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I want to lay three 2x4 in the cinder block notch(as shown in the pic) as joist for synthetic deck, I need to fasten the wood to the cinder block in order to align the three 2x4 and to make sure it doesn't move, I thought about filling the notch with new concrete and bonding agent but not sure if such a small notch of concrete will provide enough strength and durability. I might be able to put in an angled screw or nail into the wood and block, but not sure if that is the best option. Any advice is appreciatedenter image description here

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    How big are those notches in relation to a 2x4? They look like a 2x4 would fit reasonably snugly in there. Once the wood's in the slot, if the fit is snug, it won't go anywhere...
    – FreeMan
    May 17 at 17:23
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    Building floor joists are held in notched in masonry walls by nothing more than gravity, quite well. Do you have a reason to expect substantial uplift forces here?
    – Ecnerwal
    May 17 at 18:17
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    I think this is a deck. So worst case up-lift forces (wind storm, hurricane, etc) may be more than can be resisted just by weight/gravity. Joists in a typical deck construction are fastened to the beam and ledger.
    – SteveSh
    May 17 at 20:48
  • Looks at Simpson or UPS for hurricane tie down straps, or something similar.
    – SteveSh
    May 17 at 20:49
  • What is the 'cement pond' beneath this 'bridge' design? I question even the use of PT lumber in an always wet environment. Jun 17 at 1:13
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Wedge them in.

I think @Freeman is right in the comments - it looks like you could tap the 2x4s down into the slots with a rubber mallet and they would wedge tight.

If the slots are little too wide and the 2x4s rattle back and forth you could tap in some wood shims to wedge them tight.

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Suggest detail to fasten the 2 X 4.

enter image description here

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  • It looks like the CMUs are already filled, so it might be necessary to drill and epoxy the rods.
    – K H
    May 18 at 2:49

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