Waterproofing Plywood

Affiliate Disclosure: We may receive a commision from some of the links and ads shown on this website (Learn More Here)


Well-Known Member
by jimfitch on another forum....

I would say a winner is a product that works, seals the wood from moisture expansion and contraction, and hopefully doesn't cost an arm and a leg.
I did some quick searching and found this which looks cheap and cheerful:
Olympic Water Guard - $10.48 a gallon. Cheaper than the above and looks pretty good.

Most customers used it on their deck, which is subject to a lot more harsh sun and rain. Looks like that will be good for bench-work wood to help it resist expansion and contraction. My wood is all being stored until ready to install in my basement, which is being kept around 55-60% humidity with a de-humidifier:

Product Overview
WaterGuard Multi-Surface Waterproofing Clear Sealant offers convenience and value. Penetrating, advanced multi-surface sealant protects against water damage and creates a mildew-resistant coating. Perfect for a variety of substrates including concrete, brick, stucco and wood.
  • Ready mix, ready to use clear sealant
  • Provides protection on multiple exterior surfaces, including: exterior decks, fences, siding, wooden furniture and structures, concrete, brick, stucco, steps, sidewalks, patios and more
  • Durable sealant that provides waterproofing protection
  • Penetrates and protects against water damage
  • Provides mildew resistant coating
  • Clean up with just soap and water
  • Normally dries in 12-24 hours when applied at 50°F to 85°F
  • Allows wood to weather and gray naturally


Well-Known Member
Such products offer a high surface tension on which water can be expected to bead and to run off. Think polymers like wax and urethane. Think Gortex which water can't penetrate, but which allows your evaporating sweat to works its way, molecule-by-molecule, out through the micro-pores of the material. I don't know that the liquids offer impermeability to moisture, which is another kettle of fish. Moisture is a single molecule of water, perhaps several of them adhering to each other, but still much too small to be seen even with advanced microscopes, except for perhaps the electron variants. Whatever this person uses, it must not be the least bit porous, it must perfectly cover the entire surface of the material he wishes to protect, and there can't be any mistakes. Even screws and nails driven into the material through this NASA-perfect coating will allow moisture to enter the wood over time unless the room humidity is controlled somehow.


Plucked Tailfeathers
Staff member
All I needed to see was the last line in the "product overview".
Like has been said many times, "It's your RR". I am sure that it will be fine.
Hope everything works out for you.


Well-Known Member
Timber Pro Stabilizer

Over many years of outdoor projects, pine, cedar, and fir furniture, fences, and chicken coops I've used many 'water seal' products. All have needed to be resealed over time. This product (https://timberprocoatingsusa.com/products/internal-wood-stabilizer/) is amazing. Over six years of use and I've never had to reseal or found any rot. Because it worked so well outdoors, I used it in building my present benchwork. It might be worth a look or give the company a call and tell them what your doing.​

Thanks for that reference. I wrote them an email today.

Iron Horseman

Well-Known Member
I'm building a layout in a shed external to my house in the hot, humid state of FL. While I have the shed under a carport and insulated well, it does seem to remain cool for the most part. But I do not intend to run the AC full time, so it will experience temp and humidity swings.

Many of my decks/shelfs will be good grade, multiply layered 3/4" plywood, which I intend to try and 'seal up' as much as possible against moisture absorption, and the subsequent warping that can occur..
Any reason don't you don't just use pressure treated plywood to start with? It has already been saturated with water proofing rot and fungus control.


Well-Known Member
I believe he is mostly concerned with dimensional changes across the grain due to high humidity, not so much with corruption of the material.
Late to the discussion, but why not just use -

1) use exterior grade plywood
2) use marine grade plywood
3) MDO (Medium Density Overlay) this is the stuff almost all the traffic direction (think green) signs are made of.


Well-Known Member
In sunny Louisiana, the same climate you're in.
I built a wooden privacy fence in 2011, and used this product from Behr.
I can tell you the fence looks like the day I stained it, water literally will not stick. Direct sunlight all day, and from 20-105 degrees with 60% humidity. This product has lasted 2 years past the manufacturers estimate of 5 years, and still going strong. May be overkill for your application, but you asked.

That link you provided no longer worked properly.

I was looking back thru some products I had collected up from various yard & estate sales and found the full gallon of Behr waterproofing outdoor wood stain. Just a shaking test said it was a more liquidy product than many paints. I like that idea as it indicates it will penetrate the wood surface more easily. (harkening back to my boating days, I recall our diluting/thinning the first coat of varnish on wood surfaces to get a 'good grip')

Decided to give this product a try. First trial is the plywood sheet I will be cutting up in half to make the 'floor panel' of my helix structure. As I suspected the first coat seemed to soak into the wood surface really well. I will be applying a second coat tommorow.

I did 2 coats of this 'stain' on both sides and edges. I might even add another coat (&color) of regular paint eventually.

Was pretty happy with results, so today I did my first sheet of 3/4 plywood that I will be cutting up to make my staging track subroadbeds.


Plucked Tailfeathers
Staff member
OK - I have to ask: Why not cut the pieces you need before painting? That way you can seal the edges at the same time.
That product is EXCELLENT! Did my fence 2 years ago and it still looks new!


Well-Known Member
Cutting first might have been a good idea, but I just was not ready yet with the final shape of those pieces. And the afternoon rain storms had abated, so I took the chance to at least get some 'blocker' on the larger surfaces of the plywood


Well-Known Member
BTW I got 2 full 4x8 sheets of plywood painted with 2 coats, on both sides with about 1/2 gallon,... so I'm hoping to get 4 full sheets treated with the one gallon.

ModelRailroadForums.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com