty. We had 2 skilled journeymen that couldn’t go fast enough for a 1/4” pour of Schonox APF. 3/8” woulda been easier and when it was all said and done we prolly used as many bags.

 

[Csason]

I use Mapei all the time. Your situation seems to be a classic one of trying a small area first . I’ve used a 12’x12’ area on large commercial jobs for glue, patch, self leveling, etc, (especially working with composite tiles and glue that is supposed to be dry to touch ) prior to actually starting it is well worth the experiment