Wood and Water Question

[Ong]

I have some finished and/or lacquered HARDwood wooden bases and am wondering if I could lay plaster and groundwork straight on top of them. I read long ago that one should NOT do this to unfinished pine bases (such as the ones one could buy cheap in the Crafts stores) because over time, the water moisture from the plaster would bend and warp the base. The advice was to paint the pine base and lacquer it first or not even buy pine.

But would the same problem occur for hardwood bases, some with gloss finish coat? Do I need to glue on a piece of plastic to the base first to prevent water seepage or could I just lay on straight wet plaster and putty and build groundwork from there? Someone said adding plaster on top of a gloss wood base may cause the plaster to slip right off when dried, but scoring the base would allow water to seep into the bare wood. He suggested gluing on foamcore to the wood first and then building groundwork on top of the foam. A good idea, but I cannot imagine adding foamcore to every wooden base I have unless that is the only way. Any proper suggestions appreciated. Thanks!

 

[Einion]

That problem with pine bases I think would largely be on large flat ones that aren't very thick, like you'd use for a sizeable vignette or a diorama, with real plaster put on top which is very wet.

For anything smaller I doubt there's much potential for a problem especially seeing as there's no water present once the plaster has dried, and this doesn't take long.

Someone said adding plaster on top of a gloss wood base may cause the plaster to slip right off when dried, but scoring the base would allow water to seep into the bare wood.

Yes, that can happen. Scoring the surface deeply is generally enough to give it purchase but for a little extra security you could grind a few divots in the wood, or drill a couple of shallow holes; I do this sometimes. Mixing a little PVA into the plaster can be a good idea too, to improve its grip.

Einion

 

[Ron Tamburrini]

You Could simply rough over with coarse grade sandpaper in a circular motion to scratch the surface.
If the base is small and fairly deep you should have no problems, bear in mind that hardwoods vary by type and there can still be a little moisture in the wood
and sometimes shakes can appear it also depends how it has been sawn (quarter sawn is best)

If your groundwork is not that large consider magic sculpt ,no issues and no shrinkage

 

[harrytheheid]

Hi Einion, Ron and ong,
I use rotary wooden tables for most of my bases. These are 390mm diameter which is normally large enough for the relatively small scenarios I prefer, and are excellent for obtaining photos from an infinite amount of angles, but they're a bit on the thin side. The first time I tried them, knowing no better, I simply slapped on home-made paper mache for the basic groundwork and the result was a bit of a disaster due to warping, as you can clearly see in the photo below.

The base did straighten out to a certain extent after a couple of weeks and although I didn't score the wood, I haven't experienced any slippage of the groundwork.
The support on the bottom is a wooden mixing bowl I "liberated" from it's more normal role in the kitchen.

For larger dioramas, I use cheap kitchen chopping boards in various sizes. This one is 600mm x 400mm, (not including the picture frame edging), and it's earmarked for a densely populated medieval diorama which ought to be finished next time I'm home and get all the figure conversions and repaints finished. First time I tried these I used plaster for the groundwork and failed miserably due to similar problems with warping.

Another option is locally obtained display tables. This is the base for my latest project and is 430mm x 270mm - and as you can see, it hasn't warped after the first of the groundwork was shovelled on despite the fact that the base of the table is only about 10mm thick.

The steps I take to prevent warping are;
1/ A couple of thick coats of varnish where the groundwork is going to be laid down.

2/ Sand and score the varnish to provide a key. I've found that when you score through to the wood, the water seepage isn't enough to warp it.

3/ I've gone over to using celluclay, (a commercially available paper mache), and mix it with white glue diluted with 50% water.

4/ The first of the celluclay/white glue/water goop goes on as a thin layer - about 3mm to 5mm. Once this is fully dry I build various features onto it in thicker layers.

I haven't experienced any more warping of the bases since adopting this method and using these materials. Plaster would probably work as well if laid on in thin layers, but it's really heavy compared to celluclay - and can be prone to cracking.
I'm aware that Einion and Ron know all this, but hope this post backs up your responses, is helpful for ong, and provides him with some options.
Cheers
H

 

[JonP]

For small bases I score the top and used ready mixed filler designed for filling wall and ceiling cracks. As it's solvent based it isn't too wet and dries quickly so doesn't affect the wood. You do need to build it up in fairly thin layers to prevent it cracking though.

 

[chippy]

My two pence bit of advice for what it's worth is to score the area you want to cover with a scalpel knife in small diamond squares and then coat with pva adhesive , let it dry , then add a bit of pva adhesive in to what ever your using for ground work . This does three things first you give a texture for a matarial to bite into but coating with the pva glue you seal the surface but leave the texture and by adding the pva to your chosen mix it will bond with the the pva already on the base . My favourite material for ground work is floor ceamice tile adesive . You should have no further problems unless the wood was not properly seasoned !!
chippy