I've just bought a cheap bench - all fine except it has untreated a 5mm
MDF shelf and top.

As it's in the cellar, which isn't bone dry, I thought it best to seal
it. I've got some PVA (just normal evostick, not the waterproof variety)
- would a watered down version of that work?

A google search suggests that it might not - contact with moisture would
make it return to liquid, or somesuch, and to use specialist MDF
sealant. But a lot of differing opinions.

--
Cheers, Rob

On 23/01/2017 17:53, RJH wrote:
I've just bought a cheap bench - all fine except it has untreated a 5mm
MDF shelf and top.

As it's in the cellar, which isn't bone dry, I thought it best to seal
it. I've got some PVA (just normal evostick, not the waterproof variety)
- would a watered down version of that work?

A google search suggests that it might not - contact with moisture would
make it return to liquid, or somesuch, and to use specialist MDF
sealant. But a lot of differing opinions.



On a woodwork forum they advised wax it then 2 coats of polyurethane ...
I questioned applying PU over wax and they confirmed that was the
correct approach.

RJH laid this down on his screen :
I've just bought a cheap bench - all fine except it has untreated a 5mm MDF
shelf and top.

5mm for a workbench?

On Mon, 23 Jan 2017 18:26:24 GMT, Harry Bloomfield
wrote:

RJH laid this down on his screen :
I've just bought a cheap bench - all fine except it has untreated a 5mm MDF
shelf and top.

5mm for a workbench?
Just what I was thinking!

In article ,
RJH writes:
I've just bought a cheap bench - all fine except it has untreated a 5mm
MDF shelf and top.

As it's in the cellar, which isn't bone dry, I thought it best to seal
it. I've got some PVA (just normal evostick, not the waterproof variety)
- would a watered down version of that work?

A google search suggests that it might not - contact with moisture would
make it return to liquid, or somesuch, and to use specialist MDF
sealant. But a lot of differing opinions.

PVA is water soluble, and mold will love it.

Even EVA (waterproof PVA) is water soluble - it's only waterproof
when used in cement mortar mixes (although SBR is even better for
that).

Whilst you can use something like wax or polyurethane to provide
some surface protection against an occasional spill, nothing will
protect it against long term high humidity. You'll need to make
a new piece when it decays. Plywood would last longer.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 23/01/2017 17:59, rick wrote:
On 23/01/2017 17:53, RJH wrote:
I've just bought a cheap bench - all fine except it has untreated a 5mm
MDF shelf and top.

As it's in the cellar, which isn't bone dry, I thought it best to seal
it. I've got some PVA (just normal evostick, not the waterproof variety)
- would a watered down version of that work?

A google search suggests that it might not - contact with moisture would
make it return to liquid, or somesuch, and to use specialist MDF
sealant. But a lot of differing opinions.



On a woodwork forum they advised wax it then 2 coats of polyurethane ...
I questioned applying PU over wax and they confirmed that was the
correct approach.

I can see why you queried it. Are you sure they weren't pulling your leg?

Seriously, does the wax sink in, or how does it work?

Andrew Gabriel wrote:
In article ,
RJH writes:
I've just bought a cheap bench - all fine except it has untreated a 5mm
MDF shelf and top.

As it's in the cellar, which isn't bone dry, I thought it best to seal
it. I've got some PVA (just normal evostick, not the waterproof variety)
- would a watered down version of that work?

A google search suggests that it might not - contact with moisture would
make it return to liquid, or somesuch, and to use specialist MDF
sealant. But a lot of differing opinions.

PVA is water soluble, and mold will love it.

Even EVA (waterproof PVA) is water soluble - it's only waterproof
when used in cement mortar mixes (although SBR is even better for
that).

Whilst you can use something like wax or polyurethane to provide
some surface protection against an occasional spill, nothing will
protect it against long term high humidity. You'll need to make
a new piece when it decays. Plywood would last longer.

My feeling would be that, unless it is *really* wet, the OP would be
much better leaving the MDF untreated. It would then be able to dry
out to an extent rather than having the damp sealed in. I.e. like a
house, good drainage and ventilation, not hermetically sealed.

--
Chris Green
·

On 1/23/2017 6:42 PM, Davidm wrote:
On Mon, 23 Jan 2017 18:26:24 GMT, Harry Bloomfield
wrote:

RJH laid this down on his screen :
I've just bought a cheap bench - all fine except it has untreated a 5mm MDF
shelf and top.

5mm for a workbench?
Just what I was thinking!

Yes, surely not. But if it is, just plonk some 18 mm shuttering ply on
top of it. Plus a few coats of polyurethane on top if you want to be smart.

On 23/01/17 17:59, rick wrote:
On 23/01/2017 17:53, RJH wrote:
I've just bought a cheap bench - all fine except it has untreated a 5mm
MDF shelf and top.

As it's in the cellar, which isn't bone dry, I thought it best to seal
it. I've got some PVA (just normal evostick, not the waterproof variety)
- would a watered down version of that work?

A google search suggests that it might not - contact with moisture would
make it return to liquid, or somesuch, and to use specialist MDF
sealant. But a lot of differing opinions.



On a woodwork forum they advised wax it then 2 coats of polyurethane ...
I questioned applying PU over wax and they confirmed that was the
correct approach.

But they were still wrong.
TW

On 23/01/2017 20:15, Chris Green wrote:
Andrew Gabriel wrote:
In article ,
RJH writes:
I've just bought a cheap bench - all fine except it has untreated a 5mm
MDF shelf and top.

As it's in the cellar, which isn't bone dry, I thought it best to seal
it. I've got some PVA (just normal evostick, not the waterproof variety)
- would a watered down version of that work?

A google search suggests that it might not - contact with moisture would
make it return to liquid, or somesuch, and to use specialist MDF
sealant. But a lot of differing opinions.

PVA is water soluble, and mold will love it.


Ah, hadn't known that, thanks.

Even EVA (waterproof PVA) is water soluble - it's only waterproof
when used in cement mortar mixes (although SBR is even better for
that).

Whilst you can use something like wax or polyurethane to provide
some surface protection against an occasional spill, nothing will
protect it against long term high humidity. You'll need to make
a new piece when it decays. Plywood would last longer.

My feeling would be that, unless it is *really* wet, the OP would be
much better leaving the MDF untreated. It would then be able to dry
out to an extent rather than having the damp sealed in. I.e. like a
house, good drainage and ventilation, not hermetically sealed.


Many thanks Chris and everyone.

I think I might leave it. The cellar floor might become damp a few times
each year, but I've stored wood down there for years with no apparent
ill-effect.

It was just the blotting paperyness of mdf that had me thinking,
together with the 5mm.

On which, it really is surprisingly sturdy - it's one of these:

www.ebay.co.uk/itm/291866634320

I bought it for storage/light use, but it's strong enough to support a
vice once I've added some leftover kitchen worktop.

--
Cheers, Rob