Spackle & Polyurethane

Does anyone know if spackle is alright for filling fairly deep dents in polyurethane foam? As you could probably imagine I’m going to glass over the area once it’s filled.

Straight onto foam,or over existig glass?

As long as it is BONE DRY, I don’t think it should be an issue. Go for it.

Over foam. One last question. Does anyone know if spackle yellows really quickly on sun exposure? Like a lot quicker than polyurethane foam?

Over foam. One last question. Does anyone know if spackle yellows really quickly on sun exposure? Like a lot quicker than polyurethane foam?

That would depend on the brand you use. You’re in NZ and I have no Idea what’s available there.

If the hole you’re filling is deep, fill it by doing multiple layers, letting each layer dry before applying the next or it will shrink and possibly crack.

If there is any moisture in the spackle patch when you glass it, the glass job will crystalize over it.

The best way cosmetically to do it is to mask around the edge of the hole with tape, build the spackle up so it mounds higher than the surface of the blank, let it thoroughly dry, remove the tape and sand the mound of spackle flush with the surface of the blank. By doing it this way you avoid smearing the spackle over the area surrounding the hole which looks like shit and makes the patch job appear a lot bigger than the hole actually is.

Another thing-It does show up bad under resin tints. If you’re doing resin color go opaque instead.


I’ve done it on minor holes in shaped PU foam blanks. Sprayed the whole blank white after. It’s not the best solution, but it works okay.

Before you spackle, try the heat gun trick. A gentle application of heat will bring up most dents in polyurethane.

As long as the foams not torn, you’ll never know it was there.

DO NOT try this on EPS

why not glue in a piece of foam and shape it down?

Since any localized patch will always look different from the rest of the blank, it might be worth it to prep the entire blank with spackle as is commonly done on EPS foam. Patch the hole first - don’t sand, maybe better to just feather it with your squeegee. Then Spackle the whole blank with an even thin coat. A light sanding and you’re good. Not the quickest easiest production method but I’ve heard of guys doing that with Walker blanks that sometimes sucked up a lot of resin. A white water base/acrylic spray job will keep the foam looking better longer and help disguise the patch. Lots of boards are sprayed white before glassing.

The best way is to mask off dent. Mix a little lam resin with some white sugar, add a tiny seasoning of micro balloons, toss in some U.V. activator, fill hole, pull tape, throw into sunlight while rubbing off excess with your finger. You should end up slightly low. You will never see it. Great for color work hides perfectly.

Huuu Huu haaa he said “rubb it off”…