I decided to replace my cab floor board with pressure treated plywood. The original one made a great pattern and it appeared to be painted. How should I protect bottom side of the floor that faces the road surface? Paint, teak oil, paint and teak oil, bedliner or undercoating spray? Or cover with sheet metal? You get the picture. Let me know what worked for you?
For things like this, I've used thinned down spar varnish (water thin). Apply it until the wood won't soak any more, let it dry, sand and paint. The wood is permanently sealed from moisture, stronger and won't rot.
Used motor oil was the go to years ago , today lots of products , research is your friend in this case
Epoxy saturation (on both sides) is probably the most durable treatment as it really is waterproof. Paint it with whatever you like. I like bed liner for the texture then paint.
My 32 has used motor oil coating the underside of the floorboards too. Didn’t start out that way though.
Hello, Having owned several new cars, a 58 Impala and a 65 El Camino, we were sticklers for no rust under our cars. We frequented plenty of places where salt water was famous for making its presence known. So, when the “King Tides” or a normal high tide with a consistent big wave swells hit the coast, there were several places coated with salt water or underwater at some point. Parking lots were coated with a layer of salt water and some had road closures as the water was too deep for safe passage. So, our new cars got the full undercoat treatment professionally sprayed on. It was not the skimpy factory undercoat, but a full under the car coating that left no part uncovered. We got the best protection for all of our road trip adventures. The spray can undercoating was not the answer, nor were other methods. Not only did the bottom get covered, but it also made the car quieter. So, salt water in any location still covered the bottom when we drove through it. but, a simple powerwash spray hose did its intended purpose and there was no rust after years of owning the 58 Impala and 125k miles of the 65 El Camino. Jnaki As for wood surfaces, the industrial spray will cover the wood perfectly. Yes, it probably will cost more than 20 cans of spray coating, but it is/was well worth it. salt on the roads? Not a problem. Just power spray and off it comes… Having tons of years experience with all sorts of wood protection coatings from plywood to teak to oak/cedar, there are a ton of polyurethane coatings that go on smoothly, look great when finished, but after drying, protects the wood like no other. But, at the first sign of a flying rock, an errant stainless steel line wandering where it should not on a sailboat or the side safety wires that are lowered to necessitate entry/exit off of the sailboat, the stainless wires, pelican clips and whatever does hit the covered teak rails or other surfaces. The protective polyurethane coating cracks or gets a ding that you may not notice, but after washings or rain, slowly the crack absorbs and then by the time you see it, the whole area needs a refinishing coat. On places where it is seen, like the deck of a sailboat or rails, the application of a clear coat is necessary. Oils look good, but don’t last. Rub on urethane coatings also look good, but are thin applications and ding with car keys accidently hitting the wood surface and dings galore. So, if the area is viewable like a cockpit of a sailboat, those clear polyurethane coats are mandatory, but needs refinishing at some time in the coming activity months. If the surface is not seen, like under a car, then oils are too thin, shellac is also stronger but thin and cracks at the smallest rock attack. If you want the wood to show between the rails, then coat it with a thick layer of clear polyurethane and do several coats. It will crack with road grime, rocks and other attacking items that get thrown upwards. But, at least it is under the car. Eventually the polyurethane is probably the best clear protection if any. So, do you want the wood to show or get full coverage with industrial undercoating spray protection that will outlast any polyurethane coating on the market. Don’t settle for undercoating in a can. You will have to purchase many cans for the full coverage, and it is messy. Find a company that does industrial coating. Even sprays like the ones for truck beds are better than any oils, shellac or polyurethane coats. Make sure it is black undercoating. White may look nice, but it attracts dirt, the minute you drive away from the curb… YRMV
If you're using pressure treated plywood it shouldn't need anything in order to last a pretty long time. Also, I assume you aren't driving it in all weathers, at least not when you can avoid it.
I was laying underneath my 93 year old deuce pickup with the original wood floor under the steel floor and it's survived this long with a coat of some kind of black paint and of course a sprinkling of grease.
I spray painted and then undercoated the one on my 36 pickup over ten years ago, it has held up very well and looks nice too.
I replaced the wood with metal with steel and coated it with red primer followed with black enamel, I also coated the bottom side of the wood in the bed of the truck with black enamel. HRP
In my 55 F100 I brushed on marine varathane ,that was in 2012, its still good today, it doesn’t get heavy exposure to weather.
Make sure the pressure treated wood is dry before you coat it with anything. I tried painting PT 4 x 4s years ago that were a bit damp from their coating. Took over 6 months for the paint to dry, and I was using it all indoors. No kidding. Finished the project, and painted it during the fall, it was still sticky and nasty the next summer. I used regular indoor/outdoor enamel, actually Rustoleum. It finally dried and got a hard surface, and it still is good 40 years later.
another option is KDAT lumber. It’s kiln dried after treatment. https://crossarm.com/what-is-kiln-dried-after-treatment-kdat-lumber/
I gave my bed boards on the 41 the same treatment top and bottom. The timbers I burned lightly with a torch, to enhance the grain then a coat or three of spar varnish
For my irrigation boards to stop water, I used marine plywood. Been 23/24 years without an issue. We get irrigation from April through other first week of October. Starts off at two week intervals, then down to 10 days, then back up to two weeks. In the rainy times, boards just stay out back in the checks and deal with the water.
You will want to coat it with something that will encapsulate the stuff they use in the new treating process. It consists of a lot of salts that will attack the metal it contacts. That wasn't true with the old treatment process, as that used arsenic. The new stuff is so corrosive that the manufacturers warn you to used treated fasteners with it. I think the epoxy sounds like the safest thing to use. Williebill is right about KDAT. You need to wait a year to paint conventional treated materials. Retained moisture will not allow proper paint adhesion.
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