I need to block some floor vents

Forums › Home Workshop DIY › I need to block some floor vents

1 | 2

MikeAqua

8203 posts

Uber Geek
+1 received by user: 3957

#3494468 21-May-2026 14:34

pdh:

Here's a sketch of what I suggested earlier - epoxy & ply solution.

...

If it were me - I'd go to Burnsco and buy the smallest kit of WEST epoxy (2-parts - resin & slow hardener) and a small jug/bag of thickener powder. There are other brands of epoxy - I just like WEST and have used it for 40+ years. It's never let me down.

You can get small kits of Norski 'Epoxy Glue' at M10. About $25. It's a pre-thickened two-part epoxy.

Just be aware that cured epoxy is rigid. If your floorboards are exposed to significant changes in humidity they may contract and expand across the board, while remaining relatively stable along the board. Ideally this movement would be absorbed by the tongue and groove. If excessive movement occurs, you don't have any mechanical support for your infill panels. Just the adhesive.

Mike

MikeAqua

8203 posts

Uber Geek
+1 received by user: 3957

#3494469 21-May-2026 14:38

eracode:

MikeAqua:

.. you could rout a rebate around the edge of each cutout. That would allow you to recess the plywood pieces so that are flush with the floor. The rebate depth should be equal to the thickness of the plywood. I'd glue them as well, so they don't move.

What I'm suggesting is a little more complex. You'd need a handheld router, a bit and a straight edge. But if it's possible to do it this way, that would be a more solid durable solution.

Looking at the the photo now showing, looks like this could not work. The top edges of the floor box come up to floor level - which would preclude use of the router to make a recess (unless some or all of the box was removed first).

Yeah, I suggested that before OP posted photos. It wouldn't be possible, without cutting back the ducting.

Mike

Handle9

12082 posts

Uber Geek
+1 received by user: 9912

Trusted

Lifetime subscriber

#3494551 21-May-2026 16:55

johno1234:

Underfloor access is OK in most of the rooms but there's the ducting and register boots in the way - would be a lot of work to remove them to get access to the floor below the hole.

If you can get access I'd be inclined to spend an hour or two under there with a sabre saw and clear the gap and fix ply undeneath followed by insulation. The movement of those types of floor boards and/or footings is going to make any epoxy based solution really tricky.

Stu1

1918 posts

Uber Geek
+1 received by user: 503

ID Verified

Subscriber

#3494605 21-May-2026 22:18

Great post I’m horrified I will have to do this one day as well when we come off gas .Couldn’t you screw some ply underneath the hole then cut a piece to fit the gap, glue and screw it in, then seal around the edges? Kind of like patching gib.

The best solution would probably be cutting back to the nearest joist and replacing the section properly, but that’s obviously a lot more work. By the time you put thick underlay and carpet over the top, I don’t think you’d really notice it anyway.

Goosey

3053 posts

Uber Geek
+1 received by user: 894

Subscriber

#3494622 22-May-2026 06:45

Make sure you seal off the ducts at the basement end….. you don’t want to create a nest for anyone/anything.

would you pop some insulation down each vent cavity to help dampen some noise travels ? (Just the “holes).

johno1234

3484 posts

Uber Geek
+1 received by user: 2976

#3494631 22-May-2026 07:06

Handle9:

johno1234:

Underfloor access is OK in most of the rooms but there's the ducting and register boots in the way - would be a lot of work to remove them to get access to the floor below the hole.

If you can get access I'd be inclined to spend an hour or two under there with a sabre saw and clear the gap and fix ply undeneath followed by insulation. The movement of those types of floor boards and/or footings is going to make any epoxy based solution really tricky.

Possible but would be pretty uncomfortable down there. It’s crawl space and scattered with builder’s rubble.

HP

Shop now for HP laptops and other devices (affiliate link).

pdh

498 posts

Ultimate Geek
+1 received by user: 346

#3494632 22-May-2026 07:07

I won't speak for other epoxies - but WEST was originally invented for boat-building.
Anyone who has been around boats know that they flex.
So does WEST.

If you can't accept the stability of the insert/epoxy/floorboard joint - and IMO it would be very strong - then put two pillars of 100x50 underneath - resting on the bottom of the old air-duct.
Then the epoxy just has to stop it rattling - or you could use any of the silastic/silicone/no-more-nails weak adhesives, because you don't really need an adhesive at all.
It'll just be a PIA fettling down the 'pillars' to get the ply to lie flat & level.
Not hard - just tedious.
That would also probably be a cheaper alternative to using epoxy.

I mentioned other pre-mixed epoxies - but they are a one-size-fits-all viscosity (thickness).
I suggested the WEST components because then you can make the mixture as stiff as you want (by adding more powdered thickener).

eracode

Smpl Mnmlst
9452 posts

Uber Geek
+1 received by user: 6336

ID Verified

Trusted

Lifetime subscriber

#3494635 22-May-2026 07:36

IMO this thread has become totally over-thought. I do not believe high-tech epoxies are anywhere near necessary. The job is a relatively simple one - a 250x100 opening is small.

As an experienced DIYer, if it was my job, I would do exactly what was originally proposed by the OP. It will be fine.

Sometimes I just sit and think. Other times I just sit.

MikeAqua

8203 posts

Uber Geek
+1 received by user: 3957

#3494697 22-May-2026 12:19

eracode:

As an experienced DIYer, if it was my job, I would do exactly what was originally proposed by the OP. It will be fine.

1mm aluminium sheet is quite bendable. There would be nothing underneath the plywood infill pieces. The edges of the alu will deflect up overtime lowering the infill piece. If no-one is standing on it and it's not under furniture legs or whatever, that may not matter. But if there was an issue it would be PITA to address once carpet is down.

I didn't appreciate that the OP could get under the floor. That being the case, and as someone else suggested ... I'd invest the time to cut the ducting out of the way.

Then cover the hole from underneath with pieces of plywood screwed into the underside of the floorboards. That gives structural support for infill pieces (could be plywood). IME floorboards were milled to imperial thicknesses and finding plywood the same size is difficult. Packers, or a mix of plywood thicknesses may be required, to get the infill pieces flush with the floor. it doesn't have to be perfect, because underlay and carpet give you a little wriggle room as long as the infill is secure.

Mike

1 | 2