Waterproofing Plywood

[railandsail]

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.

My first thoughts turned to paints,...either oil or water based. But as I thought more about the situation I came to believe that the paints for the most part just coat the exterior of the plywood. They don't really penetrate the wood to seal it up.

 

Deck Type Sealers

I had some Thompson water sealer product setting around I had acquired from some estate sales. I looked up info on the product, and I was NOT very impressed with its capabilities for protecting outdoor decking. Seems as though many folks were unhappy with its performance.

But that said, I do NOT intend to utilize it in an outdoor situation,...where UV can be a big problem. I ran a few test samples on a portion of my outdoor wood deck, and some wood shelves I had made of plywood. I did note that it seemed to soak into the wood much more thoroughly than paint would have. That would seem to indicate a 'sealing function'?

Has anyone had experiences with sealing up plywood with deck coatings?

Can they subsequently be painted over??

Waterproofing Plywood, Sealing for longer life

I have to clarify that I went to a different search engine to find this site, which I believe is British by the currency quoted. (I'm so tired of Google search engine giving all this ad related references right up front,...no meat to a search anymore)

https://www.makewoodgood.com/waterproofing-plywood-sealing-plywood-for-longer-life/
 

This site is promoting the use of clear penetrating epoxy sealer, and makes the case with test and photos. what I also found interesting is it specially states do NOT use PVA glues, and do NOT use water based products when attempting to seal up plywood.

 

[mlehman]

If this is going to be an issue, best to get marine-grade or equivalent plywood to start with. It's glues are made to stay stable under wet condtions, which is the very first problem. If the plys delaminate, doesn't matter how good the waterproofing is.

[j. c.]

i used thompsons on deck it rotted out in about 5 years , after reparing it i used nitrocellulose lacqure in a airless sprayer , that was 8 years ago and its still going strong.

[PED]

Unless you must use plywood, you might consider using 1x12's and avoid the glue problem.

[mlehman]

PED

Unless you must use plywood, you might consider using 1x12's and avoid the glue problem.

 

Yes, considering the alternatives is important if cost matters. Really good marine is expensive, but overkill for somethung like layout benchwork. Doesn't need to be fancy, but does need the legit rating and it'll be fine. Use the "chesp" stuff but the right grade and you'll be fine in most of our applications.

Boards are a sensible alternative. If you need fancy in other situations for example, look for the New Zealand pine I was raving about a few years back. Marvelous stuff, even in 1x12, not a knot in most of the boards but was paying over $30/each for 8' lengths. That kind of beauty doesn't go into benchwork here, but I can see how it is attractive to those who can afford to use it that way given the dimensional stability and the fact you can drive a screw in anywhere without worry over knots.

For often wet areas, some of the new plastic lumber available in various decking "lumber" sizes and some other common SKUs is now not all that expensive. No need to treat it, either, a savings against the total job cst of course, plus the usual environemntal benefits to not slobbering on the treatment every few years.

[7j43k]

If you want to waterproof wood, this stuff works:

https://www.amazon.com/Smiths-Original-Clear-Penetrating-Sealer/dp/B072MRYZ5Z

 

I've used it.

 

Ed

[railandsail]

j. c.

i used thompsons on deck it rotted out in about 5 years , after reparing it i used nitrocellulose lacqure in a airless sprayer , that was 8 years ago and its still going strong.

 

As I said I am not using it outdoors.

Found this on lacquers,...

Think of the lacquers as having three basic classes: nitrocellulose, CAB-Acrylic, and Catalyzed.
The nitrocellulose is pretty much your “everyday” lacquer. Its the stuff sold at Home Depot and Lowes (Deft). It makes for a beautiful finish and its relatively inexpensive. Problem is that it tends to yellow over time. So its not really the best option for light colored woods.

CAB-Acrylic lacquers are made with acrylic resins and they dry “water white”, meaning they will not yellow over time. These are reasonably durable finishes that are a pleasure to work with.

Catalyzed lacquers consist of both pre- and post-catalyzed versions. Instead of curing by the evaporation of a solvent only, they also cure chemically. The catalyst can be added ahead of time (pre-catalyzed), or in your shop (post-catalyzed). Both have a limited shelf life as a result. The finish, however, is very durable as a result of the chemical curing process. I like Sherwin Williams products and I actually use them for nearly all of my lacquer. I’m not sure if its available in your area, but you should see if you can get the Pre-cat CAB Acrylic lacquer. It was relatively new at the time I was using it and not everyone could get it. But its kind of the best of both worlds: durable, water white, less toxic off-gassing, etc…

As far as conditions go, lacquers are not as forgiving as other wood finishes. Moisture and cold are your enemies. I don’t like to spray much lower than 70F, and humidity isn’t much of an issue here in AZ. But if its a humid day, forget about spraying lacquer. You can easily end up with “blushing” (moisture trapped in the finish). And keep in mind there are going to be some days or seasons (depending on your region), that you just will NOT be able to spray.
https://www.thewoodwhisperer.com/articles/different-types-of-lacquer/

[railandsail]

7j43k

If you want to waterproof wood, this stuff works:

https://www.amazon.com/Smiths-Original-Clear-Penetrating-Sealer/dp/B072MRYZ5Z

 

I've used it.

 

Ed

 

 

WOW, not cheap,...more expensive than my good quality plywood.

[railandsail]

In the beginning I was seriously considering 2" foam subroadbed shelves held up with some pretty nice metal brackets from Home Depot. The 2" foam is not so readily available here in FL, so I looked around for options.

Found what I thought was some decent plywood (called Blondwood) at Lowes. I monitored a stack of it at their store and i became less impressed,...and thought perhaps 3/4" rather then 1/2". I had also inherited a 1/2" piece of 4x8 from a friend and stored it in my carport, both on its edge and flat on the cement floor. I became even less impressed. It went thru all kinds of gyrations.

Then I ran across some 7 ply, 3/4" plywood from Chili being sold at Home Depot. It was the best looking stuff I had seen,....Radiata Pine

It was a little thicker (and heavier) than I had originally planned, but then again I am not supporting it with 3" wood framework on its edge as in many conventional benchworks, so a little extra thickness could be helpful for both stability and extra cantilivered strength. And if I paint it all around that should help seal it against some of the moisture of humidity.

[Doughless]

railandsail

In the beginning I was seriously considering 2" foam subroadbed shelves held up with some pretty nice metal brackets from Home Depot. The 2" foam is not so readily available here in FL, so I looked around for options.

With the conditions your layout will be in, I'd skip wood all together as much as possible.

Can you laminate several layers of skinny foam together, whatever they sell in FL, to make it thick enough?

[7j43k]

When I buy the penetrating epoxy, I realize that, over time, it WILL be cheaper than any other alternative.

Of course, each task/project has to be evaluated on the matter.

 

 

Ed

[rrebell]

Just the heat will effect the ply.

[Tinplate Toddler]

How often does it rain in your shed and how often does your layout get submerged or flooded? Let me guess, the answer is never!

Model railroaders tend to overdo things, when it comes to benchwork construction, both in selecting the dimension of the lumber employed in its construction and other protective measures, like painting it. The latter can prove to be quite detrimental, if a wood sealant is applied to lumber which is too "wet" Wood needs to "breathe" and thus shed any moisture otherwise trapped inside.

More important in a climate like yours is the use of plywood which has been made using a non-soluble glue.

[PED]

I have 3" foam (2" + 1") on my layout sitting on about 14-16" centers and I was surprised at how strong the stuff really is.

I had no luck finding 2" foam at the local stores so I asked at a local hobby shop that was popular with the RR guys. He told me about a local supply house that sold primarily to the construction industry. They had plenty 2" and even sold 4".

[zstripe]

You should have bought exterior grade plywood to begin with........end of story!

My layout is built with exterior grade ply...one side smooth.....never had any problem's with it since the early 80's. As a matter of fact, I have used the same plywood on outside projects and still do not have a problem in 38yrs. I also live in the Midwest with all four season's. Glue it and screw it. I also do not buy any lumber from a big box store......just to save money.....In the long run, you are wasting your money. Exterior grade/Marine grade is the only kind I use....there are no voids in that type of ply, adhesive is moisture proof........... I also did My 27ft. cabin crusier with Marine grade for the leather covered seating, engine cover, which covers a 350 chevy engine......works like a charm. Hull is all fiberglass......

Take Care! 

Frank

[SouthPenn]

Don't you have pressure treated plywood in your area?  

[danno54]

I’d consider a garden railway in the backyard. Rather than fight the weather I’d embrace the weather outside year round.

[railandsail]

railandsail

Deck Type Sealers

I had some Thompson water sealer product setting around I had acquired from some estate sales. I looked up info on the product, and I was NOT very impressed with its capabilities for protecting outdoor decking. Seems as though many folks were unhappy with its performance.

But that said, I do NOT intend to utilize it in an outdoor situation,...where UV can be a big problem. I ran a few test samples on a portion of my outdoor wood deck, and some wood shelves I had made of plywood. I did note that it seemed to soak into the wood much more thoroughly than paint would have. That would seem to indicate a 'sealing function'?

Has anyone had experiences with sealing up plywood with deck coatings?

Can they subsequently be painted over??

Found this on another forum...

Here in Southern California all wood warps unless it is sealed with something.  I say it is the dryness.  So, in 1998 I built a special computer desk which later turned into a train workbench.  Sense I had experience with specialized homemade furniture  and prior layouts warping and the cork roadbed crumbling I tried Thompson's Water Seal left over from another project.  I hit a home run!  Wood does not move!  Cork does not deteriorate.  19 years on my train workbench.

If you want to try it here is how you use it.

Make sure you use water soluble type.  Makes clean-up easy.  Last time I bought it it came in three tints plus clear in a metal gallon can.  I bought it at Home Depot.

Build your bench work or module as usual. When you are past the glue and screw portion stop. Apply Thompson's over all wood including legs, braces, etc. Use a 0ne and two or three inch brush. Clean with water in sink. If you are going to paint over the water seal wait four days for the water seal to finish gassing off.

I now build in modules so they have legs and braces that show. I paint these and around the edges of the module rattle can flat black.. Looks good. On the inside of the module I paint rattle can white. However, I now build the rectangular portion with the track and scenery as an insert held in with screws but I still paint the underside white so I can see. The insert I still paint with water seal as I use thin plywood for the insert.

I don't like the weight of the modules, too heavy, so I am going to try the foams for the insert on new modules.

An Aside: The way I water seal the cork roadbed is

Buy a box at a time

Tear the entire box and finish the beveled edges (I'm in N Scale)

Use a shop rag saturated in water seal and rub along and all over. Hang on a line outside. Use gloves. When dry remove from line and leave in a sheltered area outside for four days to gas off. Fumes could be bad for you.

Your done. I put back in box

So, for me these two procedures are bulletproof for me. Give it a try and see what you think.

Mike Lee

 

Thanks Mike, I was looking for someone who had first hand knowledge about these 'wood deck sealers'.

So you have actually painted over some of your sealer treated wood? Did you happen to make inquiry with the home company about doing that procedure? Or how did you come to that decision??

In a little experiment I made it did appear that Thompson Water Sealer did soak into the plywood samples I used. It was at that point that I wondered about subsequent adhesion to those surfaces??....by paint, by glue, etc??

Brian

[railandsail]

Dewaxed Shellac

 

maddragon

 

Greg, this topic always gets a lot of responses, most of them wrong. I've been a woodworker for longer than I've been a model railroader and that's a long time.

The best sealers are de-waxed shellac. or clear polyurethane. They're about equal but poly takes hours to dry and shellac takes minutes. Applying poly in a closed environment is harder on your lungs than shellac - unless you wear an appropriate mask.

For both reasons my first choice is the de-waxed shellac. It used to be that had to be mixed up from flakes, but for several years now Zinsser has marketed a 2 pound cut of dewaxed shellac as SealCoat. That's what I use.

What is a 'two pound cut'?

I looked up the qt and gallon prices on this stuff and they want $20 per quart or $60 per gallon. Not exactly inexpensive.

Does it go a long way? Is it likely one only needs to seal the edges of the plywood, rather than the whole sheet front and back??

[rrinker]

2 pound cut means it's 2 pounds of dry lac cut into the alcohol, per gallon.

The higher the 'cut' amount, the thicker the shellac(less liquid, more material)

If you intend to paint over, you need dewaxed shellac.

If the goal is to prevent moisture penetration, then all surfaces would need to be coated, not just the edges. 

                               --Randy

[railandsail]

Thanks Randy

I was doing a little looking at Zinsser products the other day and ran across this one,...

And then this mold & mildew-proof waterproofing paint, ...name would imply it will do the job,....& 15 year waterproofing guarantee
https://www.walmart.com/ip/Zinsser-270267-1-gal-Mold-and-Mildew-Paint-White/47647744

[riogrande5761]

I'm liking the description and price of the Olympic Waterguard a lot:

$10.48 a gallon at Home Depot and cleans up with water.

[NWP SWP]

Olympic seems to be the the equivalent to Thompsons WaterSeal, available in clear, and dyed versions, I can attest to the "waterproofness" of the stuff, back in 2016 Louisiana had what we call "the great flood" anyways we got about 3-4" of water in our shed, which has a 3/4" pressure treated plywood floor that was coated with Thompsons WaterSeal, no mold or anything and that was what years ago.

[rrinker]

 I might need that Zinnser stuff to paint my basement concrete block before I put up the walls.

                                    --Randy

 

[railandsail]

Timber Pro Stabilizer

BlackAdder

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.

[railandsail]

In sunny Louisiana, the same climate you're in. 

I built a wooden privacy fence in 2011, and used this product from Behr.

https://www.homedepot.com/p/BEHR-Premium-5-gal-Natural-Clear-Transparent-Waterproofing-Exterior-Wood-Finish-50005/100172793

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. 

-Dean

 

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.

[riogrande5761]

It's a bit pricey at $37/gal.  At this point I'm planning to go with the much lower cost Olympic Water Guard at about $10.50/gal.  I am running a dehumidifier to keep the basement at a fairly constant humidity.

[railandsail]

I had not priced out the retail price. As you said a bit pricey. I got it at some estate or yard sale.

I picked up a nice dehumidifier at our local flea market (and one with an external fitting for automatic discharge), but I discovered that it puts out a fair amount of heat in order to function. So I would have 2 cross purpose machines working in a faily small space,...one adding heat, one taking heat away. ...dehunidifier and AC

[BATMAN]

It will be interesting to see how the treated plywood holds up over time. I hope it goes well in the heat and humidity. I was worried about heat where my layout goes over the fireplace so I used cement board. It cuts with a circular saw like plywood, heat and moisture have no effect on it. 

Did you ever consider cement board?

 

 

[railandsail]

Never did cosider cement board as I felt it would be too heavy. But I'm sure it is likely NOT affected by temp/humidity.

When you see my 'unique steel framing/benchwork' I will be using, you will likely see that I might have been able to use cement board.