Closing gaps in ceiling panels (insulating the workshop)

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Forum topic by Ian S posted 07-27-2016 06:29 PM 403 views 0 times favorited 14 replies Add to Favorites Watch
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Ian S

19 posts in 116 days

07-27-2016 06:29 PM

Hey folks,
In this thread my wife and I ended up building a simple insulated attic for my shed, the first step in closing it in and turning it into a proper workshop (which can be used year-round in Texas!).

The next step is to do some re-wiring before we close in the walls. But before that, a more straightforward question …

When we put up the ceiling panels for the attic, we had to do a ton of little custom cuts and work around odd-sized framing. This shed was built by a previous homeowner and he did not follow any dimensional conventions such as 24” OC or whatever :-)

As a result there are a bunch of little gaps between the multiple MDF ceiling panels, and the ceiling joists and trusses, etc. We’d like to do our best to close these gaps because #1 we’ll get a better air seal from the hot attic, and #2 we want to pretty things up by painting the whole interior, and it would be nice to have a mostly-flat and finished surface to take that paint.

So, it doesn’t need to look as good as an interior tape and float job, but we want to close those gaps and end up with something that is at least … “reasonably” flat-looking.

The gaps probably average about 1/2” but get up to about 1” at the worst. I’m trying to figure what the BEST and SIMPLEST approach will be to close them all up.

One idea is to use Great Stuff to start with, come back and trim it with a knife once it dries, and then use regular drywall mud over the top of that. Which I think could go pretty quickly.

But I’m unsure if there’s something better out there that I could dry. Any thoughts?

Thanks as always!

14 replies so far

View clin's profile


485 posts in 415 days

#1 posted 07-27-2016 07:08 PM

Cheap, easy (fast), and look good (quality). As they say, you can pick two of these.

Foam in a can sounds like a good approach. After trimming the foam, I’d just paint it and call it done. If you mud over it, it will just crack without any tape. If you go to tape it, it won’t look that good without doing most of the work you’d do doing a full drywall application. Then heck, you might as well do it right and put up wall board. But I think that’s going too far for a workshop/shed.

-- Clin

View splatman's profile


542 posts in 818 days

#2 posted 07-28-2016 12:30 AM

Cut pieces of wood or MDF to fill the gaps. Glue them in. Sand flush if needed. Prime and paint away.

View JBrow's profile


744 posts in 339 days

#3 posted 07-28-2016 02:02 AM

Ian S,

If you elect to patch the gaps with joint compound, by using fiberglass drywall tape and mudding closed the gaps first and then filling the gaps with spray foam could save the step of trimming the excess spray foam. I would think fiberglass joint tape would work better in preventing future cracking than drywall paper tape. In any event, taping the gaps before applying joint compound would likely reducing future cracking.

It is difficult to know from your post or your blog whether these ideas make any sense. There may be too many corners to make these ideas workable. Both ideas would make painting a little more difficult. I assume the gaps are around the perimeter of the building. The first idea is to apply trim to the ceiling in such a way as to cover up the gaps. The trim could be 2” wide flat strips of MDF tacked to the ceiling. The second idea is to use 2×4 lumber applied to the walls tight against the ceiling. In both cases the trim would run all the way around the perimeter of the building for a uniform look.

View rwe2156's profile


2113 posts in 900 days

#4 posted 07-28-2016 12:09 PM

I would just use lathing strips.

-- Everything is a prototype thats why its one of a kind!!

View JoeinGa's profile


7364 posts in 1426 days

#5 posted 07-28-2016 12:12 PM

You’re talking about the gaps in this photo, right?


If yes, then I agree with clin above. I’d just use the expand-o-foam and shave it flat, then paint. Sure you could re-do all the “trusses” and make a flat ceiling, but you would lose a bit of headroom. Plus that little bit of peak inside will help dissipate the heat. After all, It’s not the Trump plaza, it’s a shed.

-- Perform A Random Act Of Kindness Today ... Pay It Forward

View BurlyBob's profile


3462 posts in 1685 days

#6 posted 07-28-2016 03:38 PM

I’ve found that expand foam a bit runny till it set up. You might have to hold it in those cracks with masking tape. I tried using that stuff to fill a couple of shot up duck decoys. My best advice, wear rubber gloves. That stuff is a bear to get off you hands.

View Smitty_Cabinetshop's profile


13569 posts in 2037 days

#7 posted 07-28-2016 05:27 PM

Strips is my vote. Foam = way too much aggravation w/ little benefit and when shaved isn’t a smooth finish.

-- Don't anthropomorphize your handplanes. They hate it when you do that. -- OldTools Archive --

View cebfish's profile


126 posts in 2107 days

#8 posted 07-28-2016 07:23 PM

what rwe2156 said

View Ian S's profile

Ian S

19 posts in 116 days

#9 posted 07-28-2016 07:59 PM

Hi all,
Thanks for all the great suggestions! To clarify, yes this is the ceiling we’re talking about. Here’s me last weekend, enjoying the completion of 8 hours of work:
finished project

These gaps are fairly small, but also uneven. This means putting in strips of wood might be impractical. I’ve never done anything with strips per se (aside from shimming) but it seems like it would be tough to get e.g. strips of lath to taper down from, say, 0.75” on one end to 0.5” on the other end. Making sense and sound right? Agreed, it doesn’t need to be Trump tower, but if I close the gaps at all, I’m hoping to create something that will hold paint well and sort of look like a finished surface, at least if you squint at it.

Maybe I’m wasting my energy here, that’s also a valid answer :-)

View Smitty_Cabinetshop's profile


13569 posts in 2037 days

#10 posted 07-28-2016 08:19 PM

Not to fill in the cracks, but to ride over top of them, as in battens.

-- Don't anthropomorphize your handplanes. They hate it when you do that. -- OldTools Archive --

View splatman's profile


542 posts in 818 days

#11 posted 07-28-2016 09:01 PM

Looking at the pic, I see what the issue is. I was presuming the gaps were even from end to end. Wedge-shaped gaps are a bit of a hassle to plug with strips. Smitty has the idea I would apply: battens. Rip a 2×4 into strips ~3/8” thick and tack them over the gaps. Be creative and paint the ceiling first, and the strips a diff color before putting them up. Think of this as an opportunity to build your skills. If you mess up, no big deal; it’s just a workshop, not Trump Tower Austin.

View Ian S's profile

Ian S

19 posts in 116 days

#12 posted 07-29-2016 11:32 AM

Ah now I get it. “Battens” here means using those strips the same way you use baseboard or crown molding to cover gaps in drywall. Great idea. I think I can run with that.

View hotbyte's profile


825 posts in 2395 days

#13 posted 07-29-2016 12:25 PM

I did something similar in my shop. Before putting up battens, I put a strip of the butyl rubber, adhesive backed flashing over the gap to help block air drafts. I ripped battens from a sheet of 1/4 Luan and staple in place with narrow crown stapler.

View Shawn Masterson's profile

Shawn Masterson

1294 posts in 1367 days

#14 posted 07-29-2016 09:47 PM

painters caulk and a flexible putty knife. caulk it, smooth it with the knife and let it dry. then paint

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