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Need to narrow a rough door opening through cinder block (CMU)

Need to narrow a rough door opening through cinder block (CMU)

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Old 07-06-15, 03:18 AM
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Question Need to narrow a rough door opening through cinder block (CMU)

I need to build a door for a home theater build in our basement. The current rough opening is through cinder blocks (CMU). I need to narrow the opening by about 8cm on the hinge side. The door itself will be quite heavy - around 100kg - and so will be supported by 3 heavy duty hinges.

I am wondering what my best options are for narrowing the opening along the hinge side and still giving me sufficient support for ensuring the hinges will be screwed into something that gives good support.

Two options I am considering are:

1. Building a form and pouring concrete. Here my main question is if I would need to tie this into the existing cinder blocks with rebar. If so, I could drill horizontally every 30 cm into the existing cinder blocks and insert a length of rebar, bending into an L shape at the doorway end, or even bend rebar into some long U-shape lengths that are inserted into drilled holes in the existing cinder block, then pour the concrete.

2. Laminate up 8cm of plywood and bolt this onto the existing cinder block to give a wood substructure for the hinge end of the rough opening. My hinge attachment then would be hinge screws going through the 2.5cm door jamb material, across a 1cm fitting gap, then about 4.5 cm into my 8cm plywood lamination.

The second option would be easier but happy to hear comments.

Dave M
 
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Old 07-06-15, 04:05 AM
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This is by far mostly a US site, want a lot more ansewers convert all those metric measuments for us and post a picture of what's there now.
 
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Old 07-06-15, 04:55 AM
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Welcome to the forums Dave! ... http://www.doityourself.com/forum/el...your-post.html
 
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Old 07-06-15, 06:01 AM
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I assume that the door is not just a slab, but also comes with a frame. Is the frame sized for the width of the block, or a standard wall depth? In otherwords, do you need to modify the fit and finish to fit or just the opening size?

I'm more inclined to suggest you use standard framing lumber which is around 3.5cm wide. Shoot the first one into the block with power actuated shots and then you can screw a second one to the first one for a tight sturdy fit. this will get you close enough to your 8cm fit with enough room to shim and plumb your door. Make sure at least one of the screws is long enough to penetrate to the first piece of lumber you installed.
 
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Old 07-06-15, 06:55 AM
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Thanks Czizzi. Yes that's pretty much the option 2 I described. I'm building the entire door assembly (e.g door and jambs/stops/head and casing) myself. I'll therefore build the door frame to extend the thickness of the wall depth (13cm) with some additional projection either side for casing.

I've built and hung quite a few doors in my day but this one is heavier than most and I've got the added complication of needing to narrow the rough opening on the hinge side. What I have been trying to weigh up is if I should bother with extra hassle of narrowing the opening using concrete or wood. Anchoring my hinges into concrete would be more solid, but I tend to think getting 8 cm long screws through my jamb, across the fitting gap, and 4.5 cm into some good wood or plywood that is itself bolted to the cinder blocks should be sufficient. In essence this would be equivalent to a trim stud in wood frame construction.

Thanks for your opinion, very helpful.

Dave
 
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Old 07-06-15, 09:04 AM
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Sounds like you're well on top of this. I want to throw something out for thought. I think solid hardwood along the hinge side would hold a screw better than plywood.

Also, I would pay particular attention to the top of the door frame. Get a nice rabbet on both sides. Shim the top of the latch side jamb. This will prevent the top of hinge side jamb from bending inwards. (I'm sure you've considered this)
Ideally, the latch side would be plumb without shimming. This, combined with a tight top frame member, would not allow the hinge jamb to flex.

You're still left with relying on hinges for support of the door, I think you have that covered.
 
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Old 07-06-15, 10:01 AM
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Added thought on hanging these very heavy doors. Commercial doors are similar in that they weight a ton and it is difficult to muscle into place if working alone. I get the door to the approx. opening and set the hinge side on shims. You can then rotate the door on the shim (pivot) and steady it while trying to get the pins in. One I did a week ago was a replacement to an exterior commercial solid wood door that had rotted out. I left the hinges on the jamb, transferred the hinge location to the door, mortised, drilled for the deadbolt and lock set and rehung as stated above. Here is a door that took 2 of us to carry up the stairs, yet I hung it my self effortlessly.

On a side note on the door I hung, it was a custom fit so I had to trim the for length as well as width. I noted that the previous contractor had trimmed for width and then proceeded to hang the door from the cut side (only a 1/2" of good wood to hold up the door). Half of the hinge screw were stripped in the hole as he used traditional wood screws - you know the kind with the smooth shaft close to the head and only treads at the bottom half near the tip. I had to tap them to get them out. I'm surprised the door even stayed up. Anyway, good hinges and real door screws on your project. As a wood worker, I'm sure you will not skimp any corners.
 
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Old 07-06-15, 02:31 PM
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Do you absolutely have to take all the space from the hinge side? Can you split it between hinge and strike side? I am thinking of longer protruding deadbolts needing some more than the frame to sink into. How about the header? Do you, or can you use lumber up there. I am thinking of a solid box with lateral strength from side to side to hold your door.
 
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Old 07-06-15, 02:49 PM
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a door for a home theater build in our basement
Larry, I think is is a big heavy door for sound proofing as opposed to security. But Dave will clear that up for us I'm sure.
 
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Old 07-07-15, 01:02 AM
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Thanks for all the overnight replies everyone.

Czizzi is right this is an acoustical door - 10 cm thick layup of MDF/bitumen/fibreglass/bitumen/MDF. 2 rebates and 3 stops. All perimeter stops will be lined with acoustic seals and I will integrate a threshold seal along the door bottom. I'm dimensioning the door for a tight fit - closest swing clearance is 2mm.

The tight clearance is why I thought of a laminated plywood block to narrow the rough opening rather than hardwood. I'd like to minimize dimensional change in anything I am putting in the existing rough opening. I take your point though Handyone - I will have a thought on whether I could replace with hardwood - I could mill some Doussie I have on hand but that seems a waste of nice furniture wood and even with the quite excellent radial/tangential shrinkage of Doussie I would be looking at wood movement close to the limit of what I could accept. An alternative is I could substitute the 8 cm wood screws I was planning on using to attach the hinges to the jamb with 10 cm screws, which would put 6.5 cm into plywood.

On the question of whether I could split the difference and take up space on the latch side it would be nice but I'm afraid other considerations make it necessary that the entire 8cm all comes out of the hinge side.

Thanks again everyone - think you've helped me solve my main question which was whether to narrow the opening with wood or concrete.

Dave
 
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Old 07-07-15, 02:30 AM
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I've re-read Larry's idea of some kind of a box for the header and seen that it is a great idea for my situation. I have some space above the door on either side of the rough opening that is reinforced concrete. Because of wall treatments on either side I could bolt some stock onto that and tie it into the header after shimming. I always ensure the door frame registers on the sub-floor anyway (here it will be the foundation slab), and I tailor cut the bottom of the jambs on either side to account for any differences in grade so the sides of my frames tend to be solidly grounded anway. But I like the idea of some extra solidity for the header, so thanks Larry.

On Czizzi's approach to using shims to pivot a door when hanging I use a technique that would be described in my favorite Thai phrase as "same same but different". First of all, I build the entire door assembly in my workshop and measure/mark/mortise for all hinge and latch hardware in that environment.

After installing the frame, shimming and ensuring everything is plumb I move the door (with the hinges attached) to the site. If it's heavy I'll have a helper.

In a vaguely similar way to Czizzi's shims, I keep a board of 20mm hardwood on hand just for door installs when I am installing doors prior to flooring. I use beech, but any stiff hardwood will do. The board is about 1m long and 15cm wide. It has three 5cm Allen bolts set into T-nuts. Two are set into opposing corners along one of the 15cm edges. The third is set into the center of the other 15cm edge.

I will already know the approximate clearance required between the bottom of the door and the subfloor, so before moving the door for installation I will have adjusted the Allen bolts so the beech board is level and approximately the correct height off the subfloor. When I (or me and a helper) move the door to the site, the door is set on the beech board with the hinge side overhanging the 15cm edge which has an Allen bolt in either corner. This assembly is easy to move and quite stable, particularly with thick doors, although having the helper hang around to ensure the door doesn't fall is always a good idea.

Small adjustments to the Allen bolts will put the jamb side hinge leaves into their mortises and it's at that point that I drive the hinge screws into place. Particularly with heavier doors this technique allows me to get all the hinge screws in while the weight of the door is completely supported. I find this simple hardwood base a great help in hanging doors - as long as you've done your mortising accurately hanging any door is a breeze.

Dave
 
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