Wood sealer vs. grain filler.

[Monica Campos]

Hi all,

I am new in all related with working with wood and I need some advice.

I am a visual artist and I am building some wood panels. I used pine in the frame and mansonite in the top.

It is very important for me to reduce the shrinking and expanding of the wood due to humidity and weather conditions.

I was told to use a wood sealer and I was recomended a Nitrocellulose product.

THEN... here the problems begin,
I went to Woodcrafters and after repeating this story, they recommended me Behlen Water Based Grain Filler as sealer. After applying, I did some research in internet and realized that it seems it does not work as a sealer.

Here the questions:
a) If Behlen Water Based Grain Filler does not work as a sealer, can I apply a sealer on the top of it?
b) What good be a good sealer for pine and masonite?
c) As I mentioned I am painting over this panels with acrylic paint. Do you know how much should I expect the wood to shrink and expand after these treatments?

Thanks a lot.
Monica.

[Howard Acheson]

First Monica let me correct something you seem to be thinking. Short of encapsulating a wooden item in epoxy, you can not stop moisture transfer. No finish will prevent wood from expanding and contracting with seasonal changes in relative humidity. At best, some finishes can slow down the process but none will prevent it. For example, unfinished wood of some type may take 4 weeks to change in moisture content with a change in relative humidity of 20%. The same finished with four coats of an oil based varnish will take maybe 8-10 weeks. All this is dependent on the species of wood as well as other environmental conditions.

What is the item you are working with?

Whoever told you that the grain filler was also a sealer was wrong.

The most water vapor resistant finish is four to five coats of an oil based varnish or oil based paint. Acrylic paint is quite a bit less water vapor resistant so the rate of change will be faster than with an oil based varnish.

So, to sum up, you can't change the magnitude of the change in size--you can only affect the rate of change.

[Jim Becker]

Given your panel is the hard-board (Masonite or similar) there will be essentially no seasonal movement for that component. If you frame it with the pine, you will have some movement, but not a huge amount due to the relative narrow profile of the frame rails and stiles. Using quarter sawn material for the rails and stiles will further reduce movement for something of this nature.

And Howie always gives excellent advise that you can take to the bank. BTW, welcome to SMC!

[Monica Campos]

Thank you for your answers guys.

Ansering Howard question, I am working on a panel to use instead of a canvas for my artwork (visual artist working with art-acrylics paintings).

The piece look like a big box. It is 60 x 10 inches with 2 inches deep. As I mentioned the top is Masonite. I am NOT giving any "finishing" to the wood, it will be covered with my "art acrylic painting".

It is clear now that I just can change the magnitud of the size, and I would like to ensure that I keep it minimun.

I still have the questions
a) can I apply a sealer on the top of the grain filler that I already applied?
b) What good be a good sealer for pine and masonite?

Thanks for all the advice

Monica.

[Lee DeRaud]

This may be useful:
http://painting.about.com/od/paintin.../hardboard.htm

An excerpt:
"What are the disadvantages of painting on hardboard?
If a board isn't primed correctly, there's a risk that acid or oils may leach in from the board, yellowing the painting. Acrylic gesso is regarded as an effective barrier against this. Larger pieces can weigh quite a bit and will bend or bow inward so should be reinforced with a frame or bracing struts."

[Steve Schoene]

Shellac would be a good sealer. I would use the product named Seal Coat made by Zinsser. ( You will see cans of shellac by Zinsser with Bullseye more prominent in CLEAR or AMBER. These products contain the natural wax that shellac contains unless removed. The wax just might cause an adhesion problem with acyrlic mediums should be OK under oil paint.) Seal Coat is dewaxed so that there shouldn't be any problem with paint adhering to it and it should do a decent job of sealing in any acids from the masonite. It is important to do both sides of the masonite. Seal Coat will go over the pore filler, though there shouldn't really be much of that on the surface if you followed the application process of wiping off the filler after application. Pore filler left on the surface should be sanded smooth.

Is this being used on the "screen" side of masonite? Used to level the screen side of regular masonite pore filler doesn't seem like a crazy idea, though I think I would prefer Gesso. If so I would sand until the high points of the masonite under the pore filler have been evenly exposed. As a thick coating it would be pretty soft. I'd use 150 grit paper with a random orbital sander to do that, but by hand, with a padded sanding block will do fine. That surface will soak up lots of the shellac I think. Make sure it is thoroughly dry before putting on the shellac--I'd give at least overnight, two days would be safer.

One advantage of shellac is that it dries quickly, allowing you to proceed after a few hours if a lot has soaked into the filler or into the masonite.

[Howard Acheson]

I agree with Steve. Dewaxed shellac (http://www.zinsser.com/product_detail.asp?ProductID=72) is what you want to use. Hardboard will probably take at least two coats to seal. It's very porous. But, what I would recommend is to use a piece of hardboard as a sample, coat it with the shellac and then test it with the paints you plan to use. That's the only way to determine if things will work as you expect. The pine will probably be sealed with one coat but a second won't hurt.

[Monica Campos]

Thank you everybody for the answers!

I will get the product and I am happy to know that I can apply it over the grain filler.

Ansering Howard question I paint in the smoth side of the Masonite.

I am planning to cover the top of the Masonite (smooth size) with Gesso directly over the Masonite. The pine frame and the back of the masonite I will add the shellac. If I understood correctly, that should put me in the safe side, right?

Thank you again to light the ignorance with knowledge
Monica.

[Dennis Peacock]

Safe side? Yes...that will put you well onto the side of safe.

Welcome to SMC Monica and let us see your finished project!!! We love pictures.

[Bob Swenson]

Monica,
You are on the right track.
Seal with shellac.
Sand your gesso with 320 sand paper
between coats.
Put on as many coats of gesso as needed until you get the
surface you like. Careful sanding will give you
a great base for your painting.
Bob