WOP - Question on sanding between coats

[Hermit]

I use MinWax water-based WOP for most things. The label says to rub with 220G between coats, but that's always seemed too coarse to me, so I tend to give a light scuff with 600G W&D, (dry), or 1200G W&D, (also dry), between coats, to smooth imperfections and provide a key for the following coats.
I apply multiple very thin coats and figure that 220G would rub through leaving scratches/witness marks.
I've been wondering what others do, and if there's any benefit in using 220G as the label says.

[Skew ChiDAMN!!]

I tend to use 600-800 grit for rubbing back between coats. Never felt comfortable with the lower grits, for pretty much the reasons you give.

So I'll be watching this thread with interest.

[Hermit]

I tend to use 600-800 grit for rubbing back between coats. Never felt comfortable with the lower grits, for pretty much the reasons you give.

So I'll be watching this thread with interest.

Yeah, the question's been in the back of my mind for a while. There must be a reason they say 220G. To my mind, you'd want a pretty thick coat before going that coarse, but the label says to apply thin coats.

Edit: Actually, the label doesn't say thin coats. I think I just assumed that. It says to apply liberally to a cloth then rub into the wood. Rubbing in suggests a thin coat, I guess.

More from the label, "... sand entire surface lightly with very fine sandpaper, (220 grit)".

[LGS]

Just doesn't make sense when you're sanding to 400 before adding the finish!

Regards,

Rob

[A Duke]

Hi,
Never used it myself but after the fist coat you could be cleaning up raised fibres and 220 would be about right but for subsequent coats I would say you are right.
Regards

[Hermit]

Just doesn't make sense when you're sanding to 400 before adding the finish!
Regards,
Rob

I don't think it's necessary to go to 400G before applying poly, except with end-grain. The poly coat tends to fill fine sanding marks.
I go to 220 before the first coat, then 600G for a coat or two sometimes, then 1200 after that. For the best finish, to remove application marks, I rub the last coat with 1200 too, then wax.

Regarding the thin coats, although it's not stated on the label, their website says to always apply thin coats.

Edit: I also go to 400 or even 600 before the first coat in spots where I'm forced to sand cross-grain.

[Hermit]

Hi,
Never used it myself but after the fist coat you could be cleaning up raised fibres and 220 would be about right but for subsequent coats I would say you are right.
Regards

That's a very good point.

Personally, I use sanding sealer beforehand, but if I didn't, that first coat would be slightly furry with water-based, so 220 might be best, but as you say, not for later coats.

Noticeably, no one appears to use 220g, so far at least. Does nobody follow directions?

[Skew ChiDAMN!!]

I'll usually flood coat the first time and lightly wet sand with whatever grit I last used. When that coat is dry, I'll use a fresh piece of the same grit - or finer - to rub down any raised nap, etc. This is rarely done a second time, but there've been exceptions. Some timbers are SupaSponges.

Subsequent coats are all rubbed by rag, often with no sanding between - this depends on how "clean" my shop is on the occasion - until I achieve the degree of finish I want.
When I do feel the need to sand in-between, the grit I settle on is typically finer than the one I use for the flood coat, though.

I can't say I work down thru the grits between coats, but if you're after a mirror sheen it makes sense...



Edit: I just realised that my WOP technique is almost identical to my Tung Oil technique. Funny, that!

[Hermit]

I'll usually flood coat the first time and lightly wet sand with whatever grit I last used. When that coat is dry, I'll use a fresh piece of the same grit - or finer - to rub down any raised nap, etc. This is rarely done a second time, but there've been exceptions. Some timbers are SupaSponges.

Subsequent coats are all rubbed by rag, often with no sanding between - this depends on how "clean" my shop is on the occasion - until I achieve the degree of finish I want.
When I do feel the need to sand in-between, the grit I settle on is typically finer than the one I use for the flood coat, though.

I can't say I work down thru the grits between coats, but if you're after a mirror sheen it makes sense...



Edit: I just realised that my WOP technique is almost identical to my Tung Oil technique. Funny, that!

You raise another good point, Skew. Is sanding between coats absolutely necessary to provide a good key for subsequent coats?

Sometimes, I apply 2 or even 3 coats before touching it with paper, to avoid rub-through, since the film is so thin. But is this really advisable? Has anyone done this and had coats lift over time?

N.B. I'm applying second and third coats during this discussion, but I'm not touching the 220. 1200 only.

[Hermit]

You raise another good point, Skew. Is sanding between coats absolutely necessary to provide a good key for subsequent coats?

Sometimes, I apply 2 or even 3 coats before touching it with paper, to avoid rub-through, since the film is so thin. But is this really advisable? Has anyone done this and had coats lift over time?

After some reading, (on the Globak website), I can answer these questions myself - sanding is necessary between coats to ensure adhesion, since the WOP doesn't melt into the previous coats like lacquer does.

I've never had coats lift over time, but I won't take the risk any more and will always lightly sand between coats. I'll stick with 600G or 1200G, though.

[Mobyturns]

After some reading, (on the Globak website), I can answer these questions myself - sanding is necessary between coats to ensure adhesion, since the WOP doesn't melt into the previous coats like lacquer does.

I've never had coats lift over time, but I won't take the risk any more and will always lightly sand between coats. I'll stick with 600G or 1200G, though.

I have on small wood turnings with Minwax WOP but with the solvent based version. I reversed turned the base on a finial lidded box for AWTEX a few years back and used the mummy technique with "low tack" painters tape, only to pull a substantial amount of the finish back to raw timber! It was sanded to 800 - 1000 by memory then the finish applied.

[ubeaut]

Many years ago I had a polisher friend who was using poly for the first time. Not WOP.

He had an amazing finish on a coffee table, absolutely beautiful. He was on his way home from a weekend craft market in Melb and stopped at my place to pick up some turnings and carvings, a chat and a cuppa. The table was in the back of his station wagon and it was a hot day. When he went out to go home he had the biggest blister I have ever seen.... The entire table top had delaminated all bar the edges and was a massive honey coloured bubble.

He didn't sand between coats after the first couple and the result was amazing. When he stripped it back he found the first 2 coats which were sanded were still quite solidly attached to the table the rest had parted company. That was around 1978 and there have been some pretty big advances in polish since then but the fact remains that poly of any sort is basically plastic and unlike shellac and most lacquers it will not blend/melt into itself when a new coat is applied. It needs that roughened surface to allow it to adhere to itself properly.

Hope this is of some help.

Cheers - Neil

[Hermit]

Many years ago I had a polisher friend who was using poly for the first time. Not WOP.

He had an amazing finish on a coffee table, absolutely beautiful. He was on his way home from a weekend craft market in Melb and stopped at my place to pick up some turnings and carvings, a chat and a cuppa. The table was in the back of his station wagon and it was a hot day. When he went out to go home he had the biggest blister I have ever seen.... The entire table top had delaminated all bar the edges and was a massive honey coloured bubble.

He didn't sand between coats after the first couple and the result was amazing. When he stripped it back he found the first 2 coats which were sanded were still quite solidly attached to the table the rest had parted company. That was around 1978 and there have been some pretty big advances in polish since then but the fact remains that poly of any sort is basically plastic and unlike shellac and most lacquers it will not blend/melt into itself when a new coat is applied. It needs that roughened surface to allow it to adhere to itself properly.

Hope this is of some help.

Cheers - Neil

Thanks for confirming that Neil. I had to read between the lines on the Globak site to find out.

[Hermit]

I have on small wood turnings with Minwax WOP but with the solvent based version. I reversed turned the base on a finial lidded box for AWTEX a few years bacek and used the mummy technique with "low tack" painters tape, only to pull a substantial amount of the finish back to raw timber! It was sanded to 800 - 1000 by memory then the finish applied.

On my current project, I'll need to use masking tape on some of the poly after it has cured. It should be a good test of adhesion after rubbing back with 1200 between coats.

[ubeaut]

Personally I would be more inclined to use 600 or 800 grit for the rub-back to make sure there is plenty of roughened surface for the poly to adhere to. Keep the 1200 and above for finishing the finish ie: keep it for after the final application of poly and after it has had plenty of time to cure. I would leave it a week before hitting it with the 1200 and above.

Cheers - Neil