Can I spray foam into a hollow core door?

homeboundNovember 7, 2006

Can I use "Great Stuff" foam (the blue can, which "doesn't bow doors & windows") and fill plain hollow core doors without causing damage to the door? Which edges (and how many holes) would you use to do this? I figured I'd drill holes the same diameter as wine bottle corks, and then use those to plug the holes.)

We have two doors leading to attic storage, and I'm planning on adding solid extruded foam panels behind the doors as well.


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if the doors are completely hollow, i would drill from the top and spray down. but many "hollow" doors still have a thin web of bracing inside that criss cross back and forth.

drill 2 small holes, 1/2" or so, in teh top end of the door and shine a light down one hole while looking in the other. if the door is clear, then foam away. but do not use too much or it will buckle the door. you may need to spray some, let it cure for a few hours, then check and spray more as needed. it will expand UPWARDS so make sure it falls all the way to the bottom. or you can take it off and drill several holes down the hinge side of the door and spray in.

we did this at work once just to see how well it would work to dampen sound. the door was going away in an upcoming remodel anyway since the new opening would be bigger, so we did not care if we screwed it up. worked ok, but the best results came from when we replaced it with a solid wood door.

BTW, the plugs you drill out will either fall inside the door or not fit back in the holes. you cannot drill them out with out making them smaller than the hole!

my adive would be to replace the doors with solid wood and seal them airtight.

    Bookmark   November 7, 2006 at 3:21PM
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This would be a great idea if you want to deaden sound or improve insulation EXCEPT:

These hollow doors are usually filled with a honeycomb arrangement of cardboard, so your foam wouldn't go very far into the door. I think you are wise to consider the less-agressive foam, I used some of the other and had it crush a central vac air outlet slightly, so there can be some big pressure!

I think you're better off looking for solid doors, if you're on a budget, maybe wait for a sale, or see if you can get some second-hand. Fire rated doors might be a good idea anyway.

I suppose your doors may be completely hollow, you could drill a test hole in the top edge of the door, and look with a flashlight.

If it's hollow then go for it, but make sure you put newspaper or cardboard underneath in case the stuff leaks, it's horrible (and difficult) to remove.

    Bookmark   November 7, 2006 at 4:02PM
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Thanks much. I'll drill and take a look inside.

Since they're about 30 yr old, maybe they won't have the honeycomb paper like the doors today.

    Bookmark   November 8, 2006 at 9:04AM
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There is some type of grid inside the door to prevent bowing of the face panels.
Modern doors often use corrugated cardbord, some older doors have thin strips of wood.
You could always strip off one entire face of the door, fill with foam sheet cut to size remove the bridging), then apply a new panel.

    Bookmark   November 8, 2006 at 9:39AM
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Sometimes it just doesn't pay to fix up what you have. You will use 4 or 5 cans of this stuff or more at $4 or more a can so you will be in for $25 or more. Also, your door will be full of holes.

Buy a new door on sale or see if you can get a slightly damaged showroom model at a discount.

    Bookmark   November 8, 2006 at 6:39PM
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Saw an article in Handy Man where a guy exploded his door into an oozing mess doing it. It was funny to look at but i am sure it was a total bummer when it happened.


    Bookmark   November 10, 2006 at 5:37PM
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I just looked at a table of R values for doors: 2.1 for hollow core vs. 3.0 for solid I decided to leave it alone and instead glue 1" of extruded foam board onto the back side of it (adding R 5) and be done with it.

    Bookmark   November 16, 2006 at 2:33PM
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Don't forget, if you glue foam to the back of the door you create a code violation.

Rigid foam cannot be left exposed in a storage attic and must be covered with a thermal barrier to keep it from igniting in a fire.

You need a new insulated door for this application.

    Bookmark   November 16, 2006 at 4:06PM
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Can spray foam on one pipe 1 1/2 by 4 inch Hollow inside and How because is for door frame Tankyou..

    Bookmark   August 20, 2009 at 2:51AM
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Just a general note for spray foamers.

It's best to drill at least two holes for an application, the size of the dispensing tube. Inject in one hole, the other vents. There is a degree of judgement on the spacing- more pairs of holes may be required, say for under a tub (large area). A small amount of oozing through the vent is desirable, but provide surface protection for overflow.

If the visible area around the holes are to be finished or meet cosmetic requirements, masking should be used. The foam residue is pervasive & entrenched-speaking of urethanes.

For the OP, you need to know what's behind the door skin.

    Bookmark   August 23, 2009 at 8:35AM
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I am a DIYer, but personally, I would not do what you are doing. Besides the fact that I hate the appearance of most of these hollow core doors, it would take a lot of time, make a mess, and cost you 1/2 as much as a new door. You can get a solid pine panel door at Menards for about $60 if it is on sale.

    Bookmark   August 23, 2009 at 9:19AM
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