Basement Flooring Advice, please
I’m looking for advice on how best to deal with what looks like cutback adhesive residue on a basement concrete floor. The full story: This is an apartment building basement room that had old VCT tiles installed (removed by someone else). The room measures 24′ x 18′ and is to be converted into a library for the residents. The architect wants to have vinyl tile around the perimeter of the room, with two 9’x12′ carpeted areas in the middle for seating areas. To keep the tile and carpet heights the same, he specified 1/4″ plywood as an underlayment for the tile. We tried to fasten the plywood to the concrete with Ramset nails but because neither the ply or slab is 100% flat, the result is a hollow sound when walked on, and in some cases you can see the plywood deflect under a person’s weight. BTW, this slab has lots of big aggregate and getting the nails to set correctly was a problem (tried various charge levels).
What I’m thinking of doing is ripping up the ply, and using an SLC to build up the 1/4″ height for the tile underlayment, leaving the carpeted areas without SLC. Because of the suspected cutback, I plan on using Ardex K-15 SLC after priming with Ardex P82 primer. I’ll build a form out of 2×3’s and use caulk to prevent the SLC from leaking under the wood. My concern is that I’m over complicating this and there’s a better, cheaper way. I’m also looking for tips on how to mix and pour the roughly 216 sq. ft. of SLC within the 10 minute work time. Any advice would be greatly appreciated! Sorry for the long post…
Replies
1/4" cement board
Why not use 1/4" cement board around the perimeter adheared down with thinset?
Terry
If you've already got the ply, could you glue it and hold it with fasteners?
Scott,
I was thinking of that but I'm concerned that the adhesive wouldn't fill in all the gaps caused by dips in the floor and the warp in the ply. Plus I was having a heck of a time sinking the fasteners.
Maybe prime
I doubt that primer would be necessary, but it couldn't hurt. Maybe smear some thinset in a corner and see if it adheres.
Put the thinset down with a 1/2 inch notched trowel.
As you place the cement board, use a length of 2x4 and span it over two sheets at the same time and press down to float the sheets into alignment.
If still not smooth enough for you, skim it with more thinset using a long straight edge.
Terry
Thanks, Terry. I'll give it a shot. Do you think the thinset will hold the CBU by itself without fasteners?
Do you think the thinset will hold the CBU by itself without fasteners?
Yes.
(Sorry, I thought I had replied a couple of days ago. Must have deleted instead of posting)
Terry
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Ok, I'm as confused as ever. I called the good folks at Wonderboard and asked whether they recommended just using thinset to hold down the 1/4" CBU. They said no, it's not designed for that. The thinset is really only to fill in gaps under the CBU not for a bond. Nails or screws every 6" to 8" is required. So now I'm back to thinking the SLC is the way to go...
??
The thinset is really only to fill in gaps under the CBU not for a bond.
I find that statement confusing too.
I would agree if they were refering to CBU placed over wood sheathing
BUT
You use thinset to BOND tile directly to concrete
You use thinset to BOND tile to cement board.
Why would they say it only fills gaps?
Why not attach the 1/4"sheets
Why not attach the 1/4"sheets in the carpted areas as to top to level/screed against, then pour the SLC around it?
Well, it looks like you have couple different things going on. You'll have to pause, count to ten, and repeat: there are no short-cuts. I'm in this fix because someone else tried to cut corners.
First issue is the old adhesive. I don't envy you your chore - but you'll have to find something that will soften the goo without gassing you out. Indeed, your first step ought to be to provide for LOTS of ventilation. For softening the goo, I'd try one of those expensive, non-flammable 'citrus' paint strippers. Once the stuff has set for several hours (even overnight), get out a floor scraper and scrape up as much as you can. It need not be a perfect job, but you need to expose the concrete underneath.
Next, you need to level that floor. There are various products made, often using gypsum-based concrete, that will go on very thin yet self-level to a dead-flat surface.
Once the Gypcrete is set, I'll bet you can get a pretty good finish with a stain and sealer. That's what I reccommend for your primary 'finished' floor.
Carpeting .... simply doesn't belong in basements. Sooner or later, the floor will become wet. Wet carpet = trouble. If you want carpet, do it with area rigs, each no larger than 6' x 8'. These will be small enough that it will be possible to roll up a wet one, carry it into the parking lot, and let it dry in the sun. Or, you can use the rubber-backed carpet tiles, which need no adhesive.
Amish, I agree with most of what you said: there are no shortcuts, the cutback has to be removed, the floor has to be leveled and regular carpet is not great for basements. I add to the list of problems the the idea of bumping up the level of the vinyl tile area (around the room perimeter) to allow insetting carpet in the center. Normally not a problem, but a royal pain on a concrete slab. Unfortunately, the architect really wants this. I already suggested the carpet tile idea and he said it was his (distant) second choice, with the original design as his first. I also suggested:
1. vinyl tile for the whole room, with different color/pattern to define the seating areas originally done by the inset carpet idea
2. thicker ceramic tile around the perimeter to achieve the height and the carpet inset in the middle
These were rejected. Stained and sealed would not be considered. Not "homey" enough.
So the plan is to wet scrape the cutback residue and use Ardex P-82 primer followed by Ardex K-15 SLC to level the entire floor. I tested the residue and it seemed to come up with a warm water soak and scrape with hand scraper. That was just a test. I plan on using an electric floor scraper for the job. I'm still not sure what to do about the perimeter vs. the inset part. Maybe someone here will come up with a viable solution. Maybe I'll just push forward with the "distant second" choice of carpet tile...
Check into CO2 (dry ice) blasting. The CO2 will freeze the adhesive so the ice crystals can remove the adhesive.