Paintable Water Repellent on Wood?

Have you had any experience applying a paintable water repellant to exterior woodwork before primer and top coats of paint? The intention of this treatment is to keep liquid water from penetrating woodwork joints and causing peeling paint and deep fungal decay. A study was done (early 1980s ?) by the Wood Products Lab that showed this was an effective treatment. There are several commercial products usually described as 'paintable water repellants' and you can make your own by disolving parafin wax in mineral spirits and adding a little linseed oil. The concern is that if it can repel water it may also repel the primer causing adhesion problems. I have reproduced the results of the study myself and have sometimes used this treatment on projects to good effect. Have you had any problems or success with this treatment? Has anyone published on it?

I suggest you do an archive search at: rec.boats.building newsgroup. This is a subject given great scrutiny and much informed debate in the marine community.

With the removal of Pentachlor from the hands of 'civilians', alternatives have been found but the efficacy and indeed acceptability of them is not universally acknowledged.

This method has long been used by knowledgeable painters. However, in recent years this practice has been discontinued because of the skyrocketing cost of labor. It remains a good idea for severely weathered portions of houses, notable porch floor edges, window sills and the like. Today's new growth woods are not nearly as weather resistant as yesterday's old growth wood.

The reason good long oil primers are still so much better for exterior priming is the oils itself. They penetrate far better than short oil or acrylics. It stands to reason that a mixture as you describe would penetrate far deeper than a long oil primer. And it does, I have observed. My mixture is 1/2 paint thinner, 1/2 Penetrol. I apply it heavily into joints, cracks and crevices, then apply the primer before the mixture dries. I feel you have a better bond using that procedure. I would question the use of paraffin wax in the mixture, as no commercial paint would stick to it.

Benefits are many, the ones you describe, plus the dry fibers of the wood are refreshed, and tend to swell, making a tighter seal.

I'd be interested in your thoughts, please keep this thread going.

Yes, I know about epoxy primer products. I am concerned about trapping moisture within the wood so I do not like to use overall coating treatments that limit moisture escaping from the wood. Have you tested the moisture permiability of wood coated with CPES? What perm ratings do you get with CPES?

Also, what is the 'mechanism' of rot protection afforded by CPES? How does it give rot protection?

John Leeke, Preservation Consultant

publisher: Practical Restoration Reports contributing editor: Old-House Journal website: www.HistoricHomeWorks.com

John,

Wood that has been treated with one coat of CPES will still 'breathe'. After the epoxy cure air can still be passed through it. After two coats there is still some air movement, although much less. After three coats the wood is pretty much sealed, as it would be from a coat of standard thick epoxy resin. For wood protection on good wood we recommend only a single coating; on milding deteriorated wood a single coat will still usually be sufficient, assuming the wood is allowed to absorb all the CPES it can. On severely deteriorated wood it doesn't make much difference anymore, since one is then basically replacing wood with epoxy.

CPES protects wood from rot fungi and destructive bacteria in two ways: 1)The solvents that carry the epoxy into the wood (there are 14 of them) are powerful (xylene, tolulene, alcohol, etc. etc.) and will kill anything they immerse, although we cannot officially say so because it gets us into pesticide requirements with the EPA

I used to do a bit of architectural and fine art paint restoration. Presently I am conserving bones and fossils for a large museum. We use terpolymer of polyvinyl buteral in acetone- Butvar B-76 from Monsanto Trenton Michigan to 'harden' consolidate porous, weak or crumbly bones. It is used thicker as a glue. It is in essence a plastic suspended in acetone. It is much harder than poly vinyl acetate. Butvar makes porous bones rock hard. This might be used in certain cases for wood. It can be applied one coat, very thin several times to soak deep, even thoroughly, and or built up depending on need. Ratio can be custom. I used it on a soft piece of drift wood but its compatibility with paint and exterior use I have not tested or thought about until now. I believe it could very well work. A thought. Any comment on this idea appreciated.

Deb Chory

Is this product- Butvar B-76 from Monsanto- available to the general public, and is it inexpensive?

The current darling for doing this type of fixation and stabilization in the marine market is CPES- clear epoxy penetrating sealer. It is paintable, such that it is advised to do so during curing for maximum paint adhesion. The following quote from their site may or may not be valid- I'm not in a position to judge, but it may serve to explain it's properties:

'Our epoxy products are formulated from resins derived from wood. They bond better, are tougher and more flexible than standard petroleum-based epoxy resins. '

More at:

This brings to mind a problem I am facing. My house, built in 1926, has small wood gutters recessed in the soffets. I would like to replace the gutters with new wood gutters, but would like to coat or treat the gutters to make them last longer. I imagine using perhaps a penetrating epoxy or some such product on the inside of the gutter, with latex paint on the outside for breathability. Replacement gutters are available in cedar or treated fir. I have talked to gutter people about metal gutters, and was told that condensation would rot the enclosing soffets. I want to retain the current appearence af the recessed gutters. Does anyone have comments or suggestions.

The polyvinyl butyral - Butvar 76... We get it as a powder in 50 gal drums. price off hand ? from Monsanto Co. Resins Operations Trenton, Michigan 48183 Phone 314 694 1000?
http://www.coatings-solutia.com/toc.htm check this page out from Monsanto. The Butvar is here Hope this helps. They do paints too.