Smoothing HDU

[tallen84]

I just made my first sign with 15# HDU (sign foam brand) and I am having some trouble getting the smoothness I would like. Is there any good ways of smoothing the HDU so I can apply a gloss paint without meticulously sanding every tiny detail? Maybe a self leveling primer? or a grinding / sanding bit?

Any ideas are welcome, thank you.

[joe]

Todd,

I like automotive High Build Primer. The brand I use is U Pol. It dries fast and sands to a glass smooth finish.

[joewino]

We use a high build primer from Coastal Enterprises (folks that make Precision Board) - it's water based and dries quickly and sands extremely smooth.

FSC-88 WB

We just brush it on right out of the can - sometimes with a little water if it's too thick. For spraying we just use more water and spray it through a HVLP spray gun.

[Big-Tex]

I second automotive primers, I also used Bushwacker sold at SW stors (solvent based) with good results.

[tallen84]

I will try some of those primers. How well do they self level when brushed on? Also, has anyone tried using their shopbot with a bit to do the sanding in small details. (Like a sanding dremel bit?)

[Big-Tex]

If you want to self level with brush you better use some sort of retardener to slow down drying.

[joe]

Todd,

Each of the manufacturers of HDU produces boards with different open pours. All of them are a challenge to fill. Odd as it may sound, sanding will not solve the problem of open pours.

One effective technique is to squeege a filler on the board surface. I use either Rock Hard Putty or Precision boards Crack Filler. A big window cleaning blade will do the trick. That gets you a perfecty smooth surface with no sanding.

Joe Crumley