Repairing paint - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

brenellic2000 · 10th May 2013, 7:38 am

It is a common misnomer that 'liquids soak into the wood' - they don't... except up the sap carrying tubes (end grain) or towards the heart along special rays which store nutrients. Any other transfer across cell walls is by osmosis which requires both cells to be moist and receptable. Clearly, seasoned wood especially veneers are 'bone dry' but do adjust over time to the moisture content of the ambient air or steam when press-gluing veneers. Oils don't soak in due to their surface tension which is why they are 'thinned' by organic solvents as carriers (the solvent prompty evaporates - although turpentine leaves a beneficial residue) but 'thinned oil' is less likely to travel by osmosis than water carried emulsions.

I'm surprised you were advised to thin Tung oil! The object of an oiled finish is to rub in (not pour on) thin layers of oil which, on drying, hardens by oxidation to form a water/moisture repellant finish which seals the cells.

Planing wood shaves/shears cell walls and keeps then in tact but sanding ruptures the walls and better allows transfer through the cell wall to the next cell. Oak is considerably denser than Brazilian Mahogany and should take a better polish.

This is far more exciting than boring old electronics

Radio Wrangler · 10th May 2013, 7:51 am

This may be the right place to comment that if hardwood was terribly permeable to water and oil based liquids, then barrels would never have worked.

Whiskey maturing in oak barrels loses a percentage of its alcohol content over many years storage, and ethanol is a pretty efficient solvent with a small molecule.

Most of the surface treatments we've been talking about don't sink very far in, given the time the are fluids.

David

Graham-R · 10th May 2013, 11:11 am

Quote:

Originally Posted by brenellic2000

I'm surprised you were advised to thin Tung oil! The object of an oiled finish is to rub in (not pour on) thin layers of oil which, on drying, hardens by oxidation to form a water/moisture repellant finish which seals the cells.

Oak is considerably denser than Brazilian Mahogany and should take a better polish.

This is far more exciting than boring old electronics

The instruction was on the tin of oil, first two coats - up to 50% white spirit, reducing % for subsequent coats, final 2 coats undiluted. I did try an experiment on a piece of oak veneer after the disaster by not diluting it at all and it did not cause the delamination problem. A moral there ? treat instructions with caution

Radio Wrangler - thanks for the pm - I shall get to it over the w/e (I'm supposed to be at work !).

Hopefully I will get a little time this w/e to evaluate the finish and decide what to do. Meanwhile here is a pic to be going on with - not the best because of the sun etc.

http://www.paradise.plus.com/files/i...d401_small.jpg

brenellic2000 · 11th May 2013, 8:07 am

Just to add to David's comment about permeablity, few (dead, seasoned) heartwoods of trees are permeable (but some are). In contrast, sapwood is moist as it carries the sap and is very permeable... which is why it rots!

Even high pressure treatment processes involving organic solvents, or waterborne salts, cannot permeate the heartwood of oak, chestnut and many others. As it is the heartwood which is used in barrels and furniture, any surface treatment is quite literally 'skin deep' or a 'veneer'!

The lifting of Graham-R's adhesive is most likely due to solvents passing between ruptured cell walls due to the veneer cutting/slicing and drying process. I never use veneers... but if forced, will use a proper sawn veneer

I like an easy life!

TTFN

Graham-R · 11th May 2013, 10:17 am

Quote:

Originally Posted by brenellic2000

The lifting of Graham-R's adhesive is most likely due to solvents passing between ruptured cell walls due to the veneer cutting/slicing and drying process. I never use veneers... but if forced, will use a proper sawn veneer

I like an easy life!

TTFN

With hindsight this was obvious at the time, (and the reason for the non-diluted test piece), but it was much too late to do anything about it. I did wonder if the instructions of the Tung oil tin where applicable to veneer as well as solid wood - I found out that probably not was the answer. In any case I thought the Tung oil finish was very plastic-like and domestic, (in the kitchen work surface sense), and much preferred the gentle sheen of wax.

I have heard of sawn veneers - where do you get them as they don't seem commonly advertised ?

I have had a quick look this morning and my first consideration is to flat it all and re-lacquer the top surface, and hope that the wax on the veneer is enough to deter overspray adhesion (but still allow masking tape to stick). But nothing will happen immediately - I have my second (and unpaid !) job to do.....

I just remembered how to embed pictures..... A pair of before and after images

brenellic2000 · 11th May 2013, 10:40 am

Sawn veneers are a thing of the past! The trend today is for paper thin veneers which look good on naff substrate! ('Naff' is not a specie of wood).

I still have a 30" dia veneer saw blade but have never had need to use it. Many carved reproduction pieces of furniture use 1/8" thick sawn veneers which will take carving and look like solid wood. It is still possible to buy thick veneer block-board... at a hefty price... for that purpose from specialist merchants.

If you have a suitably sized rip saw or band-saw it is perfectly possible to saw a thin veneer from a seasoned stock - but on account attempt deep sawing on a narrow band-saw unless you really do know what you are doing.

Barry

Graham-R · 12th May 2013, 11:27 am

Quote:

Originally Posted by brenellic2000

Many carved reproduction pieces of furniture use 1/8" thick sawn veneers which will take carving and look like solid wood. It is still possible to buy thick veneer block-board... at a hefty price... for that purpose from specialist merchants.

Barry

Sounds ideal, but the hefty price bit is a bit off-putting. 1/8" sounds like ordinary thin sheet ?

brenellic2000 · 12th May 2013, 1:46 pm

Sawn veneers are thick sawn from converted timber to fully show the natural grain, medullary rays etc as if solid wood - this can be carved albeit shallowly!

For standard crown-cut veneered ply (which shows the same grain) these are wet-sliced, as on bacon slicer, but can't be carved. Ply-sheet is usually rotary cut as a continuous sheet of indeterminate length which doesn't best show the timber's character. Then there is cheapo el-B&Qo imported thick-core paper thin venered ply and high-grade (imported) multi-ply furniture- and aircraft-grade ply of equally thick balanced plies...

Yes, good timber costs money! That's why people buy cheap... and get cheap!

Graham-R · 19th May 2013, 12:37 pm

I have put the 401 plinth to one side for now, partly so I can use the turntable, but mainly because of lack of spare time.

The real reason behind all this veneering I have been doing has been to get good enough to be able to repair some Spendor BC1 speakers I bought a few years ago. They work perfectly but they were not looked after at all, the veneer has been butchered beyond repair.

I want to re-veneer them in Indian Rosewood at some point fairly soon but there are two questions I have. The first is do I chamfer the sheets at right angle corners or will simple overlaps do (experience so far indicates this is so), secondly, should I remove the existing veneer or use it as a substrate ?

Thanks in advance

Graham

brenellic2000 · 20th May 2013, 1:36 pm

It depends!

How thick is the veneer, how badly damaged is it, will the old veneer lift off (Scotch glue or latex based?), what is the substrate (I guess MDF?). To lay a new veneer, the base must be perfectly smooth as, like painting, flaws and poor preparation will stick out like a sore thumb! Practice makes more mistakes... and in time, perfection!

I wish you luck!

10th May 2013, 7:38 am	#21
brenellic2000 Octode Join Date: Aug 2006 Location: Rye, East Sussex, UK. Posts: 1,647	Re: Repairing paint It is a common misnomer that 'liquids soak into the wood' - they don't... except up the sap carrying tubes (end grain) or towards the heart along special rays which store nutrients. Any other transfer across cell walls is by osmosis which requires both cells to be moist and receptable. Clearly, seasoned wood especially veneers are 'bone dry' but do adjust over time to the moisture content of the ambient air or steam when press-gluing veneers. Oils don't soak in due to their surface tension which is why they are 'thinned' by organic solvents as carriers (the solvent prompty evaporates - although turpentine leaves a beneficial residue) but 'thinned oil' is less likely to travel by osmosis than water carried emulsions. I'm surprised you were advised to thin Tung oil! The object of an oiled finish is to rub in (not pour on) thin layers of oil which, on drying, hardens by oxidation to form a water/moisture repellant finish which seals the cells. Planing wood shaves/shears cell walls and keeps then in tact but sanding ruptures the walls and better allows transfer through the cell wall to the next cell. Oak is considerably denser than Brazilian Mahogany and should take a better polish. This is far more exciting than boring old electronics

10th May 2013, 7:51 am	#22
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,902	Re: Repairing paint This may be the right place to comment that if hardwood was terribly permeable to water and oil based liquids, then barrels would never have worked. Whiskey maturing in oak barrels loses a percentage of its alcohol content over many years storage, and ethanol is a pretty efficient solvent with a small molecule. Most of the surface treatments we've been talking about don't sink very far in, given the time the are fluids. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

11th May 2013, 8:07 am	#24
brenellic2000 Octode Join Date: Aug 2006 Location: Rye, East Sussex, UK. Posts: 1,647	Re: Repairing paint Just to add to David's comment about permeablity, few (dead, seasoned) heartwoods of trees are permeable (but some are). In contrast, sapwood is moist as it carries the sap and is very permeable... which is why it rots! Even high pressure treatment processes involving organic solvents, or waterborne salts, cannot permeate the heartwood of oak, chestnut and many others. As it is the heartwood which is used in barrels and furniture, any surface treatment is quite literally 'skin deep' or a 'veneer'! The lifting of Graham-R's adhesive is most likely due to solvents passing between ruptured cell walls due to the veneer cutting/slicing and drying process. I never use veneers... but if forced, will use a proper sawn veneer I like an easy life! TTFN

11th May 2013, 10:40 am	#26
brenellic2000 Octode Join Date: Aug 2006 Location: Rye, East Sussex, UK. Posts: 1,647	Re: Repairing paint Sawn veneers are a thing of the past! The trend today is for paper thin veneers which look good on naff substrate! ('Naff' is not a specie of wood). I still have a 30" dia veneer saw blade but have never had need to use it. Many carved reproduction pieces of furniture use 1/8" thick sawn veneers which will take carving and look like solid wood. It is still possible to buy thick veneer block-board... at a hefty price... for that purpose from specialist merchants. If you have a suitably sized rip saw or band-saw it is perfectly possible to saw a thin veneer from a seasoned stock - but on account attempt deep sawing on a narrow band-saw unless you really do know what you are doing. Barry

12th May 2013, 1:46 pm	#28
brenellic2000 Octode Join Date: Aug 2006 Location: Rye, East Sussex, UK. Posts: 1,647	Re: Repairing paint Sawn veneers are thick sawn from converted timber to fully show the natural grain, medullary rays etc as if solid wood - this can be carved albeit shallowly! For standard crown-cut veneered ply (which shows the same grain) these are wet-sliced, as on bacon slicer, but can't be carved. Ply-sheet is usually rotary cut as a continuous sheet of indeterminate length which doesn't best show the timber's character. Then there is cheapo el-B&Qo imported thick-core paper thin venered ply and high-grade (imported) multi-ply furniture- and aircraft-grade ply of equally thick balanced plies... Yes, good timber costs money! That's why people buy cheap... and get cheap!

19th May 2013, 12:37 pm	#29
Graham-R Pentode Join Date: May 2006 Location: South West London, UK. Posts: 201	Re: Repairing paint I have put the 401 plinth to one side for now, partly so I can use the turntable, but mainly because of lack of spare time. The real reason behind all this veneering I have been doing has been to get good enough to be able to repair some Spendor BC1 speakers I bought a few years ago. They work perfectly but they were not looked after at all, the veneer has been butchered beyond repair. I want to re-veneer them in Indian Rosewood at some point fairly soon but there are two questions I have. The first is do I chamfer the sheets at right angle corners or will simple overlaps do (experience so far indicates this is so), secondly, should I remove the existing veneer or use it as a substrate ? Thanks in advance Graham

20th May 2013, 1:36 pm	#30
brenellic2000 Octode Join Date: Aug 2006 Location: Rye, East Sussex, UK. Posts: 1,647	Re: Repairing paint It depends! How thick is the veneer, how badly damaged is it, will the old veneer lift off (Scotch glue or latex based?), what is the substrate (I guess MDF?). To lay a new veneer, the base must be perfectly smooth as, like painting, flaws and poor preparation will stick out like a sore thumb! Practice makes more mistakes... and in time, perfection! I wish you luck!