I need to block some floor vents

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

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#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

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#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

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#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.

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#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

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#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

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#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.

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#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

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#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

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#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

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#3500474 5-Jun-2026 09:05

@johno1234 Interested to know what you ended up doing.

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

johno1234

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#3500477 5-Jun-2026 09:29

eracode:

@johno1234 Interested to know what you ended up doing.

Nothing yet. Have put off the carpeting project for the short term. Will post once something happens, but I expect it will be a plate bonded to a block as discussed. As these are central heating floor registers they are mostly close to walls and not in foot traffic locations so I am not too concerned about them moving, flexing or being noticeable underfoot

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#3500480 5-Jun-2026 09:42

I would remove the redundant boots and ductwork, screw and glue a piece of ply from the underside then get another piece to fill the hole level with the floor. Some self leveling compound would sort any unevenness and gaps. Any unevenness can usually be felt through the carpet and underlay.

Anything you do should be sealed airtight as you will get a decent heating benefit from sealing the drafts properly. One thing is that those floors are appear to be nice native timber floors and one day someone may like to restore them so maybe think about that when filling them in and doing any further damage.

I know this is the home DIY selection but a handyman or builder would make short work of this and have it done in a few hours. There are lots of builders looking for work at the moment, work is quiet out there.

Or possibly find a young person willing to crawl around under the floor removing the boots and flexiduct. You'll probably find someone on local community facebook group. Once the boots are out of the way, the patching work becomes so much easier.

Someone else mentioned getting rid of the flexi too as this is a place for rodents to nest.

johno1234

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#3500601 5-Jun-2026 14:04

Kickinbac:

I would remove the redundant boots and ductwork, screw and glue a piece of ply from the underside then get another piece to fill the hole level with the floor. Some self leveling compound would sort any unevenness and gaps. Any unevenness can usually be felt through the carpet and underlay.

Anything you do should be sealed airtight as you will get a decent heating benefit from sealing the drafts properly. One thing is that those floors are appear to be nice native timber floors and one day someone may like to restore them so maybe think about that when filling them in and doing any further damage.

I know this is the home DIY selection but a handyman or builder would make short work of this and have it done in a few hours. There are lots of builders looking for work at the moment, work is quiet out there.

Or possibly find a young person willing to crawl around under the floor removing the boots and flexiduct. You'll probably find someone on local community facebook group. Once the boots are out of the way, the patching work becomes so much easier.

Someone else mentioned getting rid of the flexi too as this is a place for rodents to nest.

This is the proper way but... a lot of work for not much benefit unless the flooring is going to be uncovered and sanded. If I drop stiffened plates in before carpeting over it hasn't made any permanent change and if someone later pulls the carpet and wants to sand the T&G floorboards and repair the holes they still can.

Note: that the ducting is not flexible ducting. It is all custom cut and riveted rigid steel tube so a massive job to remove it. Currently there's no way for rodents to get into the ducting as there are the floor registers on all the outlets (which will be covered with plates) and the only inlet is from the furnace which has an inlet screen and filter.

Note: Only the bedrooms and office planned to be carpeted. We have already sanded and wax sealed the floors in the lounge, kitchen and hallway. They look really nice with the wax - it is a matte colourless product so just looks like the natural light colour. At the moment the grotty old floor registers are still staying there. The boots are blocked off from the ducting with insulation stuffed into them. They probably should be repaired with matching T&G but that's a bit of a job to find matching timber and fit it perfectly flush.

MikeAqua

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#3500602 5-Jun-2026 14:13

Rule of thumb: If a gap is wider than a pencil, a mouse can get through.

Mike

johno1234

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#3500614 5-Jun-2026 14:59

MikeAqua:

Rule of thumb: If a gap is wider than a pencil, a mouse can get through.

Not an issue though. The only pencil sized gap is the floor register grilles. And Mickey ain't getting back out unless he can climb vertical smooth steel. And he can't eat through the ducting as it's steel too. I don't know when this system installed but looks pretty old, well more than a decade and no sign of rodents in it.

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