Bumps in finish (how did they get there?)

[Travis]

Well it turns out I have some tiny bumps in my finish. I used Arm-R-Seal Urathane and Topcoat. When I was applying the top coat with a cloth I noticed lots of tiny bubbles but did not think they would lead to blemishes. The bumps that exist are much fewer than the bubbles that were present when applying the finish. What causes these bumps, could it be dust or cured out bubbles?

 

[jeff...]

Well it turns out I have some tiny bumps in my finish. I used Arm-R-Seal Urathane and Topcoat. When I was applying the top coat with a cloth I noticed lots of tiny bubbles but did not think they would lead to blemishes. The bumps that exist are much fewer than the bubbles that were present when applying the finish. What causes these bumps, could it be dust or cured out bubbles?

Bumps in finish can be dust left on the piece finished or air bubbles, try and filter your finish, use a tack cloth to wipe down your piece before you finish it and stir your finish gently, don't shake it like your doing the jig to jail house rock.

 

[McRabbet]

If you re-used the same wiping rag for the top coat as any earlier coat, you could have bits of coagulated Arm-R-Seal in the rag that are released with the fresh finish material. I've made this mistake with a good varnish brush and the only solution is to knock those "nits" down with 320 to 400 grit sand paper and then rub out the finish to the desired final sheen or add another coat with a new, dustless wiping rag.

 

[daclgr]

I had this same problem the first time I used Arm-R-Seal. I found that if I stired and not shake, I would not have the air bubbles, I also started wiping down my project with MS and let it dry good before I started to apply my first coat. I still have a few small bumps however this greatly reduced them. I do not use rags to apply the finish I use the application pads from WC and only use it for one coat, and light pressure when appling the finish. After light buffing with 320 paper between coats by the 3rd coat I get a good smooth finish. I have also found that the more coats the better finish.

Hope this helps. I am still learning how to finish and not sure if this is the correct way, however it has worked well for me on my last few projects.

 

[Nativespec]

I sand with 600 grit before and sometimes after the final coat. I then apply fininshing wax with 0000 steel wool to remove any bumps. The wax helps protect against scratches.

 

[Travis]

Thanks for the suggestions. I have some shelf supports for the closet to do this weekend and I will try these suggestions and see what results I get. Just for fun on my test piece of board I sanded out the bumps with 320 grit paper and applied another coat of Arm-R-Seal and noticed that a lot of scratches showed up in the finish. How did this happen? I have several folks suggest 320 paper. I must have don somethig wrong or skipped a step.

 

[daclgr]

Travis,
When I buff with 320 I use very light pressure, you just want to scuff the surface of the finish, and remove and bumps. Make sure that you buff with the grain of the wood. I also use very light pressure when I apply the next coat, the coat is heavy and it took some practice to learn how much pressure I needed to get a good coat and still avoid runs.

Hope this helps

 

[jglord]

:eusa_thin Maybe what happened is your sand paper loaded up with some small particles or lumps of finish and caused the scratches.
Sanding lightly and/or changing the sanding surface frequently may help this but IMHO, wet sanding is best. You can use water, mineral spirits, paraffin oil and others. The idea is to have a lubricant between the paper and the surface to prevent build-up and scratches.
Just my .02, but it can help when sanding between coats.