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Unread 01-05-2021, 02:19 PM   #2
Nick Drake
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Join Date: Feb 2020
Location: Kent, WA
Posts: 24
Some more info on the project:

Home is 59 build with 1x6 T&G solid sawn subfloor, will be running 2" screws direct to joists. If there are significant high spots I'll sand down before adding the underlayment. Will use a 19/32 acx underlayment with 1.25" screws at 4" on edges and 6 in the field. I *anticipate* that this may still not meet flatness requirements for LFT. I'll be technically over tcna specs to lft with 11x13 hexagons, but mostly I'd just like to have a nice flat surface to set on. I've made the mistake of not getting a flat enough substrate in the past, will not ever do that again.


Going with the full ardex system I'm seeing good time savings, considering I'm doing the work on weekends/evenings this a large factor:
  • Day 1
rapid set mortars to bond the uncoupling matt to the ply underlayment. Run heat cables and apply the liquid backer SLC that evening.
  • Day 2
Waterproof with 8+9 and I'm able to snap chalk lines, plan layout and maybe even start setting the floor that same afternoon (planning on layout with hexagons to take a while)


If I went with the laticrete strata system with it's "hydration vents" the uncoupling benefit is lost if I pour SLC above. Laticrete is very direct in their TDS language that you can pour NXT level plus to prefill, but do loose all So for laticrete I'm looking at:
  • Day 1
Primer the ply underlament, apply ardex liquid backerboard (only SLC available locally which does not require a lath over ply and has a lower minimum depth for SLC on wood substrates).
  • Day 2
Apply strata matt with a rapid set thinset. Run heat cables and then prefill the uncoupling membrane that evening.

Now I'm waiting until day 3 to apply any waterproofing, given the day job constraints that means doing the work Monday evening at the earliest. I can't start snapping chalk lines until Tuesday evening at the earliest, definitely no setting until Wednesday....
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