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Old 08-22-2015, 06:02 PM   #1
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underlayment and self-leveling compound bonding


I have a 250 s.f. kitchen where I am installing 5" wide luxury vinyl planks. I have 18-24 inches around the perimeter that is from 1/4" to 3/4" lower than the rest of the floor. My plan is to use self-leveling compound. I have removed the old vinyl tiles to expose the luan plywood underlayment which is in very good condition. There is some thin adhesive residue, however, on some of the luan which gives it a tacky surface.

Can I apply my self-leveling compound over these tacky areas and expect a good bond? Would it be best to prime the tacky areas first with something like SillPro C-21? And what would be the best self-leveling compound to use: a thicker hand troweled flooring cement or a true thin-set leveler that has a pancake batter-like consistency? As mentioned, I need to fill-in up to 3/4" deep in some areas.

Thanks for your help!
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Old 08-22-2015, 07:22 PM   #2
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Hi Scout,

Wow, up to " in 24" out of wack. That's 1st degree serious.

Quote:
Can I apply my self-leveling compound over these tacky areas and expect a good bond?
No you can't, but not necessarily because of the tacky residue. Luaun is not considered a suitable surface to install/bond SLC and many other products to. Take it to the curb on garbage day.

As far as primer goes, yes of course, once you prep or install a new proper underlayment, it needs to be primed with whatever the bag of SLC tells you to use.

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Old 08-22-2015, 07:54 PM   #3
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The 3/4" difference occurs gradually over about 8 feet but becomes more pronounced 24" from the wall. Why isn't luan not a suitable surface for SLC if it is primed correctly? Even if I replace my current luan underlayment I'll still have to adjust for the height difference since, I assume, that is due to sagging floor joists. (My house was built in 1963.) So even with new underlayment I'll be in the same situation. Right?
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Old 08-22-2015, 08:31 PM   #4
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OK, if the floor is flat, it doesn't matter if it's not level. Level and flat would be best, but flat is most important. If the floor has high-low spots, in other words not flat, the spec is that it be within " in a 10 ft. radius and 1/16" in 12" of the required plane.

This is what you said;
Quote:
Originally Posted by infoscout
I have 18-24 inches around the perimeter that is from 1/4" to 3/4" lower than the rest of the floor.
So, if the floor is flat but then slopes down in the last foot or two, I would say just fix the last foot or two. However the floor will not be level and flat. Your choice.

SLC's require that ALL substrates first be primed, so priming it is not an extra thing you're doing. The data sheets specifically tell you that any plywood must be made with exterior glued plies.

Most if not all say something like this;

Quote:
Suitable Substrates
Absorbent concrete
Non-absorbent concrete
Lightweight concrete
Gypsum-based underlayments
Existing ceramic tile
Cement terrazzo
Exterior grade plywood
OSB
Cutback adhesive residue
Prepared VCT
Quote:
Originally Posted by LevelQuickdatasheet
Do not bond directly to hardwood, Luan plywood, particle board, parquet, cushion or sponge-back vinyl flooring, metal, fiberglass or plastic. Contact CUSTOM technical services for recommendations.
Jaz
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Old 08-23-2015, 08:12 AM   #5
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JazMan, thanks for your responses. They are very helpful. I have one last question relating to your comment below

Quote:
So, if the floor is flat but then slopes down in the last foot or two, I would say just fix the last foot or two.
That is my intention. But if I can't apply SLC over the luan due to moisture and delamination issues, what would you suggest as far as filling in that area to make it flat within a surrounding 10' radius? Any kind of hardboard I might install for that purpose would create a ridge on the floor. Maybe I could use some low moisture cement to fill-in between the ridge and floor? Sloping it gradually to a feathered edge?

SLC seemed like the perfect solution. But if I have to rip up the luan underlayment and purchase and apply exterior grade ply first it certainly isn't.

Thanks again.
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Old 08-23-2015, 08:52 PM   #6
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Now you know the luaun should be removed. What is the subfloor made of?

You may be able to apply SLC over the subfloor and then either of the two types of tiles. Let us know. We also need to talk about the joists before too long.

Jaz
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cement gap filler , prepare sub floor , underlayment , vinyl plank flooring


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