Polyurethane varnish plus shellac finish ?

[OldWood]

I'm working off an around 20 year memory which may well be totally inaccurate !

I wanted then to put a finish on the new window cill shelf and have this memory that I did a wipe finish using a poly varnish + shellac (sanding sealer) finish. It has remained as good as the day I did it.

Now Her-in-Doors has got me to make a coupe of corner shelves for the same area to take plants (in pots!), so I would like to see if I can use the same finish.

Is my memory a likely possibility, or something that is just a figment ? :roll:

Thanks
Rob

 

[Woodfinish Man]

Hi Rob,

From our experience it's best not to apply polyurethane varnish over the top of shellac sanding sealer(sss).

We've found there to a compatability issue. Although the PU will dry and look fine over SSS once it comes under any pressure (such as rubbing a coin over the surface) the two coatings separate causing an air pocket to appear. You would be far better sealing first with Transparent Shellac Polish and then overcoating with PU, it's the zinc stearate sanding agent in SSS that's the problem.

Hope this is of some help.

Ian

 

[OldWood]

Thanks for replying, Ian. This was actually a mixture of PU and SSS that I have the memory of using having seen it recommended somewhere. I do clearly remember wiping on PU thinned with white spirit and it's quite possible the memories have got muddled ! :roll: Time and age do tend to muddle memories !

Rob

 

[Woodfinish Man]

PU & SSS mixed together....that's a new one to us. Wouldn't have thought that a white spirit based urethane coating and methylated spirit based shellac would disperse together. I'm off to try it out!

 

[OldWood]

PU & SSS mixed together....that's a new one to us. Wouldn't have thought that a white spirit based urethane coating and methylated spirit based shellac would disperse together. I'm off to try it out!

Thanks for that, WFM. Logic does say my memory is faulty. In the end for these new shelves in the bathroom (corner ones for plants) I fell back on satin PU alone - and wished I hadn't ! But SWMBO is happy

The window sill timber may have either been finished with what I'm taking about, or I may have thinned PU and wiped on. It was done 20+ years ago and is good as the day I did it, plus it doesn't look like PU.

Rob

 

[MIGNAL]

The two wouldn't mix. You can get a bit of Oil to go into a spirit based varnish but we are talking a few atoms, perhaps a bit more.
There are some hybrid varnishes but I think they use some type of process to mix the two. My knowledge on these types is very poor.