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.

 

[tpenfield]

I do boat upholstery when I'm not playing with fiberglass. It sounds like you are on the right track. I would have used regular exterior grade plywood and spent the difference in $$$ on beer, but that's just me.

Definitely treat the wood once you have it shaped and the drainage/air holes drilled. You can mix up a wood sealer often referred to on this forum . . .

Old timers wood sealer (OTWS)

• 1/3 Polyurethane
• 1/3 Linseed oil
• 1/3 Mineral spirits

The plastic that you found covering the foam is merely used to allow the vinyl cover to slip on and orient itself during assembly/stapling. Use the drop-cloth 0.7 mil type of plastic sheeting . . . nothing special about it.

Stainless or Monel staples . . . I typically use 1/2" staples and an air gun to install them. Do glue the foam to the new base board (3M 77 spray glue should be fine)

While you are at it, you might want to take a look at the rest of your seats to see if they need some attention/replacement as well.

 

[Lpgc]

Thanks for all the replies.

I did start typing a reply yesterday, a customer turned up to collect their vehicle so I had to break off, didn't get time to finish and post my reply later.

I've bought the wood, 'silk wrap', West System 205/105 epoxy and 3/8" Monel staples already.

Should I completely coat the plywood with the epoxy or leave the base clear to allow drainage in case any water does get through? Will the epoxy make it difficult to staple to?

I did have doubts the staplers we have would be up to the task, I suppose I'd better buy a more powerful stapler...?

UV shouldn't be able to effect the wood or epoxy anyway because they're covered by the foam and vinyl above and the base of the wood faces down to an enclosed fibreglass well that partly covers the engine bay (it'll be constantly dark at the base of the wood)..?

There were/are only 2 breathe holes through the old wood, both measure around 2" x 1/2", this doesn't seam enough breathe/drain holes given the length and width of the wood / foam / vinyl. Should I put more holes in the new wood?

@tpenfield Come to think of it it is exterior grade ply not marine ply, and I did buy beer last night lol. But I've dealt with the local woodyard before and remember having a conversation with the owner a while ago about plywood, he's refused to unload truckloads of wood and plywood that didn't quite meet the spec he ordered and reckons this grade is better than some supposedly marine spec plywood some of the big chain stores sell. He was upfront about the spec and said it should be fine if it's not constantly submerged. I did visit the woodyard with intention of buying marine ply but the owner persuaded me this stuff should be easily good enough for purpose. At £15 for 72" x 13" x 18mm the wood cost less than the epoxy.

 

[MikeSchinlaub]

Coat the entire piece of wood, and yes it will make it harder to staple. You might do a small test piece first to see if your gun/staples can penetrate.

 

[Lpgc]

Coat the entire piece of wood, and yes it will make it harder to staple. You might do a small test piece first to see if your gun/staples can penetrate.

Thanks. I can understand why it's better to completely cover wood in the bilge, the bottom of wood in the bilge will probably be standing in water so not covering wood in the bilge would almost guarantee it would rot quicker than coating it all over including the bottom. I don't understand why coating it all over including the bottom is better than leaving the bottom bare if it's well above the waterline and will never be in standing water. If total coating is done well it will prevent the wood getting wet at all, but one mistake that allows wood to get wet and a bottom coating will prevent it draining?

 

[Grub54891]

I bought an air powered stapler for this task. Really saves the fingers! I used painters plastic over the foam, really helps with stretching the vynal over the foam. I didn’t use the plastic when I put the new seat cover on my sxs, lesson learned, now of it rains I get a wet ass from water that seeped through the seams. Might re- do that….. I’m also doing some vynal replacement on my boat, I am using marine plywood, but I was thinking of using Thompson water seal on the plywood as the old plywood wasn’t sealed at all. All my panels will not be exposed so that is my way of thinking.

 

[Scott Danforth]

I use garbage bags if I don't have the cheap plastic drop cloth.

Some times they are lavender scented

Do not use epoxy to seal the wood. Staples go into fiberglass easier than epoxy soaked wood

If the foam is starting to deteriorate, replace it. P65 in the middle, P80 on the horse collars

 

[MikeSchinlaub]

Thanks. I can understand why it's better to completely cover wood in the bilge, the bottom of wood in the bilge will probably be standing in water so not covering wood in the bilge would almost guarantee it would rot quicker than coating it all over including the bottom. I don't understand why coating it all over including the bottom is better than leaving the bottom bare if it's well above the waterline and will never be in standing water. If total coating is done well it will prevent the wood getting wet at all, but one mistake that allows wood to get wet and a bottom coating will prevent it draining?

My thinking is if water starts up top, and runs down to the bottom, the unsealed edge will soak up the water that touches it and wick it further up into the wood.

My shed is a good example. I did a bad job with the doors, and didn't paint the edges of the 2x4s before screwing them to the plywood. Now those ends are rotten, and I'll have to fix it eventually.