Carving

[Charles Castle]

Attached is a photo of a carving I am about to finish. It is designed as a cheese board, from a pattern in Australian Woodworking. The timber is Kauri Pine. While this has carved beautifully, the plain half is designed for use as a cheeseboard. However it is fairly soft and will not last long in use. I would like to either use a finish to make it more durable, without losing the figure, or use a contrasting insert. One of my friends suggested using dilute PVA which he said would harden it up a lot. I am concerned about the appearance if I do that. Does anyone have suggestions?

[Charles Castle]

Sorry folks, the photo hasn't worked. But hopefully you will get the idea.

[ubeaut]

G'day Charles - About time someone made use of this forum.

Do not use PVA it will more than likely come off when it gets moist and will definitely go white. It will not harden or enhanse the timber. Leave it raw or put a bit of walnut oil on it.

The soft timber won't be damaged too much. My grandmother had a 10' x 4' kauri pine kitchen table that was well over 80 years old and the only thing it ever had done to it was a regular wiping down with a soapy cloth and every few months a wash down with a bloody big block of sand soap and hot water. Apart from being used for meals, it was used for every thing from making scones to cutting up a side of beef and for washing the dishes and the kids in a big tin bath. After 80 odd years of patina it looked fantastic.

If you want to post pictures, email them to me and I will insert them into your post. Otherwise you need to have a site that will host them for you then insert the apropriate url to that site.

Hope this helps.

Cheers - Neil

[BobGilmour]

Charles

Amongst other things, I make a range of cutting boards and presentation boards ... with both oiled finish for regular use and eventual re-sanding and also fine-finish boards for mostly show and light usage - breads etc.

For the regular oil-finished boards, I use Kauri a lot ... cause it's readily available and I can get it pretty cheap in 8x1 and bigger. Plus, it stays nice and straight in board-form ... especially with a contrasting hardwood (jarrah, black bean, ironbark are some I use) end-cap which is epoxy glued and splined to the end-grain of the kauri.

One of the things I do with all the boards ... and almost everything else come to think of it ... is do an initial seal coat of thinned epoxy (laminating resin here ... not retail mixed glue). I thin up to 200% ... although mostly 150% ... with clear metho ... let it soak in for a few minutes and then rag off all the excess and eliminate smears with a dry rag. I sand down to about 320 grit first. For the oiled boards, I then give a light re-sand with 320 after the epoxy has cured and then simply oil with vegetable oil. The process works extremely well. Epoxy is food neutral - it's approved for all sorts of food system liners and tanks. Plus, it adds structural strength, by binding around the wood fibres - this is how fibreglass works.

Only problem is that the epoxy will darken the timber a little - less so with light timbers like kauri. It darkens dark timber more than will, say, single pack clear polyurethane. Also, it does tend to yellow a bit with aging. If the latter is a problem, then you can use the same process except with two pack polyurethane as a fibre-binding penetrating sealer (use the appropriate thinner instead of metho). 2-pack poly-u is also food neutral although it's strength characteristics are somewhat less.

I've been using this approach and various incarnations of it for going on 5 years now of professional woodwork and havn't been made aware of any failures yet with regard to the sealing/finishing process. Have used thinned epoxies as timber sealers/binders and finishing bases in the marine industry for some 20 years before that.

Well ... that's my bit ... fwiw


regards,


Bob.

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wood's good

[Charles Castle]

Many thanks. Your very helpful answer is just what I wanted to know. I presume any two part epoxy will do? Such as the epoxy I used when building my canoe?

[BobGilmour]

Hi Charles

Epoxy laminating resin that is ... not glue, obviously.

Yes ... two pack. I currently use West System (brand name) epoxy. It's arguably the best on the market. I've had quite a number of years in the marine scene ... running commercial boats and building them ... so have found epoxy to be one of the best coatings available for sealing timber ... and a lot of other things too.

WEST System is pretty expensive though. Another good epoxy that I've used a lot of in the past (actually about 2000 litres!!! ... true ... fairing a large'ish boat) is FGI. Look up Fibre Glass International in the phone book.

There are a few important things to watch using this stuff. As I said above, it will darken your timber more than will a single pack polyurethane ... or straight oil or wax or all the other 'usual' finishes. It also has the tendancy to yellow a bit over time.

The idea with this treatment that I use, however, is not to form a coating, but to impregnate the surface of the timber and then remove all coating-forming excess.

Epoxy is NOT UV stable. I take it from your comment that you may have built a strip plank canoe. From that exercise, you will know that you had to overcoat the epoxy with UV-stabilised polyurethane (Spar Varnish) to get long-term protection. This is usually not a problem in our applications with interior woodwork.

Most laminating epoxies are 5:1 mix for standard (=fast) brew. The mix ratio is critical. Most epoxy manufacturers state in their specs that their product can be mixed by weight or volume. If you go by weight, you need to use digital scales. I find volume is easier for mixing up small brews. I use two 30ml syringes. Either buy them from a chemist ... or, as I do, befriend your local vet. Keep one for PartA and the other for PartB ... they'll last a long time. I frequently mix tiny amounts, so the syringes are ideal. A 5:1 brew is 30mls (=1 syringe) of PartA and 6mls of PartB ... or for a bit more ... 5 syringes or A and 1 syringe of B ... easy.

The proper solvent for thinning epoxy is MEK (methyl ethol ketone). But, metho also works. I find that MEK evaporates too quick and since the idea here is to allow the epoxy to penetrate as far into the timber as possible ... then, you need to use a slower solvent ... hence, metho (which is a distant cousin of MEK anyway). Get clear metho from the hardware ... not the purple stuff from the supermarket.

I mostly thin 1.5 parts metho to 1 part epoxy mix. Mix the epoxy thoroughly before thinning!! However, for a critical application, I have gone as thin as 3:1 for a first coat, and then 1.5:1 a bit later (wet-on-wet). Paint the brew on with a brush ... wear a glove at least on the hand holding the item --> epoxy is fairly nasty stuff - can cause long term irratations and is said to be carsenogenic. Let it soak in for a while ... 'till it starts getting a bit stiff (ie the metho has evaporated out), and then wipe it all off with a rag. Make sure to get the worst of the streaking out. If you don't wipe it off, you'll have to sand it ... and that's hell. Oh, I do this treatment at the end of my sanding schedule.

If parts of the piece soak up the brew and show dry patches, coat them up a bit more. The idea is to try and fill all of the interstitial spaces of the surface layer of the timber with epoxy. Theoretically, the actual cells themselves are already fairly empty of moisture. so they may take up a bit of the epoxy brew as well.

Once the epoxy has gone off, give it some cure time, and then re-sand lightly with your finest grit to remove the furry texture. If you want to be sure, you can repeat the process.

I sometimes ... with really fine finish work ... then do one or two rub-coats with a hydrocarbon-based sanding sealer to pick up any last porosity. But that's for my high finish rub treatment ... and probably not the go for your application.

You then go on with your finish coats. Lately, I've been using Penetrol as a binder after the epoxy has cured. It works extremely well and produces a lovely base upon which to apply polyurethane or tung oil mixes.

Hope all that helps.

There are other advantages to having some laminating epoxy on hand.

One is, that you can make up your own glue. Buy some fumed silica (brand names include Aerosil and Cabosil) from the same place you get your epoxy. [By the way ... all of this gear is not hardware stuff. Go to FGI, Synthetic Resins, ATL Composites, or, at worst, any really good marine supply that sell boat-building supplies.] This is a powder that acts as an extender .. ie, it thickens stuff to make glue. Mix it with mixed epoxy to make glue of whatever viscosity is appropriate for the job. Just don't go too stiff (=dry) or you won't get good adhesion. In most cases, epoxy glue made this way is far superior to anything you can buy ready-mixed.

If you want to make bog (=filler) add talc powder to your mixed epoxy. Even bathroom talc will do ... although you can buy unperfumed stuff from the same place you get the epoxy. Epoxy bog doesn't shrink like car bog and it sticks better. If you want to make really rock-hard bog that you'll have trouble even sanding once cured, throw in some fumed silica along with the talc. For a lightweight bog, use Q-cell or microballoons instead of talc.

Let me know if you need any other info ...

Regards,


Bob.

[AlexS]

Bob, thanks for that comprehensive information. Hadn't thought of using thinned epoxy as a 'sealer' but it sounds like an eminently sensible idea now you've mentioned it.

A couple of points...not only is metho cheaper and more readily available than MEK, it's MUCH MUCH safer. Inhaling MEK is not good for the neurones.

Also, if the fumed silica is the light, fluffy powder that I'm thinking of, you should not use it without a good pressurised dust mask - silicosis is not a nice thing to have. I'm not sure of the filter size necessary, should probably check the material safety data sheet for it.