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Forum topic by MrRon posted 09-20-2019 05:24 PM 211 views 0 times favorited 3 replies Add to Favorites Watch
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5721 posts in 3756 days

09-20-2019 05:24 PM

What would be the best way to create this 1/2” radius corner? The material is high density urethane (HDU) (attn: John Smith). Various methods have entered my mind and they include using Bondo, Durham’s wood putty, wood filler, epoxy, FSC-88 WB (John Smith). I tried carving a strip of HDU and cementing it into the corner, but didn’t work too well; it left gaps. The inside corner has to be smooth and blend in with the rest of the material. I guess the number 1 question is: What will adhere to the HDU best?(John Smith).

3 replies so far

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John Smith

2017 posts in 675 days

#1 posted 09-20-2019 08:59 PM

Ron, I have successfully used Bondo and thickened epoxy
for fillets such as that after all sculpting, carving and sanding is done.
HDU is much, much softer than the fillers and will not sand the same.
so – the filler will have to be the last step after priming and before painting.
Durhams Rock Putty will not stick to HDU
FSC-88 “could” be used if applied in several thin layers, allowing each layer to dry thoroughly.
(but – the downside is that it “could” also dry too much and crack).
or – a 3/8”r. with Bondo then the 1/2” filler with FSC-88 ??
epoxy is the hardest of all the ones listed.
Bondo will sand the best, but be careful not to sand too much.
probably use a spoon to make a consistently smooth fill.
make a practice piece about 6-8” and fill with Bondo – see how it goes.

I would make a sanding block with large sides and bottom with the 1/2”r. routed
and glue sandpaper to all sides. that way you are sanding everything evenly.
not just the fillet.


-- I am a painter. That's what I do. I paint things --

View Planeman40's profile


1452 posts in 3274 days

#2 posted 09-21-2019 04:23 PM

I have used Bondo with great success with wood. I once filled in four door knob holes in some surplus glass pane doors to make a wall/entrance to an outdoor deck. Worked great and has lasted for more than ten years without problems even with the weather on one one side. Bondo sands great and has the strength to hold up.

-- Always remember: It is a mathematical certainty that half the people in this country are below average in intelligence!

View MrRon's profile


5721 posts in 3756 days

#3 posted 09-21-2019 05:37 PM

Thank you John. I knew you would have the right answer. I have been going slowly on this project due to other commitments, like looking after my sick wife, the weather and other household chores. When I get the chance, I try to work on my train project. Age is also starting to slow me down.

I also thank you, Planeman40 for your response. I remember using Bondo back in 1962 to repair the headlight fairing on my 59 Karmann Ghia that had rusted out. That was a breeze to work with. That was when garages were still using lead to patch holes in metal.

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