Swap wood panel in upholstery

[Lpgc]

My boat is a 1996 Four Winns Sundower.

The wood that forms the base of the upholstered panel that runs the width of the boat between rear seats and swim platform (the upward facing trim you'd climb over to get into the boat from the swim platform, it's hinged to the boat to allow access to the battery switch and rear of the engine) is rotten but the vinyl upholstery and sponge are in good condition. I want to keep the vinyl and sponge/foam but replace the rotten wood. I have already removed this panel from the boat and stripped it down without damaging the vinyl or sponge.

I think I'll need a piece of 3/4" x 80" x 33" marine ply to replace the rotten wood with, use the old wood as a template and jigsaw to the same rounded shape. I don't know if I should treat the new plywood after getting it to the correct shape? The foam was in some kind of clear plastic bag/wrap which was damaged during removal, what sort of plastic should I wrap the foam in? Should the foam be completely wrapped in plastic or no plastic where it contacts the new wood below it? Should the foam or plastic be glued to the wood?

 

[Chris1956]

Normally the wood in seats is 1/2 plywood. However, if yours is thicker, replace with the same stuff.

I would use pressure treated plywood that has had a chance to dry well. Apply a couple of coats of oil-based varnish or polyester resin to seal it and use stainless steel staples to reattach the vinyl.

PT plywood will not rot as fast as untreated plywood, and stainless steel staples will not rust out in a year or so, like galvanized ones.

Often a 3/4" hole is drilled in the center of the plywood to allow any water to drain. That likely provides some small benefit.

 

[jbcurt00]

Monel staples are an even better choice over stainless.

 

[Lpgc]

Thanks.

As said it's not really a seat, it's the panel that runs the width of the boat over the rear of the engine, it's behind and above the rear seat backrests.

I ordered some cushion 'silk wrap' that's apparently the same kind of thin plastic sheeting the foam was wrapped in. I didn't know the 'silk wrap' served two purposes, it apparently helps get the foam back into the vinyl by using a vacuum to suck the air out of the foam to shrink it and acts as a waterproof cover for the foam.

Not sure of the best way to refit the foam and wood back into the vinyl.. Should I tack the foam to the wood, wrap the combined foam and wood in 'silk wrap', vacuum and slide the combined unit into the vinyl? Or should I only 'silk wrap' the foam (not the wood), install the foam then try to fit the wood? I know to make some holes in the wood, the original panel had holes in it. I'm thinking the first way wouldn't allow the foam to drain if any water got in it, the second way would allow it to drain.

Should I totally seal the plywood or leave the bottom bare to allow it to drain?

 

[Lou C]

I had to replace that huge piece of plywood about 15 years ago, it was the width & length of the engine compartment so it was big and heavy. The original was 3/4" plywood so that's what I used. Still in good shape now all these years later.

 

[Lpgc]

Today I went to a local woodyard and bought the 3/4 marine ply, ordered some 'silk wrap', Monel staples and West System 205/105 epoxy.

I've still got the original hinges and at least 3 out of the 4 Tnuts and countersunk head bolts for the hinges, not sure if I've got all 4 Tnuts and bolts, might yet have to buy some replacements. I noticed the Tnuts I removed from the rotten wood were also secured with pan head screws to prevent the T nuts being pushed out backwards when screwing the bolts in.

@Lou C , did you treat the plywood, use 'silk wrap' around the foam / around the foam and wood, etc?.. The things I'm asking about in post #4.

 

[Chris1956]

Make sure you use only stainless steel tee nuts and bolts, or they will rust away.

Normally you simply lay the foam onto the plywood and wrap it with the vinyl. No need to tack it.

I always reused the plastic "wrap" over the foam, however, I would not sweat it as I think is has little value.

Epoxy resin is fine for sealing the plywood. It is overkill IMO. Epoxy does not hold up to sunshine, so you will need to protect it from sunlight.

 

[Lpgc]

Thanks Chris,

Yes I realise it needs stainless Tnuts and bolts. As said I know I have 3 of the originals, 1Tnut and bolt was missing where the wood had rotted but I don't remember if I removed it from the rotted wood last year (in which case it'll be in a 'box of bits' I keep in the boat), or if it fell out and was lost. Iirc the Tnuts and bolts are 'number 2' size and countersunk to suit the hinges, difficult to get hold of in stainless this side of the pond so I'm hoping I still have them.

The wood and epoxy should be shielded from UV by the vinyl trim?

 

[Chris1956]

Sunshine and wood are not much of an issue. Polyester resin also holds up well to sunshine, as do the "spar" versions of varnish and polyurethane.

People advise to paint the epoxy resin to protect it from the sun. I have never tried that, as I only use epoxy resin for high strength repairs, which I do not need to make often, thank goodness.

Polyester resin works just fine over epoxy resin, despite what the internet says. Just sand the epoxy to break the shine first.


I bought my last set of SS tee nuts from Amazon, a couple of weeks ago.

 

[Lou C]

Today I went to a local woodyard and bought the 3/4 marine ply, ordered some 'silk wrap', Monel staples and West System 205/105 epoxy.

I've still got the original hinges and at least 3 out of the 4 Tnuts and countersunk head bolts for the hinges, not sure if I've got all 4 Tnuts and bolts, might yet have to buy some replacements. I noticed the Tnuts I removed from the rotten wood were also secured with pan head screws to prevent the T nuts being pushed out backwards when screwing the bolts in.

@Lou C , did you treat the plywood, use 'silk wrap' around the foam / around the foam and wood, etc?.. The things I'm asking about in post #4.

All I did was use PT wood and stainless fasteners, the original was redone before I got it and it was unwrapped foam. I didn't know as much then as I do now, but I did that I think in 2009 and it's still OK now!

 

[MikeSchinlaub]

I've only done a few cushion backs, but I've never seen the plastic be sealed and vacuumed. It's usually just loosely wrapped around the foam and held in place by the vinyl, not glued. I don't see how a vacuum bag would work here. Wouldn't it just compress the foam, making it stiff and lumpy?

I don't think the plastic really helps either. It might help keep the foam dry, but eventually some water will get past it and just get trapped. It would also trap water between the plastic and wood, which also can't dry because everything is wrapped so tight.

 

[JASinIL2006]

Marine ply should work fine, but I would seal it with either epoxy or Old Timers Formula to give the wood some extra years against moisture intrusion.

 

[arks]

A year ago, I had a 20 year old bench seat that had bad plywood. Vinyl was still fine. I replaced the bottom and back with 5/8” sheathing (same as original), using old as a pattern. Hardest part was notching the bottom to properly fit the 3 aluminum brackets that hold the back.
Otherwise, it was straightforward to re-attach the padding, vinyl, and seam (where the stainless staples go). LOTS of staples and I didn’t have a power stapler. Turned out great.