Thread: Thinning Polyurethane

Cameron...

Keeping mind that I am a DIY person, and not a chemist (in this context), I have thinned poly 30% with universal thinners (sold in paint stores as both a laquer thinner and an enamel reducer.). I have even added oil to the mix and treated an outdoor set. The advantage is that this can be applied like an oil finish-rags and a rub out. Several coats can be built up this way.

The thinned mixture flows very well, and of course seems* to absorb better.

* I have no data to suggest that it does penetrate more deeply. Such a difference would probably not be easily measurable. The thinners do gas off quickly, giving the impression of absorption.

I hope that this helps.

Greg

Thanks,

But I am more using this for stability than actual finish, so that is my highest concern - that the hardness of the poly will remain relatively unaffected.

I will turn the blanks after I have hardened them with the poly.

Cheers

Cam

Hi Cameron...

The hardness of the finish is unaffected. Do I understand you correctly that you are going to coat blanks to slow the moisture exchange until you get a chance to turn them?

Greg

Have you tried West System epoxy as a hardnener? Or are you asking about the poly because you happen to have some?

No, the wood is actually a bit of Sassafras that is severely spalted and has gone a bit rotten. The result is a gorgeous piece of wood, the problem is that it is soft and crumbly.

Thus, by using a thin solution which can penetrate the wood deeply, I can effectively fill the pores in the wood with the resin.

Now I actually have West epoxy at home, but it is WAY too thick to work, thus polyurethane is a much better bet. I have also tried a commercial wood hardener, but it didn't do much.

Cam

I have actually thinned poly with both Turps and acetone for different reasons. The fine woodworking DVD on finishing actually suggests that you thin poly with 30% turps for the first coat when brushing for penetration. I have recently been spraying poly with a hvlp gun and thinned it from the can with 30% acetone and have used this for multiple coats and the result was fantastic, a smooth even finish with no runs (if you don't go crazy on vertical surfaces). The poly dried rock hard as it would have directly from the can.

OK then. You're right about the epoxy, it would be like syrup. I read an article once on some guys in Victoria who were playing around with resin impregnating timber. They subjected the pieces to a vacuum, allowing the air to gas off and be replaced by the very slowly hardening resin. In this case the epoxy (or poly, for that matter, would work). Are you able to generate a vacuum in a bag large enough for your piece? If so you could ensure deep penetration. Obviously this would take an awful lot of fluid. I imagine standing the board in the bag with the resin in the bottom, then evacuating the air.

Greg

Thanks Morry,

That sounds ideal. Which did you find worked better or were both much the same (for my use)?

Greg, yes that was the method I was going to use, but only for small bits of wood (ie pens or knife handles etc...) Thus it is OK. I am doing it in a jar.

Cam

Cam
depends on your application method. Using a brush thin with turps this will allow the thinned finish to get right down into the grain. If spraying then use acetone this allows you to thin the finish enough so it will atomise nicely through the gun and settle smoothly then the acetone being very volatile will evaportate quickly and prevent the finish from running. Just be careful as its flash point is about 0 dec c and will be as flamable as hell. Good breathing gear also if spraying.

My father likes using penetrol to thin down the varnish and says that this also helps get the poly down into the grain instead of just sitting on top.

It is a misprint mate. It should be 50%.

OK 50% is a bit extreme but I have done it before you know. 30% for the first coat is my normal practise. If fact IMO you should never apply polyU by itself. It is way too thick.

Wongo (who cannot afford to use pure polyu)

hi mate...just loged on so i hav'nt read the above posts yet but thought i'd let you know that i use feast watson satinprooof and i thin it out a little with turps no problem , i even wipe the stuff onto a job instead of brushing , then i get a very thin film that soaks in , keep doing this as many coats as you like, light sand between coats and then 0000 steel wool and beexwax at the end...


la H

Thanks.

I think that sorts things out for me now...

Cheers

Cam

Just to throw another idea in.

I think you might be better using the thin anacryolate (sp) glue. Let it soak in and then harden it with the accelerator.

Another thought.

Lacquer Thinner, Acetone, or Alcohol (meth) will all work with the Epoxy to thin it out, and will not affect the intergity of the epoxy.

, suggestion about using cycloacrylate (crazy glue) is commonly used in the US for that same problem.