Best material to fill in HDU?

[FatCat]

I have a customer who has a sign that has been up for several years that is approx 2' x 15' and made of some type of 2" HDU. It is a simple sign and just has a routed edge, routed border and applied vinyl graphics. They are doing a small name change and want it re-painted and re-lettered.

It looks like the previous makers just butted the 2 ends of the HDU together and screwed it to the building. Now there is about a 1/4" gap in the seam where the material has shrunk slightly. (Does HDU normally shrink a little over time?) Anyway, was wondering what could I use to fill in the gap? Could I use some type of wood putty or perhaps bondo, and then sand and re-paint? I'm afraid to take it down and just move it back together on the risk that it could crack or something.

*Sorry, I don't deal much with HDU.

Thanks!

 

[FatCat]

-bump-

 

[signs2trade]

HDU should not shrink unless it was placed outdoors unpainted. I believe unpainted it will shrink about 1/32" a year due to UV exposure.

 

[CheapVehicleWrap]

minimal expanding foam?

 

[FatCat]

Looks like the ends were painted, so I'm really not sure what caused it, but there is definitely a gap. Again, just looking for the best way to fill it in and be able to sand it down smooth and re-paint.

 

[CES020]

I think you're fine with what you suggested. I've used Bondo before and it stuck really well in the application I used it for.

 

[axis]

I'd go with the can-o-foam

The problem with bondo is having to hang around until it's reached the proper point in the cure cycle. Too soon and you can't shape it, wait too long and it's far harder than the HDU, making it a bear to sand evenly. I'd go with what was posted earlier, the low expansion foam in a can. Squirt it, come back later, trim it with a blade, sand lightly, prime, fill with Bondo glazing & spot putty if required and you're good to go. If you've ever gotten this foam somewhere you don't want it, you'll know how well it sticks.

I've never seen HDU shrink in any measurable manner. If left uncoated, exposure to UV will cause the surface to degrade so it would appear to shrink...

 

[FS-Keith]

paintable caulk

 

[axis]

Caulk will shrink and may also have a different surface appearance, so you'd still see a seam.

How about cutting a 1/4" slice of 2" HDU and Gorilla Glue it in. Or epoxy if you're in a hurry. A few coats of filling primer on top and you're good to go.

 

[theskipman_98]

We use rock putty but it is hard to sand smooth without damaging the hdu. The best thing I have found is a vinyl spackle that starts off pink and dries white. Easier sanding, easy to paint,

 

[signmeup]

Take the screws out, shove the panels together and put the screws back in. Paint over. They've had a gap for years... why worry about it now?

 

[axis]

Take the screws out, shove the panels together and put the screws back in.

Thought about that, could be the easiest, but you have to fill screw holes and more than likely touch up the building paint. And when I hang an HDU sign, the screws are there to hold it til the adhesive cures.

If it's screwed into wood siding, it could just be that the wood is doing it's seasonal shrinking. Especially if the sign seam is near a seam in the siding.

 

[TammieH]

Gorilla Glue also works well, just be careful not to apply to much and mask over to control the expansion, it will also bond the two parts together.

 

[MikePro]

heck, just fill it with paintable caulk, clean it up with a razor blade after it dries, paint and be done with it.

also noted: i've filled HDU gaps with bondo before, as well. My preferred method is still to use PB-FastSet (same stuff as gorilla glue, except you can buy it by the gallon from sign suppliers), and shave-off the excess expanded goop with a razor blade before it hardens completely.

 

[signmeup]

If I have to fill HDU, I use that white spackle stuff from the hardware store. Works for me. Bondo is way too hard to sand flush with the HDU. The best filler would have the same density as the substrate. Spackle comes closest.

 

[letterman7]

If the ends were painted at the gap and the customer hasn't complained about it, why mess with it? Trying to fill it with something and paint to match is going to raise more issues than just leaving it be. If it really bothers the customer, cut a slice of 1/4" pvc and paint it as close as you can and slide it into the gap, secure it with a little clear caulk before you put it in place. You'll likely never see it from 5'.

 

[axis]

Filling a 12 cubic inch gap with Gorilla Glue while the sign is on the wall sounds like trouble to me. Given the depth of the void behind it, caulking will shrink a little and you'll have a dip there, maybe the 50/50 rule applies (50 ft/ 50 mph) and it'll be good enough. I still think gluing in a shim with a polyurethane glue will give the best results. HDU or the cut side of pvc sheet have pretty much the same appearance and the foaming glue will fill any little gaps. A shim and caulk will probably look good enough and get you out of there quicker .

Hopefully, you grabbed a can of insulation foam and finished the job yesterday.