Advice on Wood finishing

[Haggy]

I am a design teacher and am puzzled as to why one of my students can't achieve a natural looking, glossy finish on the end grain of what I take to be Leylandii.  The wood is well seasoned.  My advice to her was to seal the end grain with cellulose sealer, flattening between coats. I was going to advise her to spray the surface with a melamine lacquer or buff with friction polish after the end grain had been filled.
What puzzles me after 18 coats of cellulose sanding sealer we still haven't achieved a totally sealed surface (see pic).  The surface remains patchy.
The temptation is to give up and move onto the next stage, but I also know wood turners frequently have this problem and get over it. I really don't want to be beaten by this and would really appreciate any advice.
          Thank you very much.        Haggy

[Derwent Woodturning club]

Hi Haggy,

If the picture is accurate, the brush marks used to apply the sealer are still very evident, suggesting the whole end of the piece needs a lot more sanding than just 'flattening between coats', also that this is not a turned piece of wood. The sanding sealer already applied should have filled the grain, and, once fully hardened, prevent the fibres moving when you sand them. However, if there are still areas that are patchy, (is that what the arrow is pointing to?) the fibres are still unsupported and more sanding sealer will be required. Leylandii is quite an open grain wood, and end grain of any wood will soak up large amounts of finish. The advantage we woodturners have is that we are usually dealing with smallish areas of end grain, and they are also relatively thin, so can't soak up that much. Your students piece looks to be thick and is all end grain.
One other thought, did you apply the sanding sealer neat, or was it thinned down? Most turners apply it thinned down, especially the first coats, to make sure it gets well into the wood. If it just sits on the surface, it would be relatively ineffective.
Hope that helps,

[Bryan Milham]

Haggy,

I agree with everything said in the previous post.

there are two other things that can cause problems on end grain. The first is moisture in the timber, but as you say it is well seasoned we'll discount that one.

The other is air, unless both sides are sealed air/gas can move through the fibres (they are just small straw structures) and cause problems.

So seal the reverse side (if it isn't already) and then give this face a good sanding back to remove the brush marks, It should be ready to come up nicely with just a little extra work of the right kind.

[Les Symonds]

Hi Haggy...Paul and Bryan, the previous contributors to this thread, are both very experienced and knowledgeable turners who strive to perfect their finishing techniques, so everything that they have said is spot-on. I had a thought though....could there have been a slight contamination of the surface where the arrow and the dull patch is? If a drop of oil got onto the surface prior to sealing, it just could be causing this. If this is possible, I would suggest a wipe with spirits after the thorough sanding....but wait for the surface to dry thoroughly before proceeding any further.

Best of luck and i do hope that your student doesn't become too disheartened....Les

[Haggy]

Thank you Les, Brian and Paul for your advice.
I never thought to seal both sides of the wood with cellulose - we were concentrating on the face side. The other mistake I may have made is that we wet sanded the wood after applying15 coats simply because we were clogging up the wet 'n dry paper at an alarming rate.  Although the wood appeared dry,wet sanding was obviously a mistake (although we only wet sanded the last few coats).
I took the picture just after we had given the wood yet another coat of sealer before sanding , hence the brush marks. We did thin the cellulose down by 50% initially ( first 10 coats) and are now applying it neat.  The wood is about 12 mm thick, what you don't see in the picture is another six pieces all with the same problem.  They will ultimately be assembled into a floral pattern.
Thank you for your sound advice, I will show my student your replies and we will seal both sides next lesson and do no more wet sanding.  We will not be beaten!!
               Regards
                      Haggy

[Derwent Woodturning club]

Hi Haggy,

Thanks for the additional information. A few more thoughts.

You said you changed to wet sanding as the wet and dry was clogging at an alarming rate. That sounds like the sealer hadn't fully dried and/or you were using too fine a grit abrasive. The sealer needs to have fully hardened, including the sealer that has gone into the wood, before sanding. I would suggest at least a couple of days if the wood soaked up a lot of sealer.

A slight aside - when woodturners use wet sanding, the 'wetting' is usually the finish we will be applying i.e. oils or liquid waxes, not water. Obviously you couldn't use sanding sealer as the wetting agent as it would be drying as you sand. And, if you've used water, you will need to let the wood dry out completely before moving on to the next process, which could take weeks, as sanding sealer isn't waterproof.

I would also suggest starting at a coarse grit, so that you can remove the problem fibres and get down to the surface where they are fixed in place by the sealer. The coarser grit won't clog so easily. After that you are just removing the scratches from the previous grit, so should have very little dust to clog the paper. Have you tried Abranet? Being an open weave it is less likely to clog, but still needs the sealer/finish to have fully cured.

Please post a picture of the finished project. I am sure I speak for most of us on this forum, that it is good to see other people's work.

[Haggy]

Thank you Paul for giving our problem the benefit of your wisdom. You have given me a lot to think about; I will post her work on this site when it is complete, the centre part of her design is a turned wooden boss with a clock movement- this too is giving us similar problems.
I will use 180 grit paper, we are not using abranet, but I will make sure I give that a try in the future.  The design lessons are an hour long, she probably gives her work three coats of sealer in that time - not enough time for the cellulose to cure properly, this could be our mistake.  Recently she has been coming in dinner times and after school to recoat, I told her and the technician I would try asking the AWGB!
We have broken up now for half term, I am thinking of calling into school to collect her work and try out your suggestions- the poor girl has certainly tried long enough.  I will also coat the other side of her work as Brian suggests.
Her work will not be completed for another 3 weeks or so, but I am sure she will feel honoured to post her work on this site.
          Wood turning at our school is proving really popular, we have four lathes and are about to buy a small variable speed one from Axminster.
          Thank you for your time and careful analysis .
            Regards Haggy

[The Bowler Hatted Turner]

Haggy I have read these posts with interest and wondered what I would do in a similar position, bear in mind that I earn my living at this. With an end grain piece of wood such as you have shown us I would soak it in a wood hardener,the stuff you buy for rotten timber. This will set hard over a few days and then you will be able to sand it with minimal clogging and then apply your cellulose finish. The application that you have shown us appears to be a bit thick, you need to thin it down, sometimes I thin mine down by 50%. Multiple thin coats are much better than just a few thick ones. For future use you might like to try filling the grain with plaster of Paris and then sand and apply a shaded finish.

[Nick Arnull]

Haggy,
 I have looked at this image for some time and my initial comment is there is too much sealer on the surface the second is why was it not wiped dry immediately, as leaving it to dry has allowed an excess of product to build up on the surface, the consecutive coats have also diluted the previous applications an consequently allowed an uneven coverage to occur.

My recommendation here is to cut back the surface using paste wax as a cutting agent applied with 180-240 grit abrasive/Nyweb  then allow to dry before using a piece of mutton cloth to burnish the surface this will help remove the excess product as the wax will help dissolve the product while cutting the surface at the same time if water was used it will penetrate the sanding sealer leaving a dull surface,
 When using Nyweb which is often better, I would recommend using the orange/grey grade.
Always allow the wax to dry before burnishing the surface.

Now this is the bit that many will disagree with. Dilute the sealer 50-50 with thinners and apply with a soft cloth allow this to sit for a moment or two then wipe dry and allow to cure most sealers take much longer than you think at this time of year.
When dry apply a second coat  and repeat again once more,  when fully this is dry,an hour or two should be long enough
( if the surface  feels cold it is still wet)  apply a coat of wax and again allow to dry then burnish to a good shine.

The only way to produce a glossy finish in my opinion is from some sort of spray this then has to be polished after drying.
Hope this is of help.
Finishing is a difficult subject and is one that we all have different views about.
Nick Arnull RPT.

[Haggy]

Wow, thanks Nick.  I missed this message! The honest reason why we didn't use a cloth is ignorance . I will pay carful attention to your advice it makes sense, thank you for going into detail, it really helps me now and could really help with future work.  I would have thought wax and cellulose wouldn't be good together-it just shows how wrong I can be.
        Haggy

[Haggy]

Just wanted to thank the BHT for his thoughts in this thread-hardening the material  before applying the sealer sounds a good idea. 
This thread and the helpful advice has really inspired me to get things right and not put up with a second rate finish- thank you to all who have contributed.   I will photograph the wood again after it has been finished properly.
            Many thanks.    Haggy