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Waterbased woes

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Waterbased woes

Postby 9fingers » 21 Oct 2021, 12:21

Traditionally I've used spirit based finishes and been a great fan of a Sam Maloof type mixture to give a barely visible low build finish but it does take an age to dry each coat hard enough to allow de-nibbing.

Compared to the early water based offerings that I really could not get on with, later generations of water based PU have been very good and I've had good results on numerous jobs and am near the bottom of a 2.5 litre potof the stuff.
However this current job involving oak mouldings has been a nightmare.
I've prepped the bare wood to 120 grit and then applied a thin layer of WBPU and it raised the grain. All carefully rubbed back to 120 and the second coat gave a similar rough as a badgers 4rse finish almost like it has raised the grain again.
I've just sanded smooth again and applied a 3rd coat - I'm not that confident the results will be much better.
NB I'm pretty confident that I'm not sanding right through the previous coat so the wood pores ought to be being sealed? I'm only doing 1 coat perday in between other jobs so each coat is plenty dry enough.

Anyone had similar problems or advice to offer please?

TIA
Bob
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Re: Waterbased woes

Postby Mike G » 21 Oct 2021, 12:46

Yep. Just keep at it, Bob. It goes away in the end. I had the same thing with a water-based lacquer on my stair handrail. I just kept on rubbing it back and slapping on some more.
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Re: Waterbased woes

Postby Malc2098 » 21 Oct 2021, 13:21

Is this where Sanding Sealer is appropriate to use before the finish?
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Re: Waterbased woes

Postby 9fingers » 21 Oct 2021, 13:35

Mike G wrote:Yep. Just keep at it, Bob. It goes away in the end. I had the same thing with a water-based lacquer on my stair handrail. I just kept on rubbing it back and slapping on some more.


Thanks Mike,
I'll keep the faith!

Bob
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Re: Waterbased woes

Postby 9fingers » 21 Oct 2021, 13:43

Malc2098 wrote:Is this where Sanding Sealer is appropriate to use before the finish?


Not sure Malc?
I often like to part finish some components before final assembly.
This project is rail and stile panel doors so I like to finish the field panels both to allow them to float and not show a telltale line if the field or frame moves.
In this stage of the project I've got water based varnished panels fitted into raw rails/stiles so I'd be concerned about the risk of sanding sealer solvent attacking the WBPU (never tested this to be honest)

I feel a test coming on using some offcuts.

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Re: Waterbased woes

Postby AndyT » 21 Oct 2021, 14:04

A cheaper approach is to wipe over the bare wood with hot water. This raises the grain, so sand back smooth. Then apply the water based finish.

I've done this, and it worked well, but I've only done it on softwood, on flat surfaces. Oak mouldings sound harder.
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Re: Waterbased woes

Postby 9fingers » 21 Oct 2021, 14:14

AndyT wrote:A cheaper approach is to wipe over the bare wood with hot water. This raises the grain, so sand back smooth. Then apply the water based finish.

I've done this, and it worked well, but I've only done it on softwood, on flat surfaces. Oak mouldings sound harder.


This approach may indeed help but the curious thing to me is that it appears my second coat is also raising the grain. So whilst hot water is cheaper than WBPU, I expect it won't fully solve the issue.

Adding to the sanding sealer thoughts above I now see you can get water based sanding sealer but surely that must raise the grain.
I guess for a trouble free finish, good old high VOC paints, varnishes and stains are the safe way to go!

Bob
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Re: Waterbased woes

Postby AndyT » 21 Oct 2021, 16:55

I was just thinking that with plain water you'd get enough to raise the grain as much as it's going to go. But if you only apply a sensible coat of finish, that might not be as much water as you need and the wood can still swell a bit when the second coat hits it.

But I'm just thinking aloud, and as you say, experiments on offcuts are always a good idea.
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Re: Waterbased woes

Postby Malc2098 » 21 Oct 2021, 17:00

I've used sanding sealer back as far as the 60s when I made model airplanes to stop the balsa grain rising. I use it making instruments now to stop glues leeching into the grain adjacent to joins.

You then sand after using the sealer and before applying the finish. If you're doing different parts of the construction at different times, then I suppose you should follow exactly the same process for each part at those times.

From what I read, WB polyurethane varnishes can be used on top of sanding sealer.
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Re: Waterbased woes

Postby 9fingers » 21 Oct 2021, 17:10

AndyT wrote:I was just thinking that with plain water you'd get enough to raise the grain as much as it's going to go. But if you only apply a sensible coat of finish, that might not be as much water as you need and the wood can still swell a bit when the second coat hits it.

But I'm just thinking aloud, and as you say, experiments on offcuts are always a good idea.


Good point Andy.

First test underway:
I've put some drips of liberon sanding sealed- smells alcohol based and letting it dry on a scrap piece of field pre-finished with 3 coats of WBPU no effort to brush it out to let the alcohol do its worst.

Bob
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Re: Waterbased woes

Postby 9fingers » 21 Oct 2021, 17:15

Malc2098 wrote:From what I read, WB polyurethane varnishes can be used on top of sanding sealer.


I'd be more concerned about the reverse. ie completed field finished on WBPU , then framed in raw oak and the possibility of SS put on the frame spreading onto the field and damaging that.

As per above post, I've set up an experiment for this.

Bob
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Re: Waterbased woes

Postby Phil Pascoe » 21 Oct 2021, 20:51

If you are using a water based finish use water to raise the grain as you sand. The hotter the better, on and wiped off quickly. Even down to 240 you will still raise the grain slighty, get rid of the fluff before you apply the finish. I rarely use s/s on turnery as I've been caught out a few times by its making the finish patchy - if water doesn't do anything positive it doesn't do anything negative. Be careful with oak you don't get steel anywhere near it.
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Re: Waterbased woes

Postby Mike G » 21 Oct 2021, 21:15

AndyT wrote:I was just thinking that with plain water you'd get enough to raise the grain as much as it's going to go......


Very much this ^, as people say.
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Re: Waterbased woes

Postby 9fingers » 24 Oct 2021, 14:27

A bit of an update.

I set up an experiment on the next panel before any finish on the mouldings.
Bottom half got the hot water treatment and the top left plain.
Allowed the bottom to dry and rubbed the whole lot smooth down to 120 grit.
One coat of WBPU and allowed to dry overnight.
Quite disappointing in that both top and bottom were equally rough.
This is the last panel so I will continue as per the previous three with multiple coats and rubbing down in between.

My experiment with alcohol based sanding sealer on top of thoroughly dried WBPU (just it case it strayed onto prefinished panels) now complete. Good news is that the solvent does not attack the WBPU but bad news it does colour the surface so has to be removed carefully.

Bob
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