Best way to remove sap from knots on redwood timber?

[NightShadow1991]

Hi all, newbie here after some advice.

I'm a welder by trade and work with wood, so I know wood is a nightmare to work with. However, I just wanted some advice on some timber.
I am making some outdoor seating for a client, it's redwood, planed and routered. I know any softwood outside isn't ideal, I usually use sapele or iroko externally, but the client didn't have a decent budget. I have made many of these flat pack metal picnic benches and just used over the counter C24 from travis perkins, cut to size, dried out, lightly sanded and apply a half decent decking or UV oil to it. It works fine, I've got one that's 4-5 years old and apart from some shrinkage and some splitting, it's done well.

However, TP usually send it soaking wet and twisted and warped and lately I've had shocking quality. Plus they're a bit overkill in 6x2 and 9x2. So I got a chap up North who I use for lots of sapele and oak slats to do me a load of kiln dried redwood all the same size, slightly dearer than TP stuff, but without the tanalith horrible green stain. However, it does seem quite fresh and maybe not as kiln dried as I thought. I will get the reader in it tomorrow and see what the moisture content is. They are 160mm x 32mm x 1800mm lengths and are very light, weigh about 3.5kg to 5kg each, but there are lots of knots and most the them - although not leaching - do seem damp, fresh, wet.

So! To my point. I see it as I have 3 options.

1- apply knotting solution before staining. I'm not painting, but staining with two coats of Liberon UV decking Oil, it's worked well before and it's good stuff for quick coating and coverage. Osmo UV is great, but too dear for the qty I'm doing.
However, from what I;ve learned, knotting is only really for preventing staining when painting as a top coat, they don't actually stop the resin/sap from pouring out over time. So guess this will be a waste of time. I;ve been told they are all rubbish anyway, knotting solutions, especially for external use, despite what people say. My brother recently had major issues with the heat causing pre knotted timber leaching through the paint. So I put it doen to the heat.

2- get my plumbers blow torch and add some meths to the worst - visible face - knots and burn it off. Never actually done this before, does it need a lot of sanding thereafter, or is it as simple as light it up and brush it off before staining?

3- just apply the two coats of stain and wait until the client complains about sticky/sappy wooden benches?

I'm more for the burning affair, as this seems to be what releases sap, heat and sun, so surely burning the majority out now, will help prevent too much down the line. Otherwise, worst case scenario, if down the line - a few months, a year, whatever - the sap pours out and causes problems, can you apply knotting to it even if it's stained, if you lightly prep the surface?

Ultimately, my terms and conditions cover me from such things, but just wanted to make sure my client has as little fuss and grief as possible. I'm thinking sticking with the C24 from TP might have been better/cheaper, but wanted to give the machined redwood a go as it hasn't been stained and will take the oil much better and look dead smart. Just concerned the wood will pour with sap more so than the C24 stuff, maybe it's a different kiln drying process

Anyway, apologies from the long thread, any help greatly appreciated.

Best, Jim

 

[MikeG.]

You do know you've gone from treated timber to untreated, don't you? If you were getting 4 or 5 years from your previous wood, expect less now. It's not a result of a different kilning process, either. It's likely a different species of wood. Oh and "C24" is only a strength grading thing, and is not a description of the wood. You don't need a strength grading for a piece of furniture.

Knotting shows through staining and varnishing, so it really isn't an option. Besides, it won't do anything for the sap.

Most knots are dry, and won't exude any sap because they don't have any. Those which aren't should just not make it onto the final product. They go in the waste bin. If you are determined not to put it in the bin (you really should), and if a sappy knot doesn't penetrate to the other side (ie sap is only visible on one side), you could rout out the knot past the depth of the sap, and then fill with a two-part filler. Sand it flat when dry. Obviously this would then need to go on the underside where it isn't visible.

You basic problem here is that you are using unsuitable timber.

 

[NightShadow1991]

Thanks for the message, Mike.

In my eyes, the timber I have now should be more superior than the c24 I normally buy. I thought the C24 was pine , which is the cheaper yet stronger option out of the two. I only went with redwood as I thought it was a superior timber, both with pros and cons, but redwood seemed the better choice. I thought redwood had natural properties against moisture and is less likely to warp and split like pine is.

Also, the tanalith - green pressure treatment - they use on the C24 is only to help against termites and pests I thought? I mean I guess it helps against some rot, but the best way to protect timber is through annual retreating. Also, the problem I've had with the C24 (pressure treated pine) is that it's a nightmare trying to apply a stain unless you sand it right down, even then you get a horrible greeny yellow colour. I've found the oils don't penetrate properly into the wood as it's already been treated with an antifungal, rather than a waterproofing agent. Therefore, my logic for going for fresh, untreated redwood was because it is brand new, will take 2 coats of decent stain properly and won't have a naff appearance off a dark oak stain mixed with a green tanalith underneath. That twinned with the fact that the C24 is usually soaking wet when it gets here, warped, twisted, bowed, split, covered in chips and damage and a nightmare to work with, hence the price. I mean it cost me £85 more for the redwood compared to the C24, which I don't think is too terrible, especially considering its been planed to the exact profile I need, radiused edges and pre cut the 1800mm. Ultimately, it's saved me a ton of grief and time, but it was just the sappy areas that concerned me.

I mean there are lots of knots, but none of them are leaching sap yet, they just seem dense and heavy, only way I can describe them. They clearly have sap in there, which will no doubt leach out down the line as it would with most timber, including the C24 I normally get. So there's no getting away from it really. I have bored out bad knots before and filled with filler, but not worth it for the money on the job and the deadline I'm working too. Was more just to find out whether a blow torch would work or any type of knotting, so will forget the knotting. Though I think it's probably inevitable that it'll happen at some point.

Also, I only got a decent amount of time from the C24 on my bench because I regularly treat my timber twice a year, I would guess that 99% of my clients over the years, do not.

Personally I don't think it's a downgrade at all when you weigh up all the other aspects. Granted, any external timber should be a suitable hardwood, which was originally going to be sapele lengths, but that would have added £200 to each bench, my client could barely afford that so aia just went with softwood. Which is was c24 is and which is what I've been using for a long time. I know it has it's disadvantages, but at the end of the day, it does work if looked after, especially for a budget bench. Also, I was told redwood is less likely to split and move over time like pine does? May I ask what timber would you use?

I'll just chuck the stain on and get the job done.

Cheers, Jim

 

[MikeG.]

You continue to call it C24. That's like trying to describe a car to the police by only saying "it was a 1300". "Pine" is a generic term. There are hundreds of types of pine. And I didn't say you had downgraded by going from treated CLS timber to untreated redwood. I just said you had reduced the likely lifespan. Treated timber offers protection against rot as well as insects (I'm pretty sure we don't have any termites here in the UK), but of course you have to treat the cut ends.

What would I make it of? I'd use a FSC certified durable hardwood, or perhaps Douglas Fir. I don't get involved in making or specifying things that are only going to last a year or two.

 

[NightShadow1991]

Understood. I see what you mean, whenver I've bought from travis, majority of the time it's pine, but yes all timber differs with it's own qualities and different batches have different pros and cons. I wanted sapele, that's what I've got on mine, but would have been over a grand for the timber. I'll leave as is and stain it with the worst knots facing down. Pretty sure it will last longer than a year or two even without annual staining. I know it won't be nearly as better quality as a hardwood, but it's not going to go anywhere anytime soon. If they fail to stain yearly, then that's there issue. I can't see why with regular staining it wouldn't last a good 5 years plus, even if it has some cracks and splits over time.

As a tangent, what are your thoughts of american white oak slats for external use. I prefer sapele as I think it's the best outside, I have this oak in my garden, rolled the brackets and used a2 carriage bolts through to help prevent splitting. Thought a couple of people I;ve spoken to say Oak is naff for external use, though others have told me otherwise. I know it stains easily and unless it's regularly and well treated it can rot and have a load of issues, but on the whole, yes or no to oak on outdoor furniture? I purely got it as it was the same price per slat as sapele and preferred the look for the tree it's in. I have noticed some staining, probably insect crap even with the osmo uv coating, the verticals should be fine, the only problem will be the horizontal slats, which there are only really 2, but I keep it covered during the raina and inside during winter. I did one about 4 years ago for a neighbour in oak and they have never treated it despite me telling them too, its very grey and split, but surpisingly still strong. Don't know why they couldn't just chuck some stain on it once a year. 20 minute job.

Ta, Jim

 

[Sgian Dubh]

... Treated timber offers protection against rot as well as insects (I'm pretty sure we don't have any termites here in the UK) ...

We don't, at the moment anyway. Termites are active between the 50º north and south latitudes, and all of the British Isles, except the Channel Islands, are at higher latitudes than that. Termites are accidentally imported to the UK from time to time, but conditions here are generally too cold for them to survive, being creatures more suited to warmer climates and the tropics. In 1994 The only known infestation of termites, a well established colony of Reticulotermes lucifugus, was discovered in Devon, south-west England: it was, as far as I know, exterminated and I believe there have been no infestations since. However, the effects of global warming might, given time, make conditions in the UK conducive to termite activity.

As to the choice of material in these benches, I agree that the choice of a C24 softwood is not ideal, this material possibly (very likely) being Scots pine, aka redwood. As you have pointed out C24 doesn't identify the wood species, and refers only to the material's strength grading allocated to strength tested softwoods, i.e., wood from coniferous trees so it's possible this C24 material could be larch, pine, spruce or fir, for example.

So, not a great choice from a durability standpoint (i.e., ability to naturally resist rotting, especially in ground contact) but no doubt it will last a few years (maybe 3 - 5 years) up in the air away from soil. Regular painting in service will extend the life of the material, but I've seldom (never?) come across an owner of external furniture that can be bothered with proper maintenance. And as to the knots, either don't use the badly knotted bits, or try to hide them as much as possible by putting the knots to the side of the structure least seen. If there is sap that's going to leak out, either from knots or sap pockets, there's little or nothing that will stop it in this situation bar physical removal of the resin oozing part and replacement with something that's not leaking, i.e., an inlaid piece of non-oozing wood. C24 strength graded softwood (the key being 'strength graded') is definitely not assessed and graded for appearance, i.e., basically how pretty and clean it looks; C24 graded material is primarily intended to provide adequate strength in structures that aren't seen, or if they are seen their appearance is of little or no consequence, e.g., roofs and other load bearing structures.

Better material, aesthetically, for this would be one of the alternatives already mentioned, e.g., sapele, or oak, either American white oak, and the even more durable European oak, all being classed as durable, as are alternative wood species. Personally, I generally see little or no point applying a finish to external wooden artefacts (furniture for example), unless it's just to make it pretty in the showroom or at the point of delivery, and prefer to simply use an unfinished durable timber species that can be just left to age to grey over time. Slainte.

 

[NightShadow1991]

Interesting stuff all, thanks. Interesting about the non staining of hardwoods too. I have used a lot of sapele on my swing seats and outdoor benches, I always apply a couple of coats of clear oil to help further protect it from the elements. I know sapele is fine for being left outside to naturally age. Would you say that's all it is then, purely for aesthetics? I mean, it would certainly save me a great deal of time not staining my sapele slats in future, but I was always under the assumption it would just further help any weather damage? Is it best to leave it natural so it can breathe/move to its own liking? Would applying an oil be negative in anyway to sapele hardwood?

I'm moving over to sapele on all my outdoor furniture from now on, if people can't afford the cost, then I shan't bother, but if they can, I will. I'm just wondering whether to bother with the staining on sapele slats or timbers in the future or just let the weather do it's thing.

Ta, Jim

 

[AJB Temple]

Hmmm. Oak is totally fine outside. It was used for centuries for shipbuilding, making piers and vast numbers of timber framed houses, barns and outbuildings, church gate porches doors and seems to hold up for a couple of hundred years or so.....

 

[topchippyles]

Interesting stuff all, thanks. Interesting about the non staining of hardwoods too. I have used a lot of sapele on my swing seats and outdoor benches, I always apply a couple of coats of clear oil to help further protect it from the elements. I know sapele is fine for being left outside to naturally age. Would you say that's all it is then, purely for aesthetics? I mean, it would certainly save me a great deal of time not staining my sapele slats in future, but I was always under the assumption it would just further help any weather damage? Is it best to leave it natural so it can breathe/move to its own liking? Would applying an oil be negative in anyway to sapele hardwood?

I'm moving over to sapele on all my outdoor furniture from now on, if people can't afford the cost, then I shan't bother, but if they can, I will. I'm just wondering whether to bother with the staining on sapele slats or timbers in the future or just let the weather do it's thing.

Ta, Jim

I mill a lot of stuff and you will not go wrong with larch or douglas fir.Both great for external use and joinery grade timber.

 

[Sgian Dubh]

I mill a lot of stuff and you will not go wrong with larch or douglas fir.Both great for external use and joinery grade timber.

I agree that both larch and Douglas fir are pretty good for outdoor use, even without any finish, with a non-soil contact life expectancy probably in excess of ten years, and more likely fifteen, maybe more. Slainte.

 

[topchippyles]

I agree that both larch and Douglas fir are pretty good for outdoor use, even without any finish, with a non-soil contact life expectancy probably in excess of ten years, and more likely fifteen, maybe more. Slainte.

Its what i use all the time for my outdoor furniture and always got stuff cut and seasoning for next year.Just milled a massive olive ash up and oak is my next one in 3 weeks.

 

[Sgian Dubh]

Interesting stuff all, thanks. Interesting about the non staining of hardwoods too. I have used a lot of sapele on my swing seats and outdoor benches, I always apply a couple of coats of clear oil to help further protect it from the elements.
I'm moving over to sapele on all my outdoor furniture from now on, if people can't afford the cost, then I shan't bother, but if they can, I will. I'm just wondering whether to bother with the staining on sapele slats or timbers in the future or just let the weather do it's thing. Ta, Jim.

I prefer to apply nothing. The reason being that if you apply, say, a bit of linseed oil just to provide a nice colour at the time of delivery, that within a few months the finish deteriorates until it looks pretty ugly with black stains and splotchiness, and this remains the case for a further 12 or 18 months. Eventually, the patchy looking surface fades away and the wood then starts to age and weather naturally to shades of grey to black. I have a theory, not proven as far as I know but my theory all the same, that the linseed oil provides a food source for either, or both, fungi and bacteria which leads to the ugly discolouration in the short term. I'm not sure how a short term appearance enhancing coat or two of alternative oils, Osmo for example would deteriorate over the first 12 or 24 months if not maintained at all after the piece goes into service. For me, it's just easier to apply nothing at all, and let the wood age naturally, but that's just my preference.

If a client wants to talk about finishes, then that's the time to talk to them about the consequences, including likely appearance in both the short and long term, and the maintenance needs: and it's best to have that all put down in writing, ensuring the client knows about what to expect, plus any maintenance requirements on their part, etc, and get them to sign off that they agree to all that, basically your terms and the like, so that when they phone up six months or two years later to complain about something you've explained, they understand, and they've signed off on you've got the legal bit covered, ha, ha. Slainte.

 

[topchippyles]

Very few would like plain bare wood on a table or bench.Simple thing is to add a little brass plate suggesting that the item should be treated every 12-24 months to preserve the lifespan of the timber. Pennies to do and can add the manufacturers details for others to see.

 

[NightShadow1991]

I prefer to apply nothing. The reason being that if you apply, say, a bit of linseed oil just to provide a nice colour at the time of delivery, that within a few months the finish deteriorates until it looks pretty ugly with black stains and splotchiness, and this remains the case for a further 12 or 18 months. Eventually, the patchy looking surface fades away and the wood then starts to age and weather naturally to shades of grey to black. I have a theory, not proven as far as I know but my theory all the same, that the linseed oil provides a food source for either, or both, fungi and bacteria which leads to the ugly discolouration in the short term. I'm not sure how a short term appearance enhancing coat or two of alternative oils, Osmo for example would deteriorate over the first 12 or 24 months if not maintained at all after the piece goes into service. For me, it's just easier to apply nothing at all, and let the wood age naturally, but that's just my preference.

If a client wants to talk about finishes, then that's the time to talk to them about the consequences, including likely appearance in both the short and long term, and the maintenance needs: and it's best to have that all put down in writing, ensuring the client knows about what to expect, plus any maintenance requirements on their part, etc, and get them to sign off that they agree to all that, basically your terms and the like, so that when they phone up six months or two years later to complain about something you've explained, they understand, and they've signed off on you've got the legal bit covered, ha, ha. Slainte.

Agreed, I put everything in my terms and conditions, so I'm covered. Just nice to save the grief in the first place. I will look at larch and douglas fir in future, but will push for sapele. I normally use Liberon decking oil or Osmo uv oil. I would always stain my own timber, especially hardwood as I know I always maintain it yearly or even every 6 months. Like you say, clients tend not to bother. But they're happy to get their cars serviced and give the house a lick of paint, people expect too much from wood I think, then when it goes wrong, it's too late. A coat of stain costs nothing, pennies and a touch of time.

 

[TheTiddles]

You can often get cedar of Lebanon wet and cheap, it’s perfect outdoors. Makes your tables rusty if you don’t follow up with wd40 soon afterwards but you get the bonus of having a workshop that smells like a hamster cage

Aidan