Problem with AquaCoat shrinkage

[wood2woodknot]

I've never used a grain filler until recently. I wanted something that was clear so I didn't have to worry about matching filler and wood colors. I settled on AquaCoat instead of CrystalLac.

I did some preliminary tests on western red cedar, then tried it on two projects - one with red cedar and one with rough faced plywood. On all of them I started by sanding first and then sealing with shellac. Then I tried filling the grain with the AquaCoat.

My problem is that after filling and smoothing several coats and dry sanding in between, everything looks smooth and perfect, even glassy. When I top coat with shellac or shellac followed by varnish (as Arm-R-Seal or spar varnish - not water based varnish), the AquaCoat appears crackled or alligatored under the surface as though there was shrinkage.

Looking for the voices of experience. Do I have a problem with technique or a problem with incompatibility?

[jteneyck]

My problem is that after filling and smoothing several coats and dry sanding in between, everything looks smooth and perfect, even glassy.

I think your problem stems from using multiple layers of filler.  I haven't used filler all that often, nor have I used the one you used, but when I have used filler it was always as a single application.  You put it on really heavily, let it set up some, then squeegee it off cross grain.  There should be no need to do it more than once.  

John

[wood2woodknot]

I think your problem stems from using multiple layers of filler.  I haven't used filler all that often, nor have I used the one you used, but when I have used filler it was always as a single application.  You put it on really heavily, let it set up some, then squeegee it off cross grain.  There should be no need to do it more than once.  

John

Will try that. Label suggests reapplications if first is insufficient. Maybe I should have left it overfilled and waited longer to smooth it out.

[jteneyck]

Will try that. Label suggests reapplications if first is insufficient. Maybe I should have left it overfilled and waited longer to smooth it out.

Yes, allow the filler to dry completely before sanding, I would think at least over night.  And Fred might be on to something about the underlying wood sucking up moisture during the process.  I know you said you sealed the wood first with shellac before using the filler, but it might take several coats of shellac to really seal up softwood.  Hard to say, but something to consider.  

John

[fredhargis]

I'm wondering if using the filler on softwood is part of the problem. Maybe the wood is swelling slightly from the moisture, and then drying out later. So the wood is shrinking instead of the filler. Just trying to think outside the box. I don't use fillers very often, and it's always been on hardwoods.

[wood2woodknot]

Maybe longer drying time would help, but there shouldn't be any wood shrinkage because I put one or two sealer coats of shellac on before the filler.

[FloridaRetiree]

I've never used a grain filler until recently. I wanted something that was clear so I didn't have to worry about matching filler and wood colors. I settled on AquaCoat instead of CrystalLac.

I did some preliminary tests on western red cedar, then tried it on two projects - one with red cedar and one with rough faced plywood. On all of them I started by sanding first and then sealing with shellac. Then I tried filling the grain with the AquaCoat.

My problem is that after filling and smoothing several coats and dry sanding in between, everything looks smooth and perfect, even glassy. When I top coat with shellac or shellac followed by varnish (as Arm-R-Seal or spar varnish - not water based varnish), the AquaCoat appears crackled or alligatored under the surface as though there was shrinkage.

Looking for the voices of experience. Do I have a problem with technique or a problem with incompatibility?

Fraid I don't understand. 

Why would you use grain filler on a diffuse porous wood?

The few times I used was on ring porous woods like oak.

???

[wood2woodknot]

Fraid I don't understand. 

Why would you use grain filler on a diffuse porous wood?

The few times I used was on ring porous woods like oak.

???

It's called a learning process. Simply needed a very smooth finish on one side of an inexpensive plywood box. What better place to try out a new process before trying it on something expensive. I'm not into practicing on more important projects.