Sealing / finishing plywood lining to shed walls

[Moph]

Hi all

I've ventured across here from The Shed sub-forum looking for some advice regarding finishing the plywood wall lining that I'm currently installing.

The plywood is 12mm C/D structural ply from the big green box. I'm not after a 'pretty' surface and have limited time that I'm prepared to spend on finishing it, so I'm intending to hit it with a light sand all over with 120 grit (probably just manual; I have a random orbital sander and powered belt sander but don't want to take too much off) then apply a sealant or varnish to protect the ply from absorbing any liquid spills or sprays that might occur - coffee, oil, the usual shed sort of stuff, plus of course dust.

My question is - what product should I be looking at to give a decently hard wearing surface finish without requiring more than two coats? I had a look at some varnishes initially (eg Bondall Monocel Gold) but was put off by the requirement for four coats with 24 hours drying time per coat. That'd be great for furniture but not for 60sqm of wall lining, particularly as I can normally only work on Saturdays and don't have a month total to finish the lining.

My preference is for a clear finish as I quite like the look of the ply. I originally intended painting it white to reflect light more effectively, but the timber adds a pleasing aesthetic. Brush or roller application would be best as I don't currently have an airless spray gun, nor do I have much experience with them.

Any advice appreciated =)

[ian]

I think in your case -- and not looking for pretty -- I'd skip the sanding and just give it two coats of whatever clear finish was on special.
Possibly one of the floor sealers.

If you do decide to sand, I'd use the ROS hooked up to the dust collector. Sanding by hand with a 3" block would, for me, just take far too long and generate far too much air borne dust.

[Moph]

What I was intending to use was a 100 x 200mm sanding block that takes the same sandpaper as the ROS and clamps it in place, and just spending 5 minutes per sheet tops to knock off any really rough spots. The ply surface is pretty good as it stands. I can always start with that and revert to the ROS if it's taking too long anyway. I'm just a bit cautious about using the ROS because I have a habit of taking too much off =)

By clear finish are you talking an oil based polyurethane or similar? That's where I'm a bit lost - I really haven't worked with timber finishes before.

[BobL]

If you are going to do any sanding I would do it in between the coats.

[ian]

What I was intending to use was a 100 x 200mm sanding block that takes the same sandpaper as the ROS and clamps it in place, and just spending 5 minutes per sheet tops to knock off any really rough spots. The ply surface is pretty good as it stands. I can always start with that and revert to the ROS if it's taking too long anyway. I'm just a bit cautious about using the ROS because I have a habit of taking too much off =)

By clear finish are you talking an oil based polyurethane or similar? That's where I'm a bit lost - I really haven't worked with timber finishes before.

sanding before applying a finish is mostly about producing a tactile surface and knocking down the grain before applying the finish. On timber walls it also removes the tiny crevices in which dust and dirt tend to lodge.

these factors may not be a consideration if you are not after a 'pretty' surface, and are prepared to accept that the walls remain a little rough to the touch. If you want smooth to the touch, you'll likely need to spend more than 5 minutes per sheet.

personally I like the polyurethane floor products as they are pretty bomb proof once applied, but the recoat delay (12 hours) might be too long for your situation. But then again, one coat may be all you need on a wall.
or perhaps use something like Feast Watson's Proofseal -- which has a recoat time of 20 minutes. It should control dust and dirt accumulation on the wall and at 20 minutes -- make sure you have good ventilation -- finishing in a day is doable.

[Moph]

Awesome - thanks a bunch for the advice; that was exactly what I was after =)

I'm not hoping for a surface finish that's smooth to the touch. I would be happy with the plywood unfinished if it weren't for the likelihood of surface contamination over the longer term. The work bays will be lined with 2mm aluminium sheet to around 1500H anyway.

[Moph]

Picked up 4L each of Feast Watson Proofseal and Floorclear Satin tonight. I reckon I'll try hitting the unsanded surface with a coat of Proofseal, let that cure overnight, give it a quick buzz with 120 grit on the ROS and then coat it with a single coat of Floorclear. Will use short nap mohair rollers for application. Might run short with those quantities, but it'll at least get the storage bay finished so I can get the shelving up.

Thanks again =)

[ian]

Morph

Those two products are really alternatives, not a first coat / second coat.

I suggest you try the floor seal in one area and the proof seal in another.
As I mentioned above, because it's a wall, you may only need to apply one coat of the floor seal.

The proof seal may need two coats.

If you decide you need to do some sanding, this should be done before applying any finish.

[yvan]

Just finished putting two coats of Cabothane (oil-based polyurethane) on each side of 15 sheets of plywood used to line the interior of a shed to be used as a sewing/needlework/quilting room for SWMBO.

for the 1st coat, diluted the polyurethane in the proportion of 5:1 - 5 poly for 1 turps. The dilution allows the goo to penetrate the sheet more deeply. Used a 6-inch roller to do so. Sanded with 240 grit before the second coat. I used the same diluted "solution" for the 2nd coat using the roller and then immediately followed with a 3-inch brush while still wet. Gave the surface a nice sheen.

Regardless of the product used, the bottleneck was the drying time and, as a result, the space necessary to spread a number of 2400 x 1200mm sheets. The weather was not particularly nice and the stuff didn't dry as quickly as I had wished. In the sun however, the poly would dry quite quickly, sufficiently dry within an hour or so not to leave any finger marks when handled.

In total, used 5 litres of poly.

yvan

[Yanis]

I made a bunch of ply boxes for my shed to fit in my steel shelving. I tried various finishes and preparations for the ply.

In the end I simply did a quick sand to clean up the surface. It got rid of the dust and roughness from the handling and storage. I then used three coats of a quality Bunnings poly. Sanding between coats did break down the nubs but after a bit of shed wear I don't think that it would make a big difference. The poly is very hard wearing and should last many years.

John

[Moph]

Those two products are really alternatives, not a first coat / second coat.

Hmmm. I was going by the labels on the cans - see below. The Proofseal can says it's "a clear, fast-drying sealer that provides a stable base for top coats ... can be coated with FloorClear.", and the FloorClear can says to seal new timber first with Timber Primer for porous timbers or with Proofseal for oily timbers. Bunnings only had Timber Primer in the 1L can which ended up half as expensive again, so I decided Proofseal would do.



Proofseal can on the left; FloorClear on the right.

[ian]

I was trying to minimise your outlay for a "doesn't need to be pretty" finish.

Proofseal followed by Floorclear should give you a reasonable finish -- which will still look a little rough if you're not sanding the ply before hand.

Also, with the recoat time you should be able to get two coats -- 1 x Proofseal, 1 x FloorClear in a single day

Let everyone know how you get on.

[Moph]

Ah righto, I'm with you now =)

I figured that the top coat of FloorClear would be a little more hard wearing as it's a polyurethane, and was also conscious of the recoat time. I'll have a crack at it this Saturday and post my results.

[Moph]

Seems it worked out brilliantly

Gave the raw sheets a quick sand with 120 grit on an orbital finishing sander, then cut in around the top and bottom with a brush and laid on a coat of Proofseal using a 160mm short nap mohair roller. Was impressed with everything but the coverage - only got 27sqm out of a can that should have covered 40sqm, and I'm beat if I know how I laid it on too heavy given it was vertical application with a short nap roller.

Then followed through about an hour later with the FloorClear, again cut in around the edges by brush and applied with a 160mm short nap mohair roller.

Check out the comparative result below - first photo before; second photo after. I'm pretty darn happy with it

The finish will no doubt be slightly rough to the touch, but well within the range of what I consider acceptable for a shed lining.

[Yanis]

Seems it worked out brilliantly

Was impressed with everything but the coverage - only got 27sqm out of a can that should have covered 40sqm, and I'm beat if I know how I laid it on too heavy given it was vertical application with a short nap roller.

You get that on raw wood. It also depends on the grain.

John