Phenolic or Marine ply for floor ?

[mboat01]

Going to lay floor in cabin - Was going to put BS1088 18mm Marine Ply... but found source of Phenolic Ply ('MeraForm Smooth Film Faced A/A Ext') thats cheaper. For this use would it be inferior / just as good / better ?

[Dr Bob]

Have you got a link to the MeraForm? Did a search but came up blank other than an Indian company but no product info. Phenolic coated ply would be good for fire resistance and hard wearing but water resistance is one of the key properties you are after. Someone clever should be along soon with experience of the material but post a link if you can.

[mboat01]

Here, see photo 3,  - https://www.gumtree.com/p/wood-timber/18mm-8x4-phenolic-plywood-plywood-sheets-plywood-ply/1318735108

[Alan de Enfield]

25 minutes ago, Sassy Lass said:

Here, see photo 3,  - https://www.gumtree.com/p/wood-timber/18mm-8x4-phenolic-plywood-plywood-sheets-plywood-ply/1318735108

Why would you pay £45 per sheet when its £33 a sheet at the builders merchants ?

 

(says 'high resistance to moisture')

 

http://www.builderdepot.co.uk/18mm-x-1220mm-x-2440mm-film-faced-phenolic-plywood.html?gclid=EAIaIQobChMI69WnlOqs3gIVRTPTCh2cLAOiEAYYASABEgJ3oPD_BwE

[mboat01]

7 hours ago, Alan de Enfield said:

Why would you pay £45 per sheet when its £33 a sheet at the builders merchants ?

 

(says 'high resistance to moisture')

 

http://www.builderdepot.co.uk/18mm-x-1220mm-x-2440mm-film-faced-phenolic-plywood.html?gclid=EAIaIQobChMI69WnlOqs3gIVRTPTCh2cLAOiEAYYASABEgJ3oPD_BwE

 

Good spot ('Builderdepot' was going to be my source for the marine ply , which they have on for £60, plus £55 for delivery oop north). Question though is do board think phenolic would be worse/same/better for use as floor lining ...?

[system 4-50]

In 7 years my cabin floor has not been subjected to any significant amount of water from any source, am I doing something wrong? 

[Sea Dog]

You've done a great looking job with that floor, Sassy.  Tread carefully now, because there's all kinds of quality of plywood out there and picking the wrong one now will be hard to undo later.  I can't point you to one thats the right balance of cost and performance, but I'll bet the one you want isn't the cheapest! Better to pay a bit more and be certain than take a risk on cheaper Chinese ply of unknown pedigree.  Actually, I think you already know that, but it might help confirm your thoughts.

 

[Alan de Enfield]

1 hour ago, Sassy Lass said:

 

Good spot ('Builderdepot' was going to be my source for the marine ply , which they have on for £60, plus £55 for delivery oop north). Question though is do board think phenolic would be worse/same/better for use as floor lining ...?

Today's 'top-tip'

 

Make sure you add the ballast before laying the flooring.

[Boater Sam]

OSB is now more reliable than most marine plies, and cheaper. Exterior grade is a recognised structural timber.

[Dr Bob]

49 minutes ago, Sea Dog said:

You've done a great looking job with that floor, Sassy.  Tread carefully now, because there's all kinds of quality of plywood out there and picking the wrong one now will be hard to undo later.  I can't point you to one thats the right balance of cost and performance, but I'll bet the one you want isn't the cheapest! Better to pay a bit more and be certain than take a risk on cheaper Chinese ply of unknown pedigree.  Actually, I think you already know that, but it might help confirm your thoughts.

 

I agree with Sea Dog.

[Tony Brooks]

FWIW I found that Rugby Boat Builders had fitted a house type damp proof membrane over the floor bearers and under the actual floor. Not sure how much good it does but for the cost it seems a good idea. Comments?

[Dr Bob]

7 minutes ago, Tony Brooks said:

FWIW I found that Rugby Boat Builders had fitted a house type damp proof membrane over the floor bearers and under the actual floor. Not sure how much good it does but for the cost it seems a good idea. Comments?

I have no experience of NBs but my experience with lumpy water boats with keel stepped masts is that there is always water in the bildge. Our NB bilge looks dry as a bone (touching copious amounts of wood). The problem I see in recommending a good solution is that the problems will start showing up 5 or 10 years down the road by which time the boat has changed hands and the original construction of fit out decisions forgotten.

I do like the sound of your damp proof membrane but could that yield its own problems ie does normal marine ply allow some 'breathing' so any water accumulating from say condensation can then evaporate and escape. Putting a membrane in may then help the flooring but could it compromise corrosion. Not a clue here. Work experience has always taught me to consider all risks before changing a well known way to do something, 'cause something will come out of the blue and come back and bite you. If you're right, then a couple of layers of thick PE film would do the trick - as they use in timber framed houses (only one layer of PE in ours).

[NB Esk]

I think you should be good with Phenolic ply.  Some vehicle trailer manufacturers use it for parts of trailer beds.  Pretty harsh environment, little or no maintenance and it lasts a fair amount of time.  Prices also look very reasonable, I replaced the bed of a trailer some years ago and the stuff was a small fortune.  I'd go for it.

 

 

[Dav and Pen]

There are a lot of different types of this film faced ply on the market. Some of the far eastern stuff is really not really designed for long life as you can see from the depth and make up of the layers. The original and best came from Scandinavia and was based on birch ply core, we used it to make moulds for precast concrete and it stood up to multiple castings. It is however pretty slippery.

the Douglas fir wbp exterior grade ply is strong and stable and makes a good floor but try to get a good face one side.

if using ply make sure you have a wide bearing where two sheets join.

[jddevel]

2 hours ago, Tony Brooks said:

FWIW I found that Rugby Boat Builders had fitted a house type damp proof membrane over the floor bearers and under the actual floor. Not sure how much good it does but for the cost it seems a good idea. Comments?

Unless it`s breathable one assumes it may cause additional condensation in my opinion so not blue/black plastic visqueen. 

[Boater Sam]

Best Phenolic faced ply is Buffalo board but expensive.

My floor is Stirling OSB, 30 years old and as good as the day it was laid.

Nice prep on the floor but I notice that there is still no cross ventilation gaps. Its a very shallow underfloor space not to be ventilated.

[Tony Brooks]

1 hour ago, jddevel said:

Unless it`s breathable one assumes it may cause additional condensation in my opinion so not blue/black plastic visqueen. 

I think the idea is that it prevents condensation caused by any bilge water condensing on the underside of the floor and also to provide a vapour barrier between any bilge water and the accommodation.  if condensation formed on the underside of the plastic it would also form on the metal baseplate, hull side and framing. If it formed on the top side it means the floor or the gap between the floor and membrane were ventilated to a degree, otherwise water vapour could not have got in there.

 

I would be worried that  a breathable membrane would allow condensation to form on the underside of the floor if any water were in the bilge. Breathable membranes only work if the "other side" is well ventilated.

Edited October 30, 2018 by Tony Brooks

[mboat01]

Thanks all. Think inclining toward Marine ply... 

 

Interesting you mention breather membrane as Ive just bought some !. However was planning different usage. Agree with Tony w.r.t. forming a moisture trap with condensation. I was thinking of using it simply as a substitute for bituminous felt underlay by soaking it in black bitumen paint, as follows:

 

The layers of the cake will be : Hull >> scraped and sanded original blacking >> red metal oxide primer >> bilge paint (this is point Im currently up to) >>  3mm breather membrane folded over a couple of times soaked in black bitumen paint [*] >>  class A engineering bricks 65mm solid (got hold of bargain seconds at £120 for pallet of 440 !!) as ballast >> air gap (only around 10mm Im afraid) >> underside of marine ply painted in bitumen paint [**] (edges sealed with SP Eposeal 300) >> Marine Ply 18mm >> 3mm underflooring reflective insulation [***]>> 18-20mm oak flooring T&G or maybe reclaimed parquet

 

Related questions ...

 

is [*] necessary, of would simply doing another coat of bilge paint be sufficient ?

 

is [**] necessary, or even a good idea ? - would it be better to allow the ply to breathe ? ... is it really going to breathe ... I kind of doubt it.

 

is [***] also going to form a moisture trap - this time between the top of the ply and the cabin ? ... surely less of an issue that breather memb underneath ?

 

 

Thanks for all help. Opinions from all very much welcomed ! - Im learning a lot.

 

 

[Sea Dog]

6 minutes ago, Sassy Lass said:

Opinions from all very much welcomed !

Here's mine - you're determined not bodge this, aren't you!

 

How's about you make up for the 10mm gap above the bricks by leaving some gaps between them too?

[Boater Sam]

Sound like an exceptionally fine flooring job. Have you worked out where you do not need ballast, like where the calorifier, stove, washer, etc. goes?

Leave out the equivalent weights in bricks.

Usually boats list towards the side where there is no passageway.

 

Or else you will have to alter the ballast after you have fitted out. So leave some access to the underfloor. And a trap at the rear for checking for water in the bilge.

 

 

[Bee]

This is what I would do (So no guarantee of anything) I would put down some tanalised bearers so you have everything nicely divided up into for example 2` x 2` squares then lay the floor in squares of Sterling OSB on that so that you can get at the bottom, I wouldn't bother with membranes, insulation or anything else.  Or one day you will wonder what is happening under the floor and you will have built the entire fit out on 8X4 sheets of ply and you can't get the b******** up.

[rusty69]

Marine ply is so much better than some other plywoods in my opinion.However, is it worth sealing the end grain with epoxy.Probably not, just thought I would chuck it in there before running for cover!

[mboat01]

will try to lay bricks leaving some gap channels.

 

should be reasonably balanced but will may need to have fewer bricks on port side...tried doing all manner of calculations then decided it would be much better to built up and leave access and see what its like when done and then remove/add more ballast accordingly ?

 

the 'bays' in photo above are 2' wide. going to cut ply sheets as 8' x 2' to lay one on each bearer. No unsupported joins and smaller size sections if ever have to take up again.... think you might be right about membranes and insulation ...

 

A completely different tack would be scaff boards !!: and leave some gaps and let the sub-floor / cabin bilge space breath ... before I go buying ply of any kind what would downsides of scaff boards be (I think I would treat them with some sealant unlike that chap who did these)...???

 

[Cheshire cat]

My 20 year old ply floor is good as new despite a central heating leak. Our shareboat floor was chipboard and failed in the bathroom do to a leaky loo water pipe. I think buffalo board, hexaboard is overkill but its only marginally more than marine ply.

[Boater Sam]

OSB is not chipboard.